Dividing perennials is a great way to control plant size, encourage plant growth, and multiply the number of plantings in your yard. Perennials are healthiest when they are young and have room to spread. After 4 - 5 years, we can rejuvenate these plants by dividing them. Dividing works especially well with plants that have clumpy root balls, like coneflowers, hostas, daylilies.
Here in Massachusetts, most gardeners recommend dividing spring- and summer-blooming perennials in late summer or very early fall, before the fall frost. (Fall-blooming perennials should be split in the spring). So over the next couple of months, assess your garden for opportunities to divide and follow our step-by-step on how to divide your plants:
1. Prior to digging up and dividing the plant, water it well for a few days in advance. Wait for a cooler, cloudy day to get to the digging, as extreme heat and sun stresses plants.
2. When the weather is mild, carefully dig up the plant, avoiding damage to the roots as best as you can. Rake back any mulch and your shovel or gardening spade 6 - 12 inches from the center of the plant. Work the shovel vertically down around the plant until you've formed a circle. Slip the shovel blade under the root ball and lift it out of the ground.
3. Gently separate the stems (removing any thin or weak stems) into clumps of maybe 3 – 5 shoots. Having this many new plantings from your original one will help ensure that the plant will recover quickly after being divided and replanted.
4. Using a soil knife for smaller plants (10 stems or fewer) cut straight down between your separated clumps through the roots. Continue cutting all the way through the root ball. For larger plants with thicker or heavier root balls, use a couple of garden forks to pierce at your separations and gently pull apart until your clumps are separate.
5. If you’re ready to plant your divisions right away (which is ideal), gently loosen the roots at the bottom and sides of each division. Dig the holes for your new plantings 1 - 2 inches shallower and 6 - 9 inches wider than your root ball. Plant each root ball, and backfill with soil mixed with organic matter and fertilizer. Water every two or three days for the next couple of weeks to get them established.
6. If you’re not ready to plant your divisions right away, or you’re giving them to friends/family, put them into a bucket or box in a cool shaded place like a shed or garage. Cover your plants with newspaper to help retain moisture and spray with water if the roots seem to too drying. If your divisions seem to have dried out while holding, you can still salvage them by soaking them in a bucket of water for an hour or so before replanting.