August 13, 2012

Weedy Lawns of August

The last few weeks has seen a proliferation of weeds in lawns. It does not seem to matter whether they are organic or chemically maintained, lawns are bursting with weeds. This is due to the usual August heat combined with a mild winter and regular, light rainfall.
While the midwest is experiencing drought conditions, here in the Northeast we are still getting regular rainfall. The regular rain, combined with August heat is especially favorable to weeds with horizontal roots that prefer the top inch or two of soil, such as the infamous crabgrass, clover, and creeping bentgrass to name a few. Bluegrass, Rye, and shorter fescues, and other favorable lawn grasses prefer deep waterings to shallow ones. When we have very hot weather and short regular rain bursts, water tends to stay in the top inch or two of the soil favoring weeds over desirable. Additionally, most folks like to water their lawns daily for short bursts which further favors weeds over grasses.
If you are into organics you sort of expect weeds, but for those of you with chemical services, you have to wonder what is up? Though you may have applied a pre-emergent herbacide, timing is also key as it should be applied before the weeds emerge but also not too soon before germination as the herbacide loses effectiveness with continued exposure to light and air. Crabgrass for example will germinate when temperatures are greater than 55 to 60 degrees farenheit for 7-10 consecutive days and will continue to germinate until soil temperatures reach 95degrees. If you are organic, you have applied corn gluten in the spring to prevent seed germinated, but that is only good for maybe three weeks. I you are a chemical user, you may have applied a granular pre-emergent which is only effective if properly applied and may have broken down by now depending on the brand and the application rate. Additionally, because this was one of the warmest winters on record for quite some time, many weeds that normally freeze to death lived through the winter doubling the available weed population and seeding in our lawns early in the year.
What to do? First, allow your lwn to grow in height to at least 3″. Bluegrass, Fescues, and Ryegrass will grow taller than most weeds and begin to shade them out. Second, alter your watering so that your lawn area gets 45 minutes to an hour of water every other day. this will encourage the desirable grass to grow deeper stronger roots so they can start to outcompete the weeds. Last, get rid of the weeds; pull them by hand, spot spray, or if you apply an herbacide over the whole lawn if your conscience can live with it.
If you have a situation where you are 50%weeds or more, you may want to start over. Many proponents of organics even will take a tactical chemical strike with a fresh organic base to start off with once the slate is clean rather than fight with a weedy lawn. An alternative is to de-thatch weedy areas with a mechanical de-thatcher, rake out the now uprooted shallow weeds, and over seed the impacted areas only, but be aware that though this will clean up the problem for now, it may invite a similar battle next year depending on how you manage your lawn when the weather changes in 2013.

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