BLOG
Find Inspiration Here

Heat Stress in Your Landscape

plant healthcare in sussex count nj farmside

Feeling kind of washed out from summer’s heat and humidity? You’re not alone. The plants in your landscape can be affected, too, and may be suffering from heat stress, which affects a number of processes such as photosynthesis, respiration, transpiration, membrane thermostability, and osmotic regulation. High temperatures and extended periods of time of extreme heat cause roots to struggle to draw enough water from the soil to keep up with the rate of water vapor coming from their leaves through transpiration.

 

 

A few facts about heat stress in plants:

 

  • Most plants grow best in temperatures ranging from 59o-86oF

  • When temperatures above 90oF are sustained for extended periods of time, plants can begin to show signs of heat stress

  • Heat stress is likely to occur when daytime temperatures are above 90oF and nighttime temperatures remain above 70oF

  • Heat stress is compounded when other plant stressors like drought, wind or intense sun are also present

  • Hot air and soil temperatures slow down chemical activity and growth in plants

  • At temperatures above 104oF while plants may still survive, they will often show different types of heat stress based on plant type, maturity and other environmental conditions such as drought or wind

  • Ideal humidity for most full-grown plants is between 60-70%

 

 

Signs of Heat Stress in Plants

 

Leaf Rolling/Cupping – Many plants roll their leaves or cup them in response to excessive heat. In this way, the leaf surface is minimized and stomata (microscopic openings in leaves, like pores, that allow moisture and gas to move) close, to help reduce moisture loss in the plant. Leaf rolling and cupping, and wilting can also be signs of pest/disease or overwatering on some plants.

 

Wilt – Low moisture in a plant diminishes water pressure within its structure, causing stems and leaves to wilt. Many plants recover from this once the temperature cools, but the potential for permanent damage increases with the length of time a plant remains wilted. Heat stress can often cause a plant to wilt during the hottest part of the day, then recover in the cool of the evening or early morning.

 

Dried Edges on Leaves – Dry leaf edges can often be mistaken for disease or insect infestation, but for some plants, it’s a defense, sacrificing the outer margins of the leaf while the larger portion remains viable. This is most often seen in large-leafed plants like squash that can afford to give up some leaf surface area for survival.

 

Ozone Damage – The poor air quality we experienced due to the wildfire smoke earlier this season when combined with high heat can cause ozone damage to plants. This can look very much like diseases – for example – dry brown spots between leaf veins can look like leaf spot, but bacterial leaf spot will also have yellow “halos” which ozone damage will not. For other plants like cucumbers, ozone-damaged leaves become dry-looking and bleached.

 

Blossom/Fruit Drop – Plants will drop flowers or buds after prolonged exposure to high temperatures in order to conserve resources for survival. In food crops, most will return to normal production once a heat wave is over.

 

Bolting – Bolting is the premature flowering of plants before they would typically be harvested, and most often occurs when cool-season crops like lettuces, cauliflower and broccoli are exposed to high temperatures.

 

Sunscald – Many fruits will scald in high temperatures, primarily on the side where the fruit is most exposed to the sun. Sunscald looks different depending on the type of fruit, and can appear as a watery area, discoloration, or blisters on the fruit skin, sunken or hardened areas of the fruit surface or completely dried-out fruit.

 

Blossom End Rot – Most common with tomatoes, the problem is associated with calcium deficiency and is exacerbated by sunscald. Aim to keep watering consistent and avoid letting plants dry out completely in between waterings.

 

 

How to Reduce Heat Stress in Plants

 

Things to Do

 

Water – Dry, crusty soil is a good indicator that plants will develop heat stress. While deep watering in the morning or early evening are preferred methods of watering, wilted plants should be watered as soon as possible to minimize the time they are in a wilted state. Try to water daily or every other day when temperatures are high. Be aware that shallow-rooted and young plants will need to be watered more frequently than plants with deep tap roots or established root systems. Even mature trees can be affected by heat stress, so don’t forget to water them, too.

 

Mulch – Mulch helps conserve moisture in the soil by slowing evaporation and minimizing fluctuation in soil temperature.

 

Provide Shade/Relocate Containers – Move container plants indoors or to a shady area if possible. If you can’t move the containers, consider placing a shade cloth over them to help block the sun’s rays. Check containers at least twice a day, especially if it’s windy as well as hot. You may have to water container plants one or more times a day during hot, dry conditions. Be sure the water is soaking into the soil. If the soil has dried out completely and you see it pulled away from the sides of the container, you may need to water several times before the soil will absorb water again.

 

Weed – Weeds can often adapt better to weather extremes than ornamental plants, so keeping your garden free of weeds that compete for water and nutrients will help your plants.

 

 

Things to Avoid

 

Planting or Transplanting – Hot soil temperatures can kill tender young plants or cause cankers where the stem meets the soil line. Transplanting is always stressful for plants even under ideal conditions, so don’t include the additional layer of heat stress.

 

Pruning – Pruning can expose branches and leaves previously shaded to damage from intense sun and heat, as well as stimulate growth, both of which add stress to the plant. Stressed plants are more likely to attract harmful pests, putting them further at risk.

 

Fertilizing – Inducing new growth is an additional stress your plants don’t need during a heat wave. Wait until cooler temperatures arrive to fertilize.

 

Chemicals – Even treatments like soap or neem oil can damage plants when temperatures remain consistently above 80oF.

 

 

Heat Stress Recovery

Recovery time for heat stressed plants can take from a few days to several months depending on the level of damage done to a plant. Non-native and sensitive plants or plants that were stressed and completely neglected throughout a prolonged heat wave may take several months to come back or may not survive if conditions were extreme. Healthy plants with strong root systems, weed-free, nutrient-rich soil and employing the recommendations above will help ensure your plants have the resiliency to weather almost any heat wave.

farmside landscape and design sussex county nj

LET'S STAY CONNECTED

Signup for our newsletter full of helpful landscape tips that get delivered right to your inbox!