Grain Amaranth (Amaranthus hypochondriacus)
Also known as: Prince's feather · 13 sources cited · Verified
The short answer
- Ready in
- 90–100 days
- Site
- soil pH 6.5–7.5
- Biggest risk
- Damping-off
In the UK, grain amaranth are ready to harvest 90–100 days after planting.
Grain amaranth (Amaranthus hypochondriacus) — Annual.
This crop carries an unusually heavy problem load: 4 diseases, 3 pests and 0 nutrient issues are documented for it, so most of the effort in growing it well goes into prevention.
Core growing advice on this page is checked against named horticultural and university-extension sources — see References.
Diseases
Pests
Quick Facts
| Factor | Value |
|---|---|
| Soil pH | 6.5 - 7.5 |
| Germination temp | 18C |
| Optimal growing temp | 19-23C |
| Minimum survivable temp | 0C |
| Time to harvest | 90-100 days |
| Soil texture | Loam preferred; adapted to a range of soils per genus-level RHS guidance |
| Drainage | Moist, well-drained, humus-rich |
| Lifecycle | Annual. |
| Edible parts | seeds, leaves |
At a Glance
When to plant in the USA
United States. Amaranth is timed by soil temperature at sowing and by frost at harvest — the reverse of most crops, where frost is only ever the enemy. Sow once soil reaches at least 65F, which in practice means late May or early June; Purdue notes early-season frost damage is not a problem precisely because sowing is that late, so there is nothing to gain by rushing. Seed goes no deeper than 1/2 in — it is very fine, and a firm, level seedbed matters more than depth. Soil pH 6.5-7.5. At the other end, a killing frost must arrive before harvest, followed by about a week of good drying weather: harvesting earlier is impractical because the grain is still too wet to store. The tension to manage is that seed starts shattering before that frost comes, so grain is lost whichever way you go. Dry to about 11% moisture for storage.
Soil & Growing Conditions
Growth Stages
| Stage | BBCH | Notes |
|---|---|---|
| Establishment | 0 | Grain amaranth is grown from its very small seed. Sow no more than 0.5–1cm (¼–½in) deep — Purdue NewCROP and UIC Heritage Garden both say no more than ¼–½in — onto a firm, warm, moist surface, sowing thinly and barely covering it. It is a warm-season crop that will not survive frost (RHS), so in the UK start seed under cover in warmth in spring and plant out only once frost risk has passed, or sow outdoors once the soil has warmed to about 18°C (65°F); Purdue gives late May–early June at soil ≥65°F, with best germination at 18–24°C. Space rows about 45–60cm (18–24in) apart (UIC) and thin seedlings so plants stand roughly 30–45cm apart, matching their eventual 0.5–1.5m spread (RHS). |
| Vegetative Growth | 3 | Plants grow quickly into upright, broad-leaved bushes typically 1.5–2m (5–7ft) tall (RHS lists 1–1.5m+ depending on variety). Grow in full sun on a warm, sheltered site in moderately fertile, humus-rich, well-drained soil — RHS notes that adding organic matter promotes strong growth, and that plants dislike cold, wet soils and shade. Keep young plants weed-free while they establish and water in dry spells to keep growth steady. Only moderate nitrogen is needed: Purdue/Wisconsin scale fertiliser to soil organic matter (more N on poor soils, less on rich), and excess nitrogen encourages soft leafy growth at the expense of grain. |
| Flowering | 6 | From midsummer to early autumn the plants produce dense, erect or drooping catkin-like flower panicles in shades of green, gold, red or purple (RHS). The seed heads are large — UIC notes a single head can hold up to about 60,000 tiny seeds. Keep plants adequately spaced and weed-free for good air circulation, which RHS notes helps prevent foliar disease at this stage. |
| Fruit Development | 7 | After flowering the panicles fill with grain — Amaranthus hypochondriacus is one of the principal grain amaranth species. Seed typically ripens about three months (roughly 90–100 days) from sowing (UIC; RHS). Watch for the seed heads to change colour and begin to dry down as the grain matures. |
| Ripening / Harvest | 8 | Harvest once the seed heads are dry and the grain threshes freely: gently but briskly rub or shake a flower head between your hands and see if the seeds fall readily (UIC). Work in dry weather — commercially the crop is cut in dry weather three to seven days after the first frost, once the heads have dried (UIC; Purdue: a killing frost followed by a week of good drying weather). Cut the heads, dry them fully, then rub out the seed and winnow off the chaff. Store the cleaned grain dry — Purdue gives about 11% moisture maximum — in an airtight container. |
| Senescence / Dormancy | 9 | Grown as a warm-season annual, the plant dies back after seeding or is killed by the first hard frost. Save some clean, dry seed for the following year; note that plants self-seed readily if the heads are left to shatter in the garden. |
Harvest & Storage
Grain Amaranth, Seed to Harvest
References
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Directly fetched and verified (not a blended search summary). Field survey of 43 peri-urban Amaranthus farms; identifies anthracnose (Colletotrichum), wet rot (Choanephora cucurbitarum), wilting/damping-off (Fusarium, associated genera), and stem canker (Phoma/Alternaria) as the major fungal diseases.
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country=US
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country=INTL
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country=INTL
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States Amaranth = Amaranthus caudatus, common name "Pigweed", cited to an RHS URL. That URL was checked this session and returns empty/dead -- citation hygiene issue, matches Phase 0's general finding about this document. Preserved for provenance of the dispute, not counted as an independent verification source.
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country=US
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country=UK
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Genus-level cultivation guide; used to supplement species pages lacking their own cultivation block (esp. A. hypochondriacus).
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Tier 1. Short-season field study, the closest published analogue to Prairie conditions: amaranth sown at Prosper, North Dakota in the first week of June; first seed shatter 15 September (1993) and 14 October (1994); harvest before a killing frost was not feasible because of high moisture in the sample; grain yield decreased as harvest was delayed beyond first seed shatter, especially after a killing frost; amaranth should be harvested as soon as possible after a killing frost to reduce yield loss and maximise seed germination; the cooler 1993 season yielded 20-40% of 1994 at the same harvest dates.
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Specifically about vegetable amaranth (A. tricolor), a DIFFERENT species from A. caudatus/cruentus/hypochondriacus. Used only for: (a) confirming caudatus/cruentus/hypochondriacus are the grain-type Amaranthus species, and (b) pest genera (stem weevil, leaf caterpillars) that the source itself sources from CABI as genus-wide. Explicitly NOT used for A.-tricolor-specific growing-condition numbers.
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country=US
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Addresses grain amaranth production generally (primarily A. hypochondriacus / A. cruentus, the commercial US grain species); not species-disambiguated in the source itself.
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country=INTL
13 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
How long do grain amaranth take to grow?
Typically 90–100 days, depending on cultivar and growing conditions.
What soil pH do grain amaranth need?
A pH of about 6.5–7.5. 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 grain amaranth?
Our data links 4 diseases 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
Almost everything on this page resolves to your own frost dates rather than the calendar — the last spring frost moves by roughly two months between zone 3 and zone 10. The USA Garden Planner works from your zone so the timing is already decided before the season starts.
Get the USA Garden Planner →Instant PDF download · Written for US growing conditions
Last verified 2026-07-27
Where To Go From Here
Take this crop from reading into a written plan for your own beds.
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