From Rosie Lerner, Purdue University horticulturist
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The early arrival of summer’s steamy weather in Indiana is tough on garden plants and their gardeners. It is really difficult to stay motivated to keep up with garden chores when you’re already dripping with perspiration by 9 a.m.!
High temps affect vegetable production
Although the weeds, insects, diseases and critters don’t seem to have any trouble thriving in this weather, some vegetable crops have trouble producing when under stress. Tomatoes, peppers, melons, squash, pumpkins, cucumbers and beans often drop their blossoms without setting fruit when day temperatures are above 90. There’s not much you can do but wait for cooler temperatures to prevail. As more favorable conditions return, the plants will resume normal fruit set.
Heat may reduce corn
Sweet corn is also likely to have trouble setting fruit in such hot weather. Unfortunately, you only get one flush of flowering with corn; so, if your plants just happen to be shedding pollen when the weather is stressful, you can expect poor ear fill later.
Lettuces, other crops bolt early
Cool-season crops, such as lettuce and spinach, will bolt – or produce – seed stalks, causing the flavor of the leaves to become bitter. It’s best to remove these crops and replant with heat-tolerant vegetables, such as beans, carrots or chard.
More water may be necessary
Newly set transplants will require more frequent watering and will benefit by shading from midday sun to avoid wilting. In some cases, plants will wilt during midday despite all your efforts, simply because the leaves are losing moisture faster than the root system can take up water. Watering plants wilting from heat may not be necessary because they will recover in the evening and morning hours when temperatures are cooler.
Extremes in temperature and soil moisture often bring on blossom-end rot, a dry, leathery scarring of the blossom end of the fruit on crops, such as tomatoes, peppers and squash. Irrigating during dry periods and mulching to conserve soil moisture will help minimize this problem.
Container plants out on the patio will really be stressed by the heat wave, since they have much less buffering of temperature extremes on the root system. In addition to watering more frequently in hot weather, provide afternoon shade, if possible, to help keep them a bit cooler.
The good news is that the weather is always changing. The extreme heat won’t last forever – it will just seem like it! In the meantime, try not to overdo the garden work. Aim to complete your chores very early in the morning or in the evening when the sun is less intense. And take frequent breaks and drink plenty of water to keep yourself from wilting. — Rosie Lerner, Purdue University horticulturist