Safflower (Carthamus tinctorius)
3 sources cited · Verified
The short answer
- Plant
- Early March to late May
- Site
- 6+ hours of sun, soil pH 6–7.5
- Biggest risk
- Alternaria leaf spot of safflower
In the UK, safflowers go in the ground early March to late May.
Safflowers (Carthamus tinctorius) — Annual (RHS.
Timing is the decision that matters most in the UK: sowing early March, and that same window applies across all 4 regions covered here.
Core growing advice on this page is checked against named horticultural sources — see References.
Regional Planting Calendar
| Region | Sow |
|---|---|
| Southern England | early March to late May |
| Midlands | early March to late May |
| Northern England | early March to late May |
| Scotland | early March to late May |
Southern England - detail & sources
RHS gives a UK-wide rule -- sow by seed in gentle heat from early to late spring -- with no region-specific dates. Applied as one UK-wide window (roughly early March to late May) across all four sub-regions rather than inventing a gradient RHS does not support.
Midlands - detail & sources
RHS gives a UK-wide rule -- sow by seed in gentle heat from early to late spring -- with no region-specific dates. Applied as one UK-wide window (roughly early March to late May) across all four sub-regions rather than inventing a gradient RHS does not support.
Northern England - detail & sources
RHS gives a UK-wide rule -- sow by seed in gentle heat from early to late spring -- with no region-specific dates. Applied as one UK-wide window (roughly early March to late May) across all four sub-regions rather than inventing a gradient RHS does not support.
Scotland - detail & sources
RHS gives a UK-wide rule -- sow by seed in gentle heat from early to late spring -- with no region-specific dates. Applied as one UK-wide window (roughly early March to late May) across all four sub-regions rather than inventing a gradient RHS does not support.
Quick Facts
At a Glance
Soil & Growing Conditions
Growth Stages
Harvest & Storage
When to pick: Ready to harvest when most of the leaves turn brown and the seeds are white and hand-thresh easily; typically early to late September in the northern US (Wisconsin Extension). Takes 110-140 days from planting to maturity (Wisconsin Extension; NDSU).
Diseases
Pests
Safflower Photo Gallery
References
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In North Dakota, safflower normally requires 110-120 days from emergence to maturity. Grows best on deep, fertile, well-drained loam soils with good water-holding capacity; soil pH of 6.0 appears adequate. Planting depths of 1-1.5in are optimum, do not seed deeper than 2in. Taproot can penetrate 8-10ft in deep soils.
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Erect branching annual to 60cm, spiny leaves, thistle-like orange/yellow flower-heads with prominent green bracts. Propagate by seed sown in gentle heat, early to late spring. Grow in any light, well-drained soil in full sun; tolerates acid/alkaline/neutral pH. Hardiness H5 (-15 to -10C). Height 0.5-1m, spread 0.1-0.5m. Generally pest-free and disease-free (garden-scale UK growing). Native to Western Asia. Family Asteraceae.
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Deep, fertile, well-drained soil with high water-holding capacity; soil pH of 6.0 adequate; high soil salinity reduces germination. Planting depth 1-1.5in. Seeding rate 20-25 lb/acre dryland, 25-35 lb/acre irrigated. Row spacing 6-7in, ~6 plants/sq ft. Plant late April to early May in the Upper Midwest; risk if planted after mid-May. Days to maturity 110-140. Tolerates temperatures as low as 20F at the rosette stage, but is very frost-sensitive after stem elongation. Needs a minimum 120 frost-free days and 2200 growing degree days; not recommended above 15in annual precipitation; prefers warm, sunny, dry conditions during flowering and seed-fill. Diseases: Alternaria leaf spot (Alternaria carthami) causing large, brown, irregular leaf spots; bacterial blight (Pseudomonas syringae) with yellow-green margined lesions; Sclerotinia and Botrytis flower-head rots; various root rots and wilts. Pests: wireworms, cutworms and seed corn maggots damage seeds/seedlings; thrips, lygus bugs, grasshoppers and sunflower moths damage later growth -- sunflower moth can cause 20-30% loss if damage occurs early in flowering. Harvest when most leaves turn brown and seeds are white and hand-thresh easily; early to late September in the Upper Midwest.
3 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 safflowers in the UK?
In Southern England, from early March. In Scotland, wait until early March. 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 safflowers?
Sow early March to late May.
What soil pH do safflowers need?
A pH of about 6–7.5. 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 safflowers?
Our data links 2 diseases and 6 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.
Get the UK Garden Planner →Instant PDF download · Written for UK growing conditions
Last verified 2026-09-03
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.