Linn County Master Gardener
A week of sunshine and shirt-sleeve days – it seemed like an early summer recently. Actually, it was more like the week of sun we usually get in February that starts the trees blooming. Are we two months behind?
Rain has returned and the temperatures are back to late-winter normal. 50-ish degree days and night temps in the 40s. It’ll be a while before we can safely plant most of the vegetables and flower seedlings.
Temperature is the key. Except for a few cold-hardy species and varieties, the optimum germination temperatures range above 60 degrees F. Sure, seeds will start at cooler temperatures – if they don’t rot from excess moisture first. Seeds take longer to start at cooler temperatures, so germination times on the packets are not accurate.
Starting seeds at room temperature and inside with controlled light and water is still the best approach for a while, except for some root crops that get misshapen when transplanted. The price of a package of many, possibly hundreds, of seeds seems to be about equal to a single plant at the garden store this year. Indian lore says to wait to plant when the snow is gone from the mountains.
After seedlings get “true” leaves, two or three sets minimum, they can tolerate cooler temperatures than their preferred germination environment, but there are minimum, optimum and maximum air temperatures for healthy growth.
Minimum and maximum temps can cause stunted, less productive plants. There is more research being done on maximum-tolerated temperatures because of the prediction of hotter summers.
Minimum temperatures for peas and potatoes are around 42 degrees F. Most vegetable plants do not thrive until temperatures are minimally above 50 degrees F. Melons, peppers, eggplants and other heat-loving plants require a minimum of about 60 degrees F to grow well. Tomatoes will not set fruit until night temperatures are above 55 degree F. Plants purchased with blossoms were probably brought out from a cozy greenhouse and are in for a shock (literally).
We’re nowhere near the maximum temperatures that will cause plants to shut down, but those days are expected this summer. Transplants should be placed with potential shade protection in mind for later.
Peas will stop producing in the 70 degree range. Greens and cool season crops will try to bolt – go to seed – if not shaded when the 70s arrive, so they are best planted now to get the most from them before mid-June.
Tomatoes and potatoes conserve energy and slow (or stop) growth when temperatures reach the 80s, up to 95 degrees F for some varieties if they are healthy and properly watered. Melons and cucumbers are more tolerant of 95 to 100 degrees F maximums, which we are expected to experience more of this year.
Beans and corn will produce up to 110 degree F-ish, especially if well irrigated and self-shading. That may be one reason early indigenous people grew beans in the shade of the corn, with squash to shade the roots.
Optimum temperatures for vegetable growth are on their way, but not quite here. Peas, greens and potatoes are responding to day temps in the 50s and 60s. Peppers, tomatoes and eggplants will wait for the 70s and 80s, and will not set much fruit until the 60s.
Beans, corn, cucumbers and melons will be slower to develop until day temperatures reach the 80s. Sure, they might all appear to grow, be green and not droopy, but they will really perk up when their preferred optimum heat ranges arrive.
It is early in this year’s growing season, possibly delayed by a couple of months, but then it will suddenly turn warm and dry. Possible in mid-June? Get a cheap thermometer and hang it out near the growing area to monitor air temperatures. Invest in a soil thermometer, as well. Try not to bury the soil thermometer too deep– we’re still looking for one that has gone underground!
