Choi Sum (Brassica rapa var. parachinensis)
1 sources cited · Verified
The short answer
- Plant
- Early April to late September
- Site
- 6+ hours of sun, soil pH 6–7
- Biggest risk
- Club root
In the UK, choi sums go in the ground early April to late September.
Choi sums (Brassica rapa var. parachinensis) — annual or biennial grown as an annual.
Timing is the decision that matters most in the UK: there are 4 separate regional sowing windows, ranging from early April in Midlands to early April in Scotland.
Core growing advice on this page is checked against named horticultural and university-extension sources — see References.
Regional Planting Calendar
| Region | Sow |
|---|---|
| Midlands | early April to late September |
| Southern England | early April to late September |
| Northern England | early April to late September |
| Scotland | early April to late September |
Midlands - detail & sources
UF IFAS gives a warm-climate two-window pattern (mid-to-late spring and early autumn) to avoid frost, rather than UK-specific dates; a single spring-through-autumn window covering both is applied across all four sub-regions rather than inventing a north/south gradient the source does not support.
Southern England - detail & sources
UF IFAS gives a warm-climate two-window pattern (mid-to-late spring and early autumn) to avoid frost, rather than UK-specific dates; a single spring-through-autumn window covering both is applied across all four sub-regions rather than inventing a north/south gradient the source does not support.
Northern England - detail & sources
UF IFAS gives a warm-climate two-window pattern (mid-to-late spring and early autumn) to avoid frost, rather than UK-specific dates; a single spring-through-autumn window covering both is applied across all four sub-regions rather than inventing a north/south gradient the source does not support.
Scotland - detail & sources
UF IFAS gives a warm-climate two-window pattern (mid-to-late spring and early autumn) to avoid frost, rather than UK-specific dates; a single spring-through-autumn window covering both is applied across all four sub-regions rather than inventing a north/south gradient the source does not support.
Quick Facts
| Factor | Value |
|---|---|
| Soil pH | 6 - 7 |
| Sunlight | 6-6 hours direct sun |
| Soil texture | sandy soils referenced for spacing; fertile, well-drained generally (UF IFAS) |
| Drainage | well-drained |
| Lifecycle | annual or biennial grown as an annual |
| Edible parts | flowering stems, leaves, flower buds |
At a Glance
Soil & Growing Conditions
Water: moderate drought tolerance but susceptible to waterlogging; irrigate 1-2x weekly (UF IFAS)
Soil pH range
Span reflects genuine variation between the cited authorities, not a single agreed figure.
Growth Stages
| Stage | BBCH | Notes |
|---|---|---|
| Sowing | 0 | Sow 0.24in (0.6cm) deep; transplants suit larger varieties with a longer growth period (UF IFAS). |
| Establishment | 3 | Cool-season growth at 59-77F (15-25C); spaced 11in between rows, 8-12in between plants; fertile, well-drained soil at pH 6-7 (UF IFAS). |
| Flower stem development | 5 | Flowering stems, leaves and buds develop; only the purple cultivar tolerates frost (UF IFAS). |
| Harvest | 8 | Harvest 30-50 days after sowing once flower buds are fully developed but still unopened; two to three harvests per season (UF IFAS). |
Harvest & Storage
When to pick: Harvest begins 30-50 days after sowing, once flower buds are fully developed but still unopened. Expect two to three harvests per season, 9,800-16,000 lb/acre yield (UF IFAS).
Diseases
Pests
Choi Sum, Seedling to Flowering Stem
References
-
Cool-season crop thriving at 59-77F (15-25C). Only the purple cultivar tolerates frost; grow mid-to-late spring and early autumn in warm climates to avoid frost damage. Sow seeds 0.24in (0.6cm) deep; transplants suit larger varieties with extended growth periods. Spacing: 11in (28cm) between rows, 8-12in (20-30cm) between plants in sandy soils. Soil pH 6-7, fertile, well-drained; avoid waterlogging, use raised beds if necessary; tolerates moderate drought but susceptible to waterlogging. Fertilization follows cabbage recommendations (100-150 lb/acre nitrogen depending on phosphorus levels, matching potassium). Irrigate once or twice weekly based on evapotranspiration. Harvest begins 30-50 days after sowing, once flower buds are fully developed but still unopened; two to three harvests per season, 9,800-16,000 lb/acre yield. PESTS: beet armyworm, fall armyworm, aphids, diamondback moth, green looper caterpillar, white butterfly caterpillar. DISEASES: bacterial soft rot with excessive moisture (over 40% volumetric soil water or 300mm rainfall/month).
1 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 choi sums in the UK?
In Midlands, from early April. In Scotland, wait until early April. 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 choi sums?
Sow early April to late September.
What soil pH do choi sums need?
A pH of about 6–7. That span reflects genuine variation between the authorities we cite rather than a single agreed figure — the References section lists each source's exact range.
What problems affect choi sums?
Our data links 1 disease and 3 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.
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Last verified 2026-08-29
Where To Go From Here
Take this crop from reading into a written plan for your own beds.
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.