To keep them cool, use old screens, lattice and sheets to shade vulnerable mature plants from the effects of mid-summer sun. Cover new seedlings with opaque covers to protect them from the sun until their roots are established. Commercial growers often use sprinkling to cool plants down.
Even your plants that love to soak up the sun need some form of shade to protect them. Make sure you place plants in an area where they'll get at least some shade throughout the day. This will prevent scalding or over-drying, and will help you conserve water as well.
Adding mulch to your garden is one of the best things you can do to protect plants from hot summer weather. A layer of mulch conserves moisture and keeps the area around the base of your plants cool. You don't need to get fancy with it: Shredded leaves, straw, and wood chips are all excellent options.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell: Leaves wilt.
During extremely hot weather (daytime temperatures above 90F and nighttime temperatures above 70F), try to water daily or every other day. In a 10x10-foot garden, this would mean giving your plants 8 to 9 gallons of water each day.
In times of extreme heat, 1-2 times each week may be necessary. Know your plants though! Some plants prefer almost zero water during summer (manzanita, Ceanothus, madrone and cistus) and others wilt even when they have ample water (hydrangea, rhododendron). So adjust watering accordingly.
And most importantly, plants absorb water more readily when they're not under heat stress—a condition that's more likely to occur when the sun is at its peak. So while it's perfectly okay to water plants while they're in full mid-day sun, it's not the most efficient way to go about it.
Your containers need to be watered every day, especially when temperatures are so high. Sometimes you might even have to water in the morning and the late afternoon like we do in our Garden Center.
Some plants died and others were fried by the record-breaking temperatures. Even some that look extremely bad, like rhododendrons and hydrangeas, can bounce back. Burned leaves don't necessarily equal a dead plant, so patience and observation is needed.
To the gardening world it may have always been considered a fact, but science has never proved the widely held belief that watering your garden in the midday sun can lead to burnt plants.
Signs Your Plants Are Too Hot
The leaves dry out. Excessively hot plants will dry out faster. The leaves turn yellow. One of the causes of yellow leaves is excessive heat, so this is one thing to consider!
If you forget or are too busy to water your plants on some summer mornings, you can water them at night. However, this should not be your ordinary watering time. Morning is the proper time for watering plants, though you should keep in mind that not all plants need daily watering.
The heat of summer can be a death sentence for your plants, but over watering can as well. The best thing you can do is keep the soil moist by watering when the top 1 inch (tip of your finger) feels dry to the touch and to be aware of the symptoms listed above.
Most plants shut down during extreme heat, so if it is over 100 degrees, it may be best to wait to water even if your plant is stressed.
As the weather heats up and plants reach full size, you may need to water containers (and especially hanging baskets) twice a day.
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
The best time to water outdoor plants is in the morning when temperatures are usually cooler. This gives the plants time to absorb the water so they can get through a long, hot day. The second-best time is late in the afternoon or early in the evening. Try not to water at night.
During really hot weather, water your vegetables at least two to three times a week. Watering the garden deeply is critical. The water must go down, down, down to encourage deep roots and get away from the hot soil surface.
Avoid full sun
In the current hot breezy weather it is probably best to water in the early evening. This gives the plants enough time to dry out, but there is still the chance for overnight water uptake by the roots. And if you want to water in the morning then start very early – before the sun is shining.
Morning watering is actually preferable to evening watering as the plant has time to dry before the sun goes down. At night, water tends to rest in the soil, around the roots, and on the foliage, which encourages rot, fungal growth, and insects.
We should water the roots so that the plant grows healthy.
During spring and summer in Southern California, she suggests drip watering three times a week for 18 minutes, then adjusting from there if the soil is too wet or dry. Don't know how to tell? Stick your finger in the soil. If it's consistently moist 2 inches down, your plants are fine.
There is a high likelihood that plants are experiencing heat stress if they wilt during the day's hottest period and then revive in the evening or morning. Dried Leaf Margins. Some types of crops dry off the leaf's outer edges to ensure survival.
Most plants can recover when removed from the heat as long as they are generally healthy and given plenty of water and shade to help them recover.