A perennial costs about what a tray of annuals costs and stays for a decade. Plant once, divide after a few seasons, and one plant becomes two, then four. That is the whole argument.
It is also where cold-climate gardeners lose the most money, almost always to the same three errors: spacing too tight, a bed that was never properly prepared, and cutting back at the wrong time. This guide gives the numbers most care articles skip — spacing, plants per square metre, which genera to divide in spring rather than fall, and what to cut in October.
Perennials at a glance
| Detail | Value |
|---|---|
| Site | Full sun to deep shade – species choice decides |
| Soil | Rich in organic matter, deeply worked, free-draining |
| pH | 6.0–6.5 for most perennials |
| Bed preparation | Loosen 25–30 cm (10–12 in), work in 5–8 cm (2–3 in) compost |
| Planting time | Spring after thaw, or 4–6 weeks before the ground freezes |
| Planting depth | Crown at exactly the level it sat in the pot |
| Spacing | 25–30 cm (10–12 in) low, 40–45 cm (16–18 in) mid, 50–60 cm (20–24 in) tall |
| Plants per m² | 11–16 low, 5–6 mid-height, 3–4 tall |
| Watering | 25–40 mm (1–11/2 in) per week in year one |
| Feeding | One spring application before shoots emerge |
| Summer mulch | 3–5 cm (1–2 in), never against the crown |
| Winter mulch | 15–20 cm (6–8 in), applied after the ground freezes |
| Cutting back | Spring as the rule, fall only for disease |
| Dividing | Every 3–5 years, spring or after flowering |
Contents
- Perennials at a glance
- What is a perennial, exactly?
- Hardiness, snow cover and why the zone number misleads
- Matching perennials to your site
- Soil preparation: the amounts that matter
- How to plant perennials step by step
- Spacing and plants per square metre
- When is the best time to plant perennials?
- What it takes to fill 10 m² (100 sq ft)
- Watering and feeding
- Summer mulch and winter mulch are different jobs
- Staking and deadheading
- Should you cut perennials back in fall or spring?
- Dividing perennials: spring or fall?
- Growing perennials from seed
- Month by month in the perennial border
- Zone table: perennials in USDA zones 3–6
- Designing a border that works all season
- Common problems
- Common mistakes
- Frequently asked questions
What is a perennial, exactly?
A perennial is a herbaceous plant that lives more than two years. Herbaceous means it builds no wood. Top growth dies back in autumn and the plant overwinters as roots, a crown, a rhizome or a small green rosette. New shoots come from the same plant next spring.
It differs from three neighbours:
- Annuals germinate, flower, seed and die in one season. Marigolds, petunias, cosmos.
- Biennials make a rosette in year one and flower in year two, like foxglove and hollyhock.
- Subshrubs keep woody stems through winter and are pruned differently — see the guide to growing lavender.
Lifespan varies far more than the label suggests. Delphinium and columbine fade after three to five years, while peony and hosta hold the same spot for decades. A border that thins after four years was usually planted with short-lived species.
Hardiness, snow cover and why the zone number misleads
The USDA zone on the tag is an average annual minimum air temperature. A perennial never experiences that. It spends winter below ground, insulated by soil and, in a good year, by snow.
That gap explains a lot. A zone 4 perennial under 30 cm (12 in) of continuous snow sits a few degrees below freezing all winter. The same plant in a bare, windswept zone 5 garden with repeated thaws has it far harder. Snow cover is worth roughly a zone, and open winters kill borderline plants.
The second killer is not cold at all. Repeated freezing and thawing lifts crowns out of the soil — frost heaving — and the exposed roots dry out. University of Wisconsin Extension describes winter mulch as protection against that cycle rather than against low temperature. Newly planted perennials are most at risk.
The third is drainage. Soil that stays saturated through a long thaw suffocates roots and invites crown rot. No hardiness rating helps a plant sitting in a puddle in March.
Matching perennials to your site
Start with the site, not the plant. Changing a plant list is free; changing your light and drainage is not. Count sun hours on the exact patch on a clear day in June — four hours at midday is a different list from four hours at dawn.
| Site | Sun hours | Reliable choices | Watch for |
|---|---|---|---|
| Full sun, dry | 6+ | Sedum, yarrow, Russian sage, sea holly | Rich soil makes them flop |
| Full sun, average | 6+ | Garden phlox, coneflower, daylily | Even moisture in July |
| Part shade | 3–5 | Lady's mantle, astilbe, cranesbill | Widest choice of any site |
| Shade, moist | 0–3 | Hosta, ferns, bergenia | Slugs are the main threat |
| Dry shade | 0–3 | Epimedium, lungwort, vinca | Tree roots take the water |
Test drainage before you buy. University of Illinois Extension describes a simple check: dig a hole 20–30 cm (8–12 in) deep, fill it with water, let it drain, then fill again. If the second filling drains in under an hour, drainage is adequate. Slower means a raised bed or plants that take wet feet.
If a whole bed sits in one kind of light, the lists of perennials for full sun and shade perennials go deeper.
Soil preparation: the amounts that matter
Perennials stay in the same ground for years, and you cannot improve the soil afterwards without digging everything up. This is the most valuable hour in the project.
Clemson University recommends spading beds 20–25 cm (8–10 in) deep and mixing in at least 5 cm (2 in) of compost in clay, 5–7.5 cm (2–3 in) in sand. Illinois Extension calls for 25–30 percent organic matter by volume — 8–10 cm (3–4 in) of compost turned into the top 25–30 cm (10–12 in).
| Soil | Work to depth | Compost per m² | For 10 m² (100 sq ft) | Also add |
|---|---|---|---|---|
| Heavy clay | 30 cm (12 in) | 80 litres | 800 litres (28 cu ft) | Coarse grit, 40 l/m² |
| Average clay loam | 25–30 cm (10–12 in) | 50 litres | 500 litres (18 cu ft) | – |
| Good garden loam | 25 cm (10 in) | 30 litres | 300 litres (11 cu ft) | – |
| Sandy, hungry | 25 cm (10 in) | 70 litres | 700 litres (25 cu ft) | Topsoil or leaf mould |
| Dry shade under trees | 15–20 cm (6–8 in) | 50 litres | 500 litres (18 cu ft) | Keep tree roots intact |
A cubic metre is a thousand litres, so 800 litres for 10 m² is 0.8 m³ — a small trailer load. It sounds like a lot, and that is why borders sink and run out of steam by year three.
Most perennials want pH 6.0–6.5. Acid-lovers such as rhododendron do not belong in a general border, and lime-lovers such as sea holly want the opposite. Test before you lime.
How to plant perennials step by step
- Clear every perennial weed first. Quackgrass and bindweed cannot be removed once the border knits.
- Work the whole bed, not just the holes, 25–30 cm (10–12 in) deep with the compost mixed right through.
- Set the plants out in their pots and stand back five metres. This is the only moment when moving them is free.
- Water the pots an hour before planting. A dry root ball pulls water out of the soil around it.
- Dig a hole twice as wide as the pot, exactly as deep as the root ball is tall.
- Tease the root ball open. Straighten roots that circled the pot, or the plant strangles itself.
- Set the crown at exactly the depth it sat in the pot. Too deep rots, too high dries out.
- Backfill and firm with the flat of your hand. Air pockets kill roots.
- Water in with 3–5 litres (1 gallon) per plant, even in rain. Water closes the soil around the roots.
- Mulch 3–5 cm (1–2 in) deep, leaving a hand's width of bare soil around each crown.
- Label everything. In April of year two you will not remember what is where, and that is when you dig through it.
Spacing and plants per square metre
Spacing decides whether the border closes over in two seasons or becomes a mildew factory by year three. Almost no guide prints the figures, so here they are.
Spacing is measured centre to centre. Work out plants per square metre by squaring it: at 30 cm (12 in) centres one plant occupies 0.09 m², so a square metre holds eleven.
| Mature height | Spacing | Plants per m² | Examples |
|---|---|---|---|
| Groundcover under 20 cm (8 in) | 20–25 cm (8–10 in) | 16–25 | Creeping thyme, epimedium |
| Low, 20–40 cm (8–16 in) | 25–30 cm (10–12 in) | 11–16 | Hardy geranium |
| Low to mid, 40–60 cm (16–24 in) | 30–35 cm (12–14 in) | 8–11 | Lady's mantle, catmint |
| Mid, 60–90 cm (24–36 in) | 40–45 cm (16–18 in) | 5–6 | Garden phlox, coneflower, daylily |
| Tall, 90–120 cm (36–48 in) | 50–60 cm (20–24 in) | 3–4 | New England aster, helenium |
| Very tall, over 120 cm (48 in) | 70–90 cm (28–36 in) | 1.5–2 | Joe Pye weed, bugbane |
| Specimen grass or focal plant | 80–100 cm (32–40 in) | 1–1.5 | Miscanthus, goat's beard |
The full conversion: 20 cm gives 25 plants per square metre, 25 cm gives 16, 30 cm gives 11, 35 cm gives 8, 40 cm gives 6, 45 cm gives 5, 50 cm gives 4, 60 cm gives 3, 70 cm gives 2 and 80 cm gives 1.5.
Plant in odd-numbered groups
One plant of each variety reads as clutter. Set three, five or seven of the same cultivar in a loose drift, using the spacing above. Tall specimens can stand alone.
When in doubt, plant wider than feels right and fill gaps with annuals for two seasons. Adding is free; lifting an overcrowded border costs a weekend.
When is the best time to plant perennials?
Container plants go in whenever the ground is workable and you will water, but two windows are clearly better.
Spring, once the soil has thawed and crumbles. The plant gets a full season to root and you can see what is already in the bed. This is the safer choice in zones 3 and 4, and the only sensible one for anything marginally hardy.
Late summer to early fall. Warm soil, cool air and autumn rain do the watering. University of Minnesota Extension gives the deadline plainly: four to six weeks before the ground freezes. Later and roots never establish, and the crown heaves out over winter.
Avoid midsummer. A perennial planted in July into dry soil needs water every other day for six weeks, which rarely happens.
What it takes to fill 10 m² (100 sq ft)
A border feels expensive at the till and cheap over ten years. Here is what a mixed-height bed of 10 m² needs.
| Item | Quantity for 10 m² | Cost guide | Notes |
|---|---|---|---|
| Tall structure plants | 6 | Large pots, highest unit price | 70–80 cm centres |
| Mid-height plants | 24 | Standard pots, roughly $8–25 each | Groups of 3–5, 40–45 cm centres |
| Low and edging plants | 35 | Plugs, lowest unit price | Groups of 5–7, 25–30 cm centres |
| Compost or bed mix | 500–800 litres (18–28 cu ft) | Bulk is far cheaper than bags | More in clay and sand |
| Mulch, 3–5 cm (1–2 in) | 400–500 litres (14–18 cu ft) | Bulk by the yard | Bark, leaf mould or compost |
| Supports and rings | 8–10 | Reusable for a decade | For tall, heavy-flowered plants |
| Total plants | 65 | – | 6.5 plants per m² on average |
Perennials run around $8 to $25 each in a garden centre, with plugs below and large specimens above. Three ways to halve the bill: buy small sizes, buy fewer varieties in bigger groups, and swap divisions with neighbours in spring.
Watering and feeding
Year one decides everything. A new perennial has roots only in the old pot ball, which dries out long before the rest of the bed.
Clemson gives 25–40 mm (1–11/2 in) of water per week, rainfall included. On one square metre, 25 mm is 25 litres. Give one large soaking a week rather than a splash every day — deep watering pulls roots down, shallow watering keeps them where July burns them off.
| Stage | Amount | Frequency | Note |
|---|---|---|---|
| At planting | 3–5 litres (1 gal) per plant | Same day | Even in rain |
| Weeks 1–3 after | 3 litres per plant | Every third day | More in sun and wind |
| Rest of season one | 25–40 mm per m² | Weekly | Subtract rainfall |
| Season two | 25 mm per m² | After 10 dry days | Roots now out in the bed |
| Season three on | 25–40 mm per m² | In real drought only | Established beds cope |
Feeding is simpler than the product shelf suggests. One slow-release application in early spring, just before shoots break, covers most perennials — Clemson puts it at roughly half a kilo per 10 m² (1 lb per 100 sq ft). Nitrogen in July gives soft growth that flops and never hardens off.
Perennials from lean, dry habitats — sedum, yarrow, sea holly, Russian sage — want no feeding at all. Fed, they grow soft and split open.
Summer mulch and winter mulch are different jobs
Summer mulch suppresses weeds and holds moisture. Three to five centimetres (1–2 in) of compost, shredded leaves or bark stops most weed seedlings and feeds soil life. Keep it off the crowns — packed material holds moisture and causes rot.
Winter mulch does something else. It insulates against the freeze-thaw cycle, not against cold. Extension in Wisconsin recommends 15–20 cm (6–8 in) over herbaceous perennials, applied once the ground has frozen and reduced gradually in late spring. Straw, marsh hay, pine needles and evergreen boughs work because they stay airy.
Timing is the whole trick. Mulch laid in October makes a warm, damp hotel for voles and keeps the soil soft enough to keep heaving. Wait for frozen ground, then cover.
Staking and deadheading
Tall perennials fall over. Delphinium, peony, garden phlox and globe thistle all go down in the first August downpour. The RHS is clear that supports go in during spring, so plants grow up through them and hide them. Three work: grow-through rings, twiggy birch pushed into the crown in April, or canes with a string corral.
Deadheading buys weeks of bloom
Removing spent flowers is the most profitable half hour in the border. Many perennials set a second flush of buds when stopped from setting seed. Cut the whole stem to a healthy pair of leaves, not just the flower head. Yarrow, catmint, salvia and coreopsis respond strongly.
Stop in mid-August if you want winter structure, and let the last flowers go to seed. The varieties that flower longest without help are in the guide to long-flowering perennials.
Should you cut perennials back in fall or spring?
Spring, as the rule. The old advice to strip the border bare in October has reversed, for three reasons in a cold climate.
Standing stems catch snow, the best insulation a perennial can have. Hollow stems cut in autumn funnel water into the crown. And last year's stems are where native bees and lacewings overwinter. University of Maryland Extension recommends removing debris only where disease was present.
The exceptions are about disease and seed. Here is the split.
| Cut back in fall | Why | Leave until spring | Why |
|---|---|---|---|
| Peony | Botrytis overwinters in the foliage | Ornamental grasses | Hollow stems channel water to the crown |
| Hollyhock | Rust – clear fallen leaves too | Coneflower and rudbeckia | Seed heads feed finches |
| Phlox with mildew | Spores carry over on infected stems | Sedum | Holds snow well on stiff stems |
| Hellebore with leaf spot | Old leaves infect the new buds | Yarrow and Joe Pye weed | Winter structure and insect shelter |
| Hosta and daylily foliage | Collapses to slime, hides slug eggs | Asters and Japanese anemone | Tender crowns, sheltered by stems |
| Aggressive self-seeders | Cut before seed drops | Bugbane, sea holly | Durable winter silhouettes |
| Anything with rust or blight | Bag it, never compost it | Bergenia and evergreen rosettes | Keep their leaves – never cut |
Cut in spring when the first shoots show at the base — late March in zone 6, into May in zone 3 — taking old stems to about 5 cm (2 in). Maryland Extension suggests waiting until temperatures stay above 10 °C (50 °F), so insects have left the hollow stems.
Dividing perennials: spring or fall?
Division rejuvenates a clump gone bare in the middle, keeps its size in check and gives you free plants. The RHS suggests every two to three years; tough genera are fine at four to six.
Timing follows flowering. Divide fall bloomers in spring, and spring and early-summer bloomers after they finish. You never lift a plant about to flower, or one that has just emptied its reserves.
| Perennial | Bloom time | Best division window | Interval |
|---|---|---|---|
| Hosta | July–August | Spring, at 5–10 cm (2–4 in) shoots | 4–6 years |
| Ornamental grasses (Miscanthus, Calamagrostis) | August–October | Spring | 3–5 years |
| Garden phlox (Phlox paniculata) | July–September | Spring | 3–4 years |
| New England aster (Symphyotrichum) | September–October | Spring | 2–3 years |
| Coneflower (Echinacea, Rudbeckia) | July–September | Spring | 3–4 years |
| Japanese anemone | August–October | Spring, resents disturbance | 5 years or more |
| Peony (Paeonia) | May–June | September, and rarely | 10 years or more |
| Bearded iris (Iris germanica) | June | July–August after flowering | 3–4 years |
| Siberian iris (Iris sibirica) | June | August–September | 4–5 years |
| Daylily (Hemerocallis) | July–August | Spring or August–September | 4–6 years |
How to divide
Division suits clump-forming perennials. Taproot species such as lupine and baptisia resent it and are better raised from seed or root cuttings.
- Cut the foliage back to 15–20 cm (6–8 in) first, so the plant loses less water while roots are damaged.
- Water the clump the day before if the soil is dry.
- Dig all the way round with a fork and lift the clump whole.
- Shake or hose off the soil so you can see the growth points.
- Split with two forks back to back for big clumps, by hand for loose roots, with a knife for woody crowns.
- Give every division roots and growing points. University of Minnesota Extension recommends three to five vigorous shoots per division for flowers next season.
- Throw away the old woody centre. It never flowers well again.
- Replant at once, at the same depth as before, and water in with 5 litres.
Fall division has the same deadline as fall planting: four to six weeks before freeze-up.
Growing perennials from seed
Seed is the cheapest route to many plants of one species, and the only route to species nurseries rarely carry. The price is time: most flower in year two or three.
Many perennial seeds need a cold, moist period first — stratification. It stops them germinating in September and dying in November. Two methods work.
- Winter sowing outdoors. Sow in pots or lidded jugs in October or November, stand them against a north wall and let winter do the work. Germination follows in April and May.
- Refrigerator stratification. Sow into moist compost, bag the pot and chill four to eight weeks, then move into light at 15–18 °C (59–64 °F).
Cold is needed by columbine, delphinium, hellebore, bugbane and most prairie perennials. Salvia, yarrow, sedum and daylily germinate warm without chilling. If the packet says nothing, winter sowing outdoors is the safe default.
Spring sowing indoors in March suits the second group, using the method in the guide to starting seeds indoors. Prick out at the first true leaves and plant out in August or next spring.
Month by month in the perennial border
Set for zone 5. Zone 6 runs about two weeks earlier in spring, zones 3 and 4 two to four weeks later.
| Month | What you do | Do not miss |
|---|---|---|
| January | Plan, order seed, draw the bed | Knock wet snow off standing stems |
| February | Order plants, sharpen secateurs | Check winter mulch is in place |
| March | Cut back in zone 6, start seed indoors | Stay off soggy soil |
| April | Cut back zones 4–5, divide fall bloomers, set supports | Remove winter mulch gradually |
| May | Plant, mulch 3–5 cm, clear perennial weeds | Late frost on soft new growth |
| June | Shear early bloomers, water new plants | Slugs on hosta and astilbe |
| July | Deadhead, water 25–40 mm weekly, divide bearded iris | Do not feed |
| August | Divide spring bloomers, take cuttings, stop deadheading | Mildew on phlox in dry spells |
| September | Plant and divide, sow seed outdoors, photograph the bed | Last call for division in zone 3 |
| October | Cut back peony, hollyhock and diseased plants | Winter-sow in jugs against a north wall |
| November | Winter mulch once the ground freezes | Mulching early invites voles |
| December | Leave seed heads standing, store tools | Do not pile shovelled snow on the bed |
Zone table: perennials in USDA zones 3–6
The zone number sets the calendar more usefully than the plant list. These dates suit continental cold-climate gardens; maritime zones such as coastal Scotland run later in spring and much later in fall.
| Zone | Average minimum | Spring planting from | Last fall planting | Spring cut-back | Winter mulch |
|---|---|---|---|---|---|
| 3 | −40 to −34 °C (−40 to −30 °F) | Early to mid May | Early September | Early to mid May | Essential, 15–20 cm (6–8 in) |
| 4 | −34 to −29 °C (−30 to −20 °F) | Late April | Mid September | Late April | Strongly advised on new plants |
| 5 | −29 to −23 °C (−20 to −10 °F) | Mid April | Late September | Mid April | On marginal plants only |
| 6 | −23 to −18 °C (−10 to 0 °F) | Late March to early April | Mid to late October | Late March | Rarely needed |
The fall dates are four to six weeks ahead of typical ground freeze in each zone, following the Minnesota Extension rule. A south-facing sandy slope behaves like a zone warmer; a clay hollow in shade like a zone colder.
Designing a border that works all season
Height and depth
Low at the front and tall at the back works, but reads flat. Let a few tall, see-through plants stand near the front — bugbane, tall grasses — so you look into the border rather than at it. A bed needs 120 cm (4 ft) of depth for three height layers.
Succession of bloom
Write down flowering times before you buy. The commonest disappointment is a border that erupts in June and sits green all season. Aim for three varieties in flower each month from May to September.
| Period | Backbone plants |
|---|---|
| April–May | Bergenia, primula, lungwort, brunnera, epimedium |
| June | Peony, iris, delphinium, lady's mantle, hardy geranium |
| July | Daylily, hosta, catmint, salvia, yarrow, coreopsis |
| August | Garden phlox, coneflower, helenium, sedum, Joe Pye weed |
| September–October | Asters, Japanese anemone, bugbane, ornamental grasses |
Foliage carries the border
Flowers last two to four weeks, leaves six months. Combine leaf shapes deliberately: broad hosta against fine grass, silver lamb's ear against dark green, cut fern against rounded lady's mantle. Then the bed still reads well in September.
A few low shrub roses give the border winter structure, and they are pruned on their own schedule — see the guide to growing roses.
Common problems
Why is it not flowering?
Four causes cover nearly every case. Too little light is commonest: a sun perennial in four hours of morning light grows but will not bloom. Too much nitrogen gives leaves instead of buds. Depth stops peonies — their eyes must sit no more than 3–5 cm (1–2 in) below the surface. And a dense clump competes with itself, which division fixes.
Why is it wilting even though you water?
Feel the soil 10 cm (4 in) down first. If it is wet, the problem is root rot from lack of oxygen, and more water makes it worse. If it is dry despite daily watering, you have watered shallowly.
Why does the clump go bare in the middle?
Normal ageing in clump-forming perennials. The centre goes woody and dies while the edges spread outward. It is the plant asking to be divided, and the table above gives the interval.
Slugs, mildew and voles
Slugs go for hosta, astilbe and soft new growth in May — hand-collect after dark following rain. Powdery mildew on phlox and bee balm comes with drought and crowding, so widen the spacing and water at the root. Voles tunnel under mulch and eat crowns from below, one more reason not to mulch early.
Common mistakes
- Planting too close. It looks right in year one and becomes a fight by year three. Use the spacing table and fill gaps with annuals.
- Skipping bed preparation. Compost worked into 25–30 cm of soil cannot be added afterwards.
- Stripping the border bare in October. Standing stems catch snow and shelter insects. Cut only what is diseased or seeding where you do not want it.
- Dividing at the wrong time. Spring and early-summer bloomers after flowering; fall bloomers in spring.
- Feeding in July. Late nitrogen gives soft growth that flops and never hardens off.
- Mulching for winter too early. Wait for frozen ground, or you build a vole hotel and keep the soil heaving.
- Piling mulch against crowns. Moisture held at the crown causes rot. Leave a hand's width of bare soil.
Frequently asked questions
What are perennials?
Perennials are herbaceous plants that live more than two years. They build no wood, die back to the ground in autumn and overwinter as roots, a crown or a green rosette. New shoots come from the same plant each spring. Unlike annuals, which die after one season, a perennial holds its place for three years to several decades.
Do perennials really come back every year?
Yes, provided the species is hardy in your zone and the soil drains. Most losses in zones 3–6 are not caused by air temperature but by two things: saturated soil during a long thaw, which rots the crown, and frost heaving, which lifts the crown out of the ground. Reliable snow cover is worth roughly a full zone.
When is the best time to plant perennials?
Spring once the soil thaws and crumbles, or late summer to early fall with at least four to six weeks before the ground freezes. Spring is safer in zones 3 and 4 and for anything marginally hardy. Container plants can go in any time you will water, but avoid midsummer, when a new plant needs water every other day for six weeks.
How far apart should you plant perennials?
By mature height. Groundcovers go at 20–25 cm (8–10 in) centres, giving 16–25 plants per square metre. Low perennials go at 25–30 cm (10–12 in) for 11–16, mid-height ones at 40–45 cm (16–18 in) for five or six, and tall ones at 50–60 cm (20–24 in) for three or four. A mixed border averages six or seven per square metre.
Should you cut perennials back in fall or spring?
Spring, with a short list of exceptions. Standing stems catch snow, shelter overwintering insects and stop water running into hollow crowns. Cut back in fall only what carried disease — peony with botrytis, hollyhock with rust, phlox with mildew, hellebore with leaf spot — plus foliage that collapses to slime.
How often should perennials be divided?
Every three to five years for most genera. Fast growers such as asters and catmint benefit from every two to three years, while hosta and daylily are happy at four to six. Peony and Japanese anemone prefer not to be disturbed. The signal is a clump gone bare in the centre while the edges keep spreading.
Do perennials need fertiliser every year?
Not if the bed was properly prepared. One slow-release application in early spring, before shoots break, covers most perennials, and an annual topping of compost does the same job. Perennials from lean, dry habitats — sedum, yarrow, sea holly, Russian sage — should not be fed at all, because feeding makes them soft and they split open.
What are the easiest perennials for zone 4?
Daylily, hosta, sedum, yarrow, hardy geranium, Siberian iris and coneflower are tough, long-lived and forgive a missed watering. None needs staking and all are reliably hardy to zone 3 or 4. Start with those, then add fussier plants such as delphinium once the basics work.
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