By Bob Mann, Corporate Agronomist
It's the first of April and, right on schedule, the forsythia has bloomed with a showy mass of yellow flowers. Many people associate the flowering of the forsythia with the application of preemergent crabgrass control. This really isn't the case and I'll tell you why.
Plants have a very predictable schedule that they follow as the season progresses from spring into fall. At certain points in time, certain events occur that, if we know how to measure the progress of the seasons, we can fine-tune our tasks in the landscape in order to maximize the effectiveness of our efforts.
The way that horticulturists measure the progress of the season is called Growing Degree Days (GDD), a simple mathematical formula that counts accumulated warmth as we go from one day to the next. Forsythia will begin to bloom between 1 and 27 GDD and continue flowering right up to about 100 GDD. Crabgrass, on the other hand, won't even begin to germinate until 42 GDD with maximum germination occurring between 150 and 225 GDD. Or put another way, crabgrass germinates when the soil temperature at a depth of 1 inch averages between 57 and 64 degrees with maximum germination occurring at 73 degrees and beyond.
Translating all of that into English, crabgrass seeds can reliably be expected to germinate two to three weeks after the forsythia blooms drop. That is over a month from right now.
The bottom line is this - you do not need to rush the application of crabgrass control. In planning for the care of your lawn, we have taken all of these factors into consideration and selected the best products available to minimize the development of crabgrass in your lawn.
Another common issue that we deal with at this early point in the spring is moss. If your goal is to have a thick, green carpet of weed-free turfgrass, moss is obviously not on your list of things you want to see.
Moss is an opportunistic plant that will readily fill in areas where our turfgrasses are at a competitive disadvantage. While the presence of moss is most often correlated with acidic soils, other site issues will lead to infestations such as insufficient air circulation, excessive shade, overwatering, poor soil drainage and soil compaction.
Trees have a huge influence upon what grows in our lawns as turfgrasses grow optimally in full sun. Anything less than all day full sun puts the turf at a disadvantage, the amount of disadvantage increasing right along with the amount of shade. In my observation, the growth of trees in a landscape goes almost completely unnoticed over the course of years as does its effects. What may have been a very satisfactory lawn years ago may now be severely thinned and full of moss for no other reason than a close-by tree has grown thirty or forty feet in the past two decades. Trees and their undergrowth also severely inhibit the circulation of air at the lawn surface. This phenomenon is most evident on golf courses where putting greens are surrounded by trees requiring either their thinning or pruning.
Moss is also curious in that it has an optimum temperature for growth that is significantly lower than that of turfgrass. Mosses love the average temperatures during the last part of March, while our turfgrasses are just beginning to break dormancy. As temperatures warm, the grasses will once again begin to fill in where the mosses are right now and in a few weeks the moss, while still there, will be much less noticeable.
Moss is very difficult to control, let alone kill. There are products on the shelves at garden center that will burn down the foliage of moss, most notably ferrous sulfate. While applying these kinds of products will give the impression that it has been controlled, not addressing the underlying reason the moss is there will only lead to future disappointment. Addressing the underlying causes that allow the moss to proliferate is the only real solution to this problem.
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