Lets Grow

Trees – Watering in Drought

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Published September 19th, 2010

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 established 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. Sycamore and river birch signal drought stress when their older leaves to turn yellow and fall to the ground. 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. 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, but the real 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.

We have a nice 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.

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.

Trees will naturally lose their leaves and go dormant in fall, but wind and sun will continue to suck water from the stems, trunk and buds. It’s very important (particularly with evergreens) to make sure trees get thoroughly watered before the ground freezes for winter. Winter conditions can have much the same effect as summer drought, drying the tree and doing permanent damage. Once we start getting regular rainfall, you should still pay attention to watering if you have newly-planted trees and shrubs in your landscape.

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