Perennials Divide Planning

While there is something to be said for spontaneity, planning is key when it comes to things like dinner and retirement. It’s also crucial when it comes to dividing plants. Fall is one of the best times to dig and plant perennials—those plants whose roots survive our winter’s cold so they can get growing again in spring. Perennials are the hardy beauties whose reputations for resilience are what land them in our Midwest landscapes.

Most of my dividing skills were honed when I had to move plants around to make room for new additions. Some, like Hostas, peonies, and Hellebores, can go beyond a decade without need of division. Others, like Astilbe, Salvia, and Veronica will do best when they’re divided every three to five years.

Three basic reasons for dividing perennials:

1. Maintaining the health of the plant – A plant that is overcrowded just doesn’t perform as well as it could. That means its blooms are smaller and fewer in number, and it loses its ability to withstand threats like insects and disease
2. Sharing the wealth – Like borrowing, only better, sharing a plant tends to be more permanent, especially if the giver knows how to divide a plant
3. Pursuit of more plants – Although experts recommend having a spot in mind before buying a plant, the reality is that most gardeners buy plants without a clue about where it will go until they get it home or it arrives in the mail. At that point, it’s likely that the current resident plants will have to relocate to make room for the newcomer.

The number one reason is often the most challenging to determine, but these are most common.

Signs that it’s dividing time:

• You can no longer see soil around several plants. This will happen with daylilies when they are in need of rejuvenation.

• The plant has trouble supporting its stems, especially those around the plants’ edges. This often is seen in Liatris and Phlox.

• A flowering plant’s blossoms are smaller or less plentiful, or leaves are smaller than normal.

Fall Dividing

Fall is a great time to divide plants that grow and bloom in early to mid-summer, including Astilbe, Siberian iris Veronica, and Salvia.

Siberian iris can take at least two years after planting before they bloom well, especially if the original clump consists of fewer than three growing points. A healthy Siberian iris should reach its peak in its third season, and continue growing well its fourth and fifth seasons. Beyond that, you will not want to delay the division process, because that is the point at which the beautiful clump turns into a gristly root mass that sends up a few meager blooms. If you choose to divide your Siberian irises in the fall, cut leaves back to around six inches to make it easier to handle, and dig up the entire clump before cutting apart only the healthy tissue.

If dividing an overgrown Siberian iris is a trek up the side of a mountain, then separating perennials like Astilbe, Salvia, and Veronica is a walk in the park. Dig gently around the plant at least four to six inches beyond its outer crown, and it should easily come out of the ground. Shake the soil away and you’ll see several little clumps connected by roots that you can easily untangle to separate and replant.

If you have spring blooming bulbs growing near plants that you will be dividing, use a digging fork. This lessens the chance that you’ll damage the bulbs. If the soil is dry and difficult to dig, give the area surrounding the plant a good soaking first. Try to perform digging tasks during the cooler times of day or on a day that is cloudy in order to lessen the stress on the plants’ roots.

There are no hard rules about dividing plants in the fall. But there certainly are advantages. As fall progresses into winter, days are shorter, so the ground has more time to cool off, and moisture remains in the soil longer. It’s cooler, so the plants aren’t stressed from the heat.

For some plants, it just makes sense. This is the case for lilies—those that grow from bulbs, that is. Most have finished blooming by early August, and have been soaking up nutrients through their stems, which might as well have little signs on them saying, “dig here.”

Lilies are some of the easiest perennials to dig, provided you dig deep enough. I can’t count the number of times I’ve come up with just a stem, leaving the bulb in the ground. I once dug up a patch of lilies to make room for a raised bed that contained more than two feet of soil. I had apparently missed one. The following year I had a lily that grew from its position three feet underground.

Dividing Preparation

As for preparation, consider what you’ll be dividing, even if you won’t be digging until next month. If it’s Phlox, for example, and is still in bloom, remove the flowers by cutting the plant back by at least half, which makes it easier to handle.

Think about where you will be planting your new divisions and prepare the area by removing weeds and incorporating organic matter like peat, compost or composted manure. Give your plants the good life with good soil. After all, they’ll be living in that spot for the next several years.

When the day comes to dig and divide, make it easy on yourself by setting aside an area for dividing. Keep a large bucket of water handy for plants that don’t want to let go of the soil that clings to their roots. Plunge the crown into the bucket and swish it around to get rid of excess soil. This makes it easier to see what you’re dealing with.

When it comes time to replant, it’s best to do it the same day. If you must wait a day or two, keep the plants or bulbs in a shady spot and away from drying winds. And once you plant them, even if the soil is moist, water them in well so that soil settles in around their roots.

Tools you may need to start:

• Soil knife – safer than a re-purposed kitchen knife, because it’s shorter and broader and made to be gripped differently while cutting through tough plant roots and crowns.

• Transplanting spade – made with a narrower shaft to make it easier to work in tight spaces.

• Digging fork – easier to dig with less damage to roots or to avoid skewering nearby bulbs.

• High pressure hose nozzle – useful for helping to remove soil from roots.

• Large bucket – fill with water and dunk and swish plant’s roots to help remove soil.

Helpful books

Making More Plants: The Science, Art, and Joy of Propagation by Ken Druse

The Well-Designed Mixed Garden by Tracy Desabato-Aust

The Perennial Care Manual: A Plant-by-Plant Guide: What to Do & When to Do It by Nancy J. Ondra and Rob Cardillo

Perennials: The Gardener’s Reference by Susan Carter, Carrie Becker and Bob Lily