Most cool season grasses are bunch type grasses. They grow in a bunch, but growth habits are largely misunderstood. When lawn grass seed germinates, a single grass blade emerges. At the plant’s center, or the crown, the plant has roots growing down from the crown and blades growing up. Grass plants expand as new grass blades, called tillers. They continue to grow alongside the original stalk. Hundreds of new tillers can develop, each having its own crown, roots and blades. A blade of healthy cool season perennial grass has a generally short lifespan. Because of this it must continually produce new tillers or the turf thins out.
After several years, lawns begin to slow down their reproduction rate. Because the grass lives only an average of 45 to 60 days, it is necessary that the continued production of new tillers be accomplished. Newly established seed will produce tillers much faster than older grass. In order to replenish this ability to create tillers rapidly, overseeding is the best method to achieve this. Overseeding is a great way to keep your lawn young and vibrant. Young grass is more resistant to drought and disease. Young grass is much more responsive to fertilizer applications. The ability to utilize nitrogen and thereby increase photosynthesis efficiency is also much more noticeable in younger turf grass. Overseeding lawns will reduce or eliminate competition from unwanted weeds. A thick lawn is not a welcome place for weeds to thrive. Overseeding will also help to fill in any bare areas that have developed due to foot traffic or mower damage.
When is overseeding necessary?
As far as time of the year is concerned, overseeding lawns in cool season climates should be done in spring or in the fall. The factors for determining the right time to seed have to do with soil temperature, rain availability, humidity, and air temperature. During the summer when high humidity and spiking temperatures are prevalent, overseeding is not recommended. In order to accomplish overseeding at its peak performance, it should be done after dethatching and aerating has been completed. By doing both of those mechanical services, you allow the newly applied seed to have good soil contact, as well as good transfer of air from the atmosphere. The need for carbon dioxide is imperative for photosynthesis. The efficiency of the new turf to be able to accomplish this is done with no thatch present and air available from aeration.
Once the seed has been applied to the area, usually by means of a broadcast spreader, it is top dressed with mushroom manure compost. This creates a thin layer of organic material to keep moisture in after watering. Mushroom manure is also rich with nutrients beneficial to the lawn once established. Pelletized lime is applied to bring the pH of the lawn to its optimum level. A base that is too acidic will be more difficult for turf grass to germinate in. Lime is the perfect counter measure to the acidic nature in soil. Finally, starter fertilizer is applied which has the correct measure of Nitrogen, Phosphorus, and Potash available to feed the seed and newly emerging tillers. As with most fertilizers, the coatings available on the exterior of the pellets, allow the product to be released over time. This ensures continuous feeding over the course of several weeks as the lawn area continues to be irrigated.