Top Dressing of Lawns is beneficial. It encourages new basal growth of the grass plants - giving a thicker sward of grass. Top Dressing is also a good way to 'level out' the bumps and hollows in an uneven lawn.
When do you apply a Top Dressing?
Top dressing is normally carried out in mid spring. It can be done at any time in the growing season (March-October), but a dressing in the spring soon 'disappears' under the resultant lush lawn growth. Earlier in the growing season - but not in the autumn - a suitable fertiliser or feed can be added to the top dressing to give that little bit extra.
If well mixed in with the top dressing, it is a good way of applying a 'tonic' mix to the lawn. However, if the top dressing is spread over an area that has recently been hollow tine aerated, then mixing fertliser with the top dressing can result in localised 'hot spots, as the compost sinks down into the hollow cores.
Yes it can make the lawn look a little untidy right after carrying it out - even un-usable for a week or maybe two. But the benefits of top-dressing your lawn will be seen to advantage for the rest of the year.
If you study all the fine sports lawns - tennis, and bowls for instance - you will find that top dressing of the turf is an essential maintenance operation.