How to Divide Perennial Plants
Dividing your plants in spring and fall is a great way to increase the number of plants in your yard and help your perennials thrive by alleviating overcrowding. Garden expert Christina Conner provides a step-by-step guide on dividing and caring for perennials before and after division.
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Over time, perennials can crowd each other out as they compete for root space, sunlight, nutrients, and water. Limited space and resources lead to stressed-out and sad-looking plants. If your established perennials are exhibiting signs of distress, it may be time to divide them.
Dividing your herbaceous perennials is key to a thriving and lush garden. It’s also a great way to multiply plants to replant elsewhere in the garden or to share with friends. Whatever you choose to do with your plants, spring or fall division is a surefire way to refresh your garden.
But don’t go hacking away at your plants without preparing first! It’s essential to understand what types of plants you have, prepare them for transplanting, and prepare your soil and tools. As with most things in gardening, preparation is vital to success. Here’s how to get your perennials ready for division, step by step:
Step 1: Find the right time
Start on the right foot by finding the right time to divide perennials — this step is critical to avoiding a disaster for your plants. First, figure out which plants are fall or spring bloomers. The general rule of thumb is to divide fall bloomers in spring and spring bloomers in fall, a month or two before the last frost.
While many plants can be divided in either season, the most important thing is to divide when they’re not actively flowering. This way, they can fully apply their energy toward establishing new roots.
Avoid dividing in the dead of summer or winter. Too hot temperatures can result in root stress while the plants are focused on pushing out new flowers. Cold temperatures will prevent the plants from establishing new roots after transplanting, potentially killing them.
Step 2: Verify that plants are ready to be divided
Generally, most benefit from being divided every two to four years, though slow growers can wait five years or more. Some plants with deep root systems, such as coreopsis or heuchera, can experience a greater risk of transplant shock if divided too late after they’ve established roots, so it’s best to divide these earlier in their lives, one or two years after planting.
You can also look at the symptoms of crowded or stressed plants to indicate they need to be divided. Some of these signs are:
- Sparse, smaller leaves and weak inner stalks splay outward in the center of the plant, leaving a hole in the crown area
- Sparse leaves on the bottom of the plant
- Cramped in a mass of other plants – all competing for the same resources (water, light, air circulation, and soil nutrients)
- An overall unhealthy appearance – not vigorous and lush
Important to note: Avoid dividing any perennial with a single woody stem, such as lavender (Lavandula) or Russian sage (Perovskia). Taproot perennials also shouldn’t be divided, including butterfly weed (Asclepias), euphorbia, false indigo (Baptisia spp.), and clematis.
Step 3: Plan and prepare new spaces
Before you dig up your plants, look around your garden to find their new homes. Find a location that’s as close to their current location as possible and dig a hole large enough to allow the roots to spread, about twice the size of the rootball. Amend the soil so that it’s well-draining and rich in organic matter. Hold off on adding any fertilizer for now.
If you’re not planting your cuttings in the ground – prepare your pots with potting soil and amendments like compost.
Step 4: Choose the right day
Once you know which perennials you’ll be dividing, it’s time to prepare them. The best time to divide is when the sky is cloudy, and the next few days are predicted to be rainy and overcast. If it’s been dry, thoroughly water the plants the day before division day and prune them back to six inches from the ground. This will reduce moisture loss and make division less of a hassle.
Step 5: Gather and clean your tools
Any time you prune, think of it as surgery for a plant. You’re making a cut that exposes the inner flesh of a plant, making it vulnerable to lingering pathogens on your shears.
Clean all of your tools by wiping them down with ethanol or isopropyl alcohol or dipping them in bleach, rinsing, and thoroughly drying. This is especially important if you’ve been working with any diseased plants. Here are the must-have tools depending on the size of the plant:
- A trowel, shovel, spade, and/or garden fork
- Shears or bypass pruners
- Gloves (for sensitive skin)
- Handsaw, knife, or hori hori, doing double-duty as a trowel, knife, and stick for wiggling the roots apart
- Shade cloth (optional)
Step 6: Division
With your tools, garden, and plants prepared, you’re ready to divide your perennials. Use your trowel, shovel, or garden fork to dig four to six inches around the plant’s perimeter at an inward angle to preserve the roots and pry the plant up and out, roots and all. Be generous when digging around the perimeter; otherwise, you’ll risk cutting off healthy roots.
With your plant out of the ground with roots exposed, gently shake it to knock off extra soil. Then, look at your root system to find the best way to divide. There are three main types of root systems, each with specific division methods.
Spreading root systems
Spreading root systems are found in ground covers and plants that spread outward with no discernable pattern. Their root systems are tangled together and can either be teased apart using your hands or a garden fork, cut apart with a hori hori, or a combination. Each clump should have at least three shoots to help the plant survive transplanting.
Common plants with spreading roots include aster, tickseed (Coreopsis), coneflower (Echinacea), chrysanthemum (Dendranthema), bee balm (Monarda), lamb’s ear (Stachys byzantina), black-eyed susan (Rudbeckia), bigroot geranium (Macrorrhizum), bugleweed (Ajuga reptans), goldenrod (Solidago), stonecrop (Sedum), yarrow (Achillea), and some fern species.
Clumping root systems
Clumping root systems are tight, compact, thick, and fleshy with a clumping habit. The best way to divide this type of system is by using a hori hori or other heavy-duty garden knife to cut through the roots at the crown of the plant, keeping several shoots or buds of new growth (called eyes) with each division. When you plant these divisions, plant them at the same soil level where they were initially planted.
Common plants with clumping roots include hosta, daylily (Hemerocallis), astilbe, and several species of ornamental grass, including big bluestem (Andropogon gerardii) and feather reed grass (Calamagrostis x acutiflora).
Rhizomes
Rhizomes may look like roots, but they’re actually stems that grow horizontally, mostly underground but sometimes above ground. Since rhizomes are stems, they have terminal nodes where shoots grow upward while roots grow downward, anchoring the plant in place. Over time, rhizomes can become overcrowded, discouraging flowering.
The best way to divide a rhizomatic plant is by using a garden fork to pry up a clump of rhizomes, cutting them into three-inch sections with a clean pair of shears or a hori hori, making sure that each section has an active terminal node. After they’ve been cut, plant the rhizomes in pots or in the garden.
What makes rhizomes the easiest plants to divide and propagate also makes some species particularly aggressive and even invasive, including bamboo (Bambusa vulgaris), bermudagrass (Cynodon dactylon), and trumpet creeper (Campsis radicans). Other common perennials with this type of root system include Solomon’s seal (Polygonatum odoratum) and snake plant (Sansevieria trifasciata), with one of the most notable rhizomes being the bearded iris (Iris germanica).
Step 7: Replant immediately
Division is a stressful experience for a plant! After division, the plant needs to be planted as soon as possible, regardless of its type of root system. This is why planning is so important—the shorter and faster the move, the happier the plant.
Place your root ball into the hole you’ve dug and fill it with soil until the plant’s crown is at the same level it was originally, or even slightly higher. Use your fingers to pack the soil down around the roots, leaving no air pockets. Water the plant, and if the soil sinks down around the plant, cover it with extra soil and water again.
Step 8: Provide the proper support as they adjust
Your plants are all moved into their new homes, but you’re not quite finished yet. Since division can be so taxing for plants, they’ll need some extra TLC during their adjustment period. Although it’ll hopefully be overcast, if the weather becomes unexpectedly hot and sunny, cover your new transplants with shade cloth or move pots under shade. Since the plants haven’t had the chance to grow many new roots, take care not to overwater them, which can lead to fungal diseases and rot.
Transplant shock
The biggest risk of dividing your perennials is transplant shock, which can be caused by root disturbance, poor site preparation, water stress, sunburn, and extreme weather. Signs of transplant shock are visually similar to thirsty plants: wilting, dropping leaves, branch dieback, and premature fall color.
If your plants are experiencing transplant shock, the best thing to do is give them time and keep them watered but not overwatered. Though the signs resemble drought stress, overwatering can lead to rot. Don’t fertilize newly planted divisions, and use mulch to help the soil retain to moisture.
By following these steps and being extra attentive to your plants, you can mitigate the risk of transplant shock for your perennials. Mycorrhizal fungi or liquid kelp fertilizer can help the plants adjust and boost their root production.
Final Thoughts
Dividing perennials is a required garden task for healthy and bountiful plants. With the right planning and preparation, it doesn’t need to feel risky and overwhelming. And the best part of division – free plants for other areas of your garden!
