We’ve covered in past articles how trees on residential properties need a little more care and attention than trees that grow wild in the woods. Urban trees require regular trimming, mulching, and general check-ups in order to maximize lifespan and vitality—there are many reasons for this extra neediness, but environment is a major factor. Urban trees, or trees on residential properties, are usually growing in a neatly-manicured space, free of leaf litter and dense underbrush. In the wild, this natural vegetation would act as an insulating layer and maintain wetter soil conditions, which leads in turn to healthy growth.
Trees in residential areas don’t have the benefit of this moisture-insulating layer. This is why we add mulch to approximate natural leaf litter, and it’s also why many urban trees are living in some degree of chronic dehydration.
While Minnesota is less prone to severe drought conditions than other parts of the country (looking at you, California), it’s still useful to recognize the symptoms of drought stress in trees. Broadly-speaking, there are two categories of stress related to drought: Acute, short-term stress, and long-term or chronic stress. Short-term drought stress manifests in a tree’s leaves, in the form of browning, curling, or premature fall colorations (or dropping leaves entirely). Long-term stress can take several growing seasons to manifest, but will eventually result in a thinning canopy and dying branches. Increased insect activity can also be an indicator that a tree has been living with drought stress for a while, since these pests often seek out more damaged trees to call home.
The fact is that all trees need an ample supply of water to thrive, and supplementary watering is almost always a good idea—but there is a caveat: Too much water is just as detrimental to tree health as too little. “Drowning” a tree with standing water can lead to rot, and excess water decreases oxygen levels within the root system. It is important, therefore, to know when and how to water the trees on your property.
There’s a big difference between the water needs of young trees versus old, established trees. This comes down to differences in the maturity and size of a tree’s root system—did you know it takes two full growing seasons for a tree’s root system to become sufficiently established? Immature root systems are less capable of storing the volumes of water needed for a tree to thrive. That’s why it’s vitally important, in those first two years, to regularly water your young trees. By “regular,” we mean “every two weeks or so,” and more frequently in dry weather. Regular moisture infusions will ensure that the young tree has reliable access to the water necessary to grow strong and healthy.
Young trees must also be watered in a certain way to maximize absorption. We recommend focusing your watering efforts near the base of the tree (though not right on the trunk!). Isolating your watering to the area directly surrounding the tree’s base means that most of the water gets absorbed by the immature roots. Mature trees, by contrast, benefit most from deep watering in a broad area of ground underneath the tree’s canopy—even extending beyond the “drip zone” formed by the canopy’s outer limits.
So young trees need water more frequently, delivered near the base of their trunk. Mature trees need water relatively less frequently, delivered in a broad circle of ground to cover their entire root system. But what’s the best way to actually water your trees?
Some homeowners rely on sprinkler systems to evenly water their lawns. While sprinklers can work fine for watering trees (so long as the bark and leaves aren’t getting drenched), a method which more reliably delivers water down to the roots is called deep watering. Essentially, this consists of leaving a garden hose to trickle water for an extended period of time (perhaps 30 minutes) on the ground underneath a tree, then periodically moving that hose around the tree in a circle—each time, letting it trickle water directly onto the ground. This allows for a slow, steady permeation of water into the soil—which is precisely what mature trees need to most efficiently absorb the water they’re being given. It also encourages the growth of deep roots, which securely anchor mature trees to withstand heavy winds and storms.
Like any living thing, trees need water to thrive. They’re built to withstand periods of drought, but any tree living in a state of perpetual dehydration will take a turn for the worse eventually. Give your trees the water they need in the manner they’ll use it best: slow and steady, targeted either near the trunk (young trees) or throughout the area of canopy cover. Your trees will thank you for it!