Propagating a plant refers to the process of using existing plants to create new plants. Many species of perennials multiply over time by sending out shoots that then take root and sprout into a new plant, with a separate stem and an independent root system. In this way, a single perennial develops into a cluster, or colony, of perennials.
If your perennials have formed a colony, you can separate the individual plants and replant them individually. This process, called division, can help you:
- Fill your garden quickly with more perennials
- Rejuvenate plants that are suffering from being too close to other plants
- Control the size of your perennials
Perennials That You Can’t Divide
Most perennials can be divided. But some perennials, rather than grow into colonies, remain as individual plants that either have a single taproot (a long root that looks something like a carrot) or have a root system that extends from a single crown (where the roots join the stem). You should not divide these kinds of perennials but instead propagate them from stem cuttings.
Some popular perennials that should not be divided include baby’s breath, baskets-of-gold, blue flax, butterfly flowers, candytufts, Christmas roses, columbines, euphorbias, false indigos, gas plants, Japanese anemones, lavender, lentens, lupines, Oriental poppies, rosemary, and southernwood.
When to Divide Perennials
It’s best to divide perennials when they aren’t flowering. Divide spring-blooming flowers in the fall, and fall-blooming flowers in the spring. Also, make sure to divide long before cold weather starts and frosts might occur. Perennials are vulnerable during the weeks and months just after they’ve been divided.
How to Divide Perennials
To divide a perennial, use the following steps:
- Water: Water the soil thoroughly a few days before dividing. The soil should be moist and fairly easy to dig.
- Prune: Using clippers or pruning shears, trim the perennial down to 6″ above the ground.
- Dig: With a trowel, dig down on all four sides around the perennial. Try to keep a distance of 4–6″ from the plant. Once you’ve dug completely around the plant, pry out the plant with your hands. If the plant is too big, cut into it with a shovel until you can pull it out.
- Divide the perennial: Try to pull the perennial apart with your hands. It may divide pretty easily. If it’s difficult to pull the perennial apart, try making it easier by soaking the roots in water. If that doesn’t help, try to cut the roots apart using a knife or shovel.
- Trim: Once you’ve separated the perennial, trim off all the dead parts.
- Replant: Dig a hole the same depth as the one that you dug to pull out the perennial. Plant the division in the hole, making sure that the roots are in direct contact with the soil. Repeat for all divisions.
- Water: Water each divided plant once it’s planted.