Friday, January 23, 2009
Fertilizer considerations; Maple pruning
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: I live in central Virginia and have been called on repeated occasions lately by a well-known lawn service that's trying to sell me fertilizer treatments for my fescue/bluegrass lawn. My family wants a nice looking lawn, but I am worried about adding too much fertilizer minerals to the soil and possibly hurting the nearby creeks and streams. I have done my own lawn feeding in the past, and I would like your opinion about adding the phosphorus. I recall seeing phosphorus-free lawn fertilizers in a busy garden center last fall, and I remember the big fuss that was made many years ago about taking phosphorus out of various household products, like laundry soaps. What do you think about danger to the environment from too much lawn fertilizations with phosphorus? I took soil tests from my yard not too long ago, and I recall that my soil already has medium or high levels of this nutrient.
A: Repeated fertilizations by a lawn service can strengthen a good lawn, and phosphorus is an important nutrient for root growth.
I, too, noticed “no-phosphorus turf fertilizers” in a garden center last fall. Generally, lawns and crops will not show significant improvements from receiving more nutrients that are already found in a given soil at medium to high levels. I'd say two lawn fertilizations in the fall with low phosphorus content might be adequate for your lawn to keep it vigorous.
I have heard a lot about pollution from the nutrient nitrogen, but I had to get information on the danger of phosphorus from the Virginia Cooperative Extension.
One Extension publication is “Phosphorus, Agriculture, and The Environment” by Dr. Gregory Mullins, professor and Extension Specialist in Nutrient Management.
Mullins wrote that phosphorus is one of 16 elements that are essential for plant growth. Soils in Virginia are naturally low in phosphorus -- not your soil, though, according to your tests -- and most plants in these soils require supplemental phosphorus to maximize their yield potential.
Research has documented that applying fertilizer phosphorus increases growth and yields on soils that are naturally low in phosphorus and in soils that have been depleted through crop removal. Do you remove grass clippings or let them lie? Crop fertilization represents the greatest use of phosphorus in agriculture today.
Although the economic benefits of phosphorus fertilization on crop production are well documented, too much of a good thing can be detrimental. Excessive soil phosphorus is a potential threat to water quality.
Phosphorus lost from agricultural soils can increase the fertility status of natural waters, which can accelerate the growth of algae and other aquatic plants. Algae blooms can cause fish kills. Decaying algae biomass produces surface scums, odors, and increased populations of insect pests.
Q: I live in the southern part of western Virginia and am wondering if it is all right to prune maple trees in mid-winter.
A: Yes, but be aware that some sap will drip out of the cut branch ends if the maple is in a sunny location and has warmed as a result. This doesn’t hurt the trees, although it might make things below a little sticky. Let the sap run -- pruning paints or compounds applied over the cuts are not suggested.
And don't “top” the tree, also called “hat racking,” so the afflicted tree looks like a rack on which a giant could hang his hat. Cut ends should be no bigger in diameter than 3 inches to allow the tree to naturally close off the cut area. No more than about a third of the tree’s leaf producing limbs should be removed per year. Side branches that are to be removed entirely should be cut back to the branch-trunk collar, the slightly swollen ring from which the side limb grows.
