Believe It! Your Plants Like The Heat Of Summer!

July.  The heat is on, the days are long, and you struggle to complete those outdoor tasks unless you get up and at them by 6AM.  Even the landscape crew struggles when temperatures approach 100 degrees, but we persevere.  Combine heat with the inevitable dry period we get before the July or August monsoon season kicks in here in Colorado, and many of us wonder how plants and trees survive.  Truth is, they like it!  This article looks at the physical responses of plants to heat, and some tips to help newly planted material survive those 100 degree and very low humidity summer weeks.

A plant or tree’s temperature is usually slightly above the ambient air temperature.  Plants lose heat on a hot day in order to maintain a survivable temperature by longwave radiation, convection, and by transpiration.  Think of this as radiant heat loss, buoyant air moving up from the leaves of the plant itself, and evaporation of water that has passed through from the roots to the leaves of the plants (evapotranspiration).  These processes help the plant survive on the hottest days.

Stresses to a plant from heat come from several factors.  First, the duration of the heat presents a challenge to even the most hardy plants.  If the heat wave lasts for a week, that puts more stress on a plant than one or two days of 100 degree temperatures.  The peak temperature is also a factor.  Most deciduous plants cannot survive a temperature spike above 125 degrees which can occur depending on exposure to sun and buildings.  The water content of the plant greatly affects its ability to stave off and survive hot temperatures.  The more water available in the plant’s tissue, the more the plant can transpire to keep itself cool.  Just as people sweat to stay cool, plants do the same.  And finally, exposure is key.  Areas around concrete or asphalt, or near buildings on a south or west exposure, can be up to 20 degrees hotter than the surrounding air.  A new construction site with newly planted material can be brutal on plants.  Frequent watering, including wetting the plants themselves can be beneficial to their survival. 

Glacier View plants trees and shrubs in the hottest of temperatures, but it is the attention to watering in the first few days that allows plants to survive.  While working on other facets of the landscape, the crew will continue to monitor all newly planted material and address any heat stresses as soon as they present themselves.  This attention to detail ensures that new material has the best chance at survival.  However, plants severely stressed by heat have their own mechanisms for survival.  Plants may lose some or all of their leaves in order to survive.  By losing leaves, they are signaling that they cannot transpire water fast enough to maintain the leaf “burden”.  They are preserving moisture for the stems and roots of the plant.  If given some water at that time, some plants can survive a leaf drop in summer and will put out some new leaf growth again when the temperatures finally cool.

Plants need the heat of summer.  They develop resistance to heat by being exposed to the hot summer days.  Just as people do, plants acclimate to their environment.  Part of the function of good leaf mass is to shade the roots of the plant from the extreme temperatures.  That shade allows for better root growth which, in turn, helps the plant access more water for transpiration.  It is mother nature’s way of insuring survival of the fittest plants.  The sudden spurt of leaf growth in plants when the first heat of summer really gets going is what helps it survive the brutal heat of August in Colorado.  So, don’t be afraid to plant trees and shrubs in the heat of summer.  Just remember that they need to be monitored a little more carefully than if planted in spring or fall.

Planting

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Teresa Fikes

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