How to Protect Your Garden Crops from Heat Stress

• Some plants begin to wilt by midday — They often turn their leaves downward in an attempt to protect themselves from harsh sunlight. This is one of the earliest visual cues that your crops are under serious strain.

• The flowers may drop — If you have flowering or fruiting crops, you may notice their flowers falling to the ground or failing to set fruit (transitioning from blossom to a young fruit).

• Yellowing or browning leaves are also a sign of heat stress — Internally, high temperatures trigger rapid water loss through transpiration, disrupt photosynthesis, and damage the plant’s cell structures. You may also notice the plant’s growth slowing down.

• Watch out for what’s called “permanent wilting point” — This is a situation wherein the plant wilts during early morning — right after sunrise. At this stage, your plant can only absorb about 35% of the soil’s water-holding capacity, which, unfortunately, is not enough to keep it alive. Once your plant meets this threshold, recovery becomes nearly impossible, and it is close to dying.

• Use your garden bed’s layout to provide natural shade — In the video, CaliKim explains how she uses small teepee trails where her cucumbers climb up and grow, and underneath it, she has lettuce growing. Not only does it provide protective shade, but it helps maximize her growing space.

• Maximize existing shady areas of your garden — Tall fences, shady trees, and areas near walls or other structures can provide shade in the afternoon — consider placing heat-sensitive plants here.

In the video, CaliKim shows her garden nook, an area that gets plenty of morning sun but nice shade during the afternoon, which is when the sunlight is most intense. “I have over 10 to 15 different kinds of greens, herbs, vegetables, and fruits growing in this area so I can still grow here even in the heat of the summer,” she adds.³

• Consider adding shade structures as well — Building structures like pergolas or hoop houses will provide a cooler environment for your plants, but if they don’t fit your budget, consider installing a shade canopy⁴ or using shade cloth instead. CaliKim shares why she prefers using shade cloth:

“[Shade cloth is] porous — some of the sunlight still gets through but it does block a portion of the sun’s UV rays. There’s a few different types of shade cloth you can use that block various percentage of the UV rays.

If you don’t have shade cloth, just use an old sheet. It’s better than nothing. It is definitely better than fried plants.”

• Select heat-tolerant plants — If you live in an area where the heat becomes very intense during hot seasons, part of planning your garden’s layout is making sure you choose plants that are able to withstand high temperatures. Check the predicted weather patterns for summer, and determine which plants will work best for the climate in your region. The good news is, there are numerous native plants and succulents that are naturally heat-resistant.

• Prevent this by adding mulch over your soil — According to gardening expert Madison Moulton, “Fresh mulch applied right before a predicted heat wave can make the difference between plants surviving or succumbing to heat stress.”⁷ Mulching works for both heat and cold resistance, protecting the surface of the soil while regulating the temperature underneath it.

• Mulching preserves your topsoil — Because there’s reduced evaporation at the upper soil levels, mulching also reduces the risk of soil erosion.

• What type of mulch can you use? Ideally, organic mulch varieties like straw, grass clippings, or wood chips are good choices, as they provide added nutrients to the soil when they break down.⁸ However, if you don’t have organic mulch on hand, old newspaper or cardboard covered with a thin layer of grass clippings will suffice on short notice.

• Don’t add too much mulch — This will lead to compacted soil and prevent sufficient water from penetrating the ground. If there are areas where soil compaction is a concern, apply a thinner layer of mulch.

• How about container plants? If you have plants growing in containers, Moulton recommends placing them inside larger pots then filling the space between with mulch or moist peat moss. This will protect the roots from overheating and minimize water loss.

• During heat waves, plants significantly need more water than their usual growing conditions — “A tomato plant that usually needs 1 inch of water per week might need 2 or 3 inches of water during a heat wave. Leafy vegetables like lettuce and spinach need even more water relative to their size because they lose moisture rapidly through their large leaf surface,” Moulton explains.

• However, light but frequent watering sessions aren’t recommended — Moulton says that while this technique may seem helpful, what it does is it ends up encouraging shallow root systems — as a result, the plants become more susceptible to damage from heat stress. “Plus, that shallow water evaporates quickly, making the extra effort not worth it in the end,” she adds.

• When you deep water, plant roots grow down into cooler soil layers that are more stable — Shallow watering retains roots near the surface — in this area, soil temperatures can exceed 100 degrees F (38 degrees C). On the other hand, deep watering allows plants with deep roots to reach water reserves that surface-rooted plants don’t have access to.

• Here’s how to do it — To do deep watering, soak the soil several inches deep during each watering session. Take your time — a good idea is to set up irrigation systems that consistently provide moisture over time with limited loss.

• The type of soil matters — Clay soils retain moisture longer and can go two to three days between deep watering sessions, depending on the conditions. Meanwhile, sandy soils drain faster and may need daily deep watering.

• Check the soil for moisture — Moulton recommends sticking your finger 2 inches into the soil. If it feels dry at that depth, then water your plants. If you have in-ground plant beds, digging down a few more inches may be needed to check moisture levels before you consider watering your plants.

Consider using soil moisture meters as well, especially if you have a large garden area. These handy tools give you accurate readings at different soil depths, preventing both drought stress and overwatering.

• Morning is the best time to water — Ideally, water your plants during early morning, so the plants become hydrated before the intense heat hits. Doing this also minimizes evaporation losses and provides plants with the best chance to survive the extreme afternoon sunlight.

• Evening watering works, but there’s a caveat — This will only be beneficial if you water late enough to allow plants to absorb moisture overnight. Late afternoon watering, when the ground is still hot isn’t ideal, as the heat from the soil will cause the water to evaporate before your plant can use it. It’s best to wait when the sun has set and the temperature starts dropping.

• Watering during midday is only recommended if your plants appear extremely stressed — Afternoon watering is helpful if you notice your plants wilting badly, as it will prevent permanent damage. However, doing this regularly is wasteful, as the heat will only cause the water to evaporate.

• If you have a vegetable garden — Prioritize watering the plants that are heat-sensitive or nearing their harvest date. Native plants that are adapted to your local climate are generally more heat-tolerant as well, so you can put them on lower priority.

• For plants grown in pots or containers — Make sure they get enough attention (and water). Unlike in-ground plants, they have no access to groundwater and have less soil volume, giving them limited storage moisture.

• If you have newly planted trees and shrubs — They need priority watering. This is because their root systems are not yet established, meaning they could die after just a few days of severe heat stress. They also tend to be more expensive.

• Gardening allows you to spend time outdoors — Not only are you able to reap the benefits of sunlight, but you also become one with nature, which is good for your mind and body.

• It “exercises” your brain — Gardening involves a lot of elements, and requires planning, focus, and creativity — all of which give your brain a lasting edge. I recommend reading “How Digging in the Dirt Helps Preserve Your Brain” for more insight on how gardening boosts your brain health.

• Sleep problems? Try gardening — Studies found that gardening not only improves sleep duration, but also wards off sleep apnea, insomnia, and daytime sleepiness.¹⁰

• Lastly, it slashes your food bill — Growing your own fruits, vegetables, herbs, and spices not only ensures you’re eating produce that’s free of commercially applied pesticides, but it also helps you save money on groceries. The best part? You get to enjoy the freshest food possible.