The main application should be made in autumn and the dressing used should contain mainly phosphates and some potash. Phosphates, e.g. bonemeal, encouragegrowth. A suitable dressing for autumn is a mixture of two parts bonemeal and one part sulphate of potash (by weight) applied at 68 gms/sq.m 2 oz per square yard. It is best to measure the lawn first, weigh up the required amount of fertiliser mixture and mark off the lawn into, say 8 equal sized areas, then weigh out 8 equal amounts of fertilisers.
As grass is cut frequently in spring and summer, this means that a considerable amount of nutrient is removed from the soil in order to make fresh growth. The main requirement in early summer is nitrogen. Sulphate of ammonia is commonly used as a top dressing but should not be applied at rates exceeding 17 gms/sq.m (0.5 oz/sq.yd). It is best mixed with sand to give ease of distribution. Two or three applications can be made. This fertiliser tends to increase the acidity of soils by removing its own weight of lime from the soil. (Grass grows best when the soil is slightly acid.) The fertiliser is quick acting and gives a good colour to the grass.
Do not apply in hot, dry conditions, unlesscan be done. Sulphate of ammonia is also used as an ingredient in lawn sand, which is used as a weedkiller (against broad leaved weeds) and as a moss killer. Lawn sand can be made up of 20 parts fine dry sand, 3 parts sulphate of ammonia and 1 part sulphate of iron (all parts by weight). This mixture can be used at 136 gms/sq.m (4 oz/sq.yd). In dry, fine weather broad leaved weeds like plantains and daisies can be scorched by sprinkling sulphate of ammonia on to the foliage. Sulphate of iron watered or sprinkled on at 17 gms/sq.m (0.5 oz/sq.yd) is very bad news for moss.
Another fertiliser which can be used as a top dressing is Nitroform. This contains urea-formaldehyde and is more expensive than sulphate of ammonia. It releases nitrogen slowly. It can be applied at 34 gms/sq.m (1 oz/sq.yd).
When preparing a site for a new lawn, phosphates should be applied and bonemeal at 68gms/sq.m (2 oz/sq.yd) is a suitable dressing. This will be of particular benefit to thegrass. The same dressing should be used where a site is being prepared for laying turf.