Division, in horticulture and gardening, is a method of asexual plant propagation, where the plant (usually an herbaceous perennial)[1] is broken up into two or more parts. Each part has an intact root and crown.[2] The technique is of ancient origin, and has long been used to propagate bulbs such as garlic and saffron. Another type of division is though a plant tissue culture. In this method the meristem (a type of plant tissue) is divided.
Division is one of the three main methods used by gardeners to increase stocks of plants (the other two are seed-sowing and cuttings). Division is usually applied to mature perennial plants, but may also be used for shrubs with suckering roots, such as gaultheria, kerria and sarcococca. Annual and biennial plants do not lend themselves to this procedure, as their lifespan is too short.
Most perennials should be divided and replanted every few years to keep them healthy. Plants that do not have enough space between them will start to compete for resources. Additionally, plants that are too close together will stay damp longer due to poor air circulation. This can cause the leaves develop a fungal disease.[3] Most perennials bloom during the fall or during the spring/summer. The best time to divide a perennial is when it is not blooming. Perennials that bloom in the fall should be divided in the spring and perennials that bloom in the spring/summer should be divided in the fall. The ideal day to divide a plant is when it is cool and there is rain in the forecast.[4]
Start by digging a circle around the plant about 4-6 inches from the base. Next, dig underneath the plant and lift it out of the hole. Use a shovel, gardening shears, or knife to physically divide the plant into multiple "divisions". This is also a good time to remove any bare patches or old growth. Each division should have a good number of healthy leaves and roots. If the division is not being replanted immediately, it should be watered and kept in a shady place. The new hole should be the same depth as the original hole. After the hole has been filled in, firmly press down on the soil around the base of the plant. This helps remove air pockets and makes the plant more stable. Plants that are divided in late fall when the ground is freezing should also be mulched. The division will have trouble staying rooted if the ground is freezing and thawing frequently. Continue to water the division(s) daily once until it has established itself.[5]
| Common name | Latin name | Season to divide (US) | Frequency | |
|---|---|---|---|---|
| Asters | Aster | Early spring | 1-3 years[6] | |
| Beebalm | Monarda | Early spring | 1-3 years | |
| Black-Eyed Susans | Rudbeckia | Early spring | 3-5 years | |
| Hosta | Hosta | Early spring | 5-10 years | |
| Siberian iris | Iris siberica | Early spring/Fall | 5-10 years | |
| Peony | Paeonia spp. | Late Summer/Early Fall | rarely | |
| Purple cone-flower | Echinacea | Early spring/Fall | 4 years | |
| Lambs-ear | Stachys byzantina | Spring/Early Fall | 2-3 years | |
| Garden Phlox | Phlox paniculata | Early spring/Fall | 3-4 years | |
| Chrysanthemum | Chrysanthemum | Spring | 1-2 years |