Ask a Master Gardener: Water Those Trees!

Summer is in full swing, and if you're anything like us, you're already thinking about fall. In the meantime, your garden still needs you, and there's plenty of good work to do out there.

Early mornings are your best friend right now. Getting outside before the heat picks up is the easiest way to make yard time feel enjoyable again, and your plants will thank you for the attention.

One thing that makes a real difference this time of year: mulch. Especially if rain has been scarce in your area lately. A fresh layer around your plants helps lock in moisture and keeps roots from drying out between waterings. And here's the part worth remembering: as mulch breaks down, it feeds the soil, which means it's quietly feeding your plants at the same time. When it starts to thin out, just add more. It's one of the simplest things you can do for your yard right now.

Water and Keeping Your Trees Healthy

Let’s talk about our trees. They also need water in this hot weather. But it takes more than just putting a sprinkler near your trees. First, deeper watering is better than shallow and frequent watering. In other words, when you water your trees, make sure you take time to give the deep roots a drink. If it’s a newly planted tree, it will need at least five gallons of water a week (you can do this in one go!).

Taking Care of the Dripline

The roots of a tree need the water, so point your garden hose toward the trunk all the way to the dripline.

To understand the dripline, think of an open umbrella during rain. The rain drips off of the outside edges in a circle that is the same size as the umbrella. Translate this to a tree. Most of the rain drips to the ground in a circle the same breadth as the canopy of the tree. This circular area is the dripline for most trees—it’s also the critical root zone!

Understanding the Critical Root Zone

Why do we call this area the critical root zone? Just as the name implies, these roots are the most important roots for the tree. These roots need the most protection to keep the tree healthy. Disturbing this area with trenching, paving or digging will most likely damage the tree.

Not All Trees Have the Same Zone

Different trees have different critical root zones varying in depth and spread. An oak tree, for example, has a critical root zone far beyond the canopy of the tree. No matter its size, the critical root zone is the best place to water, fertilize, and mulch this tree. (Remember: When mulching, start putting down the mulch 1 to 2 feet out from the trunk and then all the way to the dripline.)

Avoid Watering the Leaves!

Back to watering. Water the roots and not the leaves. Doing this will prevent fungal infection on the tree. When the leaves are wet, they will often scorch which interferes with transpiration. Transpiration is just one gift from our trees. Along with shade, trees release water into the air which helps keep us cooler.

A quick tip: Water early in the morning for trees as well as other plants and grass. This will avoid interference with transpiration

Why Trees Rock

Our trees are so very important to our environment—and they raise home values! I read an article that said homes (in Portland, Oregon) with street trees sold for around $7,000 more and nearly 2 days more quickly than those without trees. And houses within 100 feet of street trees sold for over $1,500 more, on average. Being near street trees had the same value as adding 129 square feet of finished space.

Plus, trees help clean our drinking water. According to the U.S. Forest Service, forested watersheds help “provide quality drinking water to more than 180 million Americans.”

Planting season is coming—KEEP PLANTING TREES!

Love our Ask a Master Gardener column? Check out Phyllis's previous columns here!