Perennial plants are favorites with most gardeners because they come back each year in greater glory than the year before. But as perennials grow and spread in your garden, there comes a time when they need to be divided. Most gardeners, particularly those new to the hobby, wonder when is the right time to divide their plants. If it has become obvious that the plants need to be divided, they may wonder which season is best for them to divide the plants. Asking these questions before you attempt to divide your plants is a good idea, particularly because incorrectly dividing your prized plants could end up killing them.
While every plant is different, you can usually tell when to divide your plants based on when they flower. If your plant is one with a spring blossom, you should divide it in the fall. If it blooms in the fall, divide it in the spring. This helps your plant to put all of its energy into growing its roots and leaves after you replant it. If you divide in the spring, make sure you give your plants plenty of time to settle into their new homes before the weather gets extremely hot. On the other hand, if you divide in the fall, your plants need time to anchor into their new locations before the first freeze.
How do you know when to divide your perennials? For most gardeners the answer is that you divide your perennials when they become overcrowded. Some perennials grow much faster than others. For example, asters, irises, daylilies, and chrysanthemums may need to be divided every two or three years. Some perennials, such as peonies and bleeding hearts, may never need division. If your perennials are overcrowding the space you have for them, or if you want to put some or your plants in a new location, go ahead and divide them.
There are some signs your plants will give you when it is time to divide them. If the flowers suddenly start blooming much smaller than normal, this is an indication that your plants do not have enough room to grow. If the foliage on the bottom of the plant is thin and sparse, you need to start thinking about dividing them. Remember, however, not to divide the plants while they are blooming if at all possible.
When you are ready to divide your plants, prepare the plants by watering them thoroughly the day before you are going to divide them. Also, get the area ready for your plant divisions so you can plant them as soon as you divide them. Finally, prepare the plants for division by trimming the leaves at ground level.
Start the division process by removing the parent plant from the ground. Be sure to remove plenty of the soil around the plant to avoid damaging the roots. Once you have the plant out of the ground, use your hose to wash off as much loose soil as you can. This will help you see what type of root system the plant has. Keep in mind that each root system is divided differently.
If you see that your plant has matted roots that do not appear to have a pattern, you have a plant with a spreading root system. You can pull these apart using your hands or a small knife. If the roots are intertwined and thick, use a digging fork to separate them. You should divide each clump into three to five groupings, which you can then replant.
If you find that your plant has a central root clump with several growing points off of the center, you have a clumping root system. Daylilies and hostas are common plants with clumping root systems. To divide these, you will have to cut the crowns of the roots with a sharp knife. Each division needs to have a developing plant attached for the new plant to grow.
Irises are perennials with root systems called rhizomes. These are plants with roots that grow horizontally right at the level of the soil. Dividing rhizomes is quite simple. All you need to do is cut the rhizome in such a way that each cutting has a few inches of the root and at least one leaf fan, which should then be trimmed.
Dahlias are an example of a plant with tuberous roots. Cut these with a knife, making sure that each cutting has a tuber and part of the original stem attached to it. These can be stored for the winter as long as they are kept dry.
What do you do when your root clump is huge and quite tangled? One thing you can do is drop the root clump from a few feet off the ground. This serves to loosen the roots, making it easier for you to pull it apart. Avoid using this process with brittle root masses, as they will break. If this does not work, you may have to use an ax or saw to break the mass apart.
Divisions dry out easily, so you should put them in a pail of water as soon as you divide them. Then when you are done with the entire division process, plant each division. If you are not ready to put them in your garden, plant them in containers so that they can start to root and grow. Remember to cover them with mulch if you are planting them in the fall, because newly divided perennials are susceptible to damage from snow and frost.