A part of the preparation of all lawns which are constructed upon the heavy types of soil should consist of correct drainage in order to secure surface conditions conducive to the growth of good lawn grasses and to provide a firm texture to the lawn. Subsoil plowing is sometimes done with the object of correcting soil water conditions. This is not permanent, however, because the soil will pack down again within a few years. Before the topsoil is applied over the subgrade all necessary tile drainage should be installed at a depth averaging from twenty-four inches to thirty inches below the finished grade of the lawn and at intervals approximating from fifteen feet to twenty-five feet between lines of tile. This interval often depends upon the expense which the owner feels justified in making to procure an ideal lawn surface.