Tip of the Week — 9/29/08

Posted in Gardening Tips, Learning Experiences on September 29 2008, by Sonia Uyterhoeven

Divide and Conquer
Sonia Uyterhoeven is Gardener for Public Education at The New York Botanical Garden.
From time to time, some of your perennials will start to languish. It’s not the heat or a lack of moisture that is the cause. Sometimes they just outgrow their space, start to sprawl all over the place, and slowly die out in the middle. When this happens, it is time to divide your perennials.

The general rule of thumb is to divide spring flowering perennials either immediately after flowering or in the fall, and to divide fall flowering perennials in the spring.

When you dig up the perennial be generous with the size of the root ball so that you get a good amount of roots. Garden forks often work better than spades since they do not slice through the roots.

If you are dividing in the fall, cut back the foliage to six inches—this will make it easier to see what you are doing and will help redirect the energy of the plant back into root growth. Water the perennial a day or two before you divide it to make digging easier and to make sure the plant won’t be stressed. Make your divisions large enough: A minimum of a quart-size pot is a good standard size.

Divide clumping plants such as astilbe (Astilbe), hosta (Hosta), ornamental grasses, or daylilies (Hemerocallis), with the double fork method or by slicing through them with a spade. For spreading plants such as lamb’s ears (Stachys), asters (Aster), and bee balm (Monarda), pull them apart by hand or sever with a knife or spade.