University of Minnesota Extension

Extension > Extension in your Community > Morrison > County Horticulture Educator > Articles > Does the Heat Impact Your Plants?

print icon email icon share icon

Does the Heat Impact Your Plants?

University of Minnesota Extension, Stearns County News
July 20, 2016        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Does the Heat Impact Your Plants?
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (7/20/2016) — The recent extreme weather can certainly cause a toll on humans, and obviously impact our pets and animals, but how about our garden plants?  Drought and heat can cause stress to plants that may be deeper than you realize.  Taking the time to give your plants extra care before and during environmental stress is important for their health.

Plants photosynthesize and create their own carbohydrates, but the rate of photosynthesis is impacted by temperature.  In general the rate of photosynthesis increases as temperature increases, but once temperatures reach around 95°F, the rate actually decreases.  This is important to realize because plants need to have successful photosynthesis to grow each season. An annual needs to mature rapid enough to mature its flowers or fruit before fall, and a perennial needs to photosynthesize enough to put carbohydrates into its roots and reserves so it can survive the winter.  Therefore an extended period of extreme heat can be detrimental.

Often with heat waves, night time temperatures stay elevated as well.  This causes the plant to have to higher levels of respiration.  Respiration is the process in which a plant breaks down the carbohydrates to provide itself energy.  Therefore if the day time temperatures are high enough to cause a decrease in photosynthesis and the night time temperatures are high enough to cause an increase in respiration, the plant is unable to replenish. This results in the plant having to use its energy reserves which should be going towards growth, flower or fruit maturity, or winter reserves. 

Another issue for plants in heat waves is that it is common they do not have enough water to complete the process of transpiration. This is where water taken from the roots is exported throughout the plant with important nutrients attached. The water then will exit the plant through small holes called stomata.  If there isn’t enough water available for this process, the stomata close and the plant is not able to cool itself down as the water exits its leaves. This will result in sunscald, where growth of the plant tissue stops, leaves will drop, or the plant may even die.

A gardener should be aware of this, and provide adequate moisture to their plants. This may involve watering pots several times a day.  Relocating sunny pots to a shaded area might also help the plants in the extreme weather.  Mulching plants with a shredded or chipped wood will help keep moisture in the soil as well as keep soil temperatures cooler.  Composted or shredded newspaper is also an option in vegetable gardens.  It is important to do this prior to the heat wave for it to be more effective.

Finally, don’t forget about the trees and shrubs.  Extreme drought or heat can stress them as well which may not be as obvious right away but instead breaks down their own defenses and makes them more susceptible to disease and insect infestations.  An example would be borers, like the pine beetles, which often cause damage due to their infestation but will not be evident for another year or more.

  • © Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer.