For Release June 5, 2005

Why Won't My Grass Grow?

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

That big old tree that used to shade the front yard to the point where the grass wouldn't grow is finally gone. It was falling apart and threatening your house so you had it taken down and then had the stump ground up. You worked up the yard, you sowed new grass seed and it is all looking great, except where that stupid tree trunk was! The grass started to grow, but then a bunch of it just died out and the rest is just sitting there doing nothing but turning yellow. What is going on?

One of the most difficult places to grow grass, or almost any plant, is in the spot where a tree has been cut down and the stump has been ground or chipped out. This isn't because of poisons or toxins in the soil, but some very basic principles of organic matter recycling, rooting depth, and moisture and nutrient availability.

Once a tree is cut down, and the stump ground into chips, you have dead wood in the soil. It's no different than if you'd buried a two by four in the ground. Normal decay organisms start to invade the dead wood and decompose it. These decay organisms are primarily bacteria and fungi, but other things, including termites, can help break down the wood and recycle its nutrients.

The speed at which this happens is dependent on three things: temperature, moisture and the presence of nitrogen, which serves as food for these decay organisms. If you have warm temperatures, moist soils and lots of nitrogen, these little critters go crazy. Another factor influencing the speed of this decay is the amount of surface area that can be attacked. The finer you chip or grind the stump, the more surface area there is for the bugs to work on. If there were no plants in the vicinity this wouldn't be an issue. But if plants, like grass, are present and trying to grow in the soil and wood chip mix, there are issues. The wood decay organisms have first shot at the moisture and the nutrients. So the grass just sits there and struggles to stay alive.

The problems don't end there though. Since a good portion of these wood decay organisms are fungi, they do their typical fungi thing. A fungus is a living organism not that much different than a plant. But instead of roots and stems it has this odd whitish stuff called mycelium that allows it to infiltrate the wood chips and the soil. Under lush "growing" conditions, this web of mycelium can be very dense, very thick and sort of holds everything together. If you've ever pulled up wood chips and found a bunch of them all stuck together with whitish stuff, that's what we're talking about. This mat can become very thick and will prevent plant roots from growing through it.

But wait, there's more! Even if the chips have been removed and replaced with soil, it often has a very limited rooting depth, sometimes less than 3 inches, because that's all the deeper the stump or large roots were ground out. This shallow soil will compact very easily and dry out very quickly. Oh, over the next several years, expect explosions of mushrooms from these areas after rainfall.

The best solution is simply time. As the wood breaks down, nutrients are released, and a fertile soil is left. You can hasten this decay process by adding nitrogen fertilizer and watering it in, keeping the area moist, but not soggy. But in the end, it will simply take time as the old tree stump is recycled into nutrients that will then become part of a rich green lawn.

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