Summer’s heat is gone. We’ve had a bit of rain that has perked up the gardens. The fall garden season is upon us.
One of the major jobs is dividing perennials, and the first few weeks of September are the perfect time to get the job done.
Perennials usually need dividing for three basic reasons. First, they have outgrown their spot in the garden and are threatening to take over. Second, overgrown perennials usually quit producing abundant flowers and look tired by the end of the summer. It’s also a good idea to divide plants if you simply want more of a particularly nice perennial or one that seems to do well in that problem spot. In my case, I am always looking for more perennials that have proved to be quite deer resistant.
As a rule in our colder climate, dividing should be done in early September so that the plants have six to eight weeks to develop a new root system. If they don’t have some roots to hold themselves in the ground they are prone to frost heaving over the winter. In my deer-infested garden, plants that don’t have a good root system tend to get pulled up as the deer sample them over the winter.
Usually it is best to divide spring and summer blooming perennials in the fall and wait until spring to divide fall blooming plants. The actual process of dividing is not hard as long as a few important steps are followed.
Wait until the forecast is for a few days of cooler weather; cloudy, rainy days are best but uncommon for us this time of year. Water the plants well the day before so they are well-hydrated and easy to dig. Prepare new beds in advance by working in compost and watering well. Add compost to old beds. If you have to keep plants out of the ground for a few days, store them in a temporary bed or place them in a shady location and cover the root balls with moist mulch.
The actual division of a perennial depends on its root structure. Plants with spreading root system or runners can simply have clumps of roots and stems pulled apart and replanted. Clumping root systems generally have new shoots that grow from the crown of the plant. These plants are best divided by cutting the crown into pieces each with some growing buds attached. Tough clumps may need to be sawed apart. Rhizomes like iris need to be divided by pulling the rhizomes apart and replanting large healthy pieces with a fan of leaves attached.
Plan on watering new plantings until the end of October and later if it stays dry. Mulch new plants this first winter with pine needles, compost or shredded leaves to reduce the potential of frost heaving over winter. Don’t fertilize the new plants.