How Much of a Soil Base Does a New Lawn Need?

Q. We have a 200 square foot lawn that gets morning sun and late afternoon shade. The whole thing is brown now and I think it's because we overwatered it for the last few months. When we first put down the sod I don't know if we had a good enough base. How many inches of good soil should we should have above the hard stuff?

A. First things first. You cannot have a good lawn without a good irrigation system in our desert climate. Please be sure your irrigation system was designed and installed correctly.

            There is a lot of engineering that must be considered when designing an irrigation system. Make sure you have "head-to-head coverage" and your operating water pressure lies within guidelines of the sprinkler manufacturer. Select pop-up sprinklers that clear the surrounding grass at the maximum mowing height.

            Soil preparation is important before establishing lawn. But lawns have been successfully established on poor soils and the soil improved after lawn establishment. I don't recommend doing it this way but it can be done.

            It seems like no soil preparation before establishing the lawn would save money but it actually doesn’t. Inadequate or no soil preparation prior to planting makes a lawn difficult to manage, particularly during the summer months. Lawns established the “inexpensive way” are subject to more disease and irrigation problems.

             How to improve it after the lawn has been already planted? Irrigate the lawn and while the lawn is still moist, aerate it with a gasoline driven aerator. Stay away from sprinkler heads and hopefully the irrigation pipe was installed more than 4 inches deep or you’ll break the pipe.

            After punching holes with an aerator, apply a top dressing to the lawn and rake it into the holes followed by an irrigation. A good quality top dressing is screened to 1/8 inch minus and can be purchased from Viragrow in Las Vegas. It's the same top dressing used on golf courses. Do this once a year for the next 2 or 3 years in spring or fall and you will see a dramatic improvement IF the lawn has a good irrigation system.

            Don’t bag your lawn clippings. Recycle them back into the lawn. Most lawnmowers now are recycling mowers and chop the lawn grasses fine enough so there are no problems afterwards. If you have an older mower that is not a recycling mower, retrofit it with a mulching blade and mow the grass more slowly than you would normally. Don’t bag the clippings.

            Ideally, new lawns should have a 12 inch base of good soil. If that is not practical, then a 6 inch base would be the minimum. Removing that much soil and replacing it with good soil would be expensive and a lot of work.

            It would be better to mix a 1-inch layer of compost with your existing soil and mixing or tilling it in. No fertilizer is needed the first season after planting if a good quality compost is used.