Ridges are appearing on my lawns for past few years. They are approx 3-5 metres long, 3cms wide and 1-2 cms high. There are up to 10 ridges perfectly parallel to one another, in three or four areas of the lawn. There are no tree roots near them. I have dug up 1 square foot samples but can see nothing unusual underneath. They are extremely bumpy when the mower passes over them. Apart from the mower (with back roller). no machinery has been used on the lawn, but the ridges are so perfectly formed/parralel, they look mechanically created. What could cause this and how do I get rid of them?
In any case, you can spread a thin layer of good top-soil and/or sand over the area of the ridges, brushing it with a yard-brush into the grooves and off the high spots. The grass underneath will grow through a thin layer of 1cm and this process can be repeated. Top soil can be bought in bags.