Beaumont-Wilshire: The Real Dirt
It hit 103° in our garden during our hottest summer weather. We didn’t like it; our plants didn’t like it. Tomatoes got sunburned, leaf edges became dry crisps, and perennials died that should thrive in warm weather. It is not clear whether this is climate change or a shorter drought cycle. Whatever it is, keep the following in mind to deal with hot weather in Portland:
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Find out where your plants naturally grow in the wild, and match those conditions as well as you can. Plants put in this year will need more water than usual until they are well established.
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Research what kind of soil and drainage the plants naturally grow in. Amend your planting areas with gravel/grit or organic materials to match this need. Those of us nearer the Alameda ridge tend to have clay and river rock. Those lucky gardeners in neighborhoods closer to the Columbia River have rich delta soil.
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Don’t water your lawns; let them go dormant. Lawns will recover when steady rains return. Save your watering for plants that will die if they don’t have more water than the weather and soil provide. Remember to water trees planted in lawns. Water plants in pots daily. For plants in the ground, run the water on the root areas long enough for the water to get down at least 12 inches to the roots. That way you don’t have to water every day. This is especially important for annuals and vegetables that have to do their entire growth process from seed to fruit quickly. Avoid sprinklers that let too much water evaporate. Instead, use soaker hoses or carefully directed hand-held watering devices.
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Consider what your pots are made of. We have tomatoes, peppers, and eggplants in large pots and full sun. The pots are dark plastic. The dark absorbs heat allowing the roots not to get too hot. Our vegetables looked strained and sunburned, despite careful watering. A wise gardening friend pointed out that our dark pots were absorbing too much heat and suggested that we shade the pots, but not the plants. We covered the pots with cardboard to reflect light and reduce heat (see image at right). We have gotten some funny looks from passersby, but it seems to be working.
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I made some planters out of foam fish boxes, carving texture on the outside and painting them. The petunias and basil in those pots are happy, even though they get full sun. They have well-insulated roots.
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Mulch placed in late spring will prevent some evaporation of soil moisture. Dry land plants in rock gardens should be mulched with gravel.
I just discovered a book about weather and gardening I like a lot. It is by Michael Allaby, The Gardener’s Guide to Weather and Climate, Timber Press, 2015. For those who are interested in weather and its relationship to gardening, I recommend it.