Now close to 10 years old, our two beautiful clumps of grasses on either side of a narrow walkway are intruding passage. The grass grows out from its centre, and my putting fresh soil into the bare centre of the clump, in spring, did not result in new central growth as hoped. I look forward to your guidance.
Thank you for your inquiry. When a hole or dead space develops in the center of a perennial it is usually a sign that the perennial needs to be divided. As a general rule, perennials should be lifted and divided every 3-5 years to clean and rejuvinate old clumps. Generally, spring-flowering plants should be divided in the autumn, and autumn -flowering plants including ornamental grasses should be divided in the spring. Most plants will not divide well in summer.
Ideally spring divisions are made when foliage is 2-3″ high. In most cases the entire plant can be lifted from the ground using a spade or spading fork that is inserted into the ground about one foot away from the outside of the clump. The dead woody center is tough and often hard to pierce. To divide large thick clumps, the double fork method is quick and easy.
Plants should be kept moist and shaded during division. Discard the old nonviable center portionof the crown and cut off any dead or damaged growth or roots. Spread roots out evenly in the hole. The time when you are doing the divisions is also a good opportunity to incorporate organic matter into the hole before replanting. Make sure to water well after replanting.
You may wish to refer to the following websites for more information: http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=461