Many people view perennials as a carefree plant. Once you have planted these in your garden, you figure you water them the first year and forget about them. However, just as pruning certain perennials can be important, so is dividing perennials.
Once your perennials have established themselves, usually in the third year, they will have grown into much larger clumps than what they were when you planted them. The new growth can actually begin to crowd out the original growth that is in the center of the plant. To prevent your perennials from getting an empty center, division is necessary.
The general rule of thumb is to wait three years after you have planted the perennial before attempting to divide the plant. The best time to divide spring blooming perennials is during the fall, when the hot summer temperatures have cooled and the plants are not in stress. All other perennials should be divided in the spring.
Spring is a great time to divide, not only because of the milder temperatures, but because the plants are just coming up for the year. They will be smaller in size than at the end of the summer when they have grown for several months, and are easier to handle for division. Dividing perennials during the hot summer months should be avoided, as the heat and sometimes drought can put a lot of stress on a plant that is trying to establish itself.
Also, to help prevent stress, perennials should be divided on an overcast day when the soil is fairly moist. If the ground is dry, water the plant before attempting to divide the perennials.
There are two routes you can take to divide your perennials. One is to dig up the entire plant, in one large clump, and then use a sharp spade to divide it into smaller clumps. You can also use a spade to divide the plant while it is still in the ground, sectioning it off and only digging up the portion you are separating from the rest of the plant.
Once you have decided how to go about dividing your perennial, you will want to have a sharp shovel or spade on hand to help with the division. When you are looking at the perennial, either the clump that you have dug up or the plant in the ground, you want to look for any natural divisions.
Once you have determined where to divide it, use the spade to help break apart the roots at the point you’re dividing. With some perennials, you may not even need to use a spade, but gently pull the roots apart with your hands into clumps. Then, re-plant the divided section, and original plant if you dug it up, just as you would with a perennial you were planting for the first time. Keep it well watered during that season, helping it establish itself in its new home.
Generally, perennials can be divided every three to four years, but there are some perennials that need to be divided more often and some that should never be divided. A few plants that you should not attempt to divide are baptisia or false indigo, butterfly weed, peonies, hellebores and Oriental poppies.
Perennial plant division is intimidating when you first think about tearing apart your plants, but the more you do it, the better you will get at it and the better your perennial plants will grow. If it makes you nervous, start with something easy, like hostas or daylilies.