Definition - What does Top Dress mean?
Top-dress, or top-dressing, refers to the spreading of an even layer of compost or manure over your garden bed once the weather starts to warm, and just before planting begins.
Top-dressing is usually done instead of tilling in most cases.
MaximumYield explains Top Dress
In order to grow strong and healthy, plants need rich soil to support them. In conventional gardening, this is achieved by first spreading fertilizer, such as 10-10-10 across the garden, and then waiting a brief period before tilling the garden. There is an alternative, though, that can provide much richer soil for healthier plants. Top-dressing is used by most as an alternative to tilling and can slowly build up soil over time.
To top-dress, you simply spread an even layer of manure or fertilizer over the entire garden. Once in place, this layer is left alone. You do not till it into the ground. Instead, you’ll simply plant on top of the new layer.
Over time, this will build up the soil in your garden, as well as improve the quality of the garden soil. Nutrients from the top layer will also work their way deeper into the soil.
There are several reasons to avoid tilling the soil in your garden, but perhaps the most important one is that it can damage the delicate ecosystem that exists within the soil.
A healthy garden is supported by a network of microbes that contribute trace elements to the soil, and unlock other nutrients. By tilling the soil, those microbes are brought to the surface, where they die.
It's best to top-dress your garden soil during the early spring, when the temperatures are still low, but once the weather has become dry enough. If your soil has a pH of under 6.2, you may also need to lime the garden at this time.