Dealing With Heat Stress: How To Protect Vegetables In Hot Weather

Dealing With Heat Stress: How To Protect Vegetables In Hot Weather

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By: Susan Patterson, Master Gardener

In many parts of the country, gardeners have considerable anxiety when summer temperatures rise, especially when they rise in combination with low rainfall amounts. While some vegetables suffer more than others, all feel some degree of stress with rising temperatures. Dealing with heat stress can be frustrating for gardeners, so it’s important to find ways for protecting plants in scorching temps. Keep reading to learn more about how to protect vegetables in hot weather.

Continued exposure to high temperatures can cause leaf scorch, leaf drop and even leaf sunburn. In addition, high temperatures interfere with photosynthesis and can cause a buildup of toxins in plants. Plants that are stressed because of the heat may develop misshapen or bitter fruit. Gardeners need to know how to protect vegetables in hot weather in order to avoid irreversible damage.

Protecting Plants in Scorching Temps

One of the most popular ways of protecting plants in the summer heat is by using a shade cloth for gardens. A simple garden shade cloth can be strung between supports or a more elaborate structure can be constructed in areas that are prone to oppressive heat.

Trellises and pergolas can also help create shade to protect plants during the hottest time of the day.

In addition, providing plenty of water during times of high heat is useful in dealing with heat stress. It is best to use a drip irrigation system and check this regularly to be sure that all plants are being fed an adequate supply of water. A misting system is also useful and helps reduce plant tissue temperature. Keeping plants well hydrated gives them the ammunition that they need to fight off the stress caused by scorching temperatures.

You should provide mulch around plants to help with moisture retention as well when protecting plants in scorching temps.

Healthy Plants Do Best When Dealing with Heat Stress

One of the best ways to protect your plants from extremely high temperatures is to be sure that you provide all of the nutrients necessary for them to be healthy. Rich organic soil, organic fertilizer, plenty of water and lots of TLC will keep your veggie garden ready to stand when the high temperatures hit.

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Shade: Hot Weather Vegetable Garden Protection

Vegetable crops should be protected from temperatures much greater than 95°F (35°C). Most vegetables will be stressed when temperatures rise to 100°F and many will die in sustained temperatures greater than 110°F.

Signs of heat stress in vegetables include wilting at the ends of new growth, blossom drop, leaf drop, and sunburn of leaves and fruit Sunburn is characterized by dull yellow patches in the center of leaves and on fruit these patches may turn white and thin as plant tissue dies.

When temperatures rise to greater than 95°F for more than a day or two most warm-weather crops will stop growing and setting fruit. (The same happens to cool-weather crops at about 80°F.)

If high temperatures persist, it is best to protect vegetables from sun and heat. The best course of action is to keep direct sun off of foliage and to lower the temperature of plants. Shade can lower plant and soil temperatures by as much as 10°F.

Shading Plants in Hot Weather:

• Use shade cloth to protect plants. Use plant stakes or fiberglass or poly hoops to build a framework over plants or planting beds and drape shade cloth over the frame much as you would drape a tablecloth over a table. In addition to protecting plants from mid-day sun, angle the frame and cloth to protect plants from the setting sun as well. Avoid completely covering plants allow space of 2 or 3 feet for air to enter and move easily around the plants.

• Attach dark-colored shade cloth to the plant protection framework do not allow dark shade cloth which more readily absorbs heat to sit directly on plant foliage.

• White- or light-colored shade cloth can be placed closer to plant foliage because it reflects away heat in addition to providing shade.

• Summer weight garden fabric made of polyprophylene or row covers made of muslin or cheesecloth can sit directly on plant foliage. Light weight row covers can block as much as 85 percent of sunlight while lowering the temperature and trapping humidity around the plants.

• Peaches, apples, and other fruits–even tomatoes, peppers, and eggplants–hanging on the ends of branches can be protected by placing paper or cloth sacks over them if hanging a shade cloth over the plant is not doable. Grapes can be protected by slipping a paper bag over fruit clusters and stapling or taping the end closed.

• Plants located on the south or west end of the garden can be protected by erecting temporary shade framework. Hang shade cloth from a line between two posts much as you would towels from a clothes line or place a section of picket fence between two stakes set the section of fence against the stakes at a 45-degree angle.

• Garden umbrellas can be stationed near vegetable beds during hot spells to keep the sun at bay. A laundry basket or bushel basket turned upside down can protect small crops. A plastic seed or plant flat can be placed upside down over seeded beds or just germinated seedlings.

• Cut branches from palm trees, palmetto trees, or evergreen trees can be stuck cut end in the soil along the west or south side of crop rows.

• Two or more rows of sunflowers, sunchokes, corn or other tall plants can be planted alongside garden beds where afternoon sun and heat is a perennial summer problem. Tall crops are commonly planted on the north side of gardens, but in hot summer regions tall crops on the west or south side of the garden may be the prudent course.

Other Heat Wave Protection Solutions:

Watering. In addition to shading plants, keep close watch on soil moisture and evaporation. Keep the soil around summer crops evenly moist. Drying soil down to 2 or 3 inches is acceptable for established crops but not for shallow-rooted crops. If the soil is not moist at 4 inches below the surface, give plants a slow, deep watering. Avoid over watering plant roots can suffer and even drown if soil air is depleted.

Mulching. Stem soil moisture evaporation and keep the soil temperature down by mulching. Apply two to three inches of dried leaves or compost around plants at midsummer to slow soil moisture evaporation.

Soil temperatures of greater than 85°F can slow plant growth mulch will moderate soil temperature by keeping the sun’s rays from directly warming the soil. The temperature of soil under mulch will change much more slowly.

8 Ultra-simple Steps to Protect Your Garden During a Heat Wave

Concerned that the scorching sun will ruin your beautiful garden? Worry not. This Gardenerdy post will help you in keeping it fresh and vibrant even through the most gruesome heat wave.

Concerned that the scorching sun will ruin your beautiful garden? Worry not. This Gardenerdy post will help you in keeping it fresh and vibrant even through the most gruesome heat wave.

Did you Know…

… that the growth and nutrient requirement of plants decreases naturally during summer, and all they need is a bit of TLC to carry them through the harsh conditions.

Gardens provide a cool, breezy space perfect for relaxation and a bit of me-time. Unfortunately, extreme weather conditions and record-breaking temperatures – a common occurrence these days, have the potential to wreak havoc on your garden.

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To minimize damage, many experts recommend planting native plants to begin with – plants that have evolved over thousands of years and are well adapted to the local conditions. But, a heat wave can damage the native plants as well and besides, we all love a bit of variety.

Another thing we must do is to recognizing the signs of heat damage and provide that particular plant some extra care or move it in the shade. A heat-damaged or dehydrated (usually both go hand-in-hand) plant will reveal itself by displaying droopy, yellow leaves throughout the sun-exposed area whereas the shaded leaves will have a healthy green coloration. The yellowing generally occurs around the edges and veins and might progress into brown, brittle leaves. Ultimately leading to a permanently damaged plant, unless immediate action is taken.

While you cannot undo the damage once done, you can definitely ensure that the garden stays happy and green, using these simple yet effective steps, before and during a heat wave.

Keep the Grass Taller

It is a good idea to keep the grass longer during the summer months. This has three advantages – two that are good for the garden, and one that is good for you. First, the longer leaf blades will help the soil retain moisture by shielding it from the sun. Two, it will keep the garden cooler, reducing the impact of the blazing sun. And three, it will cut your mowing time.

Keep the grass approximately ½-inch longer than you usually do. It is best to mow in the morning or evening, so that the lower, shielded leaves get time to get accustomed to the elements. Also, make sure that the blade of the mower is sharp, as a dull blade might damage the leaf tips.

Prune Less

Pruning might stimulate new growth, which is fine and dandy during spring, but the tender shoots and leaves become much more vulnerable to the elements. Limit it to only the dead, infested or decaying parts. A dead branch or a bunch of brown, rotting leaves are perfect candidates for pruning. Use a disinfected blade, as a new cut is an ideal entry point for bugs and pests. You may keep a few dead leaves near the roots, but do make sure they are rot-free. If you have an overgrown shrub or tree, prune it long before the high temperatures set in. The best time to prune a tree is during late winter, just before spring sets in.

Construct a Sun-Screen

The most important step to protect your garden would be to create a barrier between the hot sun and the plants. While most established, native plants may not need the shade, potted plants and newly established trees will need some protection. The shading will also reduce water loss through their leaves, as plants, like us, ‘perspire’ to stay cool. This also means the plant will need much less water to stay hydrated, an important consideration if you are facing a drought.

You can use anything to construct the barrier, as long as it stays put and is not a fire hazard, especially if forest fires are an issue in your area. Use a bed-sheet, a beach umbrella, a fancy awning, old curtains or even the good old tarp suspended on bamboo poles about 10 feet high. Although, a store-bought canopy will offer better protection as it thicker, more resistant to damage and custom-made to shield the plants.

Move Tender Plants to The Shade

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Once the canopy is set, move the delicate plants to the shade. You can also utilize the shade of tall trees or plants, or the house itself. Make sure you group the plant in a cozy manner, meaning they should be huddled closely, but have enough space to grow and breathe. Placing the plants closely will further lower the temperature around them and increase the humidity. Try to place the most delicate ones in the center, with the tougher ones around the edges.

Get Rid of Weeds

Weeds steal all the precious moisture and nutrients from your plants. Plus, they are hardy and manage to thrive even through the worst of conditions. Even worse, they attract pests, diseases and infections making your plants even more susceptible.

Pull out any weeds as soon as you notice them. The younger the weed, the easier it is to get rid of. In case of a well-established weed, cut off the top, leaves and all, with only the stump remaining. You might have to do this several times till its root taps get exhausted. Summer is also the time when you can compost the weeds, as the heat in the compost bin will destroy the seeds naturally.


Mulch helps the soil retain moisture by reducing evaporation of water. This means the plant will require much less water to thrive. It also suppresses the growth of most weeds and provides the plants or shrubs with nutrients. Mulch is an efficient organic and fully natural substitute for both, herbicides and fertilizers.

Add a thick layer (2-inch thick for finer mulch and 4-inch of the chunkier mulch) to all plant beds. Do leave a gap of a few inches around the base of the plant. Do not use a weed mat or plastic sheet as an underlay. Put the mulch deeper, over a newspaper about 16 sheet thick, to prevent weed growth. Also, do remember to weed before you mulch. Preferably, use light, reflective mulch like straw or saw dust during the summer months.

Avoid Watering at Noon

Water in the morning, before the heat sets in, ideally before 10 AM. This will make sure the plants stay hydrated during the sweltering heat and will also help in keeping the temperatures down. The next best option is late afternoon, after the worst of the heat is over, but before evening. This will ensure that the leaves stay dry during the night, which happens to be the preferred time for a fungus to take roots. Also, try to not get the leaves wet if you are watering after 5 PM.

The reason for avoiding watering the plants at mid-day is that the combination of water and heat can actually scald the plants instead of having a cooling effect. Plus, most of the water might evaporate before soaking in the soil and reaching the roots. For best results, water deep, meaning the moisture should reach at least 6 inches deep once you water the garden. Then, water again only after the top 2 inches are completely dry (usually, this means deep-watering every couple of days).

Do Not Disturb the Soil During a Heat Wave

Disturbing the soil at this time will only release the trapped water. You want this moisture to stay in the soil to hydrate your plant as well as to keep the temperatures down. So do not carry out any activity which might disturb the soil, such as digging, weeding, planting or transporting plants. The newly transported plants or young seedlings are much more susceptible and vulnerable. If you have weeds, just cut off their heads, instead of pulling them out, so as not to disturb the soil surrounding them.

In short, the best to protect your garden during a heat wave is to disturb it as little as possible, while ensuring that it is well-hydrated, cool and the plants have sufficient nutrients.

13 Tips for Gardening in Extreme Heat

Some gardeners live in climates with extremely hot summers, where daily temperatures frequently exceed 90, or even 100 degrees. If this is your situation, summer may be the most difficult season for your garden, instead of winter.

Extreme heat is not only stressful for many plants, but it can actually make many of them go dormant and stop growing – even if they are kept well watered. High heat can also keep plants from setting any fruit because extremely hot temperatures can kill the pollen. Other crops will bolt and go to seed extremely quickly.

Here are thirteen tips to help you continue gardening during very hot weather:

1. Focus on plants that love the heat.

Look for those vegetables that were bred for the desert, the southern states, or the tropics. These include: tomatoes, eggplant, melons, peppers, malabar spinach, cowpeas, and lima beans. Sweet potatoes, okra, and southern peas can handle the most heat.

However, even many of these plants may drop their blossoms and stop setting fruit when the temperatures regularly exceed 90 degrees F. Look for varieties that may have been bred to continue fruiting in extreme heat.

2. Keep your plants well-watered.

Although in some situations you may need to water daily, it's very important to water your plants deeply – a minimum of 6 inches down – at least once a week for clay soils, and twice a week for sandy ones. Don’t guess – check your soil moisture level by using a trowel to dig 6” down.

This young butternut squash split apart when the garden was watered heavily after a long dry spell.

You’ll gradually learn how much you need to water your garden to maintain a good moisture level. Expect your garden to need at least twice as much water (or even more) during periods of extreme heat. High winds can also increase water demand.

Make sure you don't let the soil dry out too much in between watering. I've had sweet potatoes tubers and butternut squash fruit split badly when the plants were heavily watered after the soil had become very dry.

3. Make sure your soil has a good level of organic matter.

Healthy levels of organic matter (about 5-9%, depending on your soil type and climate) can make a huge difference in helping the soil to retain more water. In addition, a healthy soil full of beneficial soil organisms, such as mycorrhizal fungi, helps plants to better tolerate drought.

4. Keep your soil covered with 2-4” of organic mulch.

Using straw, grass cuttings, shredded leaves, etc. for mulch will keep the soil cooler and prevent it from drying out as quickly – but don't use too thick of a layer. While mulch can help preserve moisture in the soil, a thick layer can also prevent rainfall from reaching the soil underneath, as the mulch itself can absorb large amounts of water.

5. Give your plants some shade.

Giving your garden some partial shade during periods of extreme heat can reduce temperatures by 10 degrees F or more. You can cover your garden with shade cloth , a snow-fence, or latticework supported on a frame – even old sheets or sheer curtains. Make sure your shade-producing materials are well-secured against high winds, and are high enough above the plants so that your garden will get good ventilation.

Many gardeners in extremely hot climates have found that providing about 30-40% shade usually works best. Even tomatoes, peppers, and squashes can benefit from shade cloth in desert climates.

You can also put your garden on the east side of a building, where it will receive shade during the afternoon heat. Some people choose to place their gardens on the east side of trees, tall shrubs, or trellised plants. Just be sure that the roots of the trees and shrubs won't invade your garden and compete with your vegetables. Tree roots can extend far beyond their branches. Even large vegetable plants on trellises can seriously compete for water with smaller plants in the same garden bed.

6. Avoid surrounding your garden beds with crushed stone, brick, or concrete paths.

Brick, stone, and concrete will absorb heat and keep your garden hotter during the summer.

These will absorb extra heat and continue to release it after the sun sets – the equivalent of the “urban heat island” effect in your garden. Your garden will also be hotter if you place it up against an unshaded south or west side of buildings (in the northern hemisphere). You can keep your garden cooler by surrounding your garden beds with lawn grass or organic mulch.

7. Start seeds indoors under lights

Many seeds will not germinate at all if the soil gets too hot. During periods of extreme heat, one option is to start these seeds indoors under lights, and then transplant them into the garden after hardening them off (gradually adjusting the plants to direct sunlight and wind). Make sure you keep your newly planted seedlings well-watered and partly shaded as they get established outdoors.

8. Pre-soak seeds and furrows for crops you plant outdoors

For your larger seeds (such as peas), pre-soak them for 24 hours before planting them outdoors. Water the seed bed daily to keep the soil moist until the seeds germinate.

For smaller seeds, create your furrows or planting holes, fill them with water, and let the water soak into the soil just before planting your seeds. Cover your seeds with compost or potting soil (which are less likely to crust over in the heat), and then keep the seed bed shaded and well-watered until the seeds come up.

A light sprinkling of dried lawn cuttings on the seed bed will help to shade the soil and keep it moist. You want the layer to be thin enough to still see some soil between the cuttings, so that the mulch won't block the seeds from emerging.

9. Keep ripe fruit well-picked

Harvest all of your ripe fruit promptly, as they demand a lot of water from your plants.

Ripe fruit (tomatoes, melons, peppers, etc) require large amounts of water from your plants. To reduce heat and water stress on your heavily-producing plants, harvest your ripe fruit frequently and thoroughly (including damaged fruits).

10. Space your plants farther apart

Plants spaced closely together will compete strongly with each other for water. If you are able to space your plants farther apart, they will experience less stress during periods of extreme heat.

11. Keep your garden well-weeded

Weeds usually have much more vigorous root systems than do our domestic vegetables, and they can out-compete with our crops for water in the soil. Do your garden a favor, and keep the weeds out.

12. Avoid using tall raised garden beds, if possible.

Raised beds warm up more, and dry out more quickly – a disadvantage in hot climates. The soil is cooler and moister deeper down in the ground. So, in extremely hot dry climates, I suggest focusing on improving the soil deeper down instead of creating raised beds.

13. Avoid growing large plants on trellises, if possible.

Trellised plants lose moisture much more quickly than those growing on the ground. If, due to space limitations, you need to trellis your plants, it's critical to keep them well-watered and mulched.

By taking advantage of many of the tips listed above, you can continue to garden successfully during hot summer weather!

Wind Protection

Another important way to reduce moisture loss through your plants' leaves is to protect them from wind. My garden is in a very windy location and I use a number of techniques to calm it. In the springtime, newly seeded beds get watered once, and are then covered with garden fabric. This cover keeps the soil surface from drying out and also protects the newly emerging plants from being battered by the wind. Young plants are especially vulnerable to moisture loss because they haven't established enough of a root system to keep themselves hydrated. So in my garden, I almost always cover new transplants with garden fabric for a week or so. Once their roots have taken hold, the cover can be removed.

Tomato plants getting wrapped in a protective layer of All-Purpose Garden Fabric.

For the last couple of years, I have also been using garden fabric to wrap all four sides of my tomato cages as well as the mini-cages that I use for eggplant. The plants love this protection from the wind, and they thrive with very little additional water.

Flowers appreciate wind protection as well. At my house, the prevailing wind is from the southwest, so I installed a 3-foot picket fence along the western side of my cutting garden. Like most windbreaks, this fence protects an area about one to three times its height. (At three feet high, it shields about six to nine feet of the garden that lies to the northeast of it.) I find this wind-protected part of the garden rarely needs watering.

I have also planted shrubs and trees to create windbreaks in various places around the yard. In the perennial garden, I use tall, sturdy plants such as echinops and garden phlox to shield more tender plants from wind. In the Native Americans' traditional three sisters garden, they used tall corn plants to provide wind and sun protection for the squash and beans growing below. I do the same in my own vegetable garden, using the tomatoes to shield the beans, and the sunflowers to shield the cucumbers.

What Causes Frost?

In order to protect your gardens from the ravages of frost, it’s good to have a working knowledge of what frost actually is and what conditions may create it. Frost occurs when water vapor in the air forms dew, and is then also cooled to the point of freezing — usually at night — while you’re dreaming of those bumper tomato harvests. Those specific conditions plague gardeners in the early spring and late fall.

citytransportinfo / Flickr (Creative Commons)

This is not a town-wide event, however. Frost can occur in patches across the landscape, covering one garden but leaving the garden next door barely touched. One of the factors that causes this is the shape of the land. Cold air is heavier than warm air, so any depression or low-lying area in the ground can allow the chill to pool and collect like an invisible puddle.

These areas can easily become “frost pockets” on chilly nights. Additionally, areas that slope to the north or areas with something blocking the morning light are the last to feel the sun’s warm touch every day. They are more likely to be glittering with frost on ideal mornings. To protect frost-sensitive plants in the garden, you need to create a barrier between their living surface and the dew that wants to settle on them.

Frost and Succulents: What You Need to Know

Depending on how long temps stay below freezing (32 degrees F), "frost tender" succulents may show varying degrees of damage. When moisture in the cells of a vulnerable plant freezes, it expands, bursts cell walls, and turns leaves to mush. In a "light frost," leaf tips alone may show damage ("frost burn"). In a "hard frost," temps stay below freezing for hours, which can collapse entire plants. Succulents typically don't regenerate from roots.

Crassulas, aeoniums, euphorbias, and kalanchoes are among the most tender succulents. A few succulents have a built-in antifreeze that enables them to survive temperatures well below 32 degrees F---below zero, in fact.

Should you be worried about your outdoor succulents in winter? It depends on where you live. See "Cold Weather Care for Outdoor Succulents, By Region."

Your area is frost-free (lucky you!) if.

Agave attenuata grows in gardens, and the plants look like this year-round.

Agave attenuata is the first succulent to show damage from frost in winter.

In my garden, this soft-leaved agave is the canary in the mineshaft where cold is concerned. A lot of succulents breeze through a brief frost (less than an hour), but leaf tips of Agave attenuata show damage right away.

After a brief exposure to 32 degrees, Agave attenuata will look like this.

Such damage is unsightly but seldom fatal. See the healthy green part of each leaf? Use scissors to trim off the tissue-paper-like frozen tips [see how], cutting each leaf to a point. When you're done, the damage will be barely noticeable. By summer new growth will have hidden those shorter, trimmed leaves. (Note: Such damage is similar to scorching caused by too much sun and heat, typical of desert climates, and by---believe it or not---wildfire.)

What about an agave or other succulent that has frost damage only on its leaf tips? Don't bother to trim them. It'll lose those oldest leaves in a few months anyway.

Areas of occasional, mild frosts (like inland Southern CA):

Watch the weather forecast, and if there's a "frost advisory" for your area, before dark go outside and cover your tender succulents. Frost tends to happen after midnight, with temps getting colder toward dawn. Cold air is heavier than warm, and flows down slopes and collects in low spots. Consequently, succulents in swales are more at risk than those atop berms. You may have heard that Christmas lights raise the temperature a few degrees. Yes, if they're the old-fashioned kind. Those sold nowadays (LEDs) don't generate heat. The succulents you have to worry about are those out in the open, with nothing above them. I sometimes stand over a succulent and gaze upward. If there are no tree limbs or eaves directly overhead, it gets draped.

I live in the foothills NE of San Diego at 1,500 feet (Zone 9b). And yes, I've been outdoors in my pajamas and slippers at 11 pm after hearing the weather forecast on the late-night news, shivering as I throw sheets on vulnerable plants, while my husband holds a flashlight. If frost is predicted for a series of nights, I may leave the plants covered otherwise, I remove the sheets the next morning. To make sure they won't blow off, I secure them with clothes pins and rocks. Do NOT use plastic. It doesn't allow the plants to breathe.

Frost cloth protects jades and other vulnerable succulents in my garden. SEE THE VIDEO.

Why cold damages some succulents and not others

A lot has to do with where a particular kind of plant originated. Succulents, which store water in their leaves to survive drought, are mostly from dry, hot climates. But some are from dry, cold climates---and those are the ones that don't freeze. See my article in the Wall Street Journal: Showy Succulents for Snowy Climates. Among the "hardies" are:

Stonecrops (small-leaved sedums), like those above in a Colorado rock garden.

sempervivums (hens-and-chicks, above) of which there are numerous species and cultivars certain cacti, yuccas and agaves (like Agave utahensis, A. montana and A. parryi), and lewisias from the Pacific Northwest.

Learn more in my books

Designing with Succulents (2nd ed.):
— Cold-Climate Succulent Gardens, pp. 111-113
— Cultivating Succulents in Challenging Climates, pp. 143-148

Succulents Simplified:
-- Protection from Frost, pp. 48-50
-- Frost Damage, p. 72 and p. 77

Also: Hardy Succulents, by Gwen Kelaidis, illustrated by Saxon Holt:

Watch the video: Plant Responses to Temperature Change. Biology


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