Extension

David Hillock, Senior Extension Specialist in Consumer Horticulture and Statewide Master Gardener Coordinator

As perennials mature, they often need dividing to encourage vigor and continued performance. Luckily the plants provide us a few clues when it is time to divide them - smaller leaves and fewer flowers, weaker stems, the center becomes open, and all the growth is on the perimeter of the clump, or it may have just outgrown its spot.

The general rule for when a perennial should be divided is opposite its flowering time. So, a plant that flowers in the spring can be divided after it flowers, usually in late summer or fall. Late August is a good time to start dividing these types of perennials in Oklahoma. Some plants don’t care when they are divided, but in any case, care should be taken to ensure survival of the new transplants.

Start by digging a trench around the outside of the clump and then lift the entire clump from the ground. Using a sharp knife or spade begin cutting the clump up into smaller clumps about the size of your fist or a gallon sized perennial. Each section should have at least three healthy buds or shoots.

Discard the older unproductive portions and the weak spindly portions and keep the more vigorous sections. Remove any diseased parts and make clean cuts to any damaged roots.

Prepare the area by digging wide, shallow holes to accommodate the roots. Place the plant sections in the holes by spreading the roots out over the ground and cover them back up. The crown of the plant should be at the same depth as it was before dividing it. Planting too deep may delay or completely hinder flowering of some species. Water the plants and keep the soil moist for several weeks to encourage new root growth.