Germination temperature
Warm: about 21-30 °C (70-86 °F). Research found alternating 20/30 °C or a constant 30 °C (86 °F) best.
Vegetable growing guide
Asparagus seed is slow to germinate and the bed takes about three years to give a full harvest, but one sowing can then crop for up to 20 years. This guide covers soaking and sowing, raising crowns, and what to do about male and female plants.
Warm: about 21-30 °C (70-86 °F). Research found alternating 20/30 °C or a constant 30 °C (86 °F) best.
About 6 mm-2.5 cm (1/4-1 in); deeper in light soil outdoors, shallower in pots.
Slow: up to about 3 weeks even when warm, longer in cool soil.
Not needed for germination; full sun for the ferns afterwards.
Soak the seed in water for 24 hours before sowing.
Both. Indoor transplants (12-15 weeks old) or one-year crowns from a nursery bed.
Use plump black seed. When saving your own, pick berries that are more red than green: in a Spanish study all seed became germinable once red colour exceeded green on the fruit.
Not needed. The seed coat is hard but takes up water during soaking.
Not needed. Asparagus germinates best warm; cold treatment does not make up for cool soil.
Recommended. In a trial with asparagus hybrids, soaking the seed in water for one day before sowing significantly improved seedling emergence. Sow straight after soaking and do not let the seed dry out again.
Keep pots at 24-27 °C (75-80 °F) until seedlings appear. In laboratory tests of 5-35 °C, germination was most favourable at 20 °C for 12 hours alternating with 30 °C for 12 hours, and at a constant 30 °C (86 °F). Sowing at 13-16 °C (55-61 °F) also works but is slower.
Indoors about 6 mm-2 cm (1/4-3/4 in) deep, one or two seeds per pot or module. Outdoors sow in drills about 2-2.5 cm (3/4-1 in) deep, rows 30-45 cm (12-18 in) apart, and thin to 15 cm (6 in).
A sterile seed compost in deep modules or 7-8 cm (3 in) pots to reduce transplant shock. In the bed, asparagus needs deep, very well-drained soil at about pH 6.5-7.5.
Keep evenly moist. Germination is slow, so the compost must not dry out for the whole period.
Not needed to germinate. Move pots into bright light as soon as the first thin shoots appear, then grow at 21-24 °C (70-75 °F) by day and about 18 °C (65 °F) at night.
Up to about 21 days at 21-27 °C (70-80 °F); asparagus is one of the slowest vegetables to come up, so do not discard pots too early.
Indoor seedlings need 12-15 weeks before planting out after the last frost. Direct-sown seedlings are grown for one year in a nursery row and moved as dormant one-year crowns.
Dig a trench 15-20 cm (6-8 in) deep, set crowns about 30-45 cm (12-18 in) apart with roots spread over a low ridge, cover with about 5 cm (2 in) of soil and fill the trench gradually as the shoots grow.
Do not cut spears in the first two seasons; the ferns feed the crown. From seed, the RHS advises waiting until the third year. Harvest lightly for about 3 weeks the first time, then for 6-8 weeks a year from the following season. A well-kept bed can crop for about 20 years.
Cause: asparagus is naturally slow, and cool compost slows it further. Fix: keep pots at 24-27 °C (75-80 °F) and moist, and wait at least three weeks before resowing.
Cause: waterlogged soil, Fusarium wilt and root rot. Fix: plant in raised or very well-drained beds, which matters in heavy monsoon rain.
Cause: common and spotted asparagus beetles. Fix: hand-pick adults and larvae, and clear old ferns at the end of the season.
Cause: asparagus rust, which weakens crowns and lowers next year's yield. Fix: grow resistant varieties where available, keep good air flow and remove infected ferns.
Cause: female plants drop seed from their red berries. Fix: pull these seedlings early; they crowd the bed and are not worth keeping.
Asparagus is dioecious: each plant is male or female, roughly 50:50 from open-pollinated seed such as Mary Washington. Male plants give 25-40% more spears, while female plants give fewer but thicker spears and set red berries. You can tell them apart only once they flower; removing berry-bearing females is optional, but it saves the plants' energy and stops self-seeding.
The bed will stay for many years, so remove perennial weeds and work in organic matter before planting. Do not grow asparagus where water stands after rain.
After harvest, let the spears grow into ferns until they yellow. They refill the crown for next year's spears.
Asparagus is a temperate-zone perennial, so it is most at home in the hills. In warmer areas raise seedlings in the cooler months and keep crowns out of waterlogged soil during the monsoon.
Sow Mary Washington asparagus seed once and start a bed that can crop for many years.
Yes. A 24-hour soak in water improved seedling emergence in trials. Sow the seed while it is still moist and keep it warm, ideally 24-27 °C (75-80 °F).
About three years. Raise seedlings or one-year crowns, do not cut spears in the first two seasons, take a light harvest of about 3 weeks in the third year and 6-8 weeks a year after that.
No. Spears come from both. Male plants yield more and do not self-seed; female plants give thicker spears and red berries. Seed of open-pollinated Mary Washington produces both, about half each.
Asparagus is naturally slow and can take up to about three weeks even in warm compost. Cool conditions slow it more, so keep pots warm and moist and be patient.