I used to think late summer was just for harvesting tomatoes and sweeping up dry leaves. It took me a few years to learn that August is actually the best time to divide some of my favorite plants.
This is my personal list of perennials that benefit from being split and replanted before the autumn chill sets in.
All tested. All simple. All worth the effort.
Quick Summary
- 8 hardy perennials that establish roots quickly in warm August soil.
- Covers sunny borders and shady corners across Zones 3-9.
- Best starter pick: Bearded Iris because it is dormant in August, making it incredibly easy to split without harming the plant.
The first four are my top choices for sunny areas. The last four will help you fill in those dry shade corners or damp spots.
1. Bearded Iris (Iris germanica)
| Sun | Full sun |
| Water | Low to medium, well-drained |
| Height | 12-40 in (30-100 cm) |
| Bloom | Late spring to early summer |
| Zone | 3-9 |
This is my absolute favorite plant to divide when the summer heat peak passes. I planted my first bearded iris five years ago along my gravel path, and it eventually became a crowded clump that stopped blooming.
Late summer is the natural dormancy period for these rhizomes, so splitting them now gives them time to grow new roots before winter.
I dig up the entire clump and wash the soil off so I can see the rhizomes clearly. I use a clean garden knife to cut them apart, making sure each piece has a healthy fan of leaves and a few roots.
Tip: Trim the leaves back to a fan shape about four inches (10 cm) tall to prevent the wind from rocking the newly planted roots.
This is the variety I’d start with if you want to practice your division skills, as the rhizomes are tough and easy to handle.
2. Daylilies (Hemerocallis)
| Sun | Full sun to part shade |
| Water | Low to medium |
| Height | 1-3 ft (30-90 cm) |
| Bloom | Summer |
| Zone | 3-9 |
Daylilies form thick, fibrous root systems that eventually get so dense they choke out their own blooms.
Honestly, it is almost impossible to hurt these roots. I split mine every four years to keep the flowers large and bright.
You can slide a sharp spade right through the middle of the clump to split it. I usually dig up the outer sections of the clump and replant them elsewhere, discarding the old, woody center.
Note: Water the new divisions deeply every day for the first week to help them settle into their new homes.
3. Hostas (Hosta)
| Sun | Part shade to full shade |
| Water | Medium, consistent |
| Height | 6-36 in (15-90 cm) |
| Bloom | Summer |
| Zone | 3-9 |
Hostas are incredibly tough and will handle late summer splitting with ease.
I find that dividing hostas in August is much easier than in spring because the leaves are fully grown, allowing you to see exactly how much space the new divisions will fill.
I use two garden forks placed back-to-back in the center of the root ball, then prying them apart to split the crown. It looks a bit brutal, but it works every time.
These shade lovers pair beautifully with coral bells along a woodland edge.
If you are planting new hostas, you can read my 11 easy-care plants for garden borders that thrive on neglect for more ideas on layout.
Warning: The large leaves lose water quickly, so you must plant them in a shady spot and keep the soil moist.
4. Oriental Poppies (Papaver orientale)
| Sun | Full sun |
| Water | Low to medium, well-drained |
| Height | 2-3 ft (60-90 cm) |
| Bloom | Late spring to early summer |
| Zone | 3-7 |
Oriental poppies completely disappear in mid-summer, leaving bare soil where their bright spring petals once stood.
This dormancy is the perfect window to divide them. Since they have long taproots, they do not like being moved when they are actively growing.
I always mark their location with a wooden stake in June so I don’t accidentally dig them up or slice the roots in August. I dig deep to lift the entire taproot, then cut it vertically into pieces that each have at least one growing bud.
Replant them three inches (8 cm) deep in sandy, well-drained soil.
The secret to dividing poppies is simple: do it while the plant is completely asleep.
5. Garden Phlox (Phlox paniculata)
| Sun | Full sun to part shade |
| Water | Medium, consistent |
| Height | 2-4 ft (60-120 cm) |
| Bloom | Summer to fall |
| Zone | 4-8 |
Garden phlox puts on a great show of late summer color, but crowded clumps are highly susceptible to powdery mildew. Dividing them in August improves the airflow around the stems.
I select clumps that have finished blooming and cut the stems back by half before digging. I gently pull the root crowns apart with my hands. Replanting them with more spacing helps keep the foliage clean in future seasons. This task fits right in with the other late-season chores I list in 10 flowers to sow in august.
Tip: Mulch the new divisions with pine straw to help retain soil moisture.
6. Shasta Daisies (Leucanthemum × superbum)
| Sun | Full sun to part shade |
| Water | Medium, well-drained |
| Height | 2-3 ft (60-90 cm) |
| Bloom | Summer |
| Zone | 5-9 |
Shasta daisies grow rapidly and the centers of the clumps will die out after three or four years. This is my favorite pick for creating new plants to share with neighbors.
I dig up the clump once the last flowers fade in August. I discard the woody center and save the vigorous outer shoots. Each small division will grow into a full-sized blooming clump by next summer. I find that these divisions grow best in lean soil without heavy fertilizers.
Not even close.
No other plant in my garden multiplies as quickly or as easily as the Shasta daisy.
7. Coral Bells (Heuchera)
| Sun | Part shade to full shade |
| Water | Medium, well-drained |
| Height | 12-18 in (30-45 cm) |
| Bloom | Late spring to summer |
| Zone | 4-9 |
Coral bells tend to grow upwards, leaving a woody stem that heaves out of the ground (ask me how I know).
Dividing them in August is the best way to fix this issue and bury those woody stems back in the soil.
I dig up the plant and cut the woody stems into individual pieces, making sure each piece has a few roots and a healthy leaf cluster. I replant them deeper, right up to the base of the lowest leaves. This foliage plant looks fantastic when planted alongside hostas.
For more details on caring for shade plants, you can check my 12 essential tips for growing and caring for coneflowers to see how I handle the sunny transitions nearby.
Tip: Water them consistently for the first month to help the shallow roots establish.
8. Siberian Iris (Iris sibirica)
| Sun | Full sun to part shade |
| Water | Medium to wet |
| Height | 2-3 ft (60-90 cm) |
| Bloom | Late spring to early summer |
| Zone | 3-9 |
Siberian irises form extremely dense, tough root masses that can be difficult to split. They develop a hollow center over time, which is a clear signal that they need division.
I use a sharp spade or even a pruning saw to slice the clump into smaller sections. Unlike bearded irises, these plants have fibrous roots and should not be left to dry out. Replant them immediately in rich, damp soil.
Honestly, it’s a workout to split these, but the reward is a beautiful border of blue and purple blooms next spring.
Why I Mark My Dormant Plants Early
Dividing perennials in late summer gives you a head start on next year’s garden.
By splitting these plants in August, you allow them to grow strong roots while the soil is still warm.
Just keep the hose handy, protect them with a bit of mulch, and they will be ready to grow when spring arrives.
— Anh