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Boy, from the frying pan into the fire these first few weeks of May! The vegetable garden will be responding – for better and for worse – to in the upper 80s so early in the season. One thing we can do to alleviate a little heat stress is to employ some shade devices for our spring crops and seedlings.
The vegetable garden can start doing some funny things during a heat wave. When temperatures start to rise into the upper 80s and 90s, many vegetables drop flowers before pollination and fruit set and stop blooming all together.
Beans, tomatoes and eggplant do like it hot, but there is a threshold of tolerance to heat; ideal temperatures for maximum performance is about 86 during the day for these summer vegetables.
The heat also will make other crops bolt and become bitter. Spinach, peas, and colecrops such as broccoli, Brussels sprouts and cauliflower prefer the cool temperatures of spring and fall and make haste to flower and go to seed when temperatures rise. The current weather may do them in for the season.
Tender lettuces will bolt, too. My first round of tender Bibb and Black Seeded Simpson lettuce will not be happy, but I have plans to seed a second round of summer lettuces (varieties more suited to the heat) that include the bolt resistant Jericho and a “heat wave” mix from Cook’s Garden. The summer lettuces can stand some heat but will last longer if I provide some shade.
The fruit of some crops can get sun burned when temperatures are high. Sunscald is common on ripening tomatoes, especially if the plant is a little diseased and the foliage isn’t adequately shading the fruit on its own.
Think about all the crops that tuck themselves beneath the foliage of the plant. All of these will get sunburned if left otherwise exposed on a 90-degree, full-sun day.
This is where we can step in and help out with some strategically placed homemade shade devices.
Providing a little shade will go rather far when temperatures rise into the 90s, and you may want to consider it throughout the garden. You can use latticework, old screens, shade cloth, old sheets, fine netting or mesh (like what you would use for a wedding veil).
Concrete blocks, bricks or terracotta flowerpots can provide the base for a screen to rest on several inches above a low-growing crop such as lettuce.
A picnic table bench works great as a prop for a screen set on a slant on the south side for crops that are medium height, and using a shade cloth tied to four bamboo stakes can shade anything at any height from above or on a slant depending on the length and placement of the stakes.
You get the idea.
If we continue to get ample moisture we will be lucky because the high heat will make plants transpire moisture through their foliage at a faster rate than they can take it up through their roots.
Wilting because of this transpiration may occur which doesn’t necessarily mean the soil is dry. If a plant recovers overnight, then you know that the wilting was caused by rapid transpiration not thirst.
Extra shade will help offset this; and, if you never mulched your vegetables, now would be the time to reassess that decision.
Mulch helps keep the soil moist but it helps keep it a bit cooler, too.