Down the Garden Path
Richard Hentschel, Extension Educator
This column has talked about the many impacts of our 2012 drought and why our trees, shrubs and evergreens have had such a struggle regaining their health and returning to a good annual rate of growth over the past 2 years. Lawns were clearly a victim of the drought too and so many calls to the Master Gardeners have been about identifying never before seen weeds in the lawn and then what to do about them. Lawns are perhaps the most easily stressed plants in the home landscape. In general, they are out there in the full sun with a root system that at most is 6-8 inches in depth and many times much less.
The lawns are made up of individual grass plants that spread by tillers, rhizomes and stolens depending on the grass species. How vigorous these are depends on several factors. The big one of course is that grasses in Northern Illinois are naturally cool season grasses that prefer to grow in the cooler weather of spring, late summer and fall. They will then naturally go dormant during the hotter parts of our summer. While they are dormant, the lawn weeds are not and become quite competitive in the lawn. The goal is to extend the lawn growing period in the spring to maintain growth.
Dandelions in particular used the stress of the drought to establish themselves in many lawns. Dandelions themselves are relatively easy to control using readily available herbicides. Unless the lawn is encouraged to fill in as the dandelions are managed, there can be another whole set of lawn weeds to deal with. The weed seed bank in any yard can persist for several to many years and those seeds just sit by and wait for an opportune time to germinate and grow. Top dressing with a quality organic matter or black dirt will provide both a place for your existing grass plants to fill in but also supplies the lawn with a great many nutrients not found in inorganic products. This top dressing also is necessary if you are going to overseed or re-seed those damaged areas from drought or other factors such as disease or insect damage.
Another weed that can quickly invade bare or thin spots in the lawn is crabgrass. This is an annual that needs soil moisture and warm temperatures to sprout. Lawns will easily block crabgrass seed from germinating if the lawn is thick and full. Open bare spots are all crabgrass needs to get a foothold. While crabgrass is young and small it can simply be pulled. If allowed to grow larger, it will smother the lawn grasses and root down at internodes until quite large. If a crabgrass preventer is used, you will not be able to overseed or re-seed those spots until the herbicide no longer is active.
If your are managing the lawn organically, corn gluten is also used for weed control. Be sure to completely understand application rates and it's effectiveness as you would any pesticide, so read the label before you buy, before you mix and apply and for any disposal information if you have material left over.