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Gardening in extreme heat

This year has brought record high temperatures to much of the country (again, but don’t worry, Exxon says this has nothing to do with global warming), so I wanted to say something about keeping your vegetables garden happy when the mercury soars.

Pick the right plants
High temperatures don’t just make plants uncomfortable, they can actually stop them growing and seriously affect productivity. When it gets too hot we can simply stay in the shade, or go into the house, but plants are stuck in the full sun and have to deal with it. Your choice of variety is also significant as some are more heat tolerant than others. Look for those that were developed for the tropics, desert or southern states, as many of these plants have developed several mechanisms for coping with heat stress and these are the most reliable plants to grow in hot weather. They include cowpea, okra, melon, pepper, tomato, sweet potato, lima bean, watermelon, and amaranth.

But even heat-tolerant fruiting crops (beans, tomato, eggplant, pepper, okra) can have problems when it gets much above 90 degrees Fahrenheit because flowers may not pollinate and will drop instead of setting fruit (plant breeders are working on heat resistant varieties that don’t do this).

Water them well
Just as it is essential for humans to drink plenty of water during hot weather, so it is with plants. Your first priority should be ensuring they get enough water, as this will help them to keep growing and producing (without it they are toast). The best way to water in hot weather is with a drip system, such as in-line drip irrigation tubing or soaker hose, which allows the water to quickly soak in to the ground. Overhead sprinklers aren’t as good because a lot of the water will often simply evaporate in the heat. If you must use sprinklers then avoid watering in the middle of the day, do it in the cool of early morning or early evening (early enough that plants don’t stay wet all night). Water is especially critical when plants are sizing up fruit and blossom end rot is often a problem if watering is irregular.

Mulch to keep them cool
Bare soil dries out quickly when exposed to the fierce heat of the sun, so it is also important to keep it covered as much as possible (there is no point in supplying water and then watching much of it evaporate). The most convenient mulch is a 2 to 4” layer of straw, which is readily available at feed stores. Mulch also keeps the soil cooler by shading it from the heat of the sun (plants can cope much better if their roots are cool). It also prevents the growth of competing annual weeds.

Give them some shade
In extremely hot conditions strong sunlight can be a problem because it raises temperatures even further. In such situations plants may benefit from some kind of shade during the hottest part of the day. This could be provided by shade cloth over hoops, or some kind of wooden framework covered with trellis, or even sticks (to create dappled shade). You can also create shade by planting tall plants such as sunflower or corn, but of course these require water too.

Help them recover quickly
Many plants (especially those with big leaves) wilt naturally in the heat of the day to reduce moisture loss, but they recover quickly when it cools down. If plants don’t recover quickly when the temperature drops, they are severely stressed and need water. Prolonged water stress is easily identifiable because leaves (and sometimes fruit) become bleached or scorched and growth is slower.

Take care of the gardener
It is also important to think about yourself in hot weather. Drink plenty of water and keep out of the garden during the hottest part of the day (also wear a hat). If you are an early riser the best time to be in the garden is when the sun first comes up, it is so beautiful and peaceful. I tend to come to life in the evening and get most of my work done in the couple of hours before the sun sets.