In the busyness of spring and planting all our annuals, such as flowers and vegetables, the perennials in our garden often get overlooked. To keep perennial plants performing at their peak, it is necessary to divide them from time to time in order to maintain vigor and flowering. As a general rule, spring flowering perennials should be divided in fall, while late-summer of fall flowering perennials are best divided in spring.
Although it may be getting a little late in the year, spring is the ideal time to divide many of the common perennials in our home gardens. Dividing perennial plants in spring is optimal for two basic reasons: plant demand for moisture is low and spring is typically a time of high moisture availability or rainfall.
Moisture requirements for plants are relatively low before above ground plant parts fully develop. Since leaves require soil moisture from roots, the larger the leaves, the larger the demand for moisture. If you can transplant early in the season, as leaves first emerge, you have capitalized on the low demand for moisture. The newly emerging leaves allow you to better predict where to dig and since roots do not yet have to support a full array of leaves, they are able to better handle the shock of transplanting, which inevitably reduces root biomass.
Spring rains provide needed relief to newly divided transplants and reduce the amount we need to water. Given the course spring weather thus far, it seems like hot weather may be moving in to stay which may signal the end of our annual spring rains. If you have perennials that need to be divided, it’s not too late yet. You just need to be aware of the rainfall we do receive and be ready to water as needed throughout summer.
There are many reasons to divide your perennials, with increasing flowering or plant vigor at the top of the list. Older plants can be rejuvenated by dividing, giving each plant more space. Additionally, the added space increases air circulation and decrease disease problems. Often times, the goal for dividing perennials is to increase the number of plants for development of new garden spaces. Other times, plants are divided out of necessity or emergency when growing conditions are altered.
Last fall, I removed a large oak tree near our house that was a major safety hazard since it was half dead and hanging over our house. In addition, there was extensive rot near the base of the truck which indicated a serious structural weakness. Sadly, it was time for this tree to go.
In the shade of this 200 year old oak was an extensive, dense stand of hosta. With the tree gone, these poor hosta stood little chance of survival in full sun. I tried to find time last fall to transplant the patch, knowing that there would be heavy impacts during the tree removal operation, but was unable to find space for the move.
This spring I anxiously awaited the first signs of regrowth to see what was left of the hostas. Amazingly, 80% of the stand re-sprouted this year despite the heavy traffic last fall. However, due to multiple other gardening projects that were in full swing when hosta leaves finally emerged, I was not able to find time for transplanting until last week.
Since my hostas had significant above ground growth, conditions were less than ideal. Optimal timing would have been right after leaf emergence, while leaves are still curled up. So, I know that watering will be the key to supporting the large amount of more develop, unfurled leaves I will be transporting along with each hosta root system. With that thought in mind, I added a thick layer of wood chips to aid in soil moisture retention (and weed control). I have irrigation set up to supplement May rains that may or may not materialize.
With some luck, I am hopeful that my hosta relocation project will be a great success. The rules of gardening were made to be broken, or at least experimented with, as long as you have a backup plan (like a sprinkler).