What Soil Should I Use Installing a Lawn?

Q. We are planting a lawn for the dog and kids that is about 20 X 20. We only need about 3 to 4 inches of soil in this area for the lawn. Can we put this layer of your soil mix on top of our existing soil or do we have to replace it all?

A. When two soils are layered on top of each other it can be difficult for the roots of plants to penetrate the bottom layer. It is sort of similar to putting a layer of good soil on top of cement. Instead, the roots will try to stay in the top layer. If the bottom layer does not drain water easily, it is possible to create some big problems where the two soils meet. If these soils are very different from each other this would be called a “soil textural interface”.

This is a soil core taken from this lawn that was struggling. The color difference shows you the location of the interface between the two soils that were layered. Roots in this lawn had difficulty penetrating more than 1 inch deep.

Lawn grasses should have a soil depth of at least 12 inches that is texturally similar to for good root growth. Tall fescue lawn grasses are deep rooted compared to many other lawn grasses. Because fescue is deep-rooted, it has better drought tolerance than many other lawn grasses. If lawn grass roots grow only in three or 4 inches of good soil, you will constantly fight dry spots and brown patches in the lawn. It will have very poor heat tolerance and susceptible to diseases.

This lawn also had an interface. Holes were punched in the lawn every year with a lawn aerfier. This allowed grass roots to pen a trait more deeply.

There are three ways you could do this for your existing 20×20 area. The first way is to excavate this 20 X 20 area to a depth of at least 12 inches and fill it with a soil mix such as Viragrow’s Garden Soil Mix. This would require about 15 cubic yards of Garden Soil Mix.

Viragrow's Garden Soil Mix

A second method, if the existing soil is decent enough, is to mix this existing soil with 100% compost. You would rip the existing soil to a depth of 8 to 10 inches and layer 4 to 5 inches of 100% compost on top of it. The compost would be rototilled into the existing soil as deeply as possible. This would require about 5 to 6 cubic yards of Viragrow Compost.

Viragrow's HQ Compost

The third method, if the existing soil is texturally very different from the Garden Soil Mix, is to layer Viragrow Garden Soil Mix on top of the existing soil. You would do this in two stages. The first stage you would layer about 2 inches of Garden Soil Mix on top of the existing soil and rototill to remove the interface. In the second stage you would layer the garden soil mix on top of the rototilled layer. This would also require about 5 to 6 cubic yards of Viragrow Garden Soil Mix.

The deeper you cultivate, the stronger your lawn will be in the long run. Moist soil will cultivate easier than dry soil. Wet soil, however, is horrible to cultivate. Water the soil before you cultivate and let it dry enough so you can dig in it without it sticking to a shovel. Cultivate and use a water roller on the soil surface so that the soil is firm and not fluffy. Seed likes to germinate in a firm seed bed and sod installs better on a firm bed as well. Sod or seed over the top of it. When sod is installed, water it and roll it.

Conventional lawn fertilizer at Viragrow

You will not need a starter fertilizer at the time of planting. Fertilize lightly after the grass has been mowed three or four times. 

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