Many perennial plants grow in an ever widening clump. After several seasons of growing, these perennial plants will begin to die out in the center and look more like a ring than a clump.
To keep the plants vigorous and blooming, a technique known as ‘Division’ is performed. Dividing perennial plants gives you healthier, longer lived plants and the bonus of more plants.
When to divide perennials depends on the type of plant and how quickly it’s growing. You don’t have to wait until your perennial plants begin looking like doughnuts. In fact, it’s better if you don’t. Keep an eye out for clumps that have grown 2-3 times their size within 2-5 years. Any over grown clump or any clump that has simply exceeded the space allotted is a candidate for division.
Spring is usually the best time for division, since the plants are actively growing their leaves are not so developed that the root system can’t take a little disturbance and still feed the top of the plant. However, just as different plants can go different lengths of time before being divided, some plants, like peonies, prefer to be divided in the early autumn.
It’s true that dividing perennials is good for them in the long run. However it is still a shock to their system and giving them a good soaking, preferably the day before you intend to divide, will help your success.
Disturbing the root system of any plant interrupts its ability to feed and hydrate itself. Ensuring that the roots are well saturated before disturbing them reduces the trauma.
If you find you must divide a plant with a great deal of top growth, cutting back the leaves by about 1/3 will lessen the amount of work the roots will need to do to maintain the foliage. This is often the case when dividing bearded iris, after they have bloomed.
Along the same lines as watering your perennial plant well before digging and dividing it, having the new planting hole prepared before you dig will limit the plant’s time out of the ground and the stress on the root system.
Give your new division plenty of room to expand. Remember the divisions will all be smaller and will require less deep holes than the original plant.
In most cases, it is easiest to divide a perennial plant by first digging and lifting the entire plant. If that is the case, use a shovel or flat edged spade and slice completely around the outer perimeter of the plant, a few inches away from the foliage. Slice down several inches deep, at least 6 inches for most plants and more for extremely large, well-rooted plants. The idea is to dig as much of the root ball as possible.
Try and keep the soil intact around the root ball. This is an additional advantage of watering the soil around the plant. Wet soil adheres better than dry soil.
Once you have sliced completely around the plant, you will see the plant beginning to lift out of the hole. Try lifting the plant out of the hole with the shovel. It may be too heavy to lift this way. If so, use the shovel as a lever and lift the plant manually. Place it on level ground nearby.
A very common method of dividing perennials is to use 2 pitch forks to prise and split the plant apart. Perennial plants with fleshy roots, such as the daylily shown here, are easily prized apart with forks.
Insert the forks into the center of the lifted plant so that the backs of the forks are touching each other and the tines are crossing.
Press down so that the forks go through the plant. You will probably hear some cracking at this point. Let’s hope it’s your plant and not the handle on your pitch fork. In all seriousness, some plants are so dense that this method will not work. Exercise caution, since garden tool handles can break and send you tumbling.
Once your pitch forks are securely anchored in the center of your perennial, simply pull the handles in opposite directions, away from the center of the plant. Again, you will hear cracking. The roots will not be breaking cleanly, but the plant will recover.
Sometimes a densely rooted plant will resist and it will take two people to pull the forks apart and split the plant. And as mentioned in before, exercise caution, since garden tool handles can break and send you tumbling.
Keep pulling on the handles until the plant has completely split into two plants. If the resulting plants are a good size for replanting, meaning not so large you’ll have to divide again next year or so large that they don’t fit into the space you’ve allocated, you are done dividing and ready to replant.
If you have an extremely large plant, you may have to divide it several times before you have new plants of an appropriate size. Simply repeat the steps above.
However your divide your perennial plants, you should treat them like new seedlings.
- Try and do your dividing on an overcast day or at least not in during the hottest part of the day.
- Don’t leave the exposed root ball sitting about any longer than necessary. Hot sun and breezes will quickly dry the roots.
- Keep them well watered until new growth appears.
- Provide some shade if they appear to be wilting during the afternoon. A floating row cover will protect them from the hot sun.
Perennial plant division is intimidating when you first think about tearing apart your precious plants, but the more you do it, the better you will get at it and the better your perennial plants will grow.