There are a number of ways to create shade in the garden: by draping bed sheets or specialized shade cloth over hoops, stakes, or other supports, using large patio or beach umbrellas, or even erecting large shade canopies over an entire garden area rather than individual beds or 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.
Apply mulch, preferably a reflective mulch such as dry grass clippings. The first line of defense against hot weather and the windy conditions that can dry surface soil is to apply a liberal layer of mulch around the plants. This protects the soil from direct sun exposure, keeping it moist at the surface.
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.
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.
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.
The best time to water your garden in summer is from 6 am to 10 am—before the heat of the day sets in, giving your plants plenty of time to drink up and any moisture on the leaves to dry off before nightfall. What is this? If watering in the morning isn't possible, the next best time is from 4 pm to 7 pm.
To protect potted plants from heat, you can use many of the same plant shade covers as you would in your garden. While garden plants must stay put, many containers have the ability to be moved. Place them under a porch or in full shade if possible on exceptionally hot summer days.
A fabric covering is best because it will allow moisture to escape while still protecting your plants from frost. Fabric coverings will prevent the freezing air from coming into direct contact with the moisture on the plant while also capturing the heat that is radiating from the ground.
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.
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 survive short periods of heat stress, plants activate a molecular pathway called the heat-shock response. This heat-shock response (common to all organisms) protects cells from damage inflicted by proteotoxic stress, which damages proteins.
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.
As the weather heats up and plants reach full size, you may need to water containers (and especially hanging baskets) twice a day.
In times of extreme heat, it is vital to water your lawn for about 30 to 45 minutes daily. Once the temperatures drop below ninety, you can cut back to watering three to four times a week, until that blissful thunderstorm comes and quenches your lawn's thirst!
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.
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.
Overly dry soil is a sure sign that plants will develop heat stress. Water is essential for plants to live. During a heat wave, correct watering is even more important. Early-morning or early-evening watering is the best time to provide moisture to all your plants in the garden or landscape.
Use drip irrigation and an automatic timer.
For this reason, it's best to water slowly, allowing the moisture to soak into the soil and permeate down to the root level of the plants. Drip lines, which are available at nurseries and home centers, provide very slow and effective irrigation.
Small Leaf Size or No Leaves.
Plants living in places with very little water need to save as much water as they can, and this adaptation helps with that! Small leaves have fewer stomas so they release less water. Small leaves and no leaves are an adaptation to help the plant survive in hot and dry environments.
Plastic can be used to protect plants from frost, but it's not the best or most effective material. In fact, the horticultural experts here at Green Impressions actually recommend against it. Plastic materials such as vinyl and traditional camping tarps aren't breathable, causing moisture to get trapped inside.