Do you know when to divide perennials?
In Seattle it may be winter, but the weather is feeling and acting as though it were spring. As you evaluate empty areas in your garden, it may be design and cost-effective to divide some of your existing perennials to move to new locations. Certainly location, size and other plant needs need to be considered, but perhaps starting by knowing when to divide what is a good place to start. As well, knowing how to care for the plants and the soil as you do your work is critical.
But, truly, using your own garden as your nursery is a great way to save money over time. As a perennial becomes overgrown in one location, dividing it and spreading your divisions to other areas of the garden helps save money and maintain some forms of repetition (aka consistency) in your garden spaces. Repetition can create calming spaces when done carefully.
Read on for some tips to get you started!
When perennials should be divided is a question I’m asked over and over. Are they divided in Spring or are they divided in Fall — that’s the question. The basic answer is divide them whenever you have time. But a fine-tuned answer is a little more convoluted.
Really, I do divide when I have the time. Fall is a great time because I’m in the garden cleaning up and evaluating what worked, what didn’t work, what spread too much, what I want in other locations, and so forth. Also, in fall, its easy to see where all the perennials really are. By spring, they may be cut back and dormant at ground level (or hidden completely under ground). Plus, by spring I’m likely to have forgotten exactly what I wanted to move where and why. So, I prefer to get as much moving about done in fall. But, time and weather are big factors.
Is Fall the best & only time?
In fall in Western Washington our soils may still be dry from our summer drought. So, I need to take extra care when I move plants at this time of year. As well, some late bloomers may still be lovely heading toward winter, so I prefer to let those adorn the garden as long as possible. Grasses, Monksood, Autumn Joy Sedum, Hardy Cyclamen, Anemone and Schizostylis are good examples of late bloomers. So, these usually get divided in late winter/spring instead. And, along with the potential of dry soil in fall, we may also get an early freeze. Our soils don’t harden up for the long haul the way so many do in other parts of the world during winter, but a good freeze just as we divide and transplant can zap a plant out of life quickly. Still, a fall transplant has the benefit of spending all of winter working on underground growth that will invigorate it beautifully come the following spring.
So, what about dividing perennials in spring?
Late winter/early spring are great times to divide plants, but it can also have its various issues. By spring our soils are wet, often saturated. Tramping on saturated beds can lead to soil compaction, which can ruin the rooting environment for our existing plants and our transplants. Soggy soil can also be a mucky mess to manage as we dig and divide. Too, in spring, bulbs are poking up through beds and delicate growth is emerging. Our gardens are more tender in spring than in fall, and we are more likely to crush and trample fresh growth as we work in beds this time of year. Yet, during the annual spring growth surge our beds can usually recuperate from our damage rapidly. So, if we do our divisions in early spring and manage to crush some top growth, our plants likely have the reserves to bounce back in this season and fill out beautifully.
One last note on spring divisions, I avoid dividing plants while they are blooming or as they are just getting ready to bloom. Many nutrients a plant uses to build strong roots are the same as those required for flowering and fruiting. If I divide the plant while it is blooming, I may choose to cut all the flowers off to help the plant make the decision to root in well rather than flower out. If it tries to do both, it may give up the ghost. Really, if I’m thinking of moving a perennial that blooms early in spring, I try to move it before its flower heads appear or I move it in fall. Examples include Hellebores, Pulsatilla, and Tiarella.
So, not sure what to do?
First ask yourself if you have the time. Second look at the plant to see if it is getting ready to flower (early spring) or still flowering (autumn). Third check the soil to see if it is too moist, not moist enough or just right. (Yes, play Goldilocks.) Finally, check your most reliable weather source to ensure temperatures aren’t heading for a big freeze. Everything perfect? Well, get out there and make things beautiful!