Chicago Botanic Garden Spring 2019

36 chicagobotanic.org Smart Gardener chicagobotanic.org/smartgardener It’s time to divide and multiply perennials Perennials are the darlings of many gardens. ey emerge each spring to add color, texture, and sometimes wonderful fragrance to the garden. Because many perennials form clumps of leaves that grow larger each year, the plants bene t from being dug out of the ground, divided, and replanted. ere’s a bonus too: more plants! Spring is a good time for this task because temperatures are cool and the soil is usually moist. A spade with a sharp edge, a garden fork, and a bread knife or a trowel with a serrated edge are some of the tools that make the job fairly simple. Dividing perennials in spring also allows the roots to become well established throughout the summer. Hostas ese are among the easiest perennials to divide. is task can be done in late April and May, when their leaves are just a few inches tall. Dig up the entire clump with a spade or fork and brush or water away the soil so you can see where the clusters of eshy roots join the leaves. Each cluster is a separate plant. Care- fully tease the individuals apart, so that each cluster has a few leaves and a good clump of roots. Set the new divisions in the ground at the same depth at which they had been grow- ing and water thoroughly. is method also works for daylil- ies, lungwort (Pulmonaria) , and cone owers. Ornamental grasses After a few years of growth, ornamental grasses such as fountain grass (Pennisetum) and switchgrass (Panicum) de- velop a dead spot in the center, and the leaves grow in a ring or doughnut shape. ese grasses are usually too big to dig out of the ground. Use long-handled hedge shears to cut the old leaves as close to the ground as possible. at’s the easiest way to see the “doughnut” that has developed—the inside of the clump is usually soil or debris. Next, use a sharp spade and slice a few sections of roots from the outside ring. You can move the pieces elsewhere in the garden. Siberian irises Siberian irises (Iris sibirica) also will develop a central dead spot and, if not divided, will produce fewer, smaller owers. Siberian irises bene t from division every three years or so. To divide, dig up the entire plant with a fork or spade and set the clump on a tarp or the ground. Cut through the emerging leaves and rhizomes (thick underground stems that produce the shoots and root systems of new plants) with a serrated trowel, a bread knife, or a small handsaw. Each division should have a hefty rhizome or two. Discard any woody, dead-looking pieces. Set the plants back in the ground at the same depth they were growing, add compost or other organic matter, and water them well. Asters Some runaway perennials, like asters, yarrow, summer sun- ower (Helianthus) , and bee balm (Monarda) spread by underground runners and may need dividing every other year to keep the plants healthy and to prevent them from running wild. When the leaves are just a few inches tall in spring, it’s easiest to slice a few sections with a spade, lift them out of the ground, and use them elsewhere or com- post them. is technique also works on Coreopsis , Epime- dium , Lysimachia , Pulmonaria , lily-of-the-valley, sedges, and sweet woodru (Galium) . Hostas are easy to divide.