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How to Grow White Mustards UK | Regional Planting Calendar
Move through the SoilCommander growing library like a course: keep the navigation in place, open the next lesson, and build your garden plan step by step.
In the UK, white mustards go in the ground mid April to mid May.
White mustards (Sinapis alba) — Annual herbaceous plant.
Timing is the decision that matters most in the UK: there are 4 separate regional sowing windows, ranging from mid April in Southern England to early May in Scotland.
Core growing advice on this page is checked against named horticultural sources — see References.
NDSU states seeding runs late April to mid-May; taken here as the equivalent UK spring window.
Midlands - detail & sources
Same spring sowing window as elsewhere in the UK -- RHS rates white mustard H4, hardy through most of the UK.
Northern England - detail & sources
Sowing window shifted about a week later than southern England for a cooler spring start -- RHS's H4 rating means winter cold is not a limiting factor even this far north.
Scotland - detail & sources
Sowing window shifted about two weeks later than southern England for Scotland's cooler, later spring -- NDSU notes cool temperatures actually extend flowering and boost yield, so this crop is well suited to a cooler northern season.
NDSU: sow late April to mid-May, 0.5-1.5in deep into a moist, firm seedbed via drill or air seeder -- early planting on a firm seedbed supports vigour. RHS: propagate by seed into fertile, well-drained soil in full sun.
Seedling establishment
1
NDSU: flea beetles cause early-season "shot-holed" damage on seedlings -- treatment is only warranted once defoliation exceeds 25%. Cool temperatures and good moisture at this stage extend flowering and boost eventual yield.
Flowering
6
RHS: bright yellow flowers appear from May through to August or September, valued as a food source for wildlife.
Pod maturity and harvest
8
RHS: flowers are followed by dark red-to-brown seeds. NDSU: harvest by straight combining once pods are mature and dry, ideally at 12-15% seed moisture, around 85-90 days from sowing.
When to pick: NDSU: harvest by straight combining once pods are mature and dry, ideally at 12-15% seed moisture for best quality -- crop matures 85-90 days from sowing.
Storage
Store dried seed in an airtight container; used to make table and hot-dog mustard, or in processed meats for flavour, emulsification and water binding (NDSU).
Named by RHS as the main UK disease risk for this brassica-family crop; NDSU's commercial-growing guidance does not mention it, instead flagging Sclerotinia -- a genuine regional difference kept honest rather than…
White mold (Sclerotinia stem rot)
moderate
Sclerotinia sclerotiorum
Named specifically by NDSU as a serious risk in commercial mustard production; recommends avoiding rotation with canola, sunflower or beans to reduce the risk. RHS does not mention it for UK garden growing.
Named by RHS as a general risk for this brassica-family crop.
Flea beetles
moderate
Chrysomelidae: Alticini (various spp.)
Named independently by both RHS and NDSU -- NDSU describes a "shot-holed" leaf appearance on seedlings, treatment warranted only above 25% defoliation.
RHS notes white mustard flowers are valued as a food source for wildlife -- bees and other pollinators visit readily through the long May-to-autumn bloom period.
RHS notes white mustard is grown for fodder, green manure or seed -- a dense planting like this is exactly what a green-manure cover crop looks like in flower.
Soil: fertile, well-drained, avoid drought-prone sandy soils. Size: 30-45in height, matures 85-90 days. Climate: prefers cool temperatures and good moisture, which extend flowering and boost yield. Planting: seed late April to mid-May, 0.5-1.5in deep in a moist, firm seedbed; ~100,000 seeds/lb, sown at 10-14lb/acre via grain drill or air seeder; early planting and a firm seedbed support vigour. Pests: flea beetles cause early-season "shot-holed" damage on seedlings; treat if defoliation exceeds 25%. Diseases: Sclerotinia (white mould) a serious risk -- avoid rotating with canola, sunflower or beans. Harvest: straight combine when mature and dry, ideally at 12-15% seed moisture for quality. Edible use: table and hot-dog mustard; used in processed meats for flavour, emulsification and water binding.
Hardiness H4 (-10 to -5C, hardy through most of the UK). Soil: chalk, clay, loam, sand, fertile and well-drained. Sun/aspect: full sun, south/west-facing. Exposure: exposed or sheltered. Size: 0.5-1m height, 0.1-0.5m spread, 1 year to maturity. Propagation: by seed. Pests: flea beetles, caterpillars. Diseases: clubroot. Edible use: grown for fodder, green manure or mustard seed; native British plant, bright yellow flowers May-Aug/Sept, dark red-brown seeds, valued as a wildlife food source.
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.
Frequently Asked Questions
When should I sow white mustards in the UK?
In Southern England, from mid April. In Scotland, wait until early May. Treat these as a guide rather than a fixed date — the governing rule is to sow only once frost risk has passed and temperatures are reliably warm enough.
When do I sow white mustards?
Sow mid April to late May.
What problems affect white mustards?
Our data links 2 diseases and 2 pests to this crop. See the sections above for each one and how to manage it.
Plan next season before the problems start
Most of the advice on this page comes down to timing and spacing — sowing at the right moment, rotating beds, and giving plants enough airflow. The UK Garden Planner lays your plot out month by month so those decisions are already made before the season starts.
UK vegetable growing guides · Checked against RHS & Met Office guidance
Every SoilCommander guide is written and maintained by our editorial team for real UK growing conditions, and reviewed against Royal Horticultural Society growing advice and Met Office climate data before publication.
Sketch your exact plot shape, pick your UK crops, and get a spacing-accurate bed layout with companion pairings, a rotation plan and month-by-month sowing dates — every fact sourced from RHS and Garden Organic.
