Growing Peonies: Planting Depth, Care and Reliable Blooms

Contents

• Three kinds of peony: herbaceous, tree and Itoh
• Planting depth: the one thing that decides everything
• When should you plant peonies?
• Site and soil
• How to plant a peony step by step
• Feeding and watering
• Staking that actually works
• Care through the year
• Why won't my peony bloom?
• Botrytis blight and other diseases
• Why are there ants all over the buds?
• Moving and dividing peonies
• How long do peonies live?
• Peonies as cut flowers
• Varieties for cold gardens
• Zone and timing chart
• Common mistakes
• Frequently asked questions

Three kinds of peony: herbaceous, tree and Itoh

Most confusion about peonies comes from advice for one group being applied to another. They look alike in bloom but are built differently below ground.

Herbaceous peonies

These die back to the ground every autumn and push red shoots up in April. Most garden peonies belong here, chiefly Paeonia lactiflora, the Chinese peony, with large fragrant double flowers in June. The old cottage-garden species Paeonia officinalis flowers earlier, in late May.

Herbaceous peonies are the hardiest group, reliable through zone 3 and productive to zone 8. They reach 60–100 cm (24–40 in) and often need support, because heavy double blooms soak up rain and flatten the plant.

Tree peonies

Paeonia suffruticosa is woody. It drops its leaves but keeps its stems, and next year's buds sit on that wood. An old plant reaches 2 m (6 ft) and spreads as wide. The flowers are enormous, often over 20 cm (8 in) across, and open in May.

Tree peonies are less hardy. Zone 5 to 8 is comfortable, and zone 4 works in a sheltered spot with reliable snow cover. They want shelter but not a baking south wall, where buds break too early and freeze. An east or west aspect with dappled shade suits them best.

Itoh peonies

Itoh hybrids, sold as intersectionals too, are crosses between herbaceous and tree peonies, named after the Japanese breeder Toichi Itoh. They carry the tree peony's colour range, including the yellows herbaceous peonies lack, but die to the ground each winter. That makes them as hardy as any perennial.

An Itoh reaches 70–120 cm (28–48 in), has stems sturdy enough to skip staking and holds handsome foliage long after flowering. Most are rated for zone 4, and the catch is the price.

Planting depth: the one thing that decides everything

Read this if you read nothing else. Depth is the commonest reason a peony refuses to flower, and the one mistake feeding and patience cannot fix.

The eyes should barely be covered

Next year's shoots sit as pink eyes on top of the knobbly root. They belong 3–5 cm (1–2 in) down, no deeper. In heavy clay, shallower still is better.

A peony needs cold reaching down to the eyes before flower buds develop. Bury them 10 cm (4 in) down and the soil neither chills enough in winter nor warms fast enough in spring. The plant makes leaves and skips the flowers, for decades, with nothing else wrong.

Fresh soil settles

A newly dug hole sinks, and the plant sits several centimetres lower after the first winter. Firm the base hard before setting the root, and measure from the original ground level around the hole.

Tree peonies break the rule

Here the advice reverses. A grafted tree peony sits on a herbaceous nurse root that carries it only a few years. Plant the union at the surface and the shrub depends on a root that quits. Grafted tree peonies go in with the union 10–15 cm (4–6 in) down, so the variety roots above the graft.

The union shows as a swelling between the woody stem and the root mass. Own-root tree peonies, uncommon in the trade, go in at pot depth.

Itoh hybrids follow the herbaceous rule

Itoh peonies have a herbaceous rootstock with visible eyes, so 3–5 cm (1–2 in) is right. If yours is grafted, 5–8 cm (2–3 in) is enough.

Fixing a peony that sits too deep

Do not scrape soil away from above, which leaves the crown in a bowl of old soil that collects water. Lift the whole plant in early autumn and replant at the right depth. Expect a year or two without flowers, then a full display.

When should you plant peonies?

Autumn, and the difference from spring planting is larger than for most perennials. From late August into October the soil is still warm while the air has cooled, so the plant puts everything into roots. They grow on while soil temperature stays above roughly 5 °C (41 °F).

Get the last bare-root division in four to six weeks before the ground freezes: October in zone 6, late August in zone 3.

Bare-root divisions are an autumn-only product

Most peonies are sold as bare-root divisions: a piece of storage root with a few eyes and no pot. Growers ship them in September and October because the plant is dormant and tolerates handling. A division with three to five eyes establishes better than a potted plant but rarely flowers the first year.

Potted peonies can go in any time

A container-grown peony can go in from April to October, since the root ball stays intact. Check the depth here too: potted peonies are often set too deep, and planting the ball level with the ground carries the mistake into your border. Scrape soil off the top until the eyes show.

Spring planting works but costs a year

A spring-planted bare root builds roots while carrying leaves through summer heat. It manages but ends the season a year behind. If a root arrives in spring, plant it, water it and expect no flowers.

Site and soil

Peonies are long-lived and resent being moved, so spend an extra half hour on the spot. Sun and drainage decide it.

Six hours of sun, minimum

Count on six hours of direct sun for a full display. At four hours the plant flowers thinly, in deep shade not at all. Afternoon shade is a bonus, since blooms last longer and pale colours hold their tint.

Keep a metre (3 ft) from trees and large shrubs. Root competition from a maple or an apple takes water and nutrients, and the peony loses that contest.

Deep, fertile, well-drained ground

A loam with plenty of organic matter is ideal and a touch of lime is welcome. Aim for pH 6.5 to 7.5, and work in lime if your soil is acidic.

What a peony cannot take is standing water around the crown. A root sitting in cold wet clay through late winter rots or turns susceptible to botrytis. On heavy ground, raise the bed 5–10 cm (2–4 in). Gravel in the hole does not help and creates a bathtub effect instead.

Peonies in containers

Herbaceous peonies grow in pots, but only large ones: at least 40 litres (10 gal) and 50 cm (20 in) deep, since the root runs straight down. The pot needs drainage holes and a cold but frost-free winter spot. Expect weaker flowering than in open ground.

How to plant a peony step by step

Planting takes twenty minutes and settles the next fifty years.

1. Pick a spot with six hours of sun and a metre (3 ft) from trees, shrubs and hedges.
2. Dig a hole about 50 cm (20 in) deep and 50 cm wide.
3. Loosen the base and mix the soil with well-rotted manure or compost, one part in three.
4. On acid soil, mix garden lime into the backfill, not against the root.
5. Return soil to the hole and firm it hard so the plant will not sink.
6. Mix a couple of handfuls of bone meal into the upper soil, away from the root.
7. Set the root eyes up and lay a stick across the hole to check they sit 3–5 cm (1–2 in) below the surrounding ground.
8. A grafted tree peony goes in with the graft union 10–15 cm (4–6 in) down instead.
9. Backfill, firm gently and water so the soil closes around the root.
10. Check the depth again after watering and top up if it has sunk.
11. Mulch thinly with compost, keeping it off the eyes.
12. Add a label. A dormant peony is invisible in late winter and easy to slice with a spade.

Planting several, leave 90–120 cm (3–4 ft) between them. Closer and they shade each other while botrytis risk climbs. Set among other perennials, give each peony a clear ring of half a metre, or creeping neighbours colonise the crown.

Feeding and watering

Peonies are light feeders. Overfeeding with nitrogen causes more missing flowers than any shortage, giving large soft leaves, floppy stems and few buds.

Two feeds a year is plenty

Feed first in spring when the shoots are a hand's width tall, with a balanced perennial fertiliser kept 10–15 cm (4–6 in) from the stems. Feed again after flowering in July, and that one matters most, because next year's buds form in the crown through late summer.

Bone meal in autumn works well, since phosphorus supports bud set without pushing leafy growth. Wood ash goes in a ring around the plant, never over the eyes. Keep lawn fertiliser out.

July and August are the months that count

Most gardeners water peonies while they bloom and stop when the flowers finish. That is backwards, because during bloom the buds are already made. Next summer's display is decided in July and August, when the crown builds new eyes. A drought then gives thin flowering a year later, and the delay is long enough that almost nobody connects the two.

Water deeply once a week in dry spells until late August, roughly 20 litres (5 gal) per plant, at the base rather than over the leaves. Newly planted peonies need water all through their first season.

Staking that actually works

A double peony in full bloom is surprisingly heavy, and heavier after rain. Without support the plant splays flat and the flowers end up in the mud. The plant is unharmed, the display is not.

Put the support in before you need it

The usual error is fitting a ring once the plant is down, when the stems cannot be raised without snapping. Install supports in early spring while shoots are 15–20 cm (6–8 in) tall. The plant grows up through the ring and hides it.

What to use

A metal peony ring on three or four legs lasts longest. Choose one about two thirds of the plant's final height and slightly narrower than its spread. A grid of bamboo canes with string works as well. A single stake with string around the whole clump gives a trussed sausage and is worse than nothing.

Single and semi-double varieties and most Itoh hybrids hold themselves up. The heavy doubles need help.

Care through the year

An established peony asks less of you than anything else in the border.

April and May

Clear old leaves as soon as the red shoots appear. Fit the support at 15–20 cm (6–8 in) and feed lightly. A shoot that blackens at the base and collapses is botrytis, and it comes out at once.

June and July

Deadhead as blooms fade, cutting just above the first strong leaf. That saves the cost of setting seed and stops spent petals becoming an infection site.

For fewer but larger flowers, pinch off the side buds while pea-sized. For a longer season leave them all, since side buds open after the main one.

August and September

Water in dry spells and feed after flowering if you have not. These are also the months for planting and dividing.

October and November

Once the foliage yellows, cut herbaceous stems to 2–3 cm (1 in) above the ground. This is not tidying. Botrytis overwinters in dead peony stems, and binning that material rather than composting it is the most effective disease measure there is. Tree peonies are not cut back.

Newly planted peonies and tree peonies in zone 4 and colder benefit from evergreen boughs the first winter. Established herbaceous peonies need no winter protection.

Why won't my peony bloom?

This is the most common peony question, and it has about ten answers. The chart takes them in order of how often each is the culprit.

The soil level that creeps up

Almost nobody suspects this one. A peony planted at exactly the right depth still ends up too deep if you add a couple of centimetres of compost every spring. After ten years the eyes sit 8 cm (3 in) down and nobody moved anything. Keep thick mulch off the crown.

The patience it takes

A bare-root division with three to five eyes gives no flowers the first year, one or two the second and a full display from year three. Fewer than three eyes can mean five years. Digging it up to check only sets it back.

Botrytis blight and other diseases

Peonies get few diseases, but the one they get is persistent. Botrytis blight, caused by Botrytis paeoniae and Botrytis cinerea, is behind nearly every problem you see on a peony.

Recognising it

It appears in three forms. Young shoots turn watery at the base, wilt and fall over, often with a grey-brown fuzzy coating in damp weather. Pea-sized buds stall, brown and dry up. Leaves and stems develop large irregular dark brown blotches.

Cool wet springs favour the fungus, and crowded plantings, heavy nitrogen and old stems left lying favour it more.

What actually works

• Cut out infected parts at once. Take the shoot to ground level as soon as it wilts at the base, and bin it.
• Cut the stems down in autumn and bin them. The most important measure. The fungus overwinters in dead stems and at the soil surface.
• Remove spent flowers. Fallen petals caught in the foliage are a perfect starting point.
• Give the plant air. 90 cm (3 ft) between plants, and keep tall neighbours back.
• Water at the base. Wet foliage overnight is a risk that dry foliage is not.
• Ease off nitrogen. Soft fast growth is infected more readily than firm tissue.

Other problems

Powdery mildew shows as a white dusting on the leaves in late summer. It looks bad and does almost no harm, arriving after the foliage has done its work.

Leaf blotch is handled the same way: stems out in autumn. Root rot affects peonies in waterlogged ground, and the only cure is a better-drained site. If a plant wilts suddenly in midsummer, dig up a piece of the crown. Healthy peony root is firm and pale inside, infected root brown and soft.

Why are there ants all over the buds?

Everyone who grows peonies meets this the first time the buds swell: the bud is crawling with ants. Then comes the old story that peonies need ants to open, and the worry that they damage the buds. Both are myths.

The ants are there for nectar, which the outer bud scales exude while the bud develops. They do not damage the bud and are not needed for it to open. A peony under insect netting flowers just as well.

They even do a little good, chasing off thrips. Do not spray them or hose the buds off, since water on the buds raises botrytis risk far more than the ants ever could.

They only matter when you bring peonies indoors. Shake the stem outside, or stand the cut flowers in a bucket of water for half an hour first.

Moving and dividing peonies

A peony would rather not be moved. Sometimes it must be: it sits too deep, a shrub has shaded it, or you are moving house. Division also propagates a variety, and one large crown yields five or six plants.

September is the month

Late August and September are the window, earlier in the coldest zones. The plant has finished above ground but has weeks of root growth left. Spring moves usually cost an extra year.

How to do it

1. Cut the stems back to 10 cm (4 in) so you can see what you are doing.
2. Dig a ring 40 cm (16 in) out from the centre and go 40–50 cm (16–20 in) down. Peony roots run straight down and snap easily.
3. Lever the clump up with a fork from several sides.
4. Wash the soil off so you can see the crown's shape and where the eyes sit.
5. Leave the crown in the shade a few hours. Slightly limp roots are easier to divide.
6. Cut with a clean sharp knife so each division gets 3–5 eyes and a piece of storage root.
7. Trim away soft, dark or damaged tissue.
8. Replant at once with the eyes 3–5 cm (1–2 in) down.
9. Water in well and label the spot.

Divisions with one or two eyes usually survive but may take four or five years to flower. More than five is no faster and much heavier to handle.

After the move

Expect one or two years of sparse flowering and a full display in year three. Do not feed heavily to hurry it; water regularly through that first late summer. Tree peonies tolerate division far less well and should be moved whole with the largest root ball you can lift.

How long do peonies live?

Longer than most of the people who plant them. A herbaceous peony at the right depth in well-drained soil routinely reaches 50 years, and plants of 80 to 100 years are well documented. Peonies still flowering beside abandoned farmhouse foundations are a common prairie sight.

There is also no maintenance reason to divide a peony on a schedule. Unlike many perennials it does not go bare in the middle or lose vigour with age.

Tree peonies live longer still, and two-hundred-year-old specimens survive in Chinese and Japanese gardens. Itoh hybrids are too young as a group to know, but they have the herbaceous root system.

Three things shorten a peony's life: standing water, repeated moves, and a spade through the crown in late winter when the plant is invisible. The first two you avoid at planting, the third with a label.

Peonies as cut flowers

Peonies are among the best cut flowers you can grow, and one of the few where the timing of the cut decides everything. Cut too late and the bloom lasts three days, cut right and it lasts a week.

Cut at the marshmallow stage

The moment is when the bud shows full colour but is still closed, and feels soft like a marshmallow between finger and thumb. A bud still hard as a pea never opens in the vase. One that has cracked open is on its way past.

Cut early in the morning while the stems are full of water, straight into a bucket of tepid water.

Leave leaves on the plant

The rule that protects next year's display: never take more than a third of the stems, and leave two leaves on every stem you cut. Those leaves feed the crown through late summer while next year's buds form. Cut stems to the ground and you see it the following June.

Storage and vase life

Peonies last 5–10 days in a vase. Change the water every other day, recut the stem ends at an angle and stand the vase somewhere cool overnight.

Buds at the marshmallow stage store dry in a refrigerator. Wrap them in newspaper with no water and lay them flat in the crisper drawer. They open after a couple of days at room temperature. That is how cut-flower growers stretch a season that otherwise lasts weeks.

Varieties for cold gardens

Every variety below is widely available and proven in zone 3 or 4.

Stretching the season past a fortnight

Peony season feels short because most gardeners plant varieties that bloom together. Add 'Coral Charm' for late May, 'Sarah Bernhardt' for mid-June and 'Nippon Beauty' for July, and you get six weeks of flowers instead of two.

Peonies sit well beside perennials for full sun that take over once they finish, and beside growing roses, since soil and site match. For colour late into autumn, add growing dahlias and long flowering perennials. Single and semi-double peonies also count as bee friendly plants, while packed doubles are closed to pollinators.

Zone and timing chart

The chart covers herbaceous peonies. Tree peonies flower two to three weeks earlier in the same zone, Itoh hybrids at roughly the same time as the lactifloras. A cold spring pushes everything a week or two later.

In zone 3 the herbaceous peony is fully hardy, but the season is shorter. Plant earlier in autumn so the root establishes before the ground freezes, and favour early to mid-season varieties. Paeonia officinalis and the early hybrids are safest at the cold end. Tree peonies suit zone 5 and warmer, and need shelter and snow cover in zone 4.

Common mistakes

• Planting too deep. Eyes belong 3–5 cm (1–2 in) down, not 10. The number one cause of a peony that never flowers.
• High-nitrogen feed. Lawn fertiliser gives big leaves, weak stems and few buds. Use bone meal.
• Watering only during bloom. Next year's buds form in July and August, so drought then means thin flowering a year later.
• Leaving stems standing over winter. Botrytis overwinters in dead stems. Cut to 2–3 cm (1 in) and bin them.
• Staking too late. Once the plant is down the display is lost. Fit the ring at 15–20 cm (6–8 in).
• Moving the plant repeatedly. Every move costs two or three years of flowers. Choose once.
• Mulching over the crown each spring. After ten years the soil level has risen and the peony sits too deep.
• Cutting every stem for the vase. Take a third at most, two leaves per cut stem.

Frequently asked questions

How deep should you plant peonies?
Set the eyes of a herbaceous peony 3–5 cm (1–2 in) below the surface, no deeper. It is the most important measurement in peony planting, because the crown needs winter cold reaching the eyes before flower buds develop. Grafted tree peonies go the other way, with the graft union 10–15 cm (4–6 in) down so the variety roots above it.

When is the best time to plant peonies?
Late August through October. The soil is still warm while the air has cooled, so the plant puts everything into root growth. Bare-root divisions are only sold in that window. Container-grown plants go in from April to October, but autumn planting still ends up about a year ahead.

Why won't my peony bloom?
Most often because it sits too deep. Check that the eyes are 3–5 cm (1–2 in) below the surface. Next come too little sun, since it needs six hours, and root competition from trees and shrubs. Other causes are excess nitrogen, drought the previous July and August, botrytis, and simple youth. A newly planted peony often waits until year three.

Are the ants on peony buds harmful?
No. They are drawn by the sugary nectar the outer bud scales produce. They do not damage the bud, and the idea that a peony needs them to open is an old myth. They also chase off thrips. Do not spray them or hose the buds down, because moisture raises botrytis risk far more than the ants do.

Can you move an established peony?
Yes, but in early autumn and ideally only once. Late August and September are the window. Dig wide and deep, 40–50 cm (16–20 in), wash the soil off and divide so each piece has three to five eyes. Replant immediately with the eyes 3–5 cm (1–2 in) down and expect sparse flowering for a year or two.

Should you cut peonies back in autumn?
Herbaceous peonies and Itoh hybrids yes, tree peonies no. Cut the stems to 2–3 cm (1 in) above the ground once the foliage yellows in October, and bin the material rather than composting it. Botrytis overwinters in dead peony stems, so this one job does more good than every other control combined.

Why do peony buds turn brown and dry up before opening?
Usually botrytis blight. Buds stall at pea size, brown and shrivel, sometimes with a grey fuzzy coating in damp weather. Cut infected buds and shoots down to ground level and bin them. Give the plants more air with wider spacing, water at the base rather than over the foliage, and cut all stems down in autumn.

How long do peonies live?
Fifty years is routine, and eighty to a hundred entirely possible when the plant sits at the right depth in well-drained soil. Peonies still flowering at long-abandoned farmsteads are a common sight. Unlike many perennials, a peony does not need dividing to keep its vigour and can stand untouched for decades.

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