When temperatures reach 100 degrees or more, the result can be plants showing signs of heat stress, and gardeners struggling to keep them healthy.
Signs of Heat Stress in Plants
Gardeners will recognize symptoms of heat stress in garden plants, trees and shrubs when they see any of the following:
- Browning or crunchy leaves - Browning of the leaves, especially around the edges, are a sign of heat stress.
- Yellowing leaves - In early stages the leaves can begin to turn yellow and dry up.
- Wilting leaves and foliage - In the earliest stages of heat stress and drought, plants will have wilting leaves and drooping foliage.
- Shrubs and trees dropping leaves - In prolonged drought, shrubs and trees might try to slow the loss of water by dropping leaves completely.
- Branch and stem tips dying - In severe heat stress cases a tree or shrub will even lose the tips of branches or full stems.
By recognizing early signs of heat stress, gardeners can help plants survive the drought or heat without dying completely.
Plants Susceptible to Heat Stress
Some plants are more susceptible to heat stress than other plants. Cool weather plants tend to begin shutting down whenever the heat rises above 75 degrees, and often will disappear completely when temperatures get any higher.
But even hot season plants like tomatoes, ornamental shrubs and deciduous trees can suffer when temperatures reach 100 degrees or higher. Water evaporates too quickly, damaging the cells of the plants.
Often trees and plants with broader leaves will drop their leaves to prevent or slow this loss of water, trying to preserve the plant for the following season. In the case of vegetables or fruiting trees, they will also drop fruit to preserve water loss.
How to Help Plants Suffering from Heat Stress
Water thoroughly, paying attention to soil condition. With high levels of heat, or very high heat indexes, the ground becomes dry and hard making it more likely that turning the sprinkler on for 30 minutes will result in lots of run-off and barely wet the soil at all. Try a water, soak cycle instead to ensure that water is absorbed into the soil Water the soil until run-off is noticed and immediately turn off the sprinkler or hose – wait at least 15 minutes and water again. Once the ground is softened it will absorb water more easily and allow the water to penetrate to deeper layers of the soil.
Mulch the ground after watering to preserve moisture. A thick later of mulch will help prevent the ground from drying out, keeping that water accessible to heat stressed plants for a longer amount of time.
Water frequently. When heat indexes rise into the triple digits, most plants will need 2-3 inches of water per week.
Gardeners can use careful watering techniques and pay attention for signs of heat stress during prolonged drought and hot temperatures to help save landscape plants.
Angela England - Angela England is a problogger, mother of four (yes I know what causes that), speaker, teacher, labor doula, gardener and so much more.
Join the Conversation