Most lists of perennials that bloom all summer merge two different things. Some plants stand in flower for three months untouched. Others flower six weeks, look finished by mid-July, and come back in September only if you took shears to them at the right moment.
That difference is what your border looks like in August. This guide separates the two groups, gives bloom length in weeks, sets out a pruning calendar built on the Chelsea chop and the Hampton hack, and ends with a planted plan for a bed 3 x 1.5 m (10 x 5 ft).
Quick facts about long flowering perennials
| Detail | Value |
|---|---|
| Definition used here | Open flowers 8 weeks or more, USDA zone 5 |
| Longest without any pruning | Catmint and Rozanne geranium, 16–20 weeks |
| Whole season window | Mid-May to first hard frost, about 22 weeks |
| Light | Six hours of sun; eight species take part shade |
| Soil | Well-drained, average fertility; lean for catmint |
| Soil pH | 6.0–7.5 |
| Planting time | Late April to mid-June, or early September in zone 5–6 |
| Spacing | 30 cm (12 in) low, 45 cm (18 in) mid, 60 cm (24 in) tall |
| Chelsea chop | Last week of May to first week of June |
| Hampton hack | Late June to early July, as the first flush fades |
| Feeding | 2 cm (1 in) compost in spring, light feed after cutting back |
| Dividing | Every 4–5 years, every 2–3 for short-lived species |
| Hardiness | Eleven of the 25 rate to USDA zone 3 or 4 |
| Effort | Low for the continuous group, medium for rebloomers |
Contents
- Quick facts about long flowering perennials
- Two kinds of long flowering perennials
- All 25 species with bloom time in weeks
- Eight perennials that flower 12 weeks unaided
- Perennials that flower twice if you cut them back
- Chelsea chop or Hampton hack: which one, and when?
- Pruning calendar: what gets cut, and when
- Bloom chart month by month, May to October
- Why do perennials stop flowering in August?
- Which perennials flower themselves to death?
- Zone and timing table for USDA zones 3–6
- A 3 x 1.5 m border that flowers all season
- How to cut back for a second flush, step by step
- Care that lengthens the bloom season
- Do long flowering perennials work in containers?
- Common mistakes
- Frequently asked questions
Two kinds of long flowering perennials
The labels on catmint and spike speedwell both say "summer". In the ground they behave nothing alike.
Group one: the continuous bloomers. They set new buds while the old flowers fade, so there is no gap, just a slow tailing off. Catmint, Rozanne geranium, calamint, 'Goldsturm' rudbeckia and Russian sage belong here. The Chicago Botanic Garden's trials recorded 'Walker's Low' catmint in flower from mid-May to late September and 'Joanna Reed' into October, with the note that neither needed deadheading.
Group two: the rebloomers. They put everything into one flush, set seed and stop. Remove the spent stems before the seed ripens and the plant reads that as unfinished business. Spike speedwell, Shasta daisy, coreopsis, spiderwort and hardy geraniums sit here. Left alone they give six weeks; cut back, six plus four.
A third move shifts the flowering instead of repeating it: cut a late-summer perennial back in late May and the bloom arrives three to four weeks later, shorter and sturdier. That is the Chelsea chop.
The rule: build at least half the border from group one. They are your floor of colour. Group two goes on top, and pays you back only if you use the shears in early July.
All 25 species with bloom time in weeks
Weeks run from first open flower to last in USDA zone 5, and everything shifts later by roughly a week per colder zone. A figure written "6 + 4" means six weeks of first flush, a gap of three to four weeks, then four weeks of repeat bloom. The month-by-month chart further down shows where each species sits.
| Common name | Botanical name | Weeks | Height | USDA | Light | Reblooms if cut back |
|---|---|---|---|---|---|---|
| Catmint 'Joanna Reed' | Nepeta | 18–20 | 60 cm (24 in) | 4–8 | Sun | Not needed |
| Catmint 'Walker's Low' | Nepeta faassenii | 16–18 | 60–75 cm (24–30 in) | 4–8 | Sun, part shade | Not needed |
| Rozanne geranium | Geranium 'Gerwat' | 16–18 | 30–45 cm (12–18 in) | 5–8 | Sun, part shade | Not needed |
| Calamint | Clinopodium nepeta | 14–16 | 30–45 cm (12–18 in) | 5–7 | Sun | Not needed |
| Black-eyed Susan 'Goldsturm' | Rudbeckia fulgida | 14–16 | 45–60 cm (18–24 in) | 3–9 | Sun | Not needed |
| Russian sage | Salvia yangii | 14–16 | 60–120 cm (2–4 ft) | 5–9 | Sun | No |
| False sunflower | Heliopsis helianthoides | 12–14 | 90–180 cm (3–6 ft) | 3–9 | Sun | Yes, deadhead |
| Purple coneflower | Echinacea purpurea | 12–13 | 90–120 cm (3–4 ft) | 3–8 | Sun, part shade | Yes, deadhead |
| Anise hyssop | Agastache foeniculum | 12–13 | 90–150 cm (3–5 ft) | 4–8 | Sun, part shade | No |
| Hardy geranium 'Brookside' | Geranium 'Brookside' | 11–12 | 60 cm (24 in) | 4–8 | Sun, part shade | Yes, shear low |
| Yarrow | Achillea millefolium | 7 + 4 | 30–90 cm (1–3 ft) | 3–9 | Sun | Yes, deadhead |
| Garden phlox | Phlox paniculata | 9–10 | 60–120 cm (2–4 ft) | 4–8 | Sun, part shade | Yes, deadhead |
| Showy stonecrop | Hylotelephium spectabile | 9–10 | 30–60 cm (1–2 ft) | 4–9 | Sun | No |
| Sneezeweed | Helenium autumnale | 8–10 | 90–150 cm (3–5 ft) | 3–8 | Sun | Chelsea chop instead |
| Bee balm | Monarda didyma | 8–9 | 60–120 cm (2–4 ft) | 4–9 | Sun | Weak |
| Japanese anemone | Anemone hybrida | 8–9 | 75–90 cm (30–36 in) | 4–8 | Part shade, sun | No |
| New England aster 'Purple Dome' | Symphyotrichum novae-angliae | 8–9 | 60 cm (24 in) | 4–8 | Sun | Pinch in spring |
| Goldenrod 'Fireworks' | Solidago rugosa | 7–8 | 75–105 cm (30–42 in) | 4–8 | Sun | Chelsea chop instead |
| Shasta daisy 'Becky' | Leucanthemum superbum | 7 + 4 | 60–120 cm (2–4 ft) | 5–9 | Sun | Yes, deadhead |
| Spiderwort | Tradescantia andersoniana | 6 + 5 | 30–90 cm (1–3 ft) | 4–9 | Sun, part shade | Yes, cut low |
| Reblooming daylily 'Stella de Oro' | Hemerocallis | 6 + 6 | 30–45 cm (12–18 in) | 3–9 | Sun | Yes, deadhead |
| Spike speedwell 'Royal Candles' | Veronica spicata | 6 + 4 | 60–90 cm (2–3 ft) | 3–8 | Sun | Yes, shear low |
| Threadleaf coreopsis 'Zagreb' | Coreopsis verticillata | 6 + 4 | 45 cm (18 in) | 5–9 | Sun | Yes, shear low |
| Ornamental onion 'Millenium' | Allium 'Millenium' | 6 | 30–45 cm (12–18 in) | 5–8 | Sun, part shade | No |
| Blazing star | Liatris spicata | 5–6 | 90–180 cm (3–6 ft) | 3–8 | Sun, part shade | Yes, cut spikes low |
Add the halves of a "6 + 4" species together and the total matches the continuous group. It just arrives in two blocks with a gap between, which is why a border of only rebloomers looks empty in late July.
Eight perennials that flower 12 weeks unaided
The backbone: eight species that hold open flowers for at least twelve weeks with no more help than the removal of the worst-looking stems.
Catmint, 16 to 20 weeks
Nothing in the trial data beats catmint. 'Joanna Reed' flowered mid-May into October at the Chicago Botanic Garden and 'Walker's Low' to late September, both 60 to 75 cm (24 to 30 in), USDA 4 to 8. Full sun, sharp drainage, no feeding. Shear it by half in July if it sprawls and it returns tight and blue within a month.
Rozanne geranium, 16 to 18 weeks
Violet-blue saucers from June until frost on a sprawling plant 30 to 45 cm (12 to 18 in) tall and twice as wide, rated USDA 5 to 8 by Missouri Botanical Garden. It is sterile, so it never diverts energy into seed — most of why it never pauses.
Calamint, 14 to 16 weeks
A low cloud of tiny white to lavender flowers from July to frost, 30 to 45 cm (12 to 18 in), with minty-lemon foliage. Full sun, free drainage, USDA 5 to 7. Illinois Extension describes the 2021 Perennial Plant of the Year as flowering "from early summer all the way through the growing season, until frost".
'Goldsturm' rudbeckia, 14 to 16 weeks
Golden daisies with dark centres, June to October, on 45 to 60 cm (18 to 24 in) stems, hardy to USDA zone 3. NC State Extension calls it a nonstop show from midsummer until the first frosts. No deadheading, and the seed heads carry the winter border.
Russian sage, 14 to 16 weeks
Hazy violet spires above silver stems, June to October, 60 to 120 cm (2 to 4 ft), USDA 5 to 9. Full sun and dry, sharply drained ground; it flops in rich soil or shade. Cut back in early spring, never autumn.
False sunflower, 12 to 14 weeks
The toughest of the tall yellows, June to September at 90 to 180 cm (3 to 6 ft), hardy to USDA zone 3. It takes clay, drought and poor soil, and deadheading prolongs the display. Tall cultivars need support or a chop.
Purple coneflower, 12 to 13 weeks
The Chicago Botanic Garden's coneflower trial put first flowers in mid-June, peak a month later, and a repeat flush on every entry with the last flowers in mid-September. Expect 90 to 120 cm (3 to 4 ft), USDA 3 to 8 for the straight species. The new hybrids are shorter-lived.
Anise hyssop, 12 to 13 weeks
Dense blue-purple spikes from late July until frost on 90 to 150 cm (3 to 5 ft) stems, USDA 4 to 8, with liquorice-scented leaves. It self-seeds freely, which is either a feature or a chore. For the last three weeks of the season, add showy stonecrop: flat pink heads August to October at 30 to 60 cm (1 to 2 ft), USDA 4 to 9, standing dried all winter.
Perennials that flower twice if you cut them back
The logic is simple. A perennial flowers to set seed, and once the seed ripens it shuts flower production down. Remove the spent stems first and the energy is still there, and many species spend it on a second flush.
Three things decide whether it works. Cut early, the moment the flush fades, not three weeks later when seed is forming. Make sure the plant has season left, which is why it works on June-flowering species and rarely on anything starting in August. And cut properly, down to the basal rosette, not just the flower heads. It is the same principle as repeat flowering when you prune roses.
Spike speedwell is the clean example: NC State Extension says shear it to the basal rosette when it finishes and it returns in autumn. Hardy geraniums such as 'Brookside' were cut to the ground in the Chicago trials and rebuilt a healthy mound in two to three weeks, often with a second scatter of flowers.
Spiderwort collapses into scruffy foliage after its first flush; cut the clump to the ground and it makes new leaves and a late bloom. Threadleaf coreopsis needs the same — left to run, it exhausts itself.
Shasta daisy, yarrow and false sunflower are pruned selectively: take the finished stems out at the base, leave the rest standing, and side shoots flower three to four weeks later. Blazing star responds to spikes cut back to the basal foliage, which the Chicago Botanic Garden notes can push bloom into September.
Some species do not answer. Russian sage, stonecrop, Japanese anemone and the asters flower once and finish, as do astilbe, bluestar and oriental poppy.
Chelsea chop or Hampton hack: which one, and when?
Two named techniques, six weeks apart, doing different jobs. Most gardeners know one and use it at the wrong time.
Chelsea chop: late May, to shift and shorten
The Royal Horticultural Society describes it as a way to "limit the size and control the flowering season" of herbaceous plants, done in late May or early June around the Chelsea Flower Show. Cut the stems back by up to half; the plant branches from lower nodes and returns shorter, sturdier and later, with more but smaller flowers.
RHS lists golden marguerite, coneflower, sneezeweed, garden phlox, showy stonecrop and goldenrod as reliable responders, and warns that species outside that group "do not respond well and you can lose the flowers for one year". The refinement worth knowing: cut only the front half of the clump. The uncut stems flower on schedule, the cut ones three to four weeks later, so a phlox that normally gives six weeks covers nearly ten.
Hampton hack: late June, to get a second flush
The Hampton hack is the follow-up, timed to the Hampton Court festival in early July. RHS defines it as cutting back early-flowering perennials after flowering, taking the clump "to nearly ground level, just above the base of the plant". Delphiniums, hardy geraniums, lupins, oriental poppies, salvias and veronicas are the named candidates. The caveat is water: cutting into dry ground during drought gives neither new foliage nor new flowers.
Which to use
Chelsea chop a plant that flowers in August and falls over. Hampton hack one that flowers in June and looks tired by July. Late May controls height; late June buys a second bloom.
Pruning calendar: what gets cut, and when
Dates are for USDA zone 5; add a week for zone 4, two for zone 3.
| Species | When | How much | Purpose | Result |
|---|---|---|---|---|
| Sneezeweed | 25 May–5 June | Half the stems to 30 cm | Chelsea chop | Bloom 3 weeks later, no staking |
| Goldenrod 'Fireworks' | 25 May–5 June | Back by one third | Chelsea chop | Shorter, self-supporting |
| Garden phlox | 25 May–5 June | Front half of the clump | Split bloom | Second half flowers 4 weeks later |
| New England aster | Late May | Pinch growing tips | Bushier habit | More stems, later bloom |
| False sunflower | Late May | Back by one third | Height control | Shorter stems, more flowers |
| Hardy geranium | 25 June–10 July | All growth to the ground | Hampton hack | New mound in 2–3 weeks |
| Spike speedwell | 25 June–10 July | Shear to basal rosette | Hampton hack | Repeat bloom in autumn |
| Threadleaf coreopsis | 1–15 July | Back by one third | Rejuvenation | Second flush in 3–4 weeks |
| Spiderwort | 1–15 July | Whole clump to the ground | Hampton hack | New leaves and late bloom |
| Catmint | 10–20 July | Back by half | Tidy plus denser rebloom | Compact September flush |
| Shasta daisy | Through July | Finished stems at the base | Continuous bloom | Side shoots, 3–4 weeks |
| Blazing star | Through July | Flowered spikes cut low | Extend the season | Bloom into September |
| Yarrow | 20–31 July | Finished stems at the base | Repeat bloom | Side shoots, 3–4 weeks |
| Purple coneflower | Through August | Spent flower heads | Smaller second flush | Flowers to mid-September |
| Reblooming daylily | June–August | Spent blooms and scapes | Keeps flushes coming | Continuous |
Nothing on that list should be cut after mid-August; late pruning pushes soft growth that never hardens before frost.
Bloom chart month by month, May to October
When each species actually holds open flowers in USDA zone 5. A filled circle is full bloom, a half circle means starting, finishing or reblooming, a dash means nothing. Each month is split into halves.
| Species | May | June | July | Aug | Sep | Oct |
|---|---|---|---|---|---|---|
| Catmint 'Joanna Reed' | —◐ | ●● | ●● | ●● | ●● | ◐— |
| Catmint 'Walker's Low' | —◐ | ●● | ●● | ●● | ●◐ | —— |
| Geranium 'Brookside' | —◐ | ●● | ●● | ◐— | ◐◐ | —— |
| Rozanne geranium | —— | ◐● | ●● | ●● | ●● | ◐— |
| Spike speedwell | —— | ◐● | ●◐ | —— | ◐● | ◐— |
| Spiderwort | —— | ◐● | ●◐ | —◐ | ●◐ | —— |
| Reblooming daylily | —— | ◐● | ●◐ | ◐● | ●◐ | —— |
| Shasta daisy | —— | ◐● | ●● | ●◐ | ◐◐ | —— |
| Threadleaf coreopsis | —— | ◐● | ●◐ | —◐ | ●◐ | —— |
| Yarrow | —— | ◐● | ●◐ | —◐ | ●◐ | —— |
| Purple coneflower | —— | —◐ | ●● | ●● | ●◐ | —— |
| False sunflower | —— | —◐ | ●● | ●● | ●◐ | —— |
| Rudbeckia 'Goldsturm' | —— | —◐ | ●● | ●● | ●● | ●◐ |
| Russian sage | —— | —◐ | ●● | ●● | ●● | ◐— |
| Blazing star | —— | —— | ◐● | ●◐ | ◐— | —— |
| Allium 'Millenium' | —— | —— | ◐● | ●◐ | —— | —— |
| Bee balm | —— | —— | ◐● | ●● | ◐— | —— |
| Calamint | —— | —— | ◐● | ●● | ●● | ●◐ |
| Garden phlox | —— | —— | ◐● | ●● | ●◐ | —— |
| Anise hyssop | —— | —— | —◐ | ●● | ●● | ●◐ |
| Sneezeweed | —— | —— | —◐ | ●● | ●● | ◐— |
| Showy stonecrop | —— | —— | —— | ◐● | ●● | ●● |
| New England aster | —— | —— | —— | ◐● | ●● | ●◐ |
| Goldenrod 'Fireworks' | —— | —— | —— | —● | ●● | ◐— |
| Japanese anemone | —— | —— | —— | —● | ●● | ●◐ |
Read down the columns and the gaps show up. May is nearly empty, which is what bulbs are for. The second gap is early August, when several rebloomers sit between flushes; calamint, Rozanne, rudbeckia, phlox and Russian sage carry it.
Why do perennials stop flowering in August?
Four causes, in order of how often each is the culprit.
Seed has ripened. By far the most common. Fix: deadhead on the calendar above.
Drought in July. Many species abort buds under water stress while the foliage still looks fine, so nobody spots it until the flowers fail to appear. Fix: 20 to 25 litres per square metre in one soaking after two dry weeks.
Too much nitrogen. A generous June feed gives tall soft stems and fewer flowers. Fix: compost in spring, plus a light feed only where you cut hard in July.
The clump is too old. It competes with itself, flowers for less time each season and goes bare in the middle. Fix: divide — see the next section.
Which perennials flower themselves to death?
Some of the hardest-working bloomers pay with a short life. They flower so heavily they never build a proper crown, and by year three they are gone. Penn State Extension describes coreopsis as flowering itself to exhaustion, and NC State flags blanket flower as short-lived. Divide or replace these more often:
- Threadleaf coreopsis — divide every second spring or it thins by year three.
- Coneflower hybrids — the species persists, the coloured hybrids last two or three years.
- Blanket flower — short-lived by nature; let it self-seed or take divisions.
- Shasta daisy — NC State recommends dividing every two to three years.
- Delphinium and lupin — reliably short-lived in heavy ground.
- Sneezeweed — divide every second or third year or flowering falls away.
- Bee balm — runs outward and empties in the middle; divide every third year.
At the other end sit catmint, stonecrop, Rozanne geranium, Russian sage, blazing star and Japanese anemone, which hold eight to ten years untouched. The survey of perennials covers the division cycle, and the list of perennials for full sun the drought-tolerant end.
Zone and timing table for USDA zones 3–6
The bloom weeks above are for zone 5. This converts the dates that govern how long the display lasts.
| Zone | Typical areas | Catmint starts | Chelsea chop | Last useful cut-back | First frost, average |
|---|---|---|---|---|---|
| 6 | Southern Ontario, Pennsylvania, southern England | 10 May | 20–31 May | 15 July | 20 October |
| 5 | Chicago, southern Michigan, central Scotland | 18 May | 25 May–5 June | 10 July | 10 October |
| 4 | Minneapolis, Vermont, Nova Scotia, central Sweden | 28 May | 1–10 June | 1 July | 25 September |
| 3 | Northern Minnesota, Manitoba, northern Scandinavia | 8 June | Not advised | 20 June | 10 September |
In zone 3 the season is too short for a second flush before frost, and a Chelsea chop usually costs the whole year's flowering. Build length by staggering start dates: speedwell and hardy geranium early, catmint and yarrow in the middle, rudbeckia and stonecrop last. University of Minnesota Extension makes the same point about daylilies, noting that most rebloomers do poorly in a short season.
A 3 x 1.5 m border that flowers all season
Four and a half square metres, about 48 square feet, against a sunny fence. It holds open flowers from mid-May to mid-October in zones 4 to 6, with more than half from the continuous group so it never empties.
| Row | Species | Number | Height | Bloom | Pruning |
|---|---|---|---|---|---|
| Back row | Sneezeweed | 3 | 90–120 cm (3–4 ft) | Aug–Oct | Chelsea chop, late May |
| Back | Garden phlox | 3 | 90–120 cm (3–4 ft) | July–Sep | Chop front half, late May |
| Back | False sunflower | 2 | 120–150 cm (4–5 ft) | June–Sep | Cut by a third, late May |
| Middle row | Black-eyed Susan 'Goldsturm' | 4 | 45–60 cm (18–24 in) | June–Oct | None |
| Middle | Purple coneflower | 4 | 90 cm (36 in) | June–Sep | Deadhead in August |
| Middle | Showy stonecrop | 3 | 45 cm (18 in) | Aug–Oct | Cut down in March |
| Middle | Spike speedwell | 4 | 60 cm (24 in) | June–July and fall | Shear low, early July |
| Front row | Catmint 'Walker's Low' | 5 | 60 cm (24 in) | mid May–Sep | Cut by half in July |
| Front | Rozanne geranium | 4 | 30–45 cm (12–18 in) | June–frost | None |
| Front edge | Calamint | 5 | 30–45 cm (12–18 in) | July–frost | None |
| Front edge | Reblooming daylily | 4 | 30–45 cm (12–18 in) | June–Sep | Deadhead all summer |
That is 41 plants over 4.5 square metres, nine per square metre. Dense borders shade out weeds; expect to lift a few in year three.
Catmint and speedwell open in mid-May, then Rozanne, daylily, coneflower and false sunflower in June. July is the peak. Early August is thin, with speedwell sheared and daylily between flushes, so calamint, phlox, rudbeckia and Rozanne carry it. September brings the speedwell rebloom with sneezeweed and stonecrop; October is rudbeckia, calamint and stonecrop. For a shadier version, see shade perennials.
How to cut back for a second flush, step by step
- Walk the border in late June, looking for plants more than half gone brown.
- Check the crown. Small green shoots or leaf buds near the ground mean the plant will respond.
- Use sharp secateurs, or shears for a large clump — blunt blades crush stems.
- Cut flowered stems to the first leaf pair above the rosette, or to ground level on hardy geraniums and spiderwort.
- Clear the cuttings away; material left lying invites powdery mildew and slugs.
- Water deeply straight afterwards if the soil is dry — drought is why the hack fails.
- Give a handful of balanced fertiliser per plant, only where you cut hard.
- Mulch a couple of centimetres of compost around the cut clumps.
- Allow three to six weeks. No buds means it was not a rebloomer, but you gained clean foliage.
- Stop cutting after mid-August in zones 5 and 6, and after late July in zones 3 and 4.
Care that lengthens the bloom season
Water rarely and deeply
Bud drop in July is nearly always drought. Give 20 to 25 litres per square metre in one soaking after two dry weeks, not a splash every evening. Deep watering drives roots down, and deep roots keep setting buds.
Feed lean
Two centimetres of compost in April covers the season for most of this list. Catmint, calamint, Russian sage and stonecrop want no feeding at all — they go soft, split open and flower less on rich ground, exactly as when you grow lavender. Phlox, sneezeweed and bee balm repay a spring feed.
Remove seed heads, with exceptions
Even on species that do not repeat, deadheading pays: energy spent ripening seed comes out of next year's flowering. The exceptions are plants you want to self-sow and those whose seed heads carry the winter — rudbeckia, coneflower and stonecrop.
Stake in May, not August
Sneezeweed, phlox, false sunflower and tall bee balm go down in wind and rain. Supports belong in place in May while the plant is 30 cm (12 in) high, so it grows through them. A ring dropped over a collapsed plant in August looks exactly as it sounds; the alternative is a Chelsea chop. Stop cutting in mid-August and leave the tidy-up until March.
Do long flowering perennials work in containers?
Yes, though the shortlist is narrower. A pot dries out, freezes from every side and holds less nutrition than open ground, and all three shorten flowering.
Best are the low, drought-tolerant species with compact roots: catmint, calamint, speedwell, coreopsis, stonecrop and reblooming daylily. Rozanne works in a container of at least 40 litres (10 gallons).
Three rules. The pot must be at least 30 cm (12 in) deep with real drainage holes. You will water daily in July and feed fortnightly from June. For winter, wrap the pot against a wall, sink it to the rim in a border, or move it into an unheated garage.
Drop two zones in a container: a plant rated zone 5 in the ground behaves like zone 7 in a pot. That makes stonecrop, yarrow and rudbeckia the safest cold-garden choices, and roses in pots follow the same logic, covered in the guide to growing roses.
Common mistakes
- Buying only rebloomers. A border of speedwell, coreopsis and hardy geranium is glorious in June and blank by late July.
- Cutting back too late. Mid-August instead of early July means no second flush and soft growth that frost kills.
- Snipping off flower heads only. Cut to the first pair of leaves or the basal rosette instead.
- Cutting back into dry soil. RHS is explicit: in drought the plant will not re-flower.
- Feeding to get more flowers. Nitrogen builds leaves, and catmint and Russian sage flop on rich ground.
- Chelsea chopping the wrong species. Cut something outside the RHS list and you can lose the year's flowers. Test on half a clump.
- Never dividing. Coreopsis, Shasta daisy and sneezeweed lose bloom length fast if left alone.
- Expecting May. Almost nothing here flowers before mid-May; bulbs fill that window.
Frequently asked questions
What perennial blooms the longest?
Catmint, on trial evidence. The Chicago Botanic Garden recorded 'Joanna Reed' in flower from mid-May into October and 'Walker's Low' to late September, both without deadheading. Rozanne geranium is close behind, flowering June until frost because it is sterile and never sets seed. Calamint runs July to frost.
Which perennials bloom all summer in zone 4?
'Goldsturm' rudbeckia, purple coneflower, yarrow, false sunflower, speedwell, reblooming daylily and catmint are rated to zone 4 or colder and carry June through September. Stonecrop and New England aster take over in August. Calamint, Rozanne and Russian sage sit at zone 5 and want a sheltered, sharply drained spot.
Do long flowering perennials need deadheading?
Not all of them. Catmint, Rozanne geranium, calamint and 'Goldsturm' rudbeckia flower just as long untouched. For the rebloomers it is the difference between one flush and two, because ripened seed shuts flower production down. Leave the seed heads on rudbeckia, coneflower and stonecrop over winter.
What is the difference between the Chelsea chop and the Hampton hack?
Timing and purpose. The Chelsea chop comes in late May and cuts stems by up to half, making a late-summer plant shorter, sturdier and three to four weeks later. The Hampton hack comes in late June or early July and cuts an already-flowered perennial to near ground level to trigger a second flush.
Which perennials flower from June until frost?
Rozanne geranium, catmint, 'Goldsturm' rudbeckia and Russian sage all cover June to October in a normal season, and calamint starts in July and runs to frost. Add reblooming daylily for continuity through the August gap, and showy stonecrop for the last three weeks when everything else is done.
Do long blooming perennials come back every year?
Most do, but the heaviest bloomers are often the shortest-lived. Coreopsis, blanket flower, Shasta daisy and the coloured coneflower hybrids often last two or three years because they never build a substantial crown. Divide them every second or third spring, or let them self-sow. Catmint, stonecrop and Russian sage hold for a decade.
What can I plant for colour after the coneflowers finish?
Showy stonecrop from August to October, Japanese anemone from late August, New England aster and 'Fireworks' goldenrod through September, and calamint to the first frost. Add the September rebloom from speedwell and catmint and a zone 5 border holds five or six species in flower in October.
Why did my catmint stop flowering in July?
It probably sprawled open at the centre rather than stopping. Catmint splits and goes bare in the middle after its first heavy flush, especially in rich soil or after rain. Shear the whole plant by half in mid-July, water it, and it rebuilds a tight mound and flowers again within four to six weeks. Do not feed it.
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