How to Divide Clump-Forming Herbaceous Perennials
Clump-forming plants, such as herbaceous perennials, and some alpines that produce more than one stem at ground level, may be divided to produce several plants complete with roots, crown, and growth buds. This method is not suitable for increasing your stock of single stem plants??the Oriental poppy (Papaverorientate) (4-9), for example, cannot be divided but should be propagated by root cuttings.
There are two times when division is most practical??early spring (when growthis just about to start) and late autumn (when the plant’s foliage is dying down for the winter). With plants that come into growth early in spring, such as hostas and agapanthus, I prefer to divide in autumn when there is less risk of damaging the new shoots. Clump-forming perennials with fine roots, on the other hand, such as asters, polyanthus, and gentians, are easy to tease apart and don’t suffer from being lifted out of the ground in early spring. Choose a day when the soil is moist.
Border irises that produce rhizomes (thick, fleshy roots) may be divided in summer after they have finished flowering. As the plants become old, the leaves and flowers form a circle away from the center of the plant. The rhizomes are easy to see because they tend to grow close to the surface where they are exposed to sunlight. Dig up the plant, exposing the roots. Using a sharp knife, cut away the old woody part of the root and discard it. This leaves the young portion closest to the leaves. Trim the fan of leaves to 6 inches and replant or pot up, keeping the rhizomes at soil level.
Some house plants lend themselves to division. We have already discussed propagating mother-in-law’s tongue by leaf cuttings. However, these plants can also be propagated by division, especially as they mature and naturally form a clump in the pot, with numerous leaves growing directly out of the compost on fleshy roots. When you come to repot the parent plant, it is a good time to tease out some of the rooted offsets and cut them from the main plant. They can then be planted up separately in pots.
Dividing Clump-Forming Herbaceous Perennials
1. Dig up the clump and, where possible, tease it apart by hand.
2. For congested clumps, you may have to resort to using two garden forks to separate the roots. I have never been very successful using this method, but try it yourself. Push two pitchforks into the center of the dump, back to back, and lever the roots apart without causing the plant too much damage.
3. If necessary, use a sharp spade or hatchet to cut the clump into several pieces, taking care not to damage the growth buds.
4. The youngest, healthiest roots are the ones toward the edge of the clump, so try not to damage these. The center of the clump, which is the oldest part of the plant, will have become woody with old roots and this should be discarded.
5. Plant the divided clumps at the same depth as before, directly in the soil or in containers of potting compost. Water thoroughly to settle the soil around the roots.
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