how to keep plants cool

Heat waves, sunscald, and drought – what’s not to love about summer? If you are worried keeping your heat-stressed plants cool in the summer, you are not alone. So, how do you protect plants from heat & sun? Some of the best ways to protect plants from heat and sun are shade cloth, row covers, shade structures (awning, trellis, or pergola), planting near other tall crops, mulching, windbreaks, avoiding fertilizer in dry soil, and watering thoroughly. Combining multiple methods can keep your plants much cooler than they would be without protection. Of course, some of these methods require some work up front – but it might be worth it to save your plants (and your harvest). In this article, we’ll take a closer look at 8 methods to keep plants cool by protecting them from heat and sun. We’ll also look briefly at how you might protect potted plants from heat & sun. Let’s begin. How To Protect Plants From Heat & Sun In many places, summer brings extreme heat and strong sunlight. Unfortunately, this can cause all kinds of problems for plants. Summer sun can ruin your garden fun if it is too intense. For example, extreme heat and sun can cause the following in tomato plants: Wilted leavesUneven ripening of fruitSunscald Strong sunlight can cause sunscald spots on tomato fruit. Some plants can tolerate full sun, but sometimes, even those plants need a little protection from the sun's harshest rays. Luckily, there are several ways to protect plants from heat & sun, including: Shade clothRow coversShade Structure (awning, trellis, or pergola)Place Near Tall PlantsMulchWindbreaksAvoid Fertilizer In Dry SoilWater Thoroughly A row cover is just one way to protect plants from heat or sun in the summer months. Shade cloth is a helpful method that is not too difficult to use, to we’ll start there. Use Shade Cloth To Protect Plants Shade cloth is a great way to protect plants from the summer sun – and cool them down at the same time. In fact, shade cloth can reduce temperature by 10 degrees Fahrenheit (6 degrees Celsius). Shade cloth blocks 20% to 90% of sunlight (depending on grade) and can keep plants 10 degrees cooler.Image courtesy of T.R. Shankar Ramanvia Wikimedia Commons:https://commons.wikimedia.org/wiki/File:RJDRP_Nursery_DSC0282.jpg Shade cloth is made from woven or knitted material, such as polyester or polyethylene. It filters out sunlight and provides shade so that plant leaves and fruit do not get damaged. Shade cloth with a higher density is more durable and blocks more sunlight to provide more shade. Shade cloth comes in various percentages, from 20% (blocks 20% of light) to 90% (blocks 90% of light). Shade-tolerant plants may require higher grades of shade cloth. For example, lettuce may need 70% shade cloth. Penn State University Extension recommends 30% to 50% shade cloth for most garden plants. Make sure the shade cloth does not come in contact with plants (if it does, it can burn them). To prevent this problem, use stakes or cages to support shade cloth and hold it a few inches above your plants. You can use twine to tie the shade cloth to the supports. You can also use rocks or stakes to keep the shade cloth in place if the edges touch the ground. You might also be able to use old screens from a window as a makeshift shade cloth. You can learn more about shade cloth (and the different types and uses) in my article here. Row Covers To Protect Plants A row cover is another method you can use to protect plants from summer sun. A row cover is a lightweight material that protect plants from pests and can also provide shade. Row covers are more often used to keep plants warm in spring or fall. However, they can also help to keep pests away while blocking intense sunlight during the height of summer. Thicker row covers are heavier, but provide more protection from both pests and sunlight. Row covers are often made from polypropylene, polyester, or polyethylene. You can leave row covers on for days or weeks at a time, which is helpful during a long period of intense sunlight with few clouds. There are two basic types of row covers: Lightweight row covers – sometimes called insect barriers or summerweight garden fabric. They only block 5% to 15% of sunlight.Heavyweight row covers – thicker than lightweight row covers, these can block 30% to 50% of sunlight. You can learn more about row covers (and the types & uses) in my article here. Set Up A Shade Structure For Plants Building some type of structure to provide shade for part of the day can help your plants to beat the heat and sun in summer. An A-frame or lean-to trellis works well for shorter plants that tolerate shade (such as lettuce). An added benefit is that vining plants (like tomatoes) can climb up the sides of the trellis and provide even more shade for the plants below. An A-frame shape gives you place to grow tall plants (above) and short plants that need shade (below).Image courtesy of user :VanTucky via:Wikimedia Commons: https://commons.wikimedia.org/wiki/File:A-frame_chicken_coop_back.JPG An A-frame has an A-shape (two diagonal pieces of wood meet at a point). On the other hand, a lean-to trellis only has one diagonal piece, supported by a vertical support. You can learn more about the materials you can use for a garden trellis in my article here. An awning may be useful for providing shade to plants near your house (such as those on a patio or in a window box). You can also provide shade by using a pergola with vines growing up the sides and over top. However, this is a more involved building project that requires more space than trellises or awnings. You can learn more about pergolas (and their uses) in my article here. Locate Near Tall Companions To Protect Plants Instead of building structures to provide shade, why not use other tall plants to protect against sunlight? For example, you can plant shade tolerant plants (like lettuce) near taller plants that will provide shade, such as: CornPole beansTomatoes Tall plants (like tomatoes) can provide shade for short plants (like lettuce). Another good option is to choose heat-tolerant varieties of your favorite plants in your garden. The University of Delaware has a list of heat tolerant varieties for several crops, including: BroccoliGreen BeansLettuceSweet CornTomatoes Choosing heat-tolerant broccoli varieties will prevent them from bolting before you get a good head of broccoli. Heat-tolerant plant varieties may still need some heat protection during the summer, but every little bit of resistance helps. Use Mulch To Protect Plants From Heat Mulch insulates soil, but that doesn’t mean it causes it to warm up. Instead, mulch keeps warm soil warm, and it keeps cool soil cool (by preventing heat from moving between soil and air). If you add a layer of mulch around plants in the morning (when the air and soil are cool), it will stay cooler during the day. Removing the mulch at night to allow heat to escape from the warm soil into the cool air will also help to keep plants cool. There are lots of types of mulch you can use. Straw is a good choice, since it is light, easy to apply, and easy to remove. If you want to use straw to protect plants from heat, you can buy it online in bales from Ace Hardware. Straw is a good choice for mulching around plants to protect against heat. Apply mulch in the morning, before the sun starts beating down on plants. This will keep the soil cool. As an added benefit, mulch can also protect potato tubers from sunlight (sun exposure causes them to turn green and produce the toxic substance solanine). Just be sure not to apply too much mulch to your plants – too much can kill them if you overdo it! Build A Windbreak To Protect Plants From Heat A windbreak near your plants will help to reduce the hot summer wind that can damage plants by drying out their leaves. When hot, dry summer winds blow, a windbreak can protect plants from the worst of it. According to the Penn State University Extension, seedlings are especially vulnerable to hot, dry wind. This is especially true if they were transplanted recently without proper hardening off. You can learn more about how to protect plants from wind (and storms) in my article here. Avoid Fertilizing Plants In Dry Soil Extreme heat and intense sunlight are hard enough on plants in the summer months. Don’t make it worse by fertilizing them at the wrong time! Fertilizer will burn plants if you apply too much, or if you apply it in dry soil without watering. The nutrients in fertilizer need to dissolve in water so that plant roots can absorb them. This won’t happen in dry soil (this is why you need to water in fertilizer after using it). Even worse, applying fertilizer to plants when the soil is dry can burn them. Remember to get a soil test to make sure that you really do need fertilizer, and follow the package instructions when using it. Water Plants Thoroughly & Early Watering plants will keep them a little cooler and help them to survive the hottest, sunniest part of the day with less risk of damage. The best time to water is early in the day - with a deep, thorough watering. Water plants early in the day to let the water soak into the soil before the sun can evaporate it away. Watering early in the day allows more water to soak into the soil before the sun can cause evaporation. According to the Penn State University Extension, there are two benefits to watering plants early: Wet soil stays cooler than dry soil, despite heat and sun (it takes energy to evaporate water, which has a cooling effect – just like when we sweat).Wet soil does not become crusty and dry in the sun (dry soil absorbs water poorly – in fact, it often forms a crust and repels the water, making it hard to soak the soil). In addition to watering early in the day, you should also water thoroughly. Watering plants deeply has two benefits: Your plants have enough water to get through a hot, dry day.Your plants will develop deeper, more extensive root systems than if you watered shallowly and frequently. The University of Arizona Extension suggests using an irrigation system on a timer to automate morning watering. You can even set the timer to start watering before dawn to take full advantage of cool morning temperatures. How Do You Protect Potted Plants From Heat & Sun? Some of the same methods mentioned above can be used for plants in containers (such as grow bags, raised beds, planter boxes, window boxes, or pots). However, another good option is to take advantage of the mobility of potted plants. That way, you can move them into a shaded area, at least during the hottest part of the day (mid-afternoon). To move potted plants, use a dolly or flat moving cart to help with transportation. Remember that the soil in a pot can hold a lot of water, which can make it very heavy. The best time to move a potted plant is when the soil is a little on the dry side, so there isn’t so much water weight to move around. Potted plants are easier to move when the soil is not so heavy with water. Conclusion Now you know how to protect plants from heat and sun. Hopefully, a few of these methods can help you to keep your plants cool and save your harvest this summer. I hope you found this article helpful. If so, please share it with someone who can use the information. If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy! ~Jonathon