Top dressing means applying a solid fertiliser, compost or amendment to the surface of the medium rather than mixing it in or dissolving it in water. In organic and living-soil growing it is the main way of feeding: water and soil life carry nutrients down to the roots over days to weeks.
In practice
Typical top dressings are worm castings, compost, and blended organic dry fertilisers, scratched lightly into the top 1-2 cm (about 0.5 in) and covered with mulch to keep them moist and active. Many growers top-dress around the flip and again in early flower, timed ahead of demand because release is slow. Rates follow the product's guidance; over-application can burn and attracts fungus gnats.
Mineral slow-release granules are also top-dressed in some soil grows.
Don't confuse with
- Mulch: a protective surface cover; may or may not be a nutrient source.
- Compost tea: a liquid extract; top dressing is solid.
