Did your perennials underperform last year? Are they looking tired, dead in the center, and not producing bloom? Or are they too overcrowded? The answer to these problems is to divide your perennials! Not only will you rejuvenate your plants and open up more space in the garden, you will also be creating more plants to move to another bed or give away to family and friends.
Most perennials that bloom in late spring, summer, and fall can be divided in early spring once the ground begins to thaw and new growth starts. Choose an early spring day when the soil in your garden is not wet since working in wet soil causes compaction and can destroy soil structure. Plants that produce blooms in early spring should be divided in the fall for minimal impact on flowering and to prevent transplant shock. Ideally, most perennials should be divided every 3-5 years to keep them looking their best.
Start at the drip line of the plant to ensure that you’re digging a big enough root ball (if dividing in the fall, cut plants back before digging). Using a sharp spade or shovel, cut at an angle down and under the plant at several points around the root ball, until you can lever the plant out of the hole. Place onto a tarp or into a wheelbarrow for easy dividing and transport. To make the actual divisions, you can use your hands or various tools like spades, knives, pitchforks, or even saws for heavily rooted grasses. Divide “parent plants” into at least 4 sections – smaller sections that are, at most, 20-25% of the original clump are likely to grow more vigorously. Your divisions should have several growing points (or eyes) and plenty of strong, healthy roots. Keep only the healthiest pieces and be on the lookout for pest damage, discolored stems, or eroded crowns/roots. Fill in holes left from digging out parent plants with fresh compost.
Divisions should be replanted in wide holes with plenty of space in between to account for their adult size. The roots of the individual divisions should be spread wide in the hole. Do not try to fit the plant into an undersized hole by smooshing the roots together or turning the root tips up – this will prevent the roots from growing vigorously right away. Mix in fresh topsoil/compost to the planting hole, and be sure to water your divisions well during their first year! Keep an eye on them during the heat of the summer to be sure they’ve established well and are not stressed.
Some perennials just want to be left alone and not divided. These include Baptisia, Bleeding Heart, Asclepias, Hellebore, Columbine, and Oriental Poppy. Other woody perennials like Lavender, Rosemary, Russian Sage, and Iberis (Candytuft) should be propagated by cuttings instead of by dividing.