A Few Comments about Constructing New Lawns or Completely Renovating an Existing Lawn

The minimum depths of soil are specified for 3 situations:

1. over prepared subgrade which retains the A horizon (this refers to situations when the soil is NOT stripped off a site): 6 inches (15 cm) of topsoil advised;
2. over subgrades where the soil drains rapidly: 8 inches (20 cm) of topsoil advised;
3. over subgrades where the soil drains slowly: 9 inches (23 cm) of topsoil advised

As a rule of thumb, we could say that when a soil is being renovated or a new lawn constructed, there should be at least 8 inches (20 cm) of top soil.

For soils low in organic matter (less than 3-4%), which includes most manufactured topsoils, (see Section IV (Factors) Part 7 of this website) 1 to 2 inches ( 2.5 to 5 cm) of compost should be added and worked in to 5 to 7 inches (13 to 18 cm) with a rototiller or by hand digging.

Soil samples can be taken and sent to a soil testing lab to determine requirements for lime, phosphorous, potassium and trace elements. As compost can supply substantial quantities of nutrients and has neutralizing qualities similar to lime, these soil samples should be taken after the compost has been incorporated. Alternatively, samples of the soil and compost could be taken separately, e.g. from the piles delivered to the yard, and mixed in the proportions that will be realized when they are laid down, e.g., if 2 inches of compost are being added to 8 inches of soil, mix 2 parts of compost and 8 parts of soil to make a sample to send to the soil-testing lab.

The soil analyses and accompanying recommendations for supplements are satisfactory for most of the nutrients and for lime. However, assessing needs for nitrogen is a bit trickier, especially if it is desired to avoid overfertilizing with nitrogen, which can exacerbate disease and pest problems.

Most of the nitrogen in soils is bound up in organic matter (humus) and is made available as the organic matter breaks down. The natural supply of nitrogen is very low when soil organic matter is low (1-2%), and regular annual supplements of nitrogen are required (unless clover is abundant); when soil organic matter is in the 5% plus range, there is little need for nitrogen supplements. Adding compost adds nitrogen, however if the compost is not fully mature, the nitrogen may not be released for the first several months to a year. In order to avoid overfertilizing with nitrogen, we suggest adding 2 lbs N per 1000 sq feet (1 kg nitrogen/100m²) to the seedbed to ensure there is ample nitrogen for seedlings, and then to assess subsequent need by the sorts of observations listed under Control Level 3 on this website.

Sodding or seeding

If grass is established by use of sod and the sod is mostly Kentucky bluegrass (which it usually is), the sod should be overseeded with diverse grasses in the fall. If the new turf is being established from seed, a diverse seed mix should be used (See subsection (1) under Control by Redesign on this website).