The intensity of midday sun is welcomed by certain plants, but can mean death to others. Even those garden plants that thrive in morning or evening sun can be damaged by direct sun in the middle of the day. To avoid losing your favourite plants, learn their proper level of sun exposure -- and the signs of sun and heat stress.
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Signs of Heat Stress
The first sign of heat and sun stress in your plants is wilting, as the leaves lose water through evaporation and transpiration. This occurs faster in dry and windy conditions than in humid conditions. If you live in an area with high humidity, pay closer attention to your plants, since this first signal that your plants are in trouble may be difficult to detect. As the plant loses moisture, the leaves and stems can burn. Depending on the type of plant, heat and sun stress can kill it after only a few days of exposure.
Some plants thrive in six or more hours of sun a day. This includes midday sun. Plants such as cactus, warm-weather vegetables, citrus trees and a wide variety of annuals and perennials fall into this category. As long as they are healthy and have their water needs met, these plants will show little sign of heat stress in the midday sun, except for mild wilting that goes away when the sun goes down. Identifying features of sun-tolerant plants include small or narrow leaves, leaves with a waxy coating, fleshy leaves or leaves with a whitish appearance.
Many shade-loving plants have large leaves that provide a wide area for photosynthesis to occur. These plants can handle some morning and evening sun and include hostas, bleeding heart and astilbe. However, if left fully exposed in midday sun, these plants will suffer. At first, they will wilt as water evaporates from their large leaves. The leaves dry and will burn if the plant isn't moved. It only takes two to three days for midday sun to kill a shade plant.
Helping Your Plants
Act at the first sign of sun stress. If your plant is in a container, move it to a shady location and give it some water. If your plant is in the ground, cover it with a sheet or pillowcase to protect it. If you know your plant is a sun-loving plant, simply ensure the plant has been watered that day and it should recover. To revive a shade-loving plant that has been left too long in the sun, soak it as much as possible, remove any damaged leaves and protect it from the sun in the future.
Some locations, such as coastal areas, do not experience intense midday heat. Plants that prefer part-sun conditions inland, can be left in full-sun along the coasts. This includes the mandevilla vine, as well as leafy vegetables like lettuce and hydrangeas. Always learn about your plants' growing requirements and watch them closely during sunny, summer conditions.
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