How to Grow Achillea
'Marshmallow' from Seed
The compact first-year flowering sneezewort — masses of fully double white pompom flowers from June to September, outstanding as a cut flower, and genuinely one of the easiest perennials you can grow from seed
If you have been charmed by the white pompom flowers of Achillea 'Ballerina' but want something even more compact — a tighter, mounded plant that smothers itself with flower from early summer and requires almost no attention — then 'Marshmallow' is the variety you are looking for. This is a Benary FastraX selection of Achillea ptarmica, bred specifically for first-year flowering from seed, compact habit and an exceptionally high proportion of fully double flowers. The name is perfectly chosen — the blooms genuinely do look like tiny marshmallows or puffs of popcorn, dancing on slender branching stems above a neat mound of dark green foliage.
Like Ballerina, 'Marshmallow' belongs to the sneezewort group of achilleas — the ptarmica species — which tolerates moisture-retentive soil and partial shade far better than the flat-headed millefolium yarrows. This makes it genuinely useful in spots that would defeat most achilleas, and it is one of the best-performing white perennial fillers you can grow from seed in the UK.
Quick Facts at a Glance
Plant Type
Hardy Perennial
Sowing Time
Feb–Apr indoors · Autumn outdoors
Flowering Months
June – September
Position
Full sun or partial shade
Height & Spread
30cm · 45cm spread
Difficulty Rating
2 out of 5 — Easy
Understanding the Plant
'Marshmallow' is a FastraX perennial — a term used by breeder Benary to describe varieties specifically developed to bypass the juvenile period that prevents most perennials from flowering in their first year. This means that unlike many hardy perennials that spend their first season establishing roots and only begin flowering in year two, 'Marshmallow' will flower freely in its very first season from an indoor sowing in February or March. This first-year flowering performance, combined with its compact 30cm habit and exceptional percentage of fully double flowers, makes it one of the most useful white perennial fillers available from seed.
The plant forms a near mound of dark, narrow, serrated foliage from which branching stems carry the white pompom flowers from June through September. It spreads gently via rhizomes — less aggressively than the wild species but steadily enough to fill gaps and form generous clumps over two to three seasons. Unlike its cousin Ballerina (which reaches 40–60cm), 'Marshmallow' stays compact at around 30cm, making it ideal for the front of the border or for container growing.
Often Listed as 'The Pearl'
This variety is often grown under the name 'The Pearl' — a well-established Achillea ptarmica cultivar that holds the RHS Award of Garden Merit. 'Marshmallow' is a more compact, more fully double, first-year flowering development of this classic variety, with all the same garden value and rather better performance from seed.
The Chelsea Chop
We recommend a "Chelsea Chop" in late May — cutting stems back by about one-third — to encourage lateral branching and a more generous second flush. This is excellent advice for 'Marshmallow': the resulting plant becomes bushier, produces significantly more flowering stems, and the second flush of flowers tends to be even more abundant than the first. Do this in late May or early June and again if the first flush begins to fade in midsummer.
When & How to Sow
As with all achilleas, the essential rule is surface sowing — the seed is photoblastic and requires light to germinate. Buried seed simply will not sprout. Beyond this, 'Marshmallow' is genuinely straightforward, with reliable germination in 10–14 days at the right temperature.
Sowing Options
February to April indoors at 18–20°C — the recommended approach for first-year flowering. Autumn outdoors — sow onto a prepared seedbed in September or October; seedlings overwinter as small rosettes and establish strongly for flowering the following summer. Both approaches produce excellent plants; the indoor sowing gives flowers sooner.
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Prepare moist seed compost in pots or modules. Water from below before sowing. Fine peat-free seed compost works well; add a little vermiculite if it feels heavy.
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Scatter seed on the surface. Do not cover. The seeds are very fine — scatter as thinly as possible and press gently but firmly onto the compost surface to ensure contact. Light must reach the seed.
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Cover with a clear lid and place at 18–20°C. Germination typically occurs within 10–14 days. Once seedlings emerge, remove the cover and move to the brightest available position immediately to prevent legginess.
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Prick out at the two-leaf stage. Handle by the leaf. Pot into individual 7cm pots and grow on in a cool, bright position. 'Marshmallow' is more compact than other ptarmica varieties so seedlings are slightly smaller — handle with care.
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Harden off and plant out from May. Gradually acclimatise to outdoor conditions over two weeks. Plant out after the last frosts, spacing 45cm apart. Water in well and consider a light top-dressing of balanced fertiliser to support first-year establishment.
Growing On Tips
Sun & Shade
Full sun produces the most prolific flowering, but 'Marshmallow' is genuinely tolerant of partial shade — a key advantage over most achilleas. It will flower well with four to five hours of direct sun per day, making it useful in spots where other varieties would struggle. Avoid deep shade, which produces very leggy growth.
Moisture Tolerance
Unlike millefolium achilleas which need sharp drainage, ptarmica types including 'Marshmallow' tolerate and even prefer moisture-retentive soil. It will thrive in conditions that would rot most yarrows, including heavier clay soils. Avoid truly waterlogged ground, but consistent moisture is welcomed.
The Chelsea Chop
Cut stems back by one-third in late May to encourage bushy branching growth. This is strongly recommended for 'Marshmallow' — the resulting plant flowers more generously and for longer than one left uncut. A second light cut when the first flush fades in July extends the season significantly.
Division
Divide every three years in spring to maintain vigour and manage spread. 'Marshmallow' spreads less aggressively than older ptarmica varieties but still benefits from regular division. Divided portions transplant readily and a divided clump rejuvenates quickly, producing generous new growth within weeks.
Feeding
A light balanced feed in spring is all that is needed. The compact nature of 'Marshmallow' means it is less prone to the floppy growth that over-feeding produces in taller varieties, but lean conditions still produce the best flower colour and the firmest, most upright habit.
Winter Care
Fully hardy throughout the UK — H7 rating. Cut back to basal foliage in late autumn or leave through winter for a little structural interest. New growth emerges reliably each spring. No winter protection needed in most UK gardens; in very exposed or wet positions a light mulch of grit around the crown helps.
Common Problems & How to Fix Them
| Problem | Likely Cause | What to Do |
|---|---|---|
| No germination | Seed covered | The universal achillea problem. Resow on the surface at 18–20°C without any covering. Keep moist throughout. Germination takes 10–14 days — do not give up if nothing appears in the first week. |
| Few or no double flowers | Seed variation or stress | Some variation in doubleness is natural from seed. Plants grown in good conditions produce the most fully double flowers. Ensure adequate sun and consistent moisture. Division of clumps that produce particularly good double flowers allows you to propagate true-to-type plants vegetatively. |
| Leggy seedlings | Insufficient light after germination | Move to the brightest available position immediately after germination. Rotate pots daily on a windowsill. Draw seedlings usually recover when grown on in better light. |
| Powdery mildew | Dry at roots, poor airflow | Water consistently at the base, not overhead. Improve airflow through correct spacing. Remove affected leaves. 'Marshmallow' is slightly more susceptible than drier-growing achilleas — consistent root moisture is the best prevention. |
| Spreading too widely | Rhizomatous spread | Divide every three years. Dig out unwanted rhizomes in spring. More manageable than the wild species but still benefits from occasional containment in smaller gardens. |
| Flowers browning early | Hot, dry conditions or natural ageing | Cut spent stems promptly and apply the Chelsea Chop to stimulate a fresh flush. Water in dry periods. Flowers naturally age to cream and then brown — cutting regularly prevents the plant from looking tired. |
When to Expect Flowers
As a FastraX perennial, 'Marshmallow' is one of the few hardy perennials that reliably flowers in its first year from seed. An indoor sowing in February or March, given good light and warmth, will typically begin flowering by June or July of the same year — a remarkable performance for a perennial. The flowering season runs through to September, with the Chelsea Chop extending and renewing it. From the second year, established plants flower even more freely and the expanding clumps provide an increasing abundance of cutting material.
Sow indoors from February — this first-year flowering perennial can be in bloom by June in its very first season, with the clump becoming increasingly generous in subsequent years.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| 🌱 Sow Indoors |
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| 🪴 Plant Out |
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| 🤍 Flowering |
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Cutting & Drying
'Marshmallow' is an exceptional cut flower — the compact double pompoms, produced in generous sprays on branching stems, create the same airy, cloud-like effect as gypsophila but with far more character and a considerably longer vase life. The stems are strong and the flowers last well in water, making this one of the most useful and most versatile white cutting flowers you can grow as a perennial.
Cutting for the Vase
Cut when pompoms are fully open and brilliant white — before any ageing begins. Cut in the morning with long stems to a visible side shoot. Condition in deep cool water in a dark place for several hours before arranging. Typically lasts seven to ten days in the vase. A classic partner to roses, sweet peas, lavender, and any bold-coloured summer perennial.
Drying 'Marshmallow'
Cut for drying when flowers are fully open and firm. Strip leaves, bunch loosely in small bunches of six to eight stems and hang upside down in a warm, dry, ventilated space. 'Marshmallow' dries to cream-white and holds its double pompom structure beautifully — a wonderful material for winter wreaths, dried bouquets and botanical arrangements.
The Classic Rose Partner
Achillea ptarmica is the traditional partner for shrub roses — the sprays of white pompoms hiding the often-leggy lower stems of roses while complementing the blousy flowers above. 'Marshmallow' is particularly well-suited to this role thanks to its compact 30cm height, which fits neatly at the feet of most shrub roses without overwhelming them. A planting of old roses underplanted with 'Marshmallow' is one of the great classic cottage garden combinations.
Plant Specifications
The white filler perennial that flowers in its very first year
There are very few hardy perennials that will reward you with flowers in their first season from seed — 'Marshmallow' is one of them, and the flowers it produces are among the most charming and most useful in the cottage garden. Compact, generous, first-year flowering, tolerant of damp conditions that defeat most achilleas, and an outstanding cut flower to boot. Our Achillea 'Marshmallow' seeds are selected for reliable germination and strong first-year flowering performance — sow them in February and enjoy clouds of white pompoms by midsummer.
Shop Achillea Marshmallow Seeds →