If You Are Obsessed About A Great Lawn
Often when I give a talk about overseeding the lawn, I will get the question that asks whether there are some additional steps one might take when overseeding to kick start the improvement of the soil at the same time. The answer is yes, there are several options to consider.
Here is the Cadillac version. After I had killed the weeds, mowed the grass real short and raked up all the debris, I would rent an aerating machine. I would aerate the area in three directions; one way, the other way and diagonally. With 4 to 6 holes per square foot, it will look like a thousand Canadian geese have just walked over your lawn. Do not rake up the cores, we’ll take care of them in a minute.
Next I would spread a mixture of Canadian sphagnum peat moss with some compost. The formula would be one bale of pest moss to one 40 lb. bag of commercial compost (3 bales per 1000 square feet). Before I spread this mix I would add a couple of cups of Plant Growth Activator (www.organica.net, 1 lb $18)which contains billions of beneficial soil bacteria and soil fungi. To this pile I would also add an envelope of Mychorizae, also in powder form (Google “Roots 1-Step, $3.80). These valuable fungi attach themselves to the roots of plants and help them get more moisture and nutrients.
There is a new compost recently on the market (available at independent garden centers) called Organimax. It is a high quality compost that already contains the soil microbes and the root fungi, saving adding those critters separately. One other optional ingredient to this pile is a couple of cups of a slow release nitrogen fertilizer such as Turf Nurture or Milorganite (both available at independent garden centers). This amount of fertilizer is a very light dose, but it gives the new grass seedlings a little boost over the next few months.
Spreading this peat moss/compost mixture is not very complicated. You make piles of the stuff around the area and then take a grass rake and rake it around so it just covers the soil. Lots of it will fall down into the holes made by the aerating machine. That is terrific because you are getting valuable organic matter, soil microbes, and Mychorizae right down into the root zone directly.
Now you are ready to spread your grass seed.Then you water, water, and water some more. Twice a day is minimum. Three times a day is best. You are not soaking the soil. You are just keeping that grass seed moist trying not to let it dry out even once. If it does dry out, you lose up to 40% germination. How frustrating is that?
Most people are starting this process with a pretty thin lawn populated with lots of weeds. The root system is very likely only two inches deep. With this gold star approach to overseeding you are not only getting the turf to become thicker, you are getting a kick start in improving the quality of the soil. In most cases, I recommend yardeners overseed once more next fall.
This time you will not be doing all the fancy stuff with aerating and organic matter. You will kill any weeds that have snuck in. You will mow close, rake real well, and spread some more grass seed. When you overseeding two times within twelve months, you are very likely to have a lawn that is as dense as new sod.
Remember, you spoil the whole show if you get all that nice thick turf and then continue to mow the grass below two inches. You must raise that lawn mower to two, preferably two and half inches to avoid causing survival stress to the grass plants and allowing enough light to reach the soil so weed seeds can again germinate. Tall thick turf has no weeds. You should plan on overseeding every four years even if the lawn looks terrific. Otherwise the weeds will sneak back as the turf thins.