Lawn top dressing is when you apply a thin layer of material onto the lawn. It is often done with sand and that’s where the problem is.
Sand is used because people think it will improve air space and water infiltration and drainage. These are important organic gardening goals, but sand does not help achieve them. No matter what your soil is composed of, putting sand on top can cause drainage problems and dry pockets in the soil. And there’s more.
If you’re lawn top dressing with sand onto your clay soil, it can form a soil that is like concrete. And since sand doesn’t have any nutritional benefit or any ability to hold onto nutrients, you are decreasing the fertility of your organic soil.
It is not as bad to use sand on golf course greens because they are already made of sand, but even then, it is not very helpful. Regardless, in a residential lawn, it is harmful.
But there is something else commonly used in organic gardening that you should absolutely use for lawn top dressing and that is 10cm to 18cm of good quality, well-screened (finer textured than normal compost mixed with good quality soil) composted lawn dressing! Well-made composted lawn dressing brings many benefits to the lawn and organic garden, including:
- a broad range of nutrients
- a huge number and diversity of beneficial microorganisms
- reduced thatch due to specific microorganisms
- reduced disease
- improved water-holding capacity
- improved soil structure and reduced compaction
This method of lawn top dressing is what should be done after aerating a lawn. An organic gardening tip for if you want to do a really good job, after aerating and before adding the compost, you can add other soil-enhancing products such as mycorrhizal fungi, liquid kelp and any minerals that you need based on a soil test, such as calcitic lime and soft rock phosphate.
Doing all of these things is organic gardening heaven for your lawn.
Lawn top dressing with normal compost as an alternative produces a thick, green lawn
It is best to do all of this after aerating because the amendments and compost get down into the root zone where they belong. While you shouldn’t need to aerate every year once your lawn is healthy, topdressing with compost is always a good idea. Spring or late winter (August/September) is the recommended time for lawn top dressing.
Apply with a shovel and rake.