Why divide perennials?
To rejuvenate the plant and stimulate new growth - Avoid overcrowding
To control the size of the plant
To increase the number of plants
Perennials are a great investment in any garden, but once established, perennials can double and sometimes triple in size over 3-5 years creating an overcrowded cluttered garden. Mature perennial gardens benefit from being divided. As plants age you will notice a significant decrease in flower production and weaker growth. Another tell-tale sign that it’s time to divide your perennials is when the crown of the plant starts to separate in the middle and the newer surrounding shoots produce more flower buds and are healthier looking, this is very evident in old Siberian Iris clumps, Ornamental grass clumps and Shasta daisies. By dividing older perennials this stimulates new growth, increases airflow and is a great way to fill in empty spaces in your garden.
When to divide your perennials:
Spring
Early spring is the ideal time to divide perennials that flower in late spring, summer, or fall. It’s also a time to divide those perennials that have only foliage and no flowers.
Fall
Spring is not the only time that you can divide perennials. Warm soil temperatures, greater frequency of rain, shorter day-length and cooler nights make Fall an ideal time to divide perennials. The key to dividing in the fall is to do it early enough to allow for proper root establishment before a hard frost.
How to divide perennials:
When you’re ready to divide your perennials choose a day that is cool and overcast, with rain forecasted in the near future. This places less stress on your plants.
1. With a spade, dig around the perennial’s root ball, trying to get as much of the roots as possible and carefully lift out the plant. If the perennial is too large to come out in one piece, use your spade to cut the root ball in half or even in thirds, then lift out one section of the plant and leave the rest in the ground.
2. a) If the entire plant was lifted out of the ground use your spade or garden knife to create a division.
2. b) Look for any natural separations and use your spade or knife to cut the plant in those areas.
3. a) The divided perennial should be immediately transplanted, the goal is to minimize shock to the roots and to keep the roots moist. Adding a transplant fertilizer will minimize transplant shock. Make sure to follow dilution direction on the package. Once planted make sure to water the new transplant deeply. Adding transplant fertilizer or bone meal and watering deeply will minimize transplant shock.
3. b) If you plan on are dividing a plant that is still flowering, make sure to cut the flowers off first so the plant can focus its energy on the roots.
4. Surrounding the newly planted perennials with a 10cm layer of cedar mulch or clean (not diseased), dried mulched leaves helps retain moisture and adds an extra layer of protection against extreme drops in temperature, minimizing plant stress.