Q • I have a clump of Zebra grass that is about 2 feet wide and 10 feet tall that I would like to divide. Last spring, I considered doing this, and it seemed so thick I could not get a spade through it. Do you have any advice as to if I can divide it, when to do it and how to make it easier? A • For most of the ornamental grasses, early spring division is best to avoid the potential for cold weather injury from fall division. Old clumps of Zebra grass (Miscanthus sinensis ‘Zebrinus’) can have very dense root systems and may require a great deal of “elbow grease” to lift and divide.
Try watering the clump a day or two before division to soften the soil. Cut the entire plant back to several inches to get all the dead foliage out of the way. To cut directly through the roots it’s sometimes necessary to place your foot on the back lip of the shovel blade and hop on as though you were jumping onto a Pogo stick. If the blade is sharp, the weight of your body helps to slice through the roots. Be sure to wear thick-soled footwear when you do this.
Digging a trench around the perimeter along the edge of the roots also allows you to “chunk off” sections more easily. Other than that, there really are no tricks, as you just have to muscle large clumps out of the ground. Think of it as good aerobic exercise. The strongest divisions are normally those at the edge of the clump, and these are the ones to replant.
As with any garden perennial, be sure to dig in a generous helping of finished compost or other well-decayed organic matter to improve the soil and get the new divisions off to a vigorous start.
Write to Chip Tynan of the Missouri Botanical Garden at firstname.lastname@example.org or Horticultural Answer Service, 4344 Shaw Boulevard, St. Louis, 63110.