It’s hot enough out there to fry an egg on the sidewalk, can you imagine what it’s doing to your plant’s roots? It’s time to step up your watering efforts – but just how much should you increase your watering? Learn about heat wave watering and tips for keeping plants safe during high temperatures in this article.
When the mercury rises, it might seem like the best thing to do is to pour yourself a nice cold glass of tea, prop your feet up and soak in the air conditioning, but there’s something you’re forgetting. Your plants! When it’s hot for you, it’s hot for them, too! Watering in a heat wave is one of the most important things you can do to keep your big green buddies from shriveling into tiny brown lumps. But just how much to water during heat waves is really the question, isn’t it?
There’s no simple answer to heat wave watering. The water needs in heat waves vary wildly from plant to plant and even from place to place, based on both the air temperature and the soil type that’s in your garden. If your plants are potted, that’s another wrench in the works. But luckily, plants give us some signs that they really need a drink right now.
For example, if you check your plant in the morning and it’s doing just fine, but by mid-afternoon it’s droopy or discolored, you need to water that plant. If your vegetable garden that was growing furiously suddenly grinds to a halt, you need to water that garden. If your baskets are drying out completely between waterings because of the heat, you need to water those baskets.
It doesn’t matter if you hand water or use tools like soaker hoses and irrigation systems to get the job done, you simply need to be consistent. It may take a few tries to figure out just how much water to apply, but here’s a good way to figure out just how much water is necessary. Water your plants in the way you think they need to be watered, then go back out about a half hour later and dig a hole about eight inches (20 cm.) deep nearby.
If the soil’s moist, but not wet, all the way through, you nailed it. If it’s dry, you need to water more. If it’s really wet, water less, but also do something to improve your drainage for the future health of your plants.
Of course, watering isn’t all you can do to keep your plants cool when it’s hot outside. Here are a few other tips:
Mulch heavily. Sure, mulch is great to protect from winter’s cold, but it’s also amazing for protecting from summer’s heat. Mulch is pretty much good for everything. Apply two to four inches (5-10 cm.) of mulch around your landscape plants, being sure that the mulch doesn’t touch the plants themselves. Now when you water, more will stay in the ground where it belongs.
Move potted plants. Many houseplants spend their summers on the patio, but sometimes those patios can get pretty hot. If you don’t have a spot in less direct sunlight, try installing a solar sail or other shade to block some of the intense solar radiation that’s drying your containers out during the day.
Keep a watering log. It can help to track how much you’re watering and for how long so you can see how your plants respond. You may find that your Musa zebrina, for example, prefers for you to water it directly with a garden hose daily for five minutes during 100 F. (38 C.) degree heat in the morning, rather than being chintzy and only giving it two minutes’ worth of watery goodness in the afternoon.
Associate Professor of Botany, University of Reading
Alastair Culham receives funding from BBSRC, NERC, Royal Horticultural Society, The Cyclamen Society. He is a member of the Royal Horticultural Society Science Committee and co-author of 'Gardening in a changing climate'. He teaches Botany at The University of Reading.
University of Reading provides funding as a member of The Conversation UK.
The Conversation UK receives funding from these organisations
When the warmer weather strikes, our gardens and outdoor spaces become a perfect oasis for rest and relaxation. But as nice as the hot weather might be, extreme conditions and record-breaking temperatures can wreak havoc on your plants.
There’s of course no question, that when it’s hot, plants will need watering, but knowing when’s the best time to do this can be tricky. Evening watering gives plenty of time for the water to penetrate the soil and for the plant to take it up, but there is a concern that leaves staying damp overnight will provide access to disease.
On the other hand, morning watering means leaves will dry out faster – but there is less opportunity for the water to penetrate the soil and for plants to take it up before the day gets hot. So what’s the answer?
All living things need water to allow chemical reactions in their cells that provide energy for growth. Plants also need water to carry nutrients from the soil to the growing cells. This water is drawn up to replace water lost through stomata – the breathing holes in leaves. These stomata are needed for gas exchange – carbon dioxide in, oxygen out – during photosynthesis. In high light levels, on sunny days, a lot of carbon dioxide is fixed to make sugars by photosynthesis. Loss of water is also important to cool plants on hot days.
If plants run short of water they shut down their stomata and photosynthesis stops and is replaced by photorespiration – a process that releases carbon dioxide. Desert plants get around this by breathing at night and storing carbon dioxide for release to photosynthesis during the day while the stomata are shut. But in our gardens, few plants are adapted to do that.
As the water shortage gets more severe plants will wilt – the beginning of cell collapse. Initially this is temporary wilting and the plant can recover rapidly when water is available. But further drying will cause permanent wilting, which results in the death of parts of the plant – or even all of it. Some plants survive drought by dying down below ground – this is the case with garden bulbs such as bluebells, daffodils, tulips and snowdrops. Others may shed their leaves or survive only as seeds.
There are a few problems that can arise from a heatwave.
Here’s how to give your plants a fighting chance.
If you haven’t already put down a layer of organic mulch, before a heatwave hits is a fantastic time to do so. Putting down mulch provides a damp layer of insulation that locks in as much moisture as possible. Mulch shows down the evaporation process, keeping that much-needed moisture at the root level for just a bit longer.
Another benefit of mulching is that it can keep the soil temperature lower. During a heatwave, the soil becomes warmer. By locking in moisture, the soil is kept cooler.
Also, if you’re growing anything that has surface roots, mulch can help stop the roots from burning.
Be sure to add mulch to your containers as well!
There are many different mulch materials that you can use. During a heatwave, it’s best to pick a light-colored mulch because it reflects sunlight while maintaining cool, moist soil conditions.
Grass clippings are a great choice and readily available. After a few days, green clippings turn light brown, so they reflect sunlight. Bark mulch is an option for shrub beds.
One of the major benefits of container gardening is that you’re free to move your potted plants out of the sun whenever you want.
Containers dry out faster, so they’re even more vulnerable to a heatwave. If you have some shady locations or areas that receive more shade, put your potted plants there.
If you don’t have any shady areas, you can try shade netting to keep them cool or make some curtains to hang in front of your containers. It doesn’t have to look perfect, but it just needs to offer some protection.
Something you don’t want to do is go outside at 3 PM and start to water your garden. That’s an invitation for the sun to burn your plants.
During a heatwave, the best time to water is either in the evening as the sun starts to go down and isn’t as intense or the first thing in the morning. Not only does it decrease the risk of burning your plants, but it lets your plants soak up as much of the moisture as possible before it evaporates.
Also, watering in the middle of the day gets your plants on a schedule where they aren’t reaching peak dryness during the hottest point of the day. It can decrease their strength, which is the last thing you want to do.
Established plants can survive a few days during a heatwave without a lot of watering, but young plants will struggle. They’re still trying to become established, and the roots need the most water to help them grow.
Since they’re so tender, they also burn easier. If you’re planting during a heatwave, try to put your seedlings behind a taller plant that can cast some shade as the sun moves throughout the day.
You can also cover them with a cloche or pot turned upside down to give them a little protection during the worst heat of the day.
If you want to cut some flowers from your garden, hot days aren’t the best time to do so. So, cutting during a heatwave really isn’t ideal.
If you need to cut flowers, be sure to get outside as early as possible, potentially even before the sun comes up.
Another option is to use shade cloth on your garden during a heatwave, providing partial and temporary protection from the sun. You can find shade cloth in most garden centers or nurseries, and they’re available in a range of sizes and shade factors.
What does shade factors mean?
It refers to the degree of blocked sunlight, ranging from 25 to 90%. You have to pick the right shade factor based on the plants you’re covering.
For example, sensitive plants, such as lettuce or other salad greens, need a shade factor of 50-60%. Plants that tolerant heat well, such as beans, can use a 30% shade factor cloth.
Using a shade cloth should be temporary, blocking the sun without reducing the air circulation. Typically, you only need to position it to one side or above the plants don’t enclose the plants as you do with season extenders.
Shadows are your friend during a heatwave in the garden. It might be a good idea to keep your grass taller because it will cast longer shadows.
At the same time, leaving the grass taller helps to retain more moisture in the soil. If you want shade benefit, keep your grass 3 inches at the shortest, but some lawn experts suggest 6 inches during heatwaves.
When temperatures go above 90°F, some plants struggle more than others. You might notice that some plants have curled or rolled up leaves, which is a natural response by plants to help reduce water loss.
Fruiting plants might drop their flowers or stop producing new flowers throughout the heatwave. Expect a decrease in your harvest during these times.
You might think that fertilizing your plants is a good idea to help them stay strong. However, doing so is actually a bad idea because then your plants need even more water to process fertilizer.
When you apply fertilizer, it tells your plants that its time to grow due to a sudden increase of nutrients. During a heatwave, telling your plants that it’s time to grow can be dangerous during a heatwave in the garden.
So, don’t fertilize – focus on watering.
When you harvest before the heat hits, it means there is less foliage, flowers, or fruits on your plants to sap their energy. You can let some fruits ripen up fully in your kitchen, giving your plants a much-needed break.
If the heatwave takes place when you’re still planting seeds, try planting the seeds a bit deeper than you regularly do. Warm temperatures and direct sunlight will dehydrate the topsoil faster, and seeds need moisture to germinate.
All of those weeds in your garden soak up the water in your soil, leaving less moisture behind for your plants that you want to stay hydrated.
For best results, it’s best if you weed your garden at least one time a week or twice a month at a minimum.
Most importantly, be sure that you’re using safety techniques while gardening in a heatwave.
Originally from Long Island, NY, Greg Seaman founded Eartheasy in 2000 out of concern for the environment and a desire to help others live more sustainably. As Editor, Greg combines his upbringing in the cities of New York, Boston and San Francisco with the contrast of 40 years of living ‘off-grid’ to give us a balanced perspective on sustainable living. Greg spends his free time gardening, working on his home and building a wooden sailboat with hand tools.