Typing Kelowna into the website gives you a hardiness of Zone 7a for the most recent period of evaluation (1991-2020). For Armstrong you get a hardiness of 6b. Zone 6b is half a zone colder than 7a. Note, however, that this calculation was done for a 20 year period from 5 years ago and climate variability has become much worse, keep reading.

If you look up a Purple Ice Plant on the OXA website, it tells you that it is hardy to Zone 6. Normally then it should survive winter in any area rated as Zone 6 or higher. Also remember that you can often increase your effective hardiness zone by covering plants with mulch or snow or planting them in an area that is sheltered from the cold like a calm area beside a house.

Complications

Global Warming provides the first complication. We have all experienced generally warmer winters in Canada over the past decades. Okanagan Lake has not frozen over since 1969, whereas it used to freeze over more commonly as in both 1950 and 1949. The Government of Canada website mentioned above compares the period of 1961-1990 to the period 1981-2010 and the zones are all higher on the website for the later date, usually half a zone to a full zone. Note that the Government of Canada is scheduled to come out with an updated plant hardiness zone map later this year.

Climate Variability adds a bigger complication. As our climate warms on average, it is also becoming more variable. This means that we are more likely now to have occasional extreme cold snaps. The winter of 2022/23 is a good example of this pattern. At the Kelowna airport we had 2 days at Zone 5 temperatures and 2 days at Zone 4! This resulted in an unusual amount of winter kill for our plants in the Okanagan. Looking at the last 12 years in Figure 2 you can see that these extreme low temperatures are becoming more common. In fact, we just had another extreme cold snap of -30°C in January 2024. It is beginning to look as though we should subtract one to two zones off the maps and lookup tables presented at the beginning of this article.

Calculation Methods provide another complication, but it is relatively minor. There are two common calculation methods for hardiness zones. One comes for the USDA and it is based simply on the lowest temperature experienced in a given area averaged over 30 years. The Government of Canada uses a more refined and complex formula which incorporates six other winter weather variables such as snow cover in addition to the lowest temperature averaged over 20 years. Historically the two methods produce similar results in the Okanagan. You can view a map calculated using the USDA method at this website: USDA Zones. This map probably uses data from the period 1978-2008 and there is a lack of topographic detail but it is quite close to the Canadian version. Any differences attributable to calculation method likely be minor compared to the variability from climate change and the time period used for averaging.

Because the landscape industry in the US is so much larger than Canada’s, you can safely assume that any hardiness zone given on a website, or a plant tag is almost certainly a USDA zone. Gardeners in the Okanagan can use the two methods interchangeably.

Microclimates provide the final complication. These are local variations in plant hardiness zones that are generally related to local variations in elevation but can also be caused by the moderating effect of a nearby large body of water. Looking at the zone map you can clearly see the effect of regional variations in topography as the Okanagan is a narrow valley surrounded by high hills and mountains. The higher elevations around our valley have the much lower zone rating of 3a to 3b. At a more local scale we can see an example of a microclimate in the Kelowna area where the airport is about a half to one zone colder than central Kelowna. This seems to be related to both the slightly higher elevation at the airport and the higher elevations that surround the airport. These elevation changes have created channels where the cold air sinks down from the higher elevations.

Summary

Plant hardiness is a relatively simple and important concept for Okanagan gardens, but with climate change it is difficult to predict. Gardeners should take this uncertainty into account in their planting plans.

If you want to try out an interesting perennial rated close to your maximum zone, then it might be worth the risk. On the other hand, if you are planting a tree or hedge that you want in place for a long time, it is better to choose a species two or three zones colder than your maximum.

To avoid disappointment give careful consideration to plant hardiness when selecting plants for your garden.

2. ROTOTILLER

This method takes patience, as you need to rototill several times. Between each tilling, let the lawn sit four to six weeks to allow the grass/weeds to re-sprout.

• Easier to maneuver than a sod cutter.
• Retains the layer of soil containing the most nutrients and organic matter.
• Area will be disrupted for several months.
• Must remove sod under trees by hand to avoid root damage.
• Do not rototill if your turf contains bindweed or any noxious weed that propagates by rhizomes.
• Do not rototill unless you are certain your underground irrigation system is deeper than the tines of the rototiller
• Mark sprinkler heads of underground irrigation before beginning.
• Be prepared to spend time raking and leveling the tilled area.

3. HERBICIDE SPRAY

This method is worth considering particularly if you are planning to overseed or reseed your existing turf. You can get a contractor in to make certain that the local rules are being followed or you can buy the product and apply it yourself. You can use a ‘mild’ acid herbicide called ‘Eco-Clear’ or you can use a stronger broad-spectrum glyphosate-based herbicide.

• Little labour required.
• Kills turf and growing weeds.
• Does not remove organic matter or nutrients from the soil.
• Eco-Clear is relatively new on the market; it is expensive and may need several applications to kill some perennial weeds and is only effective on actively growing vegetation.
• Herbicides generally do not kill weed seeds, only vegetative growth.
• Residential use of herbicides by other than certified applicators is being reviewed in BC. Some communities such as the City of Kelowna have already banned such use.
• Always follow the label directions closely.
• Notices should be posted, (this may be a local bylaw or strata requirement).
• Do not spray on a windy day or when rain is forecast within 24 hours.
• Once you have confirmed that the herbicide has killed the sod (7-10 days), you can cover the dead sod with a soil/compost mix and let it rot in the ground for a couple of months.

4. SOIL SOLARIZATION

Solarization is accomplished by completely covering an area with clear or black plastic, 4-6 mils thickness, during July and August. The intense heat that builds up under the plastic kills the turf and weeds.

• Little labour required.
• Does not remove organic matter or nutrients from the soil.
• Can cause an anaerobic effect, killing beneficial micro and macro-organisms in the soil.
• Strong winds can displace the plastic; anchor it very well with stones, soil, or wood.
• Unsightly.
• Mow the grass as short as possible and water well before covering the area with the plastic. The combination of heat and water speeds up turf decomposition.
• Generally, need to leave the plastic on the soil for 6-8 weeks in the summer.

5. LASAGNA METHOD

• Moderate labour required. • Improves the quality and thickness of topsoil. • Looks good immediately. • Mow the grass as short as possible and water well. • Mark sprinkler heads of underground irrigation before beginning. They may need to be extended later. • Cover the area with newspaper (not coloured and not glossy) or cardboard. Newspaper should be 5-8 sheets thick and overlap both the newspaper and cardboard at least two inches • Cover the paper product with 4 to 6 inches of a soil/compost mix, and soak thoroughly. • Cover the soil/compost with 3 to 4 inches of organic mulch. • Leave the area moist and fallow for 2 to 3 months so that the paper product and sod rots in place.

Use one or more of these options to remove your lawn and set yourself up for a fine xeriscape garden.

Article and Photos by Mark Godlewski

The following is largely put together from information provided by Jim Brockmeyer and Muriel Neale as part of their Bluestem Nursery webpage. Both have now retired, but their excellent website lives on with funding for the hosting provided by OXA.

Trimming Cool Season Grasses

Normally you want to trim your cool season grasses in early spring. During the winter, depending on the species and the weather, grasses can create a great deal of interest in your garden. However, you will want to trim all your cool season grasses down to about 3-4 inches above the crown before they start growing in the spring. If you are late and there is significant new growth your best bet is cut down only two thirds of the grass. For thin grasses you may want to use hedge trimmers. Otherwise, a coarsely-serrated knife is the best tool for this. You may be able to pick up an old bread knife from your thrift store. It is also a good idea to wear gloves and long sleeves. Some of the grasses can give you a nasty cut if they slide along your skin.

Fig. 1 – Cutting Tools

A tip regarding cutting back larger grass clumps is to tie one or two bungee cords around it before you start to cut. You want to keep all the stalks and leaves in a tight bundle. This makes it much easier to get rid of the mess later….and a mess there will certainly be if you don’t!

Trimming Warm Season Grasses

There is no great rush to prune these grasses in the spring depending on how they look in your garden. You can wait until late spring. Some warm season grasses such as Miscanthus or Saccharum have very thick stems. Here you will need pruning shears, or a pruning saw to cut them off 4-6 inches above the crown.

Fig. 2  – Warm Seson Grasses in Winter

Trimming Evergreen Grasses

Some Fescues and Blue Oat Grass Helictotrichon fall into the evergreen (everblue?) category. A few people, especially those at landscape maintenance companies, like to cut these grasses back early but that is not the best for the health and shape of the plant. Blue Oat grass responds well to being combed (with a gloved hand) in the fall and maybe again in the spring. The dead leaves and flowers will come loose relatively easily. Some of the tan-coloured leaves will remain until the next season. Some other evergreen grasses and Carex experience a fair bit of dieback in our winters. You can shear back the dead leaf ends in the spring but be careful not to cut back too much into the living part of the plant.

Fig. 3  – A nice variety of grasses in the late summer

Take care to trim your ornamental grasses appropriately to achieve the best long term results.

Fig. 3    Warm Season – Fountain Grass

To see the trimming guidelines for different types of grasses, please visit the blog post titled Trimming Ornamental Grasses

Get to know the different seasons of ornamental grasses to maximize your enjoyment of these versatile plants. 

CHECK YOUR EMITTERS

There are two main types of drip emitters: dripline emitters and point emitters.

Dripline (built-in) emitters have drip emitters located at regularly-spaced intervals along a distribution pipe as in Fig 1. Dripline systems are best suited to linear features such as hedges or areas of high-density planting of plants that all require the same amount of water such as a vegetable garden. Dripline emitters formed into a circle are useful for watering large pots or trees. Dripline emitters are available in a variety of spacings from 6” to 24”+ and a variety of flow rates from 0.25 gal/hr to 1 gal/hr.

Point source drip emitters are more versatile and useful for most xeriscape designs which feature plants spaced out in informal, natural looking patterns. The emitters generally come in 3 flow rates: 0.5, 1.0 and 2.0 gal/hr. Fig 2 shows an example. They can be tapped directly into larger-diameter flexible supply lines (polyethylene tubing), or they can be run off ¼” spaghetti line that is tapped into the larger supply line. Knowing how many individual emitters can operate off larger or smaller diameter pipe sizes, can be determined with some simple math. Flow charts and irrigation distributors can help you find out how much water can safely flow through whatever size of tubing you are working with. As you add individual emitters, keep a tally of how much water they require in total. Make sure that the total water required by the emitters, does not exceed the water available through your supply line. For example, a typical black poly distribution pipe with an inside diameter of ½ inch should have no more than 300 one gallon per hour emitters to ensure the zone will operate properly.

It is nice to have a detailed plan showing the location of all the distribution lines, emitters and flow rates. This makes it easier to check and maintain the system. Most information is available online or through an irrigation distributor, to determine what kinds of emitters have been used in your garden and roughly where they are located. Point emitters are often colour-coded for their flow rate and have a number stamped on the plastic (small print and may be in gallons or liters). Dripline emitters are generally not marked with flow rates.

Understanding the flow rates of your emitters or built-in dripline, is required information for matching the amount of water delivered, to the plant water needs. There is a lot of variety on the market. I have attached a short video “Drip Emitters in Action ” that shows 5 emitters in action. The three point emitters are colour-coded: red, black, and blue for 2.0, 1.0, 0.5 gal/hr. flow rates respectively. There are also two dripline emitters in the video. The one in the middle is 0.25 gal/hr. and the one on the right is 0.5 gal/hr. For dripline emitters, there is generally no way of telling what their nominal flow rate is unless you have this information from when the product was purchased The two in this video look identical but one is half the flow rate of the other. If you do not know the flow rate, schedule as if the emitters have a 0.5 or 0.6 GPH rate and monitor the soil moisture and plant material.

Almost all the point emitters on the market at this time are pressure regulated which means that regardless of being at the beginning or the end of the line, or at the top or bottom of the hill they will drip at a constant rate. The same is not true of built-in dripline. Many of these are not pressure regulated and so their rates can vary quite a bit from the specifications depending on where they are located.

Generally, you should keep your emitters above the soil level to avoid roots getting in and clogging the flow. For aesthetic reasons, the supply lines are often placed under mulch which is less likely to create issues and generally allows for easy access to “expose” and check the tubing from time to time.

CHECK YOUR ZONE FLOW RATES

As mentioned above, it is a good idea to know the flow rate of each emitter and then by adding up all emitters within a zone, you will know the flow rate for each zone. Zone flow rates matter because the total amount of water flow you have available for each zone, is restricted by how much your house water supply can provide, and by the size of the supply lines you install. If the emitters on a zone require more water than you have available, the zone will not perform well. Once you have established the total zone flow(s), you can write it down beside the controller and periodically check the rate (at least once a year). If the flow rate is higher than normal you should look for a leak. If it is lower you should clean your filters, check for kinked lines, and check for plugged emitters.

Checking the flow rate is easy with modern water meters. Pick a time when none of your other appliances is using water and then shine a flashlight on the meter. The rate should be showing 0.0000 cubic meters m3/min. It may be slightly higher if you have a slow leak inside your house such as a leaking toilet. Then go and turn on your drip zone and wait for a couple of minutes for the flow to stabilize. You should see a rate of approximately 0.0150 m3/min which equates to 15 liters/min for your drip zone depending on how many emitters you have. Note that if you have a flow rate of more than 20 liters/min and you are using a single ½ inch poly line, you may have too many emitters on your line.

If you have an older water meter you must calculate the flow rate yourself, but it is not too big a deal. Meters in Canada are all set in cubic meters, and mostly they have an odometer type numeric readout. There is some variation in the precision of the numeric readout. Sometimes it shows two decimals, or three, or four. Note carefully where the decimal point is on your meter. Use a watch with a second hand or the timer on your phone. Turn the zone on and then wait for a couple of minutes for the flow to stabilize. Take a reading of the numeric readout and then take a second reading one minute later. Subtract the two numbers and you have your flow rate in m3/min.

ADJUST CONTROLLER TIMING

This is where you can save money and conserve water.

Irrigation frequency, start times, run times, and seasonal percentage are the four main adjustments to most irrigation controllers. Some controllers have a rainfall adjustment, but these are not particularly useful in the Okanagan because most of our effective precipitation tends to happen in the months when the irrigation is off or at a low setting.

Irrigation frequency (weekly, daily, etc.) is mainly controlled by your soil texture and plant types. It can also be controlled by local watering restrictions. Good loam soils can often be watered just once a week for a relatively long run time. Clay soils will need shorter, more frequent watering so that the water does not pool and run off. Very sandy soil will also need more frequent watering (perhaps every second day) because much of the water will tend to go straight down below the normal root zone. Plants with deep root systems will be okay in this scenario. Containers also tend to need more frequent watering because of their limited storage capacity.

Start times are relatively straightforward. Except for special situations, irrigation is generally set to run at night when evaporation is lowest. Again, this may be influenced by local watering restrictions.

Run times per zone are the primary controls for how much water you use. If we could get everybody’s run times optimized, it would make a huge difference to water bills and water usage. This topic can get complicated and so I am going to give a couple of guiding principles here and then create a separate blog article to address some of the complexity.

If you have point emitters, then use the fact that a single small shrub or large perennial that is a moderate water user, and is well established, will need about 2 gallons of water per week in Kelowna in July. Larger shrubs will need 4 gallons. This means that you should be running each drip zone for a total of two hours per week if you are using 1 gal/hour emitters. That could mean twice per week for 60 minutes per zone.

If you have a dripline system, then it makes more sense to use a square foot rule of thumb. Moderate water use plants that are well established will generally need about 0.6 gallons of water per square foot per week in Kelowna in July. This means that if you have a dripline with 1-gallon emitters built-in and the emitters are spaced 1 foot apart and the lines themselves are spaced 2 feet apart then you only need your zone to be on for a total of 60 minutes per week in Kelowna in July.

Seasonal percentage is an important parameter that is often neglected. Fig. 4 shows the variation of evapotranspiration (soil moisture evaporation plus plant transpiration) in Kelowna as a function of the time of year. This is measured in mm of moisture per day, and it relates directly to how much water is being used. This actual evapotranspiration varies a bit from one year to the next, but the overall pattern is very strong. July is the highest month for water use whereas September only requires 55% of the amount of water used in July. The averages for the main irrigation months are:

April – 55%
May – 75%
June – 90%
July – 100%
Aug – 90%
Sept – 55%

It is interesting to compare the rainfall chart for Kelowna for 2020 (Fig. 5). Note that the scale is the same between this chart and the previous chart for evapotranspiration. There were only 8 days with over 3 mm of rain in the late spring and summer in Kelowna whereas every day lost more than 3 mm of water to evapotranspiration. 2021 has been even worse. This is why we are so dependent on irrigation and why installing efficient irrigation and maintaining and scheduling correctly, matters so much.

Fig. 4  – Daily Evapotranspiraton for 2020 and seasonal percentages

Fig. 5 – Daily precipitation for 2020 in Kelowna

Hopefully this article will provide some knowledge to help properly maintain your drip irrigation system and provide a beautiful garden without wasting water.

Article and Photos by Mark Godlewski

A good understanding of your soil is one of the keys to successful gardening, especially if you are committed to following xeriscape principles. In Part I, I provided some general information about soils in the Okanagan. Here in Part II, I will suggest some methods for evaluating your own particular soil.

From a gardener’s perspective there are three key soil parameters: pH, nutrient level, and texture.

The pH of soils: in the Okanagan basin soils are almost invariably alkaline. This is typical of areas of low to moderate rainfall. Even if you somehow had neutral or acidic soils, our water is alkali so the soils will soon change. This alkalinity is not generally a problem. It gets reduced to some degree by the addition of organic material. The plants that really like acid soil such as azaleas and blueberries also love moisture and so are not good candidates for a xeriscape garden.

The nutrient level of soils: in the Okanagan is variable. The glacial silts and sands of many of our subsoils are low in nutrients and organic content. As a result, most gardens have a fair bit of variability within themselves with respect to nutrients and, in fact, while some xeriscape plants like rich soil, others really prefer poor soil. For plants that like rich soil it is a good idea to constantly add organic material. More about that below.

Soil texture: is an important topic for gardeners. Examples of soil textures are sandy loam, silty clay, etc. There are 13 of these terms and they are shown on the soil texture triangle Fig 1. It is worthwhile for every gardener to know their soil texture because it has a strong impact on how you handle the soil, how you irrigate the soil and how well your plants perform. Generally, you would like your garden soil to plot in the parts of the texture triangle that contain the word “Loam”. For example the soil you see in the cover photo of this blog is a sandy loam (Gammil type) in Kalamoir Park. 

Fig. 1 – Soil Texture Triangle

To gauge your soil texture, one of the first things you can do is to select a couple sample areas that are representative of your garden. For example, I live in a house with a walkout basement. The elevation of my back garden is lower than the front and the soils are quite different between the front and back because of this elevation difference. Also, after the foundation was finished some sandy fill was brought in and used around the foundation in the front garden. Often backfill just uses the subsoil from digging the basement but it is not uncommon for some of the backfill to be brought in. Although I requested a thick layer of topsoil, it is a bit of a rare commodity in these parts. There are quite a few areas where the landscaper only put in 4-6 inches of topsoil over the subsoil. For my representative sample areas, I have chosen a location in the front garden and one in the back. They are located far away from the foundation, from the hardscaping, and away from any large trees or shrubs that required a lot of digging when they were put in.

In each sample area you want to dig a hole at least 8” in diameter. Do your best to dig down to a depth of about 12”. As you dig note the thickness of your topsoil. There is usually a marked difference in colour and texture between the topsoil and subsoil. The topsoil is almost always darker and more organic. Take a representative sample of the topsoil and subsoil and put it in a plastic bag marked with the location.

Glass jar method for texture – If you look on the web you will find several different sites that explain how to find your soil texture by mixing soil and water in jar and watching how it settles. Although this method is clean and effective for some soils, it has a couple of serious problems. If there are a lot of fine particles (fine sand, silt, and clay) and if they are all similar in colour it can be exceedingly difficult to see the sediment/water contact or the silt/sand contact in your jar at any given time. The bigger problem is that in parts of our valley the glacial clays tend to easily mix with and coat the glacial silts so that they settle together as a single unit in the mixing jar. This means you cannot use this jar method to reliably distinguish between clay and silt and therefore you cannot determine the true texture of your soil. The jar method is somewhat useful, however, in terms of providing a measurement of the quantity of sand and organics in your soil. The sand sinks to the bottom in about 30 seconds and the organics form the darker material that floats on top or settles gently on sediment after a day or so.

Handheld method for texture – This is a better method for estimating soil texture, and it involves getting your hands dirty by playing your soil. The method is well demonstrated in this link from  Australia . It is quite effective at estimating relative clay and silt percentages which people often struggle with. Silt can be mistaken for clay, but it is generally more benign. You can get an idea of what the results from this method look like from Fig 2. If you are careful with your observations, you can locate your topsoil and subsoil quite nicely on the texture triangle.

Fig. 2  – Soil Extrusion Textures

Percolation tests for texture – Percolation tests are strongly correlated to soil texture. In many ways, they are the most useful measurement because they are simple and direct. You can perform one easily using the same holes you dug to get the topsoil and subsoil samples. Make certain that the hole has relatively straight sides, is about 12” in diameter and 8”-12” deep. Carefully fill the hole with water and leave it overnight to saturate the soil. The next day fill the hole again and lay a straight edge across the top (see Fig 4). Measure the level of the water down from the straight edge in inches. Come back in an hour and measure how much the water has gone down. You can come back again after two hours and measure again to get the average number of inches per hour for your Perc test. Generally, a rate of between 1 and 4 inches per hour is considered acceptable for most plants.

One thing to keep in mind about percolation tests is that they are affected by shallow water tables. If the water table is within about 20 inches of the bottom of your hole, then it can slow down the percolation flow appreciably.

The effect of texture on irrigation – Your soil texture controls how water permeates your garden. A nice illustration of this (Fig. 3) comes from a particularly useful publication from the University of California Santa Cruz

Fig. 3  – Water Movement in Soil

UnH2O garden – It is interesting to apply these texture analyses to the UnH2O garden. I performed this analysis in two different locations in the garden (Fig 4 and Fig 5) and got similar results. We know from Part I of this blog that the garden is in an area where the subsoil texture should be a loam (sandy loam, loamy sandy, silty loam) which is popular with most plants. On the other hand, the percolation tests in the UnH2O garden gave a drainage of just 1.5 inches per hour which is on the low side of the preferred range. While the texture of the soil is reasonable the problem is that the water table is quite shallow in this part of the city. You can contrast that with my “vegetable garden” in West Kelowna 100m above lake level where I measured a drainage rate of 11 inches per hour. I clearly have a problem with my subsoil in that part of the garden and have plans to fix that immediately.

Fig. 5 – Water filled percolation hole

Improving your soil – It turns out that the recipe for improving your soil is remarkably similar for most of our soils in the Okanagan. In almost all cases you should be adding organic matter. If the soil is too sandy add composted organic matter to slow down drainage and improve the nutrient level. If the soil is low in nutrients, again adding organic matter will help considerably. It is a good idea to work some of the organic matter into the soil and lay 3” of organic mulch on top.

Clay soils also benefit from the addition of organic matter to improve the drainage. These soils are difficult to work with, however, because it is hard to effectively incorporate materials such as coarse sand and organics into clumps of clay. Clay soils will hold moisture for longer, but it is hard for many plants to access. Irrigation water can run off instead of penetrating, and walking on wet clay soil leads to over compaction.

If you suspect that you have a problem with a high water table then the best solution may be to build raised beds of loam. This will allow your plant root systems to penetrate as far as they want to get the moisture level that they prefer.

Get to know your own soil characteristics and you will find that your knowledge will pay big dividends in success of your gardening.

Article by Mark Godlewski

A good understanding of your soil is one of the keys to successful gardening especially if you are trying to follow xeriscape principles. In this first article I will provide some general information about soils in the Okanagan. In the second I will suggest some methods for evaluating your own particular soil.

Anywhere you live in the Okanagan, a good part of your soil likely comes from the last major glacial episode that occupied the valley. From 30,000 to 13,000 years ago this valley was filled up with ice to a level at or above the tallest mountains that surround us. That ice sheet slowly melted leaving behind all the boulders, gravels, sands and rock flour (silt) that form the sediments in the valley. The soil may have been reworked and moved around since that time, but it originated from that Fraser Glaciation episode.

One of the most interesting features of the Okanagan from a soil point is the presence of a series of benches that rim the present-day system of lakes including Kalamalka, Wood, Okanagan, and Skaha. These benches attest to the presence of a significantly larger lake (Lake Penticton) that filled this valley to a level about 115 m above the current lake level about 10,000 years ago. The lake extended down to the Okanagan Falls, Vaseux Lake area. Here the valley narrows and was filled up with a dam of ice and glacial debris for an extended period. It is quite likely that the dam was periodically broken and reformed depending on the vagaries of ice movement.

The ancient lake benches comprise deposits of mainly fine sand and silt (glacial rock flour) with smaller amounts of coarser sand and clay laid down by multiple glacial streams from the melting ice sheet carrying a heavy sediment load into a large, turquoise glacial lake.

The distribution of soils in the Okanagan can be understood in a general way by looking at surficial geology maps. There is an excellent one from the Geological Survey of Canada for the greater Kelowna area and one for the Vernon area.

Kelowna Surficial Geology
Vernon Surficial Geology

Fig. 1 – Surficial Geology of Kelowna, Geological Survey of Canada

To get a sense of what these maps mean we can look in detail at the Kelowna area example. The areas coloured red are the rock outcrops of the surrounding hills and mountains. The green areas are generally mixed glacial till often derived directly from the local rocks. The light-yellow area is a broad flood plain formed by creeks and rivers flowing from the north and east down the valley. These were much larger than the current Mill Creek, Mission Creek etc. and they have reworked and redistributed the glacial sediments. In some parts of the light-yellow area there are patches of organic rich soils from swamp type environments, but these are relatively rare. 

The purple areas on the map show the Lake Penticton bench sediments. These are the same sediments that form the light grey bluffs of fine sand and silt on the west side of the Bennett Bridge and also the prominent bluffs further south in the Summerland and Naramata areas. These benches are the source of some of the most consistent soils in our area and home to extensive vineyards and orchards. These Lake Penticton bench sediments are dominantly fine sand and silt but contain some pockets of coarser sand and clay. 

While these surficial geology maps give a good general picture of the types of sediment on the surface there is a much more detailed soil map dataset available on the web. The data come from a major soil mapping project completed in 1986 titled “Soils of the Okanagan and Similkameen Valleys”. This mapping is oriented principally towards agriculture, but it can be quite useful to gardeners and there is other environmental data there like frost free days. 

There are a few things to keep in mind about the government soil mapping: 

• The central urban areas such as central Kelowna  have been left out of the mapping but sometimes you can get an idea of what to expect by looking at adjacent polygons
• Much of data is quite technical in nature and contains many elements that are not particularly useful to a gardener
• Gardens inside housing developments often contain a certain amount of soil that has been moved in from somewhere else. This is particularly likely if your house is on a lot with a steep slope nearby.

 To see how to use this soil mapping data go to: 

BC Government Soil Map

 and type your postal code into the search box on the top left-hand side. The map will zoom to your area and then you can click inside the yellow polygon that covers your garden. A text box comes up.

Here is what you will see in the text box if you were to check our UnH2O garden location:

Fig. 2  – Text box for the soil polygon containing the UnH2O garden

The area in and around the UnH2O garden contains a mix of 60% “Tanaka” type soils and 40% “Rumohr” type soils. The part highlighted in yellow is some basic soil information for those types of soils. The blue highlights are links that provide more detail on the soil types and how they can be used in agriculture. The sections highlighted in green are useful environmental information. It is interesting to compare the 3 environmental estimates with data from a similar polygon in near Vernon and one near Osoyoos.

If you take the time to cruise through the soil descriptions in the valley you quickly realize that there is really an exceptionally large variation. Soils are generally silty or sandy but there are some areas of heavy clay. Soils are usually alkaline and low in organic material but there are some acidic, high organic soils often located in lower areas. Soils are generally well drained but again in the lower areas there is some very poor drainage.

Once you have done what you can to determine the likely soil textures and drainage for your area you can move on to some specific tests for your garden in Part II of this blog. The general description from the mapping is probably accurate for your subsoil and is a good starting point for what was originally in your garden.

Take the time to get to know where your soil came from. You may have brought the top few inches from somewhere else but what is below greatly effects your trees and shrubs.

Gardening with Nature | January 2021

Article by Sigrie Kendrick

Planning your garden should unquestionably include bulbs. There are many drought-tolerant bulb options available, ranging from common crocuses to specialty Triteliea and everything in-between.

One of the ‘everything in-between’ categories which offer both common and uncommon varietals can be found in the Allium or Onion family. The Allium genus is comprised of more than 700 species grown for both culinary and ornamental purposes.

In the Okanagan Xeriscape Association’s demonstration garden on Gordon Drive in Kelowna, we grow a variety of Alliums and we always have bulbs available for purchase at the annual OXA Spring Plant Sale, the primary fundraiser for this non-profit organization.

Both Allium cernuum and Allium karataviense are great drought-tolerant bulbs to consider adding to your garden.

Allium cernuum, commonly called Nodding Onion is featured in our native garden and it occurs locally in grasslands and dry, open, rocky sites. This species is the most common native onion in the Southern Interior and is easily identified by its pink to rose, occasionally white, drooping or nodding flower heads held on top of leafless stocks, reaching a height of 12-18 inches with a spread half its height.

Like all the Allium family, Nodding Onion emits a strong onion odour when cut or bruised and as such is not favoured by deer. Interior native people had many culinary uses for Allium cernuum and it was also used traditionally as a disinfectant and to alleviate insect bites. This perennial is hardy in zones 4-8, blooming from June to August in full sun to part-sun locations and it attracts a variety of pollinators.

Fig. 1  – Nodding Onion (Allium cernuum), Gwen Steele

Allium karataviense or Turkistan Onion is an ornamental onion native to Central Asia, specifically Kazakhstan, grown for both its soft pink umbrel flowers, reaching approximately 12 inches in height, and for its green-grey foliage. Allium karataviense blooms earlier in the season and is typically in flower in the OXA demonstration garden in May, delighting those in attendance at our annual Spring Plant Sale.

Allium karataviense is an important source of food for pollinators, especially butterflies. This perennial is seldom bothered by pest or disease but can suffer from bulb rot in overly irrigated, poorly drained sites.

Allium bulb types are late spring/early summer bloomers that go summer dormant. You can cut bulb-types to ground level when foliage begins to turn yellow in summer.

Fig. 2  – Turkistan Onion (Allium karataviense), Gwen Steele

A relatively new addition to the Allium scene is the cultivar, Allium ‘Millenium’, and while not currently planted in the demonstration garden, volunteers have been testing this perennial in their private gardens and we look forward to introducing it to the UnH2O demonstration garden in the coming year.

This hybrid ornamental onion is easily grown in average, well-drained soil in full to part-sun locations and produces masses of rose-pink globe-shaped flowers at a height of 15-20 inches, with a similar spread. This Allium is not a bulb and hence blooms later in the season. It can be found in flower in mid to late summer, often covered with hungry pollinators. It should be cut to the ground in the late fall.

Allium ‘Millenium‘ was awarded the ‘Plant of the Year’ by the Perennial Plant Association for 2018.

All the above Alliums make excellent cut and dried flowers where their globe-shaped blooms provide an interesting contrast to more traditional flower forms.

Though many Allium are traditionally planted in the fall, ‘Millenium‘ is available from many bulb companies with a shipping date to our planting zone beginning in the first week of May.

Fig. 4 – Allium Millenium, provenwinners.com

If you want some stunning floral displays in your xeriscape garden, think of the Allium family.

Article by Sigrie Kendrick and Mark Godlewski

This is the second in a pair of blog articles discussing appropriate hedge choices for the Okanagan. This article will address non-native options.

European Privet (Ligustrum vulgare) is a good candidate for a hedge in our valley. It has been used extensively in the UK since Victorian times. Given its’ frequent use in rainy Britain people often do not realize that it is actually very drought tolerant. Privet is a fast-growing hedge that can reach up to 12 feet high with a spread of 10 feet. It takes pruning very well so it can be kept to a much smaller size. How frequently it needs to be pruned depends on whether you are looking for a traditional clipped hedge or a more casual natural look. The clipped hedge will likely require two or more clippings per year. Once established, Privet will require supplementary irrigation only in the hottest Okanagan summer months.

Fig. 1 – European Privet (Ligustrum vulgare), Mark Godlewski

Mugo pines (Pinus mugo) can make an excellent evergreen hedge. There are many cultivars of Mugo pine available, from dwarf to those which can reach a height and spread of 15 feet or more. The cultivar ‘ Columnaris’ slowly reaches a height of 10 feet, spreading 3-4 feet and as such it is perfectly suited for use as a drought-tolerant hedge. It can be successfully grown in an area of full to part-sun and once established will only require minimal water. Pinus mugo ‘Columnaris’ has finely textured foliage and produces small ornamental cones. It is not bothered by deer.

Amur maple, (Acer ginnala), is another option for a large hedge. It is really a small tree, but it can be pruned to a large multi-stemmed shrub suitable for use as a hedge in full sun or part sun, reaching up to 20 feet. Amur maples feature early-season yellowish-green flowers followed by red-winged samaras. The glossy, green-lobed leaves of Amur maples turn shades of yellow, red, and purple as the days cool in the Autumn.

Fig. 2  – Amur maple (Acer ginnala), Mark Godlewski

Hedge Cotoneaster (Cotoneaster lucidus) should also be considered, especially for smaller spaces. Native to Siberia and China, Cotoneaster lucidus is well adapted to the cold Okanagan winter and can eventually grow to 8 ft in both width and height. However, it responds very well to pruning, and can easily be kept to less than half of this maximum. The plant has small pink spring flowers transitioning to black fruit in the fall. It features stunning fall foliage in shades of orange and red. Flowering is best in full sun but Cotoneaster lucidus will tolerate partial shade, poor soil, and windy locations.

Fig. 3  – Cotoneaster lucidis, Mark Godlewski

Fig. 4  – Cotoneaster lucidis late fall, Mark Godlewski

Japanese Barberry (Berberis thunbergii) can make an admirably attractive hedge if you are content with its natural dimensions of 6 feet by 6 feet. It certainly discourages through traffic with its thorns. There are several shorter varieties if you are looking for a shorter hedge. Barberry hedges are often best pruned only occasionally which is a relief because it can be a painful experience.

Fig. 5  – Japanese Barberry (Berberis thunbergii), Mark Godlewski

Dwarf Burning Bush (Euonymus alatus ‘compactus’) and Golden Currant (Ribes aureum) are two other deciduous shrubs that can make excellent hedges. You can look up their attributes on the OXA Plant Database.

Or, if you are looking for a more modern-looking line of plants to delineate your property, why not consider a grouping of one of the many ornamental grasses on the market? A favorite is Andropogon gerardii or Big Bluestem. This is a warm season grass, meaning it will not offer you early-season privacy, but by midsummer the foliage will reach 5 feet and the attractive late season flowers extend another 2 feet on top of this. The foliage that starts out bluey-green, and transitions through the season to end with russet tones. If you want a grass that starts out early in the spring, you should consider Panicum virgatum ‘Heavy Metal’. Most ornamental grasses are not bothered by deer and their extensive root systems makes them good candidates for erosion control on many of our sloped Okanagan properties.

Whatever you choose to plant it is important to have a definite long-term strategy for pruning. The strategy will depend on the type of plant you are using and the maximum dimensions you want. Many homeowners plant and forget – until it is too late. All hedges need to be pruned regularly and some, conifers especially, respond very badly to heavy deep pruning. Some other hedges (e.g., Privet, Amur maple, Golden Currant) are prone to getting leggy if they are not pruned heavily sometime around their third year of growth after transplant. Hard pruning should be done in the late winter or early spring.