“How can I garden in this awful heat?” has become a plaintive cry as winter whisked through a very chilly spring and bumped headlong into summer. Not only are we never satisfied with the temperature, but our plants are also having a hard time, too.
Irrigation is one sort of insurance we have against dry weather. Because we live where we live, we do not depend on rain to provide water for our crops. We must add it ourselves — judiciously.
Frequent shallow watering will keep plants alive on a sort of life-support. If you have watered deeply and infrequently, your plants should have developed deep roots and they stand a better chance of holding out against hot summer days and low humidity. Nevertheless, the tops will still have to deal with the low humidity, high temperatures and scorching winds.
Leaf and other tissues of most plants die at about 115 degrees. The air temperatures haven’t gotten there and likely they won’t. Plants are normally about the same temperature as the air, but they can still suffer setbacks.
Everybody talks about the weather but nobody does anything about it. Fortunately, it is not entirely up to the gardener to protect garden plants from the weather. To varying degrees, plants are pretty good at fending for themselves. They have built-in temperature regulators to help keep them from overheating.
They can reflect the sun’s rays and the heat of those rays, transfer the heat to the air by convection and transportation, or allow water to escape from their leaves to create their own evaporative cooling system.
Our over-arching, blue-sky days certainly provide the sunshine plants need, but when other conditions are wrong too much sun can damage crop production. The sun’s heat can cause considerable harm to growing and reproductive structures.
When we get very hot, dry winds, plants struggle to cope. Leaves carry water away from the roots faster than they can absorb it. Plants produce their own food through photosynthesis. When temperatures increase above 94 degrees, photosynthesis declines so hot weather limits production.
High heat in the daytime causes major heat problems, but one of Utah’s best features is our summer nights that typically cool down. This allows the plants to rest during the evening and nighttime hours so they do not continue to consume the food they produce during the day and can store it. However, sometimes nighttimes stay warm and plants go on using food that was produced during the day.
Where plants are placed also affects how they grow. Heat is reflected from soil and walls during the day, and the surface temperatures on black plastic mulch can exceed 150°F.
All of this sets the stage for problems we often see. Tomatoes are a favorite garden plant and are thus one of the first we notice when they do not produce well. “Why are the vines not setting fruit?” becomes a common query.
Many of us got our tomatoes planted a little late this year and perhaps they are not yet mature enough to set fruit. Time and the right conditions will cure that problem.
Tomatoes set fruit best when night time temperatures range between 60 and 70 degrees. When nighttime temperatures go above 75 degrees, pollen tube growth stops. Although blossoms form, the heat causes them to drop off the plant without producing fruit. Daytime temperatures above 95 degrees cause the same problem. Blossoms abort and fruits that do set often become misshapen and small.
High temperatures also affect fruit set and quality of beans, cucumbers, squash, pumpkins and melons. Some cultivars are more heat tolerant than others, but none are completely immune. When they are poorly pollinated due to heat, the fruits become misshapen.
Blossom end rot is a regular problem in our summers and it is worse when the weather is hot. It appears as a brown, sunken spot on the blossom end of partially grown fruits. Tomatoes show it most commonly, but peppers, squash and melons can also develop this anomaly. The spot withers and becomes leathery.
There are things you can do to help with this problem. Much of the problem comes from allowing garden soil to become alternately dry and wet. Keep plants uniformly moist and protect the roots from injury. Overwatering and keeping soil wet is not a solution. Use mulch to maintain a more uniform moisture supply.
Fruits often crack in hot weather. Rain and sprinkling does not help the problem, the moisture on the fruit exacerbates it. The excessive heat and low humidity dehydrates the skin of the tomato and makes it shrink slightly. A thunderstorm or sprinkling tomatoes that have not been previously watered that way or too much water makes the fruit swell inside. This cracks the skin.
Some tomato cultivars resist cracking more than others. Heirlooms are very prone to this problem. Try to keep water off the fruit and pick and use cracked fruit as promptly as possible.
Sunscald is a problem when the plant does not have enough leaves. The part of the tomato that is exposed to the sun turns tan and looks unattractive. The skin may also become tough. Very high temperatures also prevent fruit from developing the good color we would like.
You cannot manage the weather, but by managing your gardening skills, you can help your plants to cope.