When and How to Divide and Replant Popular Perennials
In addition to creating new plants, division brings benefits to many perennials, like rejuvenating growth and flowering, and managing size. Garden expert Katherine Rowe outlines how and when to divide and replant our favorite perennials for renewed vigor for seasons to come.
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Division significantly benefits some of our top-performing perennials, including many natives. It rejuvenates less vigorous, declining crowns. It also reduces crowding, maximizing air circulation around stems, and improves access to resources to support growth.
Dividing frees up root and growing space. Less cramped conditions stimulate growth and mean fewer pest and disease issues. Division also manages size, controlling overgrowth and reining in robust spreaders. And, the best part is that it propagates new plants to increase our collection.
Early fall is the best time to divide spring and summer-flowering perennials, while spring is optimal for fall-blooming selections. The mild conditions of each season allow tender transplants to develop roots before sweeping temperatures.
If it’s time to divide and replant your perennials, follow this guide to get it right.
How to Tell if Perennials Need Dividing
While some perennials never need dividing, others benefit from it every few years. Every three to five years is a good gauge for assessing when to divide many of our favorites. Some, like Christmas ferns and other vigorous spreaders, can handle it annually. Most, though, need time to regrow and fill a space before another round.
So, how do you tell if you need to divide and replant your perennials? Signs that it’s time to divide established specimens include:
- Declining central crowns
- Fewer flowers
- Woody stems with less new growth
- Sparse foliage
- New growth popping up mainly on the perimeter
- Growing outside of optimal conditions (in too much shade, poorly draining soils, and so on)
When to Divide
Save dividing fall-flowering perennials for spring. For those that bloom in spring and summer, fall is the go-to season. Both seasons pose the least stress when replanting after dividing, minimizing transplant shock, and giving the best foundation for healthy roots. Skip digging, dividing, and replanting during extreme hot or cold conditions, as they can stress young transplants.
It’s best to divide and replant perennials when they aren’t in flower. Spring and summer-flowering perennials begin to slow toward season’s end. In early fall, when not focused on blooming and reproducing, they can direct energy into developing roots and settling in before winter.
From clumping, rhizomatous perennials to those with fleshy tubers, fall offers a less busy season to divide. Spring is the best time to divide fall-flowering perennials, and any late-season bloomers we didn’t capture in the fall.
In addition to seasonality, there are local conditions on the day of dividing. Choose a mild, overcast day that’s not overly hot or sunny for the least stress on the new and existing plants.
Fall Timing
Using our anticipated first frost date as a guide helps plan fall dividing and replanting. Allow at least four to six weeks before the first frost, especially in cold climates. The month or more of moderate conditions lets roots develop, situate, and absorb moisture before the soil freezes.
September and October are the best times for many of us to divide and replant perennials. Roots and tubers have adequate energy reserves from the growing season, and an early fall division gives new roots time to set before heavy frost. In addition to lessening stress, dividing in the fall provides a necessary chill blast over the winter for perennials that benefit (like peonies).
Spring Timing
In spring, wait until after the final frost and as new growth emerges to divide perennials. The new transplants will be tender, and avoiding any late-season, bounce-back frosts gives them the strongest start.
Roots and shoots develop most quickly in warming temperatures, best indicated by new growth reaching several inches tall on existing specimens. Catch them before budding and flowering.
Perennials to Divide in Fall
We mentioned spring and summer bloomers as being prime for splitting up in the fall. Popular selections to divide in the fall include:
- Coreopsis
- Daylilies
- Hosta
- Iris
- Lilies
- Peonies
- Phlox
- Poppies
- Rudbeckia
- Yarrow
Perennials to Divide in Spring
Those late-season blooms we couldn’t bear to miss and other fall-blooming perennials are ideal for propagating in spring. Favorites include:
- Aster
- Autumn Sage
- Chelone
- Chrysanthemum
- Dahlia
- Helianthus
- Liatris
- Monarda
- Penstemon
- Sedum
- Solidago
Perennials Sensitive to Division
Some perennials never need dividing, thriving just fine without rhizomes or tubers that spread or become crowded. Others are sensitive to root disturbance.
In some cases, roots sensitive to transplanting don’t mean the selection won’t benefit from division. A garden peony in too much shade, for example, or planted too deeply, stands the best chance of success with dividing and replanting in a better position. Slow to establish, it may not flower for a year or two, but it may prove more resilient in its new locale.
Perennials sensitive to root disturbance during division include:
- Baptisia
- Bleeding Heart
- Milkweed
- Peonies
Tools and Prep
With only a couple of basic garden tools, we can successfully divide and replant perennials to boost our garden collection. A digging fork, shovel, or spade lifts the roots and crown. Sharp pruners or a blade cut the stems and roots into sections, and tidy up the existing plant.
Sanitize tools to help minimize the spread of diseases, especially when pruning and clipping roots and shoots. Disinfect tools with an alcohol wipe, spray, or dip in 70% isopropyl alcohol. Sharpen blades to minimize tearing and shredding stems or roots, which creates wounds susceptible to disease.
Before dividing, deadhead aged blooms, cut away weak stems, and remove any dead and diseased portions. Light trimming helps us capture the healthiest parts of the plant to propagate.
Decide where you’ll replant, whether in the existing location or a new spot elsewhere in the garden. If the perennial is happy, mirror the conditions in the next locale. Prepare the bed by removing any plant debris to prevent the harboring and transmission of pests and diseases. Check soil quality and add compost to increase organic richness for those who prefer fertile loams. Turn the soil lightly to aerate it to aid the new transplants’ root growth.
Water deeply the day before dividing. Moist, but not wet, soils make for easy digging, while turgid, water-filled stems and roots create resilient offshoots.
How to Divide
Now to the straightforward process of making the divisions. With a spade or digging fork, dig a wide berth around the main crown or entire clump. The goal is to lift the whole plant out of the soil, capturing as many intact roots as possible. For some perennials, this may be only four to six inches away from the core, depending on the size and depth of the root system. Loosen the roots and gently shake off excess soil.
With a sharp knife, pruners, or spade, separate the clump or core into sections. You may even be able to tease them free by hand. Each segment should have three to five viable stems with roots attached. Every workable segment becomes a new transplant.
With clumping selections like rudbeckia, coneflower, and salvia, it’s easiest to start from the outside working in, as fresh growth occurs mostly on the perimeter. For tuberous perennials like peonies and dahlias, make sure to use tuber sections that have bud eyes (the point on the tuber where roots and shoots emerge). Peonies show the most success with divisions that have three to five bud eyes, while dahlias need at least one viable point.
After separating the established plant into sections, determine if the central crown of the mother plant is worth replanting. If the crown is dense with woody stems and shows less growth and flowering, compost the old portion and focus on replanting the next generation.
How to Replant
Plan to replant the newly separated segments as soon as possible for viability. Situate the transplants in their prepped site according to proper spacing for the variety. The correct spacing promotes air circulation and allows space for mature growth.
Maintain the same planting depth as the successful original planting. Crown depth may vary by selection, with some preferring to be planted slightly high and others slightly lower. Sticking with the same depth as the previous growing situation works in most cases.
In addition to borders and beds, replanting the divisions in containers and raised beds works well. Use a high-quality potting mix with good drainage, and ensure the pots have ample drainage holes. With fall transplants, prepare to provide winter protection in cold climates, as containers face more cold exposure than in-ground plantings.
Tending New Plantings
After you divide and replant perennials, water thoroughly to moisten the surrounding soil. Aim for even moisture, taking care not to oversaturate the roots, which leads to fungal problems.
In fall, continue watering until the first frost for the hardiest specimens heading into winter. Depending on your climate, regular seasonal moisture is often enough, with supplemental irrigation during dry spells. For spring divisions, keep an eye on soil moisture throughout the summer and adjust during heat waves or drought.
Topdress with mulch to regulate soil temperatures, retain moisture, and suppress weeds. Maintain a two-inch layer, keeping it off the stems. For fall plantings, add a thicker layer of mulch in cold climates. Several inches of straw, pine needles, or leaf litter help protect against natural freeze/thaw cycles and frost heaving, which can damage the young, sensitive roots. Thin the layer in early spring to warm the soil and to make way for emerging new growth.
In nutrient-rich soils (or even lean ones for some tough perennials), you won’t need additional fertilizers. If you want to supply a boost in nutrients, do so in spring. Wait until active growth emerges in warming conditions.
