When to Divide Perennials by Zone | Tennessee Wholesale Nursery

Divide perennials when they are not in bloom. Split spring and summer bloomers in fall, at least 4 to 6 weeks before your ground freezes. Split fall bloomers in early spring, as new shoots appear. In zones 3 to 5, finish fall division early. In zones 8 and 9, the fall window runs into October.

Here is when to divide perennials in your zone, from Tennessee Wholesale Nursery, a family-owned wholesale nursery in Altamont, Tennessee, near McMinnville, growing trees, shrubs, perennials, wetland and native plants.

When to divide perennials by USDA zone

Two rules set the window. First, divide a plant in the season it is not flowering. Second, give fall divisions 4 to 6 weeks of root growth before the ground freezes. University of Minnesota Extension says that second rule matters most in cold, northern areas. Your zone decides how early that freeze comes.

For the warm Southeast, Clemson Cooperative Extension puts fall division between early September in the Piedmont and mid-to-late October on the coast. It also notes that plants split in spring often bloom later than normal that year.

Tip: By late October, the fall window in zones 6 and 7 is closing. If your usual first hard freeze is less than about four weeks away, wait and divide in early spring instead.

Natives that flower in spring or summer have finished blooming by fall. They can put their energy into new roots. Divide these in early fall, inside your zone's window.

Natives that flower in fall are still blooming in the fall window. Splitting them then costs them their show. Divide these in early spring, as the first shoots appear. Clemson also lists plants with spreading roots, such as asters, for spring division.

• Solomon's seal: a shade plant that flowers in spring and summer. Keep a bud on each piece you cut.
• Blue flag iris: it grows from rhizomes, thick roots that run along the soil. Clemson advises dividing rhizome plants after bloom through early fall.
• Black-eyed Susan: divide once flowering winds down, so roots settle in cool, moist soil.
• Tall phlox: split it in early fall, or in early spring if fall slips away.
• Blazing star: its purple spikes come in midsummer, so it is done in time for fall division.

• Goldenrod: a fall bloomer. Lift and split it in spring, just as new growth starts.
• Purple coneflower: if it is still flowering when your fall window opens, divide it in early spring instead, before it grows fast.

Natives that flower in late summer and fall are still blooming in the fall window. Splitting them then costs them their show. Divide these in early spring, as the first shoots appear. Clemson also lists plants with spreading roots, such as asters and bee balm, for spring division.

• Goldenrod: a fall bloomer. Lift and split it in spring, just as new growth starts.
• Blazing star: it flowers late in summer, so spring gives it the whole season to recover.
• Purple coneflower: it blooms into late summer. Divide it in early spring, before it grows fast.

Native perennials not to divide

Some natives do not like their roots disturbed. Clemson Cooperative Extension names butterfly weed, false indigo (baptisia) and columbine among plants not to divide. University of Minnesota Extension adds that baptisia's long, deep roots are hard to dig without breaking. Leave these in place, and add new plants instead of splitting old ones.

Signs a clump needs dividing

Most perennials need dividing every 3 to 5 years, according to Clemson. Asters can need it every year. Look for these signs:

• Flowers are smaller than they used to be.
• The center of the clump is hollow or dead, with growth only around the edge.
• Leaves at the base are thin and sparse.
• The plant no longer blooms freely.

How to divide and replant perennials

1. Water a day or two before

   Soak the clump one to two days ahead. Pick a cool, cloudy day, ideally with rain in the forecast.

2. Cut the tops back

   Trim the leaves and stems to about 6 inches. Fewer leaves means less water lost while roots recover.

3. Dig out the whole clump

   Use a sharp shovel. Start 4 to 6 inches out from the base and lift the clump free.

4. Split it into pieces

   Shake off loose soil. Pull spreading roots apart by hand or with two digging forks. Cut tough crowns with a sharp knife. Keep pieces with 3 to 5 strong shoots. Throw away the dead center and weak bits.

5. Replant at the same depth

   Set each piece as deep as it grew before. Plant iris rhizomes with the top barely above the soil. Firm the soil around the roots.

6. Water and mulch

   Water deeply right away. In cooler areas, mulch fall divisions with a loose layer such as pine straw. Keep pieces shaded and moist if you cannot replant them at once.

Planting new natives beside your divisions? Our planting instructions cover how to set bare-root perennials in the ground.

Dividing perennials: common questions

Can you divide perennials in the fall?

Yes, for plants that flower in spring and summer. Finish 4 to 6 weeks before the ground freezes so the roots can settle before winter. In zones 6 and 7, that usually means September into October. Wait until early spring to divide fall bloomers like goldenrod, so you do not cut short their flowers.

What is the best time to split perennials?

Split a perennial when it is not in flower. That means fall for spring and summer bloomers, and early spring for fall bloomers. Pick a cool, cloudy day with rain on the way, and water the clump a day or two before you dig.

Is it too late to divide perennials in late October?

In zones 8 and 9, late October is still inside the fall window. In zones 6 and 7, it is near the end. Count back from your usual first hard freeze. If fewer than about four weeks remain, leave the clump alone and divide it in early spring as the shoots appear.

How often should you divide perennials?

Clemson Extension says most perennials need dividing every 3 to 5 years, while asters can need it every year. Go by the plant, not the calendar. Smaller flowers, a hollow center or sparse leaves at the base all mean a clump is ready.