Sunday, May 26, 2019

Moving & Dividing Perennials, Part 1

When it comes to moving or dividing perennials, there is a general rule of thumb that is expressed in opposites: 

If the perennial blooms in early spring, move or divide them in late summer/early fall. This gives the plant time to recover before it blooms the following spring.

If the plant flowers in summer/early fall, move or divide them early in the spring. This allows the perennial the spring and summer months to get reestablished before their normal autumn bloom time. 

These are both good all-purpose guidelines. It makes sense not to move anything that is about to flower or is flowering. Though plants are amazingly resilient, it is asking a lot to uproot a plant and expect it to recover while putting on a show of blooms.

Sure Signs that you Need to Move or Divide a Plant

A plant will always give you hints it needs attention. It blooms poorly or looks straggly. When faced with disappointing results, a gardener needs to call upon their sleuthing skills. If there is no pest or disease issue, it could be inappropriate soil or moisture conditions. It could also be a simple indication of the lack of proper light. If you suspect any of the plant's growing conditions might be the concern, it can't but help but improve things to move the unhappy perennial to a more appropriate spot.

After an initial spring cleanup, it became all too apparent that this Miscanthus should have been divided sometime ago. Perennials grow outward. The old core has died leaving a ring of new growth.

A bare patch surrounded by a ring of fresh growth is a sure sign that a perennial needs division. Cutting a big clump into smaller pieces always feels a bit brutal, but the rewards are great. Dividing mature perennials always encourages fresh new growth.

Not all perennials are created equal. Some plants are just more vigorous than others. In this situation, a gardener plays a role in maintaining an even balance. Cutting back a more dominant plant can give a less vigorous plant a chance. When you have a big garden, keeping on top of things can be a challenge. Sometimes it is better to move a perennial that is being crowded by other more vigorous plants.

Moving Plants in the Spring

As well as moving spring-flowering perennials in the fall, you can often move or divide them right after they finish blooming. But if you find yourself really busy and there is a time delay that ushers in hot weather, hold off until the fall.

Of course, this is real life, where not everything goes to plan. Sometimes you'll find yourself having to move a plant at a less than ideal time. This is exactly the position I found myself in this spring. I am reducing the size of the front garden and all the perennials had been moved except one ancient Baptisia. Ideally, I should have waited until after it had flowered to move it, but the rest of the area was ready for grass seed. I didn't want weeds to move in before the grass had a chance to get established. So I bit the bullet, and moved the Baptisia, knowing I might be sacrificing the usual display of spring flowers.

How early is too early?

I usually wait for the ground to warm and plants to shows signs they have begun to break their winter dormancy before I do any moving or dividing. That being said, I like to make this one of my first tasks of the gardening season. The days warm up quickly and the heat of the sun adds to the stress a plant experiences when disturbed.

The moment fresh growth peaks up out of the warming ground, I begin to shift plants around. Just be careful. Plants that flower late in the summer or fall are often slow to emerge in the spring. If you're not mindful, you can think an open area is empty when it's not.

I move plants around unapologetically. Everyone makes mistakes. Often I plant things too close together or in a spot that, I soon come to realize, doesn't suit them at all. Sometimes foliage or flower colors clash. Most often, I find myself shifting plants around to improve my companion planting. An isolated plant in flower always looks better when placed in the company of blooming friends.

Take a few notes or pictures in the fall for the following spring.

Fall tends to be a hectic season, but if you can get yourself organized, take a few pictures and even make notes. Spring is months in the future. Without notes or the visual reference of a photograph, it's much harder to remember everything that will need to be done in the new year.

One Clever Trick for Moving Herbaceous Perennials in the Spring

When plants first emerge, they are small and low to the ground. If you've cut them back to the ground in the fall, there isn't really any indication of how wide they spread or how tall they grow. Gauging their full summer size is either a guessing game or a feat of a good memory. The more plants you move at one time, the more complicated predicting size and spacing can seem. Most gardeners (myself included) tend to underestimate the space a plant requires.

How big and wide will the Sedum on the left grow? On the right, the old-growth (brown) answers the question for me. Use this old growth to help you judge your spacing when you move a perennial. 

So, here's a little trick I've learned over the years. If you know you are going to want to move a plant in the spring, don't cut it back in the fall. Allow the old growth to remain over the winter. In the spring, the old skeleton will be a perfect indication of how tall and wide the plant is likely to grow. Once you've moved the perennial to its new spot, trim away last year's growth.

One very large root ball. I had to have my husband help lift it onto the paper!

The divisions just before they were planted.

One of the 4+ divisions of the hosta newly planted. No wilting occurred. A day of rain really 
helped with the speedy recovery.

Timing is Everything

Spring weather has the double blessing of cool temperatures and lots of rain. Both make it easier for the recovery of a plant that has been moved or divided. Fall offers cool weather, but it tends to be a drier season (here in Toronto at any rate). 

No matter which season you choose, your timing has the potential to give a plant an extra leg up. The sun can give an uprooted plant a real beating. I always try to move or divide plants on a cloudy day. 

Even better, I move or divide plants early in the evening just before a day of rain. That extra water and a break from the sun can do wonders!

Always water a plant thoroughly after you move or divide it. Until it shows signs of recovery continue to water it especially if the weather is dry.

Watch out for Hitchhikers!

The last thing you want to do is move a problem from one area to another.

This year I had to move a few hostas that were in shade but are now in the sun (after the death of a tree). To complicate things, some Goldenrod managed to infiltrate the areas where the hostas were growing. I certainly didn't want to move the Goldenrod when I moved the hostas.

To avoid an issue, I gently knock the dirt from the hosta's root ball. If I am really concerned, I might even wash the roots off with the hose. Next, I do a visual inspection looking for errant passengers (Goldenrod has bigger, more coarse roots). If I find a suspicious root, I will give it a little tug. Roots that aren't attached to the hosta will usually pull free.

It's hard to show but, in the picture above, orange daylilies have infiltrated a clump of hosta. The only way to separate the two plants is to dig up the clump of hosta. Then you need to clear enough dirt from the roots to see what's going on. Once you identify the two types of roots, you can carefully separate the two plants.

Just do your best!

Plants have a strong will to survive! Last week I moved some self-seeded Bleeding Hearts (they were too crowded and in the wrong spot). I was able to lift most of them successfully, but the tail end of the roots snapped off a couple of them. I planted them anyway. Initially, they slumped, but after two days of rain, they seem to have recovered nicely from their ordeal.

More to come in Part 2.


  1. Wish I had kept in mind "Timely" separation! My hostas, daylilies, iris, Shastas, have multiplied so's going to be a major undertaking to lift and separate. It has to be done, just wish I hadn't postponed it.

    1. I have an idea that might help you out coming in part 2 Melissa. Basically, it suggests that you do your divisions right in the ground and then try to lift the sections.

  2. I am not a gardener but still found it interesting

    1. I always worry about doing posts on rather dry subject matter, so your comment made my day Jo-Anne!

  3. Thanks for your suggestions regarding identifying errant roots. I need to move a hellebore from a bed that we are about to smother, due to uncontrollable gout-weed. I don't want to lose the hellebore, but I sure don't want to carry any of the problem child with it! I will wash the root ball free of dirt and check carefully. Thank you!

    1. I have a similar problem Kathleen. In the fall I need to move some peonies from one of the last areas where I have Goutweed. Watch for the white roots of the Goutweed in the hellebore and hopefully you can catch them all.

  4. Very timely information, and I've been doing the same thing this spring, dividing hostas and daylilies, and moving them to and fro. Heavy work, isn't it? We've had so much rain this past week, in excess of 4" and right now, the garden is swamp. :-(

    1. It is very heavy work! We have days of intermittent rain forecast so the push is on to get those last things moved!


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