when should you cover your plants

Protecting your plants from cold and pests is great. However, leaving them covered all day can overheat them, doing more harm than good. There are certain situations when you can leave plants covered all day – but when? So, can you leave plants covered all day? You can leave plants covered all day if you use a thin fabric row cover supported by hoops or stakes. Each morning, you should remove plant covers that trap heat or block light, or your plants will overheat or suffer from a lack of light. During cold days in spring, you can leave plants covered all day with a cloche (plastic cover) if it has a vent. Leaving plants covered with thick blankets all day will deny them the sunlight they need to grow and can cause them to overheat. Of course, there are times when leaving a row cover on your plants all day may be the only way to protect them from aggressive pests or strong sunlight during the height of summer. In this article, we’ll look at some of the ways you can cover plants, and when you might use each method. We’ll also talk about when to cover and uncover plants, and what to avoid doing. Let’s get going – we have a lot of ground to cover. Can I Leave Plants Covered All Day? Depending on the type of cover you use, you might be able to leave your plants covered all day. Some plant covers (such as cloches and row covers) are specifically made for this purpose. Row covers are specifically made to be left on plants for days or weeks at a time. However, there are certain covers (such as frost blankets) that should be removed during the day (in the morning) and replaced at night before a frost. Otherwise, they will cause plants to overheat or prevent them from getting the sunlight they need. How Long Can You Keep Plants Covered? For a cloche or row cover, you can keep plants covered indefinitely (for many weeks, or at least until they outgrow the cover!) For a frost blanket, you probably only want to keep your plants covered overnight. Let’s take a closer look at each of these covers and how long you can cover plants with each one. Cloche A garden cloche is a clear plastic or glass cover, used to protect plants from cold, wind, and pests. A cloche can also keep soil and air moist to help plants survive a drought. Make a cloche from an empty plastic water bottle. Cut out the bottom and use the cap as a vent! A cloche is often used to provide overnight cold protection for young plants when the weather forecast calls for a late spring frost. In some cases, it might make sense to wrap a cloth or blanket around the cloche to provide extra cold protection. However, remember to remove the cloche in the morning before it gets too hot. In warm and sunny weather, leaving the cloche on all day could cause plants to overheat (due to the greenhouse effect on a small scale). On cold days without much sun, it might be fine to leave a cloche on a plant during the day. This will protect the plant from wind, cold, and pests. A vent on your cloche will give your plant some fresh air flow to avoid overheating. A vent could be as simple as taking the cap off the top of a plastic water bottle during the day to keep plants cooler. You could also drill extra holes into the top or sides of any clear plastic container that you want to use as a cloche. Another option is to use a wire cloche, which protects against rabbits, squirrels, and other pests without causing plants to overheat. The best part about a wire cloche is that you can still wrap a blanket around it at night to provide cold protection. Use a wire cloche or cage with a row cover to protect plants from pests and cold. Just remember to remove the blanket in the morning to avoid overheating, and to give your plant sunlight. The only drawback of cloches is that many plants (such as tomatoes) will eventually outgrow them. If you want to learn more about cloches and how you can make them, check out my article here. Frost Blanket A frost blanket is used to protect larger plants from cold at night. You will often use a frost blanket in the fall to extend the growing season by a few more days or weeks. A frost blanket can provide several degrees of cold protection for plants. When using a frost blanket, your best bet is to set up 3 or 4 stakes around your plant. The stakes should all be a little taller than the plant. Then, hang the frost blanket over the stakes so that it covers the plant all around. Try to avoid having the blanket touch the plant, since this can cause cold damage due to condensation and freezing. The blanket should be long enough to hang all the way to the ground. Use bricks, stones, or soil to cover the bottom of the blanket to prevent it from blowing around in the wind. According to the University of Georgia Extension: “Covering plants is simple and effective, but to protect the plant, the cover must reach all the way to the ground and be anchored. Be sure to remove covers as soon as temperatures rise, or you can “cook” the plant.”https://extension.uga.edu/publications/detail.html?number=C1027-14&title=Extending%20the%20Crop%20Season:%20Unheated%20Spaces Put a frost blanket over your plant in the evening before it gets too cold. This will trap more heat in the air around the plant and under the blanket. Remember to remove the frost blanket in the morning after temperatures warm up a bit. Otherwise, your plants will not get the sunlight they need to continue growing. They could also overheat if the sun is too strong. Row Cover Row covers are a good way to protect an entire row of plants all at once. They can be used to protect both young and mature plants. Row covers let some sunlight through, so they can be left on plants for days or weeks at a time.Image courtesy of user:Keith Evans via:Wikimedia Commons Keith Evans / Polythene Field / CC BY-SA 2.0 https://commons.wikimedia.org/wiki/File:Polythene_Field_-_geograph.org.uk_-_367720.jpg According to the University of Georgia Extension, row covers can provide up to 8 degrees of frost protection. This can make a huge difference when trying to protect your plants from cold. Row covers are often made of a light fabric (such as polyester). Row covers are meant to rest on top of supports, such as stakes or hoops. Row covers will also protect plants from pests. In addition, most fabric row covers are also breathable and permeable so you can water right through them. This means that they won’t cause plants to overheat due to the greenhouse effect. Generally, row covers are made to allow enough light through so that plants can continue to grow (there are row covers with varying levels of light protection). You can learn all about row covers (and the different types available) in my article here. When Should You Cover Your Plants? If the weather forecast calls for a freeze, you should cover your plants just to be safe. If a frost is expected (borderline freezing temperatures, 32 degrees Fahrenheit or 0 degrees Celsius), then you will need to cover some frost-sensitive plants, such as tomatoes. Cover your plants if a frost or freeze is expected - especially cold-sensitive ones like tomatoes. Certain cold-hardy plants (such as spinach, broccoli, and onions) can tolerate some frost. You can learn more about the temperatures that vegetable plants can tolerate in this article from the Old Farmer’s Almanac. In general, you should cover your plants in the evening, before sunset. That way, you can trap more heat under a blanket to protect the plants. Cover plants in the evening, before sunset and colder temperatures arrive. To trap more heat under a plastic cloche, use it to cover your plants a little earlier in the day (late afternoon). The greenhouse effect from the sun will warm up the air and soil, and the plant will have a better chance to make it through a cold night. If you are going to wrap a blanket around a cloche, do it later in the evening but before sunset. When Should I Uncover My Plants During the Day? You can uncover your plants when temperatures are safely above freezing. Usually, this will happen by mid-morning. If not, you can leave the plants covered. However, if plants are covered by a frost blanket for too many days in a row, they will start to suffer from a lack of sunlight. If you expect an extended period of cold, try using cloches or row covers instead. You can leave cloches and row covers on for weeks or months at a time. However, there is one exception. When bees start working and flowers start appearing on your plants, you will need to take off the covers if you want to get any fruit! When bees start to work, remove plant covers to give them access to flowers! You have the choice of letting the bees pollinate the flowers during the day, or doing it yourself with a toothbrush or other tool. If you aren’t sure how to start with hand pollination, you can learn more about it in my article here. What Should I Cover My Plants With? Use stakes to hold up covers and keep them off of plants (the weight of a heavy blanket can damage plant stems or branches, and if the cover touches the plant, cold damage can also occur during a frost.) The materials you use to cover your plants will depend on what type of protection they need: Cold protection – try using frost blankets to keep your plants warmer at night. Gardener’s Supply Company has lots of different types of frost blankets available on their website. Row covers and cloches also work.Sun protection – floating row covers made of fabric are a great way to protect against strong sunlight while still letting your plants breathe. Gardener’s Supply Company has a fabric row cover material that lets 70% of sunlight through. Of course, a row cover will also keep your plants a little warmer overnight. Shade cloth is another option for sun protection - it generally blocks more sunlight than row covers.Pest protection – a plastic cloche is a great way to protect young plants from pests. For example, a cloche made from a clear plastic bottle will be too tough for cutworms to bite through (your tomatoes will thank you!) For older plants, a row cover wrapped around the entire plant will do a good job of keeping pests away (unless they have already laid eggs on the plant!) If you don’t have time to cover and uncover your plants during the work week (I’ve been there!), then you might want to go with row covers. Row covers can stay on for weeks or months, and they can serve all three purposes: protection against cold, sun, and pests. Is It OK To Cover Plants With Plastic? You should avoid covering plants with plastic. For one thing, if you forget to remove a plastic cover, then you could cook all of your plants (thanks to the greenhouse effect) if the following day is warm and sunny. If you use plastic to cover plants, use stakes to hold it up. Frost could damage a plant anywhere the plastic touches it. Even worse, putting plastic right on top of your plants can cause more severe cold damage – strange but true! According to the Utah State University Extension, a layer of plastic can cause freeze damage to leaves and stems where the plant touches the cover. According to Michigan State University: “Do not cover plants with plastic sheeting or poly tarps as they collect moisture inside and cause the plants to freeze more rapidly.”https://www.canr.msu.edu/news/create_a_longer_growing_season_for_your_vegetable_garden However, there is one exception. If you can ensure that the plastic cover does not touch the plant at all, then you can consider using it. One way to manage this is to drive tall stakes into the ground around the plant. Then, the wrap plastic over and around the stakes. Use stakes to hold up plastic away from plants. Another way is to put a layer of fabric between the plant and the plastic. According to the Oregon State University Extension: “Don’t use plastic sheeting unless a fabric or other cover (see above) is between the plastic and the plant; leaves and stems that touch plastic will freeze. “https://extension.oregonstate.edu/gardening/techniques/protecting-your-garden-frost Conclusion Now you know when you can leave plants covered all day, and when to remove the covers when you can’t. You also know what materials to use, depending on what type of protection your plants need. You might also want to read about more ways to cover plants in my article here. 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