What gardener out there doesn’t like a good bargain? Well, if you’ve planted perennials in your garden, it’s about time for some freebies. Simply dividing your perennials is like getting free plants.
As perennials mature, they often need dividing to encourage vigor and continued performance. But, how do you know when to divide them? Luckily, the plants provide us a few clues when the time is right - smaller leaves and fewer flowers, weaker stems, the center becomes open and all the growth is on the perimeter of the clump or it may have just outgrown its spot. The most vigorous growers may need to be divided about every three to five years.
The general rule for when perennials should be divided is opposite its flowering time. In other words, a plant that flowers in the spring can be divided after it flowers, usually in late summer or fall. Late August is a good time to start dividing these types of perennials in Oklahoma. Some plants don’t care when they are divided, but in any case, care should be taken to ensure survival of the new transplants.
Before dividing, make sure plants aren’t water stressed. Give them a good watering a day or two ahead of when you plan to divide them. It’s best to water during the morning hours because plants are less stressed at that time.
Use a spade, shovel or fork to dig around and under the entire plant and lift it out of the soil. Remove most of the soil from the roots by hand or by washing gently with a hose. Use pruning shears or a sharp knife to cut apart the healthiest part of the plant. Each section should have at least three healthy buds or shoots.
Discard the older unproductive portions and the weak spindly portions and keep the more vigorous sections. Remove any diseased parts and make clean cuts to any damaged roots. Replant divisions as soon as possible after preparing the soil. If you end up with more plants than you need, share with a friend or neighbor.
Prepare the area by digging wide, shallow holes to accommodate the roots. Place the plant sections in the holes by spreading the roots out over the ground and covering them. The crown of the plant should be at the same depth as it was before dividing it. Planting too deep may delay or completely hinder flowering of some species. It’s always a good idea to protect the plants with a layer of up to 3 inches of mulch. This will help keep the plants from drying out too quickly in the late summer and will protect them as the weather begins to cool in the fall. You’ll want to be sure and water the plants and keep the soil moist for several weeks to encourage new root growth.
David Hillock is a consumer horticulturist with OSU cooperative extension.