Irrigation during a dry spell

Posted on August 10th, 2016 by John Foegley

Irrigation – Don’t over water

It’s been hot and dry for several weeks so  cranking up the run times on your irrigation system might be the first thing you want to do.  However, it’s important to understand that  trees, shrubs and groundcovers typically don’t require as much irrigation as turf.  If you increase run times for all zones you’ll end up over watering your trees and shrubs.  During the first year after installation, we see far more plant losses due to overwatering than we do from underwatering.

Irrigation soil moisture check

Irrigation soil moisture check

The symptoms of over and underwatering can be similar, so checking soil moisture levels manually is crucial for plant health.  Here is a short explanation  from Clemson University.

To determine whether the amount of water being supplied is adequate for the site conditions, conduct the following tests. …Gently dig a small hole in the ….soil just outside the root ball and half its depth. Do this several hours after watering. Squeeze soil taken from the bottom of the hole in the palm of your hand. If water drips out between your fingers, you are watering too much; if soil crumbles and falls out of your hand as you open your fingers, you are watering too little. If soil stays together as you open your fingers, moisture in the backfill is just right, but the root ball might be bone dry. If your plants are recently installed, poke a finger into the root ball to check the moisture there. If it feels dry, increase the amount of daily irrigation. If you can squeeze water from it, it is too wet. With practice, these techniques become quick and easy ways to evaluate soil moisture.
Excerpted from the South Carolina Master Gardener Training Manual, EC 678.

On the other hand, trees that are newly installed in turf may not get sufficient water from a turf zone during a hot dry period.  We suggest letting a hose trickle slowly overnight, directly on the root ball so the water can penetrate below the surface.