The right tree in the right spot is typically the focus of most tree planting programs. Finding what works for our intended purpose and then making sure we have it located appropriately is an important part of the planting’s success, and cannot be ignored.
What often does get overlooked however, are some of the finer details we need to pay heed to after planting.
We always think about watering. That’s important. We might give some attention to wildlife damage if deer or rabbits are issues. That’s also important. What about weed and grass control? Any cause for concern? Research says definitely.
Three K-State researchers at the John C. Pair Horticultural Center wanted to take a look at the effect of grass control (or lack thereof) on newly planted trees. This study was designed to look at landscape trees, but the same effect can be had on windbreak plantings as well.
Their study included five treatments on pecan and redbud and three species of grasses: bare soil maintained with herbicides, area under tree mulched 3 inches deep, and grass (tall fescue, bermudagrass, or Kentucky bluegrass) allowed to grow under the tree. All trees were fertilized according to recommendations and watered as necessary during the growing season. Trees were monitored and information collected on diameter at 6 inches above ground, weight of aboveground portions of the tree, leaf area, and leaf weight.
The results were clear cut, showing no differences in any measure between the mulched and bare soil treatments for either tree species. When compared to treatments where the turf grasses were allowed to grow, all measures showed significant growth increases if lawn grasses were controlled around the tree. Tree diameter was compromised if any grass was allowed to grow with cool season grasses reducing diameters by almost half as compared to treatments were grass was controlled. Top growth weight, leaf area, and leaf weight were all significantly greater when grass was controlled as well.
The obvious conclusion: control grasses under a newly transplanted trees to get the best possible growth. If herbicides don’t leave the look you want or you don’t want to risk damage to trees, give strong consideration to mulch or even weed barrier fabric. No matter how you do it, make sure grasses are controlled to a minimum of 3 feet from the trunk of the tree.