Terran's Tips

Beating the Heat

This month’s Tree Tip was written and researched by Tim Story, one of our ISA Certified Arborists.

hotIt’s hot, and no doubt about it, the extreme heat and lack of rain fall has been a subject that has gained global attention over last few months and rightfully so.  We are hearing more and more about the potential for wide spread damage to crops, livestock, and anything else that depends on Mother Nature’s gift of rain to survive. 

I am fortunate in that I get to meet with so many people throughout the year, and see different landscape ideas and review the health of trees.  With that, I can conclude, watering your plants, shrubs, and trees especially during the “dog days of summer”, is extremely important to their overall health.  Water is a natural resource that I like to try and conserve as much as possible, but in times like these, I strongly recommend watering your plants and trees thoroughly.  A deep soaking 2 to 3 times a week would seem to be a standard approach, but due to differences in elevation, soil composition, compaction, and mulch, the exact amount to water is subjective. 

How Much Water does a Mature Oak Tree Drink in a Day?

A mature oak can uptake hundreds of gallons of water a day, and a mature Eastern Pine can utilize in excess of 100 gallons in one 24 hour period. Compare that to an animal such as an elephant, which can drink up to 60 gallons in a day, and understand any large living creature needs a substantial amount of water to survive.

Oak Tree
100-200 gallons/day
Eastern Pine Tree
100 gallons/day
60 gallons/day


What Role Does Heat Play?

transpiration diagram

Oak trees will lose water through a process called transpiration as illustrated at the left. Transpiration is part of the water cycle, and it is the loss of water vapor from parts of the plant, mainly the leaves, which also triggers a flow of mineral nutrients and water from the roots back to the shoots of tree.  Another way water is removed from the soil or roots of a tree is through evaporation.  When temperatures exceed normal, the evaporation process speeds up, and the need for additional water is needed.  During June, many areas of the U.S. saw (P) precipitation levels below the normal (4”), but (PE) potential evaporation levels exceeded 4”.  When (P) – (PE) values go negative, the result can be very difficult for anything that depends on rain to survive.

What Can You do to Help?

Water is a natural resource that I hate to waste, but there are a few things we can do in our yards that will help minimize the amount of water we use when watering our plants, shrubs, and trees.  In the urban environment, leaves are usually picked up in the winter, leaving little to no mulch/compost under the canopy of our trees. The result is increased evaporation, overheating of surface roots, and compacted soil making water less able to penetrate soil surface when available.  Looking ahead, many farmers in the south are moving into a practice called “Land Forming”.  Land Forming is basically trying to level their land in a way which water, either through irrigation or rain, is run back across their fields limiting waste and runoff into a ditch.  Instead of row plowed, the land is flat and has a gentle slope that allows the water to cover the largest area possible.  The “purpose” is defined as “to facilitate the efficient use of water on irrigated land”.  Point being, for us in the urban areas trying to water and limit waste, before turning hose on in the yard, spend a brief second studying the slope of the yard. 

Mulch, Mulch, Mulch

mulchDid you know that mulched areas require almost 50% less water than areas without?  Mulch serves as an insulating blanket that greatly reduces evaporation.  Years ago I had a garden spot at Shelby Farms with a few friends.  About half way through the summer once the heat kicked in, the excitement of meeting at the garden faded, and I was on my own. To save time, I remember using the sprinkler on one end of the garden, while I pulled weeds on the other and then would switch.  I will say it was hot, and the soil was sandy, but I am telling you I watered for about an hour with sprinkler, and when I went to pull weeds, the water never got past 2” of depth.  Given 95% of trees roots are as deep as 12”, a sprinkler in this heat throwing in turf grass as well, it is important to be watering directly with the hose 2 days a week to make sure the tree is getting the water it needs. Wood chips are used in this example, but other forms of mulch are fine.  Wood chips give off a lot of carbon during compost process, but if used on top of ground and not tilled into soil (vegetable garden) the amount of carbon is limited and safe to use as mulch. Four to six inches of mulch when using wood chips is preferred depth.

Benefits of Mulching with Wood Chips

  • Saves water - less watering is required
  • Soil service is shaded – less irrigation and rain water is retained
  • Safer - no need for chemical weed killers or herbicides(deter weeds)
  • Stimulates growth - mulched trees grow faster than un-mulched trees
  • Makes plants more resistant to disease and insects
  • Keeps soil and roots from overheating in hot Summers

Reviewing information from several sources, this summer’s heat and lack of rain, puts the “Precipitation Evaporation Value” at a level not seen since 1988.  I do battle with recommending watering more as I appreciate water as a natural resource, but I also care about the trees in our community, and they are very thirsty.  A deep soaking even one day a week will help, but if this dry spell keeps going, twice a week wouldn’t hurt.  Please keep in mind slope of yard as not to waste water to street, and when the leaves fall this winter, maybe leave a few under the oak tree to help hold moisture in the root zone for next summer.  In large areas without irrigation systems or a water source, such as public parks or wood lots in urban areas that leaves are picked up, a truck load of wood chips spread throughout the root zone of trees will make a big difference in the health of the trees and the cost is minimal compared to cost of future maintenance.

Call us at (901) 309-6779 or email us at info@woodlandtree.com for information regarding this subject or anything else that relates to the overall health of your plants, shrubs, and trees.

Posted by Mark Allen at 13:30