How often should we water newly planted trees?

I read an interesting comment recently: "If trees produced free Wi-Fi, we’d be planting them everywhere. Too bad they only produce oxygen. "

It's a rather tongue-in-cheek statement about trees, but it does remind us of their importance, while encouraging us to keep planting.

On the positive side, the Upper Midwest has done very well with tree planting over the past century-and-a-half. Cities and farmsteads are well-planted with trees, and we can pat ourselves on the back. Kudos to all who plant trees.

A newly planted tree, given a healthy start, can be on its way to a century or more of growth. How often to water a new tree is a common question. Let's investigate.

To begin the discussion, watering immediately after the planting operation is a key to success. Thorough watering moves small soil particles into air pockets, so the roots are in close contact with the soil. Roots have great difficulty growing through air pockets, and contact with the soil is essential if the tree roots are to take up moisture and nutrients needed to survive.

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How much water should we give immediately after planting is completed? It's helpful if a slight saucer is created in the soil around the tree, to catch and hold water instead of running off.

At least two five-gallon buckets of water, slowly poured over the root system, are usually needed to firm the soil around the roots and eliminate air pockets. I continue adding water, as long as it's soaking in, until it puddles up on the surface. The puddle will disappear, but it tells me the soil in the rootzone has been thoroughly wetted.

If giving the initial watering with a garden hose instead of by bucket, water the soil saucer thoroughly until it starts to puddle up. I often carry along a five-gallon bucket to fill from the hose as a gauge, since it can be easy to short-change a tree if we’re impatient to stand holding a hose.

Even if you’re installing self-watering tree bags that slowly allow water to soak around a tree, the initial watering is best given more rapidly, with the hose or bucket method. The tree bag watering system is a great way to water trees following that first watering.

Now comes the tricky part. After the initial after-planting watering, how often should a newly planted tree be watered? Once a day, once a week, twice a week, every other week?

If you do some searching, recommendations vary, because of all the variables involved. Is the soil light sand or heavy clay? Is the weather hot and windy or chilly and damp? Even with these variables, we can determine when to water new trees, with a little observation.

During the first two weeks, check the trees daily by brushing aside the soil surface to feel the original rootball soil. Water if the rootball soil feels dry, but if it's moist, wait a day and check again.

During hot windy weather, daily watering might be necessary, but don't water if the soil is still moist upon checking. Young trees can easily be killed by drowning if over-watered. Don't water daily without first checking to see if the soil needs it.

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Checking to see if the soil is approaching dryness is the best rule of thumb for how often to water a new tree. Trying to water on a set schedule such as once a day or twice a week is dangerous. Trees can be killed both by underwatering and by overwatering.

Light, sandy soil will dry quicker than heavy clay soil that retains moisture longer. Killing a tree by overwatering is of more concern in clay soil.

According to an old rule of thumb, new trees need about 10 gallons of water per week, for every one-inch of trunk caliper. This trunk diameter measurement is taken six inches above ground level.

Ten gallons per week can provide a guideline, but checking the soil first is important. When dry, apply enough to thoroughly water the root system. Avoid frequent light waterings.

Be cautious when planting trees in lawns with automatic lawn sprinklers, which don't substitute for the initial hand watering. Sprinkler systems sometimes keep the soil around trees too wet, or they might not apply enough to penetrate the root system.

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