Tips for dividing plants all season in the shade

’Tis the season to divide plants and move them around the garden, so that’s what I’m going to cover in this column. First, though, I want to add a couple more things to what I said in my mulch column a while ago because several people e-mailed me with questions that I think might be of interest to others, too. Yes, I completely forgot to mention that the Minneapolis Park and Recreation Board has several piles of free woodchips that residents can use all season. Just bring your own buckets and a shovel and fill ’em up. To find the location nearest you go to ci.minneapolis.mn.us and type in “free woodchips.”

A couple of people wondered whether it was OK/safe to use these free woodchips anywhere in the garden. That’s something people debate, to be honest. Mostly, there is some concern over how clean the wood is, so I use it in my gardens everywhere but around herbs and vegetables. Other gardeners I know use it everywhere and don’t worry about it, so it’s an individual choice, really. One last thing people wanted to know is whether gardeners need to be concerned about using mulch that has come from trees that have been cut and chipped due to emerald ash borer infestation. The answer is, no, as long as the chipping cuts the wood into pieces smaller than an inch, which kills the insects at the same time.

OK, now on to the subject of dividing. Come early June, people are always asking me if it’s “too late” to divide plants and move them. This fear no doubt stems from all the articles and books out there that offer details on dividing that are so over the top in their precision as to be reminiscent of that Monty Python skit where the teacher (John Cleese) instructs his students to move their clothes to the lower peg “… after lunch, before you write your letter home, if you’re not getting your hair cut, unless you’ve got a younger brother who is going out this weekend as the guest of another boy …” It just doesn’t need to be this complicated.

While it is true that most perennials do best when they’re divided in early spring as new growth begins to emerge, that isn’t always the time when gardeners can get outside and work. It’s also hard sometimes to know what something is when all you can see is a bit of it. For these reasons — as well as the simple fact that a garden is always a work in progress — I, and most of the other gardeners I know, divide and move plants around all summer. We’re just careful to baby the plants a bit more than you would have to if you moved them earlier. (More on this in a minute.)

Mature plants are the ones that need dividing. And you can tell when it’s time to do it when you see things like fewer blooms, slower growth or the telltale doughnut ring in the center of a plant. A lot of perennials die out from the center because the roots in the center get overcrowded and can’t get the water and nutrients they need. Dividing not only makes plants looks better, it also helps keep them healthy.

You can divide perennials in two ways: dig up the entire clump of whatever you’re working with or use a shovel or spade to just get in there and cut out a portion of the plant. If you do the latter, the plant may look maimed for a little while, but it will fill back out quickly. If you’re dealing with a doughnut hole in the middle of your sedum or Siberian iris or whatever the plant may be, it’s best to dig up the whole plant and then use a sharp knife to cut out the parts of the root system that look dead. (Sometimes it’s possible to just separate roots by hand, too.) Once you’ve gotten rid of old, dead roots, divide the plant into several sections and replant them around your garden being mindful that you’re choosing spots that offer the right amount of sun for the plant.

It’s tough to do, particularly if a plant is flowering, but when you’re dividing and transplanting, always start by cutting plant foliage back to about half. That way, the transplant’s smaller root system won’t have to struggle so much to support a lot of greenery or blooms. This is particularly important when transplanting in the hot summer months rather than the cool spring, which is easier on plants. When you plant your new divisions, be sure to put them in the ground at the same level they were growing before, not too high and not too low.

If you can, try to divide and transplant in the early morning, on cloudy days or in the evening so the plants won’t have to endure the sun and heat of the day when they’re most fragile. If you do transplant in the middle of the day, try to provide some shade for divisions that seem particularly fragile: coral bells, ferns, bleeding hearts. (As opposed to hostas, which you could run over with a truck before transplanting and they would be fine.) Leave your shade structure up for a week or so if you can to give plants a chance to get established a little bit. (I sometimes just put an old sheet over a couple of chairs to create a bit of shade for plants.)

Water your plants right away after dividing and transplanting, and keep them well watered until they seem to be holding their own without flopping over or wilting or looking generally bedraggled and sad. This may take a week or two and you might have to water twice a day for a while if it’s really hot outside. To give plants time to establish a good root system before winter comes, finish all of your dividing and moving four to six weeks before the ground freezes.

Meleah Maynard is a Master Gardener and freelance writer. If you’ve got a gardening question you’d like her to address in her column, you can e-mail it to meleah@everydaygardener.com.