Much ado about mulch; use it to conserve moisture and control weeds

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By Staff Brunswick Beacon

Everyone knows mulch is a great thing to add to newly planted trees and shrubs. It helps conserve moisture, keeps the soil cooler and helps control weeds.

As we do applied research and learn more about how plants respond to various practices, we often find out “what everyone knows” isn’t necessarily correct. Information generated by Dr. Ed Gilman at the University of Florida over the last few years is changing the way we think about using mulches.

Research on newly planted trees in containers suggests 99 percent of the water lost on a hot day is through transpiration—leaving through the foliage. That means only 1 percent is lost from the top of the root ball. Other research has shown over a period of three non-irrigated days mulched and bare soil areas lost essentially the same amount of water. Since it’s only 1 percent of that which is lost anyway, it really isn’t significant when it comes to keeping your newly planted tree alive.

Add these findings to other studies that have documented that mulch—especially when applied at depths greater than 2 to 3 inches—tends to repel rain or irrigation, encourages the formation of girdling roots and invites trunk damage from critters like voles.

It’s time to reconsider how we use mulch around newly planted trees.

Does this mean we don’t use mulch anymore? Mulch makes beds look better and helps with weed control, so we’re going to keep using it. But since mulch applied over the root ball of newly planted trees doesn’t provide any benefit, consider mulching from the edge of the root ball out as far as makes sense. If you just don’t like the look of that, place a thin layer over the root ball area and make sure you don’t pile mulch against the trunk. Voles and boring insects really like it when you cover those young trunks with lots of mulch.

One of the best things you can do to help new trees get established is to not force them to compete with turf grasses. How many tree islands do you see with small donuts of mulch surrounded by great expanses of turf? Put that in the middle of an asphalt parking lot and you have your very own “new tree purgatory.”

Another question that always comes up about mulch is, “Which one is the best?”

If you have lots of pine trees around that drop needles anyway, you may as well use pine straw. If you already have high soil pH’s that create problems, avoid hardwood mulch that drives the pH even higher. Areas where water collects periodically, such as rain gardens, don’t need mulch like pine bark nuggets that easily float. Other than these practical considerations, it boils down to what you like and how much money you want to spend.

Sounds like lots of other things in your life, doesn’t it?