Spring is a good time to divide established plants, and many herbaceous perennials need to be divided every few years anyway to stay healthy.
Plan to dig on a cool morning, preferably one with cloud cover – not too hard around here.
- Before digging sharpen your tools. Use a spading fork or flat-bottomed spade rather than a shovel.
- Water plants thoroughly between 12 and 24 hours in advance. Sink a spade into a nearby spot to test that the soil has indeed been saturated to the depth of the root ball.
- Remove any mulch from around the plant, 6 to 8” beyond the foliage spread.
- Dig out the plant by sinking the spade or fork vertically to its full depth outside the foliage spread/drip line. Continue lifting and sinking the spade in a line all around the plant. Repeat this process a second time, pushing even further into the soil. On the third go-round, use the spade like a lever to begin lifting the root ball out of the hole.
- When lifting a very large plant, ask a friend to push a 2×12 board under the root ball as you work to add leverage to allow you to remove the root ball from the hole.
- Keep roots moist and cool until they are replanted. If not potting up or replanting immediately, then “heel” them in by covering them with a blanket of soil, mulch, or moistened burlap until ready to plant.
- After planting, water well. Avoid leaving air pockets in the soil around the new planting.
Dividing Fibrous-rooted Plants
There seem to be two types of plants with fibrous root systems: those whose roots grow in every direction, and those whose roots are a tidy collection of well organized, and often delicate, strands.
- Gently tease apart the roots with your bare hands or use a tool to cut the clump into pieces, whichever is appropriate.
- Look for the buds at the top of the root system when the plant is dormant. Each of these will become a new stem as the plant begins its spring growth. Give each division two or three buds to improve its ability to withstand the transplant process.
- Timing is important: Divide Fall bloomers in the early Spring. Divide Spring and summer bloomers in the Fall.
Dividing Fleshy or Woody Crowned Plants
Crowns of these types of plants are sizable, dense and packed with growth.
- Once the plant is out of the hole, check the growth buds to work out the best path for cutting the plant apart. Give each division 3 to 4 growth buds with lots of roots.
- Plants resistant to division, such as Peonies and Dicentra may be better divided by taking cuttings.
- Use sharp tools to cut through the fleshy or woody crowns without applying too much pressure. Pressure will cause bruising, leaving a chance of rot at the site.
Dividing Suckers from Plants
Suckers form at nodes along a plant’s underground stems, known as stolons or rhizomes. Each sucker is capable of becoming an independent plant. You can easily divide the suckers formed the previous summer. If you are unsure about separating a sucker, follow these steps the year before you plan to dig the plant.
- In early Spring, find the stolon from which the sucker is growing.
- Sink the spade in a circle around the sucker, 8 to 12 inches away, on all sides except through the stolon.
- Repeat this process throughout the growing season, so by season’s end the sucker will have created new roots “inside the pot” you have created.
- Dig the sucker as usual when you are ready, cutting through the stolon this last time.
Dividing Plants with Rhizomes
Many rhizomatous plants should be dug and divided every 3 to 5 years. Keep a watch on the plant’s performance to determine when to do this. Divide when flowering decreases or flower size diminishes, or it just looks crowded.
- Best time to divide these plants is in the Fall when blooms are finished, and the root system is firmly established.
- Divide in Spring as long as the flower buds forming are snapped off. This will allow the plant to put its energy into forming a strong root system before it blooms.
- Dig the entire plant taking care not to damage the roots.
- Divide leaving at least two buds per division and a good supply of roots.
- Cut off the leaves so the plant is not stressed having to provide water to the leaf area.
- Replant rhizomes at the same depth as the original plant. Water well.
Dividing Plant with Tubers
Technically, tubers are swollen underground stems, like rhizomes, which they resemble. These plants are propagated in the same way as rhizomatous plants, the structure is the same. Dahlias are treated like tubers although they are technically a swollen root.
Many tuberous plants come from warm regions, so they need to be lifted before they freeze in the Fall, and stored in a frost-free environment. Replant in the Spring after the last frost.
- Dig the plant after the top growth has been killed by frost. Allow to rest and for a week to harden the skin. This also allows the soil adhering to the tuber to dry out before handling.
- Cut back stems to several inches above the tuber. The next year’s eyes will grow from this area, so check for disease or broken stem necks. If found, discard the tuber.
- Gently wash the tuber to remove soil, and let the surface dry completely.
- Cut the tubers apart, making sure each tuber has at least one eye. Otherwise, leave it.
- Allow the cut surfaces to dry overnight, then pack upside down on top of a layer of sand or peat moss in a sturdy box.
Dividing Plants with Offsets
Offsets are young plants that grow from the crown or stolon of a parent plant. An offset is similar to, but not the same as a sucker. Sever the offset from the parent in much the same way as a sucker.
Many plants that produce offsets are from warm, dry regions where seed germination is not guaranteed. Offsets take water and nutrients from the parent plant until they can safely be rooted on their own. Many houseplants grow this way, and, consequently, you will be moving them into plants rather than into the garden.
- Examine the plant to find the offsets large enough to live on their own.
- Remove the plant from its pot, and gently tease the offset, along with its roots, away from the parent plant.
- Plant the offset into its own pot as soon as possible. Do not let it dry out.
- Place the pot in indirect light, and allow it to grow there until well established.
– Gordon Polson