Horticulture & Chemicals

Bermudagrass and pH What is the proper pH for a bermudagrass fairway?-Tennessee

Bermudagrass is not considered finicky when it comes to pH. Any pH close to neutral (7.0) is optimal. However, you'll find published recommended pH ranges for good bermudagrass performance that extend as low as 6.0 and as high as 8.0.

In the trenches What's the rule-of-thumb for removing roots when trenching or digging around trees?-Ohio

Obviously, the risk to a tree rises as you remove more of its root system. The point at which the risk becomes unacceptable is a matter of judgement. You may hear people say that you should not trench along more than 1 or 2 sides of a tree, but such guidelines vastly oversimplify the matter. Pat Kelsey, an arborist with Morton Arboretum (Lisle, Ill.), explains that anytime you trench along more than one side of a tree, you are likely to see some decline. However, the distance from the trunk is a critical factor. A trench close to the trunk will remove a great deal more roots than one at the drip line, although, strictly speaking, you've trenched on just one side of the tree in both cases. Further, close-in trenching removes more structural roots, so you increase the potential for wind failure as well as decline. Thus, Kelsey recommends trenching no closer than the drip line of the tree if at all possible.

Depending on the situation, you may be able to use a directional borer to run a pipe or line under a tree. This eliminates the whole issue of root-system damage. In Kelsey's opinion, considering the value of a mature tree, it's difficult to rationalize trenching close to the trunk of a tree when boring is an option. If boring is not an option, as it is not with many irrigation-system installations, at least try to design the system so that it minimizes trenching near the tree.

When you do remove a tree's roots, be ready to give extra care to the tree. Removing roots reduces the trees ability to meet its water needs, but you can help compensate for that loss by ensuring ample water is available to the remaining roots. Also, thinning out 10 to 15 percent of the crown, preferably before the root loss occurs, helps lower stress to the crown of the tree and may therefore reduce resulting dieback.

Evaluating organic mulches Many grounds-care professionals prefer particular mulches, but what's best for a site actually depends on the needs of the situation. Although mulch producers often makes claims about the durability, composition or color, little research exists to confirm such claims. A team of Florida researchers recently evaluated the characteristics of six organic mulches to define their qualities and usefulness for certain situations.

The researchers obtained commercially available mulches derived from cypress, eucalyptus, pine bark, pine needles, melaleuca and utility trimmings, and tested them for chemical, allelopathic and decomposition properties. So which was best? That depends.

* Nutrients. The most nutrient-laden mulch was the utility trimmings, which makes sense considering that this material included green leaves. (However, to put this into perspective, even this mulch contained less than 1 percent nitrogen.) Pine straw also was relatively rich in nutrients.

* Decomposition. The most decompostion-resistant materials were pine straw and bark, cypress and melaleuca. This is consistent with measured levels of lignin (which is highly decay-resistant), which were lower in the utility trimmings and eucalyptus. Lower decomposition rates result in longer intervals before mulches need to be reapplied.

* Allelopathy. All of the mulches tested were initially allelopathic due the presence of certain aromatic compounds. However, the most allelopathic mulches were pine straw and the utility trimmings, which both suppressed seed germination after 1 year. The other mulches lost their allelopathic qualities within a few months. (The researchers measured allelopathy in terms of germination suppression. This could be an advantage for weed suppression, but the whether this could affect established landscape plants is less clear. More research is needed clarify this.)

* Acidification. All mulches lowered the pH of the underlying soil. The initial soil pH of the soil was 5.0. after 1 year, eucalyptus lowered pH to 4.8, utility trimmings and melaleuca lowered it to 4.7, and cypress and pine bark lowered to 4.6. However, pine straw dropped pH to 4.4.

* Color. Pine bark and cypress both largely retained their original color after 1 year. Other mulches changed to pink or pinkish gray.

Based on these results, the researchers concluded that the best all-around mulches they tested were cypress, melaleuca and pine bark. However, if you desired more nutrient release, pine straw or utility trimmings would be better choices. Though the researchers considered soil acidification a drawback (which it obviously can be), this trait can also be beneficial depending on initial soil pH and whether existing plants prefer acid soils. Thus, pine straw could be advantageous rather than problematic.

Although this study shows that no perfect mulch exists for all situations, it is helpful to understand the differences between materials. Such an understanding should help grounds managers choose the most ideal mulch for a given site.

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