How and When To Water a Landscape Tree

And When Not To Water A Tree

A woman with gloves watering a tree in her garden.

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Few tasks for homeowners are more complicated than knowing if, when and how to water a landscape tree. Much of it depends on the type of tree, your climate, current weather conditions, and a host of other variables. A watering schedule that works well for one tree species in one region of the country can be disastrous for a different tree species or in a different climate region. 

Water is the single most essential resource for a tree's survival and growth, far more important than fertilizing, disease and pest control, or any other biological need. Most of us understand the need to water trees during dry times, but what we often forget is that a tree can also be harmed by too much water. Unfortunately, the symptoms for a water-starved tree can appear to be the same as symptoms caused by water-logged tree roots. A tree that is beginning to wilt may be shutting down because too much water has introduced a vascular fungal disease into the roots, for example. In many cases, a homeowner then responds by watering more frequently and more heavily, which can lead to much bigger problems. 

Symptoms for both under-watering and over-watering can be the appearance of wilted and scorched leaves. Both conditions can prevent tree roots from effectively transporting water to the top of the tree and the tree will react by wilting. In addition, too much tree water can also shut down sufficient oxygen to the roots. Some tree species can handle "wet feet" but many trees can not. Always read up on your tree species and learn what it wants and doesn't want in terms of its environment and watering needs. 

Trees known for vibrant fall color will show disappointing color in the fall if you overwater them. Bright leaf color is triggered by the naturally dry conditions that occur in the early fall, and a tree that receives too much water during this time of year may respond by disappointing you with its leaf color. To maximize the fall display, keep the tree well-watered during the main part of the growing season, but withhold water in the late summer and early fall. Once the tree's leaves have fallen, do water the soil adequately, because you want good soil moisture to be present in the ground going into winter. 

How To Water a Tree

A person holding a hose watering a small tree in a yard.

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Supplemental watering during drought conditions can prevent tree decline, pest problems, and non-recoverable damage to tree roots and the canopy. Young trees recently planted in the landscape and certain drought-prone species need regular watering during dry periods. This essentially means that most trees that have seen no rainfall in a given week should get a hand watering. This is not a hard and fast rule, though, because many native species are adapted to local conditions and may not need extra watering. Consult with a nursery specialist or a member of your state university's Extension service to learn the needs of your trees. 

Depending upon soil texture, the density of water-competing plants found around the tree, daily temperatures, and recent rainfall amounts, about one inch of water per week should keep a tree healthy. Trees should be watered once or at most twice a week in the growing season if there has been no significant rainfall. A few slow, heavy (high-volume) waterings are much better than many short, shallow waterings, because long, infrequent waterings encourage the tree to send out deep, robust roots. Frequent shallow waterings will encourage the tree to rely on shallow, weak roots, which is not to the long-term benefit of the tree. 

However, to say that a tree needs deep watering does not mean dumping huge quantities of water on it in within a few minutes. When this is done, much of the water simply sinks through the soil layer past the tree's roots and is never taken up by the roots at all. The best deep watering is a slow watering left in place for an hour or so. Turning a garden hose on so it produces a small trickle and leaving the end of the hose a foot or so away from the trunk is ideal. Another excellent method for watering young trees is to use one of the tree-watering bags available. Made from dense flexible plastic or rubber, these bags fit around the lower tree trunk, and when they are filled with water, they allow a slow, steady trickle of water to run down into the earth. This provides the deep, slow watering that is ideal for trees. 

All landscape trees should be properly mulched, which means blanketing the area directly under the tree canopy with a 2- or 3-inch layer of organic material, such as shredded wood or compost. This layer of mulch will cool the soil and keep moisture trapped in place. But don't pile the mulch up against the tree trunk, because this will encourage pests and fungal diseases. 

Don't Over-Water a Tree!

Damp soil around a small tree surrounded by cut grass.

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As mentioned, if the tree's leaves look wilted or scorched even though you have faithfully been watering, it's quite possible that there is too much soil moisture for the tree to handle. This can be a problem in landscape with automatic watering systems that apply water by timer even during weeks when rainfall amounts have been good.

The best way to check for wet soil is to dig down 6 to 8 inches and feel the soil. The soil should be cool and slightly moist but not soaking wet. Examining the soil with your hands may also tell you much. You should be able to press most non-sandy soils into a ball with your hands and have it stay together without falling apart--this indicates proper soil moisture. If the soil ball falls apart when squeezed, then the soil may not have sufficient moisture.

If the soil ball you just made will not crumble when rubbed, you either have clay soil or soil that is too wet to crumble. This is an indication of too much water, so watering should be stopped. Neither loose sandy soils nor dense clay soils are ideal for growing most trees, although you may be able to find species well adapted to these soil conditions. In general, sandy soils will adequately support trees adapted to droughty, low-moisture conditions, while clay soils will work well with trees known to thrive in wet, boggy environments.