How to Grow Skirrets USA | Planting & Establishment

Soil & Growing Conditions

Water: moist but well-drained; water during dry spells if roots are to be harvested (RHS)

Soil pH range

6 7.5

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Growth Stages

Stage	BBCH	Notes
Sowing/planting	0	Grow from seed sown after all danger of frost, or from a purchased crown/root offset for a head start; can also start indoors 8 weeks before the last frost (PITH + VIGOR).
Root and foliage growth	3	Grows 3-4ft tall with large, glossy, dark green, compound pinnate leaves; harvest follows 6-8 months after planting (PITH + VIGOR).
Flowering	6	Delicate white flower umbels appear in summer, also giving the plant ornamental value (RHS).
Dormant-season harvest and division	8	Lift and divide clumps when dormant, November to March, harvesting some roots and replanting sections for continued growth (RHS).

Quick Facts

Factor	Value
Soil pH	6 - 7.5
Sunlight	6-6 hours direct sun
Soil texture	chalk, clay, loam or sand, deep and fertile (RHS)
Drainage	well-drained
Lifecycle	herbaceous perennial
Edible parts	root

At a Glance

Harvest & Storage

When to pick: Lift and divide clumps when dormant, between November and March; white roots taste like sweet carrots and parsnips, harvested for culinary use while some sections are replanted for continued growth (RHS).

Pests

Stem and bulb nematode

moderate

Ditylenchus dipsaci

RHS names this directly: susceptible to stem and bulb eelworm.

Voles

low

Microtus spp. / Arvicola spp.

RHS names this directly: voles may eat the roots.

Skirret, the Sweet-Rooted Perennial the Tudors Grew

A cluster of sweet roots

Each crown lifts as a bundle of slender, sweet roots -- the part that made skirret a staple before the potato.

Pinnate foliage

Neat pinnate leaves form the low clump from which the flowering stems rise.

Tall umbels in summer

Flowering stems carry the plant well above the foliage, topped with white umbels.

Umbellifer flowers

The white compound umbels place skirret firmly in the carrot family, alongside parsnip and carrot.

Sium sisarum

A labelled specimen: skirret is a hardy perennial, increased by division as well as from seed.

References

1. Cultivariable - Skirret (Sium sisarum) -- how to grow

   Specialist grower guide for unusual root crops. Direct sow mid-autumn to late spring, or start indoors 8 weeks before last frost for full-size first-year roots; seed germinates slowly and erratically, first germinations around 3 weeks and 50% emergence by week 6, helped by consistent moisture and bottom heat. Propagates easily from offsets ringing the stem -- select offsets with large shoots and rootlets, pot them with the sprout tip just below the surface, which improves survival over direct planting. Space 18in apart in rows 3ft apart, sowing seed about 1/8in deep. Acidic to neutral, well-drained soil rich in organic matter; responds to nitrogen and tolerates heavy, swampy ground. Full sun optimal, tolerates shade with reduced yields. Harvestable after the first year once foliage dies back, with yields improving markedly in year two. DISAGREES WITH RHS ON TWO POINTS: says frost does NOT appear to improve the roots (commonly claimed elsewhere), and names black blight (Septoria) as a major disease threat plus root knot nematodes, where RHS reports the plant as generally disease-free. Pests: voles eat the roots; tiny seed-feeding beetles damage flower heads.

2. RHS (Royal Horticultural Society) - Sium sisarum | skirret

   A herbaceous perennial formerly cultivated as a root vegetable before potatoes arrived in Britain. White roots harvested when the plant is dormant (autumn to early spring), tasting like a mixture of sweet carrots and parsnips. Also ornamental, with delicate white flower umbels in summer. Native to Europe and East Asia, not native to GB/Ireland. Hardiness H6 (-20 to -15C). Full sun; benefits from south-, west- or east-facing aspects. Soil: chalk, clay, loam or sand; acid, alkaline or neutral pH; moist but well-drained. Height 1-1.5m, spread 0.1-0.5m. Time to maturity 1-2 years. Propagate by seed. Pests: susceptible to stem and bulb eelworm; voles may eat roots. Diseases: generally disease-free. Lift and divide clumps when dormant (November-March), harvesting roots for culinary use while replanting sections for continued growth.

2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.