Dividing Perennials Can Be a Matter of Timing
I find that I like to write about projects as I am doing them. In this particular case I am dividing daylilies and moving hosta. While a perennial can be divided and moved at about any time of the year you can get a shovel in the ground, I have found that the best time for me to do this is after the plant has bloomed for the year. The general rule for perennials is that there is tremendous foliage growth after a winter of sleep. Then the plant blooms. After this it is time for the perennial to make the roots and potential new meristem for next year’s growth, bloom and root cycle. Just remember grow, bloom and lastly root when thinking about most plants.
You may find some long lived plants that will have a slightly different system for their cycle of growth. For example, a peony doesn’t completely make a new root system each and every year. For the peony the root can continue to grow and get larger by the year. It divides by new buds sending down their own root system from a primary meristem location. This is a bit more economical for the plant and offers the means for longevity since a plant can hold onto a more or less permanent root. So, the general process of growth, bloom and root development while it holds for most perennials does not mean that all plants grow and use roots for just one year and replaces them the next. In my case, my favorite plants, hosta and daylilies do have this system and I like to use this to my own advantage.
Timing plays a huge role in this too. I rarely have the time to lift and move plants in the spring. I have done this in the past. However, I have found that when I move the plant in the spring it is often “set back” for the whole season. Plants moved in the spring remain undersized and puny looking. Bloom is often weak or the flower is undersized. Sometimes color is affected. Fortunately, I rarely have time to move plants in the spring. When I do, I have found that they completely recover the next year.
Timing works in my favor after the plant has bloomed in the summer. The weather is quite warm. I divide my time between working in the sunny daylilies in the morning until it gets hot and then move to the shade and work on the hosta. Most daylilies take time to recover from all the energy they put into making bloom. This means that they stop feeding flower scapes depending on if pods of seeds happened to have set on them. Even if a pod has set, the scape still starts dying off. It just happens a few weeks later than if a pod have not set seed. All this means that a bunch of brown, dead looking sticks are sticking up all over the garden and need to be cut down. The foliage also takes a turn for the worse. Since the amount of rain is at a low this time of summer too there is a great deal of dying foliage to look at. Daylilies really look terrible after blooming.
Hostas are at full size for the season after spring growth. I like to divide after spring growth and bloom has completed because the divisions I take off of the mature clump have full size leaves at least for the rest of the season. The leaf is already there and it won’t get smaller unless I have cut into its root system too much and it needs to abort some foliage the root can’t support. And, hostas are making roots from mid-summer through fall for next year’s plant.
If I divide these plants mid to late summer I have the chance of making sure that fully developed roots have a chance to grow into their new location. This holds the plant in the ground so that the freezing and thawing of the soil will have minimal numbers of them heaving up out of the ground. And by having a fully developed root system means a faster recovery. For daylilies this means that most produce full size bloom the next season and all have recovered completely by the second season. Hosta can be a bit slower. It depends on how much one cuts into them and divides them down. I have found that if I can move a larger piece of the plant where several hostas are coming off of a shared old root crown that recovery is faster. Sometimes when one divides a large hosta down it can take years for the plant to recover.
Watering and fertilizing and soil type aid recovery. I try whenever possible to make large divisions for hosta except when I pot up the extra. The parts I pot up I cut down to single or double divisions. This has to do more with what will fit into a pot and how a customer views a potted plant. Believe it or not but most shoppers don’t like containers with large plants in them. I do but then I am a different sort of buyer. Most shoppers of new hosta like to find containers with a decent sized single division and avoid those containers with numerous divisions.
Neither of these plants requires anything special when you are dividing them. I have found that there are some products that are beneficial and encourage faster recuperation from surgery. Dusting the roots of your plants with mycorrhizae when planting encourages superior plant growth. Mycorrhizae are a symbiotic fungi group that has a symbiotic relationship with plants. Rooting compounds help too. These encourage greater root development at a faster rate. Some of these products require special handling so do follow package directions carefully. I have found with hosta and daylilies that just applying a fertilizer with higher phosphorous and potassium and low nitrogen levels works just about as well as these specialized rooting compounds. Phosphorous and potassium are second and third numbers in the NPK label you see on fertilizers. Both of these macro nutrient chemicals are necessary for superior root development. There are some rooting solutions that hydroponic gardeners use in their cloning solution reservoirs that work quite well and are a bit less toxic to people should any happen to get on your person when applying to the plant.
It is wise to amend the new hole when planting your new division. This improves drainage. It improves the soil texture. This provides additional organic nutrients to the plant as it is decomposing. Be sure to water frequently until the fall rains and cooler temperatures begin. The newly divided plant needs extra help with water until the roots re-grow. Do not over water. Usually no more than twice a week should be enough. Lastly, try to cut back foliage when you replant your divisions. For daylilies this means taking a pair of hedge clippers and cutting them back until they are about 6 or 8 inches long. For hosta my brother likes to take all the leaves off except one. I play it by ear. If I have managed to divide a hosta at a natural division where the clump in breaking down into natural divisions and I managed to include most of the old roots as well as all the new white ones that are just growing in, then I leave the leaves on the hosta. Because I am giving them extra water after dividing them I am not anal about leaf removal. These plants will let you know if you left too many leaves. If I notice that some are being aborted I will take them off. Otherwise I like to leave leaves on hosta because it is so hard for the plant to make food in the shade to begin with.
That’s it. Dividing perennials is easy. There is no bad time of the year to divide. Old timers who have mostly passed in the American Hosta Society used to do bud divisions in the very late fall. This is a specialty division task I may explain later. I just happen to prefer late summer to do my dividing tasks. Remember that a huge plant will not bloom as well as a plant that is still trying to grow into its location. I know it sound like a lot of work. I normally divide a large clump of daylilies about every 3 or 4 years. Hosta can grow for quite a number of years in between division. I average about every 7 to 10 years between division times on hosta. I have had great luck with this timing schedule finding plant recovery to be fastest with the least amount of set back.