Xeriscape in the Okanagan
The Okanagan Environment
The Okanagan Valley features a string of seven lakes along its length of approximately 160 kilometres (100 miles). The valley follows a major extensional fault system that is at least 24 million years old. Many of the soils and sediments are a product of the last glacial age and the associated glacial lakes and rivers. Today, the Okanagan Valley is a semi-arid climate, and includes the only desert in Canada at its southern end. The average annual precipitation is about 280 millimetres (11 inches).
Natural vegetation along the valley bottom, which is at about 300 metres in altitude (1,000 feet), is predominantly Ponderosa Pine and Bluebunch Wheatgrass habitat, along with cactus, Rabbitbrush and sagebrushes in the south.
The land slopes up on either side of the mainstem lakes to 500 metres (1,700 feet) on the benchlands. Here in spring, the showy Arrow-leaved Balsamroot turn the hillsides yellow with their blooms against a backdrop of abundant white-flowered Saskatoon bushes. In summer the hills turn brown as the grasses die back for lack of rain. A fall feature is the red berries of the sumac, paired with the grey foliage of the sagebrushes and vivid yellow bloom of Rabbitbrush.
Wildlife include white-tailed and mule deer, yellow-bellied marmot, coyotes, cougars, lynx, black bears and the occasional grizzly bear, as well as moose and elk at higher elevations, and small populations of California bighorn sheep and mountain goats.
GROWING CONDITIONS
TEMPERATURE
The mean daily temperature in January is between 0 and -5C (32 and 23F), while in July, it’s 20 to 22C (68 to 72F). However, in winter it is not uncommon for temperatures to plunge to -32C (-26 F), while in summer, they can soar to 40C (104 F). Hot, sunny summers and fairly mild, overcast winters put the Okanagan in plant hardiness zones four to six.
*USDA plant hardiness zones are calculated by the average lowest winter temperature- the Okanagan is zone 1 to 5.
PRECIPITATION
The average annual precipitation is about 280 millimetres (11 inches), approximately half of this falling as snow in winter. Summers are getting drier and two to eight weeks without any rainfall is becoming common. When it does rain, it often comes as a very short, heavy downpour in a thunderstorm. Frequently this welcome rain falls too fast for the parched soil to absorb the water and so it runs off into streams and storm drains.
SOILS
The soils have a tendency to be alkaline rather than acidic, with an average pH of 7.6. Due to low precipitation, growth of natural vegetation is slow and there is very little organic matter in the soils.
