When drought strikes, it’s tempting to cut back on watering of established trees or stop watering altogether. And maybe water restrictions in your area force your hand. I hate to see it happen, because trees can offer many benefits – most notably shade for homes to cut down on energy use, and shade for other plants to keep them alive and in need of less water. Of course, you can’t beat the enjoyment of sitting under the shade of your favorite tree. I won’t even get into how depressing it is to see dying trees in front lawns…
Ideally, your lawn has only native trees, and especially xeric varieties. In that case, the trees adapt to conditions more easily. Some survive on rainwater alone, but most need a deep watering about once a month during the heat of summer.
To water your a mature tree that requires irrigation, avoid a common mistake — watering only near the trunk. Trees do not have tap roots, but instead have a root system that extends out from the tree, more or less mirroring and extending just past, the tree’s branches above. So, when you set out your hose or set up a drip or soaker system, begin near the trunk, and then work your way out to the edges of the tree’s canopy. Scroll down in this handout on caring for trees from Colorado State University for a photo of a soaker hose layout.
To water deeply, you have to water slowly. That means setting your hose or irrigation system to deliver the water at a lower rate for a longer period of time. To reach the roots, the water needs to penetrate the ground to at least 12 inches. If you’ve ever seen roots growing at ground level, they’re probably doing so because the tree is receiving too little or too shallow watering.
Don’t dig a hole around the tree to help get water to go down deeper. The hole allows air in and dries out roots!
If possible, avoid using a sprinkler to water trees. In addition to producing shallower roots, the sprinkler wastes water by dispersing it into the air, where it evaporates. And some trees are subject to leaf diseases from constant watering. The only time I ever spray a tree or bush is if it has aphids, and I give it a fine-water spray in early morning to wash the aphids off.
If you can’t reach a tree with your hose, you can drill a few holes in a 5-gallon bucket and carry it out to your tree. The water will flow more slowly through the hole than if you pour the water on the ground. Move the bucket out and around the tree’s base with each refill.
If you want to save tap or well water, reuse! Direct roof water to a tree using the downspout and a dry river bed. Save shower water in 5-gallon buckets (with no holes – you have to get them outside!) but only use the water that flows while the shower warms up, not any soapy flow.
If you have other clear water to dispose, such as kid or dog pools, empty the water onto tree roots instead of a random place in the yard.