A question we master gardeners get quite often is: “when do we divide our perennials and how do we do it?” There are some general guidelines but no hard and fast rules. And remember, if something has always worked for you in the past, there is no reason to change what you have been doing.
Why should you divide or split a perennial? For one thing, it gives you multiple plants and helps the plant to perform better. There is more space for roots to grow and absorb nutrients and moisture. When plants get overgrown (i.e., daylilies), flower production can decrease or will produce smaller blooms, develop a bald spot at the center of their crown or require staking to prevent their stems from falling over. When any of this occurs, it’s time to divide perennials.
Are there other reasons to divide perennials? Overcrowded plants compete for nutrients and water. Restricted airflow can lead to diseases. With all the rain, heat and humidity this summer, you might have noticed powdery mildew in the flower bed if there isn’t enough space and air movement. Another benefit is it gives you an opportunity to share and trade plants with your gardening friends.
When should you divide perennials? A cloudy, overcast day is the best. Water the soil a day ahead of time if the area is dry. Ideally, divide plants when there are a couple days of showers in the forecast to provide enough moisture for the new transplants.
Dig up the plant using a spade or fork. Lift it out of the ground and remove any loose dirt around the roots. You can separate the plant by either of these methods: pull or tease the roots apart with your hands (it can be difficult with daylilies or a root bound plant); cut them with a sharp knife or spade; or put two forks in the center of the clump and pull the forks apart. Each division should have three to five vigorous shoots and a nice supply of roots. Keep these divisions shaded and moist until they are replanted.
Perennials are easier to divide in the spring before they have gotten too much growth on them. Hosta should be divided in the spring before they get too large. Also in the spring, plants have stored up energy in their roots and rain showers generally come in the spring and that is helpful to get the new divisions established. The newly divided plants will have the whole growing season to recover before winter. It is best to divide when the plant isn’t flowering so there isn’t as much stress on it. I have heard “any day” is a good day to divide daylilies, but I wouldn’t do it when they are in bloom.
If you decide to divide perennials in the fall, there is less garden work at that time of year and it’s easy to recognize which plants need attention. In the spring, my flower beds look like there is lots of room between plants. However, by July the landscape has completely changed when plants have achieved full size. It’s a good idea to take pictures of your flower beds at this time to remind you what needs attention next spring.
If you are going to divide in the fall, do it four to six weeks before the ground freezes so the roots can become established. Perennials with fleshy roots such as peonies, Oriental poppy and iris are best divided in the fall. (Late July to early August for iris and the first part of September for peonies.) Echinacea reseed, so you only need to spread the seeds in the fall where you wish plants next year. But remember if you do that, don’t use Preen for weed control next spring in that area or you won’t get that seed to germinate.
Several years ago I got a call from Master Gardener friend LaVonne saying that she was getting rid of some of her young grape plants, and if I wanted any, I better get over and get them that day. I said it was 90 degrees and mid-July, not a time for moving plants. She told me that she was getting rid of them that day, and if I was any kind of a gardener, I could get them to grow. Well, that motivated me and with a lot of TLC, I was successful. Amazing what you can do when challenged!