Hot, dry weather has been with us for some time and there’s no drought relief in sight, so it’s time to pay attention to our thirsty trees. In particular, trees you’ve planted within the past two or three years need emergency watering right now.

We’re seeing some of the warning signs of permanent damage from dryness. Trees typically wilt, and the edges of their leaves turn brown, and leaves fall off. This leaf drop slows water loss by reducing the need for water, and it’s a useful sign that lasting damage can occur if you don’t do some deep-root watering. Sycamore and river birch signal drought stress when their older leaves to turn yellow and fall to the ground. The new, tender tip growth on spruce trees sags and droops.

Spring drought is particularly damaging because trees and shrubs are actively growing, and typically blooming, at this time of year. Trees are made of long cells like tubes, for transporting water. If the tubes dry up, they shrink and collapse, and the damage is permanent.

All trees need water, so the question is how much? Trees that have been established for at least 3 or 4 years are tougher and can go without water longer. If they are young or have been transplanted more recently, they will need water more often. Small trees need at least 5 gallons of water each week to survive. Five gallons of water per week for every inch of trunk diameter is a good rule of thumb for larger trees.

Older, established trees can go longer, but once you see the edges of the leaves begin to turn brown it’s time to water them. Two inches of water on the entire area under the tree branches will help the tree survive another 3- 4 weeks without rain. Don’t rely on passing scattered thundershowers; a good steady, gentle soaking is necessary for the water to soak in and not just run off. Once we start getting regular rainfall, you should still pay attention to watering if you have newly-planted trees and shrubs in your landscape.

Drought stress weakens trees and makes them more vulnerable to insects and diseases. Very often the symptoms don’t show up until several years later, but the damage is done. We’ve all seen trees mysteriously die or lose major limbs for no apparent reason. The real cause often goes back to drought conditions a year or two earlier. A few dollars worth of water applied in weather conditions like we have right now are well worth the trouble and expense because removing and replacing trees is much more costly.

We have a nice, simple little sprinkler called the “Pound of Rain”, and we’ve been letting it run for a few hours under each of the trees in our yard. This works best at night when there’s less evaporation loss. Newly-planted young trees can be watered by setting a trickle of water right at the base of the tree for a few hours.

Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are on the “Garden Advice” page at www.goodseedfarm.com. For more information is available at www.goodseedfarm.com or call GoodSeed Farm Landscapes at (937) 587-7021.