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Not the leaf wash. A neem leaf wash is for foliage you look at closely and want to shine, and nobody polishes grass. Mist it over a lawn and you will have spent an hour to no visible effect.
Neem cake on a lawn
The neem product that does belong on turf is neem cake, the pressed residue left after the oil is taken from the seed. It is a slow-release organic fertiliser, and it is used on a lawn the way any organic feed is: scattered evenly in spring or autumn, brushed in, and watered if the ground is dry.
- Use the same rate as for beds and borders, 100 to 200 g per square metre; the pellets break down over several weeks.
- The earthy neem smell is noticeable for a day or two after spreading and fades once the pellets are damp and worked in.
- Keep it to the soil; there is no point sprinkling it over the blades.
More on the cake and pellets: neem cake powder and neem cake pellets.