Fall is an ideal time to divide many perennial plants. As summer’s heat fades and soil temperatures remain
warm, newly divided plants have an opportunity to establish roots before winter arrives. Dividing also gives
homeowners a chance to rejuvenate crowded plants, increase the number of plants in the landscape, and
move perennials that have outgrown their assigned spaces.
Not every perennial should be divided in autumn, however, knowing which plants benefit from fall
division—and which are better left undisturbed until spring—can make the difference between a successful
transplant and a struggling plant.
Why Divide Perennials?
Perennials often become overcrowded after several years in the same location. A mature clump may develop
a bare or weak center while growth becomes concentrated around the edges. Crowding can also reduce
flowering, encourage disease by restricting air circulation, and cause plants to compete for water and
nutrients.
Dividing one established plant can produce several smaller plants for other areas of the garden. It is also a
useful way to share favorite perennials with friends or replace older sections of a planting bed. Fall division is
particularly useful for plants that bloom in spring and early summer. Once their flowering season has ended,
they can be divided while they are entering dormancy rather than being disturbed just before they flower.
Perennials That Can Be Divided in Fall
Several popular garden perennials respond well to fall division, provided they are divided early enough for
roots to become established before the ground freezes.
Bearded iris (Iris × germanica) is a classic candidate. Divide rhizomes after flowering and allow freshly cut
surfaces to dry briefly before replanting. Discard old, unproductive sections and retain healthy rhizomes with
strong fans of leaves.
Peonies (Paeonia lactiflora) can be divided in early fall, although they generally prefer to remain undisturbed
for many years. If an established plant must be moved or has become too large, divide it carefully. Each
division should have several healthy buds, or “eyes,” and a substantial portion of root.
Daylilies (Hemerocallis spp.) are among the easiest perennials to divide. Large clumps can be lifted and
separated into smaller sections by hand, with a sharp knife, or by carefully cutting through the crown.
Hostas (Hosta spp.) can also be divided in fall. Smaller divisions establish more quickly than large pieces, but
each section should contain several healthy shoots and enough roots to support new growth.
Garden phlox (Phlox paniculata), black-eyed Susan (Rudbeckia fulgida), bee balm (Monarda didyma), and
Siberian iris (Iris sibirica) are additional candidates for fall division in many gardens.
A good rule is to divide plants after flowering has finished but while there is still enough time for new roots to
develop.
Plants Better Left Alone in Fall
Some perennials are more sensitive to fall division and are better handled in spring.
Coral bells (Heuchera spp.) can be divided, but spring is often preferable, particularly in areas with cold winters. Fall divisions may have difficulty becoming firmly established before freezing weather.
Russian sage (Salvia yangii) generally does not need frequent division and can be difficult to separate successfully. If propagation is desired, cuttings are usually a better approach.
Lavender (Lavandula angustifolia) is another perennial that does not respond particularly well to being dug up and divided. Its woody growth makes traditional division impractical.
Sedum (Hylotelephium spp.), particularly the tall, fall-flowering types, are best left alone in autumn. These plants are often still actively flowering when many other perennials are ready for division. Their fleshy stems and roots can also be susceptible to damage when plants are disturbed late in the season. Spring is generally a better time to divide established clumps.
Japanese anemone (Anemone hupehensis, Anemone × hybrida) should also be left undisturbed in fall. These plants can be slow to establish after being divided, and newly separated sections may be vulnerable to winter conditions. If division is necessary, spring is generally a safer choice.
Asters (Symphyotrichum spp.), including many of the perennial asters commonly grown in home gardens, are better divided in spring. Fall-blooming asters are often still flowering when the ideal window for establishing new divisions is closing. Waiting until spring allows the plants to develop roots during the beginning of the growing season.
Hardy hibiscus (Hibiscus moscheutos and hybrids) is another perennial best left alone during fall. Its large, fleshy crown can be damaged during division, and newly separated sections may struggle to establish before winter. Spring, just as new shoots begin to emerge, is a better time to consider dividing an overcrowded plant.
Garden mums (Chrysanthemum × morifolium) are also best divided in spring. Because mums often flower late
in the season, fall division can interfere with their preparation for winter and leave small divisions with
insufficient time to develop a strong root system. Spring division gives the new plants an entire growing
season to become established.
Avoid dividing ornamental grasses, such as fountain grass (Pennisetum alopecuroides), late in the season
unless the species is known to tolerate fall division. Many grasses establish better when divided in spring as
new growth begins.
It is also wise to leave newly planted perennials alone. A plant that was installed only recently needs time to
develop a strong root system before being disturbed again.
How to Divide Perennials
Choose a cool, cloudy day if possible. Water the plant thoroughly a day before dividing it, particularly if the soil
is dry. Moist soil is easier to work with and helps reduce stress on the roots.
Begin by cutting back the foliage if the plant has already finished flowering and the foliage is becoming
dormant. Leave enough growth to identify the plant while working.
Use a spade to dig around the outside of the clump, keeping the blade far enough from the crown to avoid
cutting through the main root system. Push the spade deeply beneath the plant and lift the entire clump from
the soil.
Shake or wash away some soil so the crown and roots are easier to see. Look for natural points where the
plant can be separated. Depending on the species, divisions may be pulled apart by hand or cut with a sharp
knife or spade.
Each division should have healthy roots and sufficient crown or shoots to support future growth. Remove
damaged, diseased, or dead portions rather than replanting them.
Replant the divisions promptly. Dig a hole wide enough to spread the roots naturally and position the plant at
approximately the same depth at which it was growing. Avoid burying crowns or rhizomes too deeply. Bearded iris rhizomes, for example, should remain close to the soil surface.
Water thoroughly after planting to settle the soil around the roots.
Keeping Divided Plants Healthy
Newly divided plants need consistent moisture while they establish. Keep the soil evenly damp but avoid
keeping it saturated. Water slowly and deeply rather than providing frequent, shallow watering.
A layer of organic mulch can help retain moisture and moderate soil temperatures. However, keep mulch
away from the crown of the plant. A thick layer pressed against the crown can encourage rot and other
problems.
Avoid heavy fertilization immediately after dividing. The plant’s priority is developing roots rather than
producing lush top growth. If the soil is already fertile, additional fertilizer may not be necessary until the
following growing season.
Label newly divided plants, especially when several varieties are being moved around the garden. Fall is also a
good time to make a simple garden map, so you remember where each division was planted.
Finally, resist the temptation to divide everything simply because autumn has arrived. A healthy perennial that
is flowering well, has plenty of space, and shows no signs of overcrowding may be better left alone.
With the right plants, careful technique, and attentive watering, fall division can turn one established
perennial into several vigorous additions to the landscape. It is a practical way to refresh an aging garden
while giving treasured plants a new opportunity to thrive.
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