Plant asparagus crowns about 4 weeks before your last frost, 15 inches apart in rows 48 inches apart, and take no harvest in year one — a light cut in year two, a full one from year three. Good companions are tomatoes, basil and parsley; keep onions and garlic out.
Asparagus is a twenty-year decision
Everything else on this page follows from that. Asparagus is a perennial: you dig the bed once, plant crowns once, and then it produces for fifteen to twenty years in the same spot.
That changes what matters. Siting, drainage and weed control before planting are worth far more effort than they would be for an annual crop, because you cannot fix them later without destroying the bed. Pick a spot at the edge of the garden where nothing will need to be dug around it, and get the perennial weeds out before a single crown goes in.
The other consequence is patience. Nothing is harvested in the planting year. A light cut of about two weeks comes in year two, and a full six to eight week harvest from year three. Cutting earlier or longer than that starves the crown and shortens the bed's whole life — this is the one mistake that does lasting damage.
Asparagus companion plants
Good neighbours, and why.
Tomatoes are the classic pairing and one of the few with a plausible mechanism in both directions: tomatoes produce solanine, which is claimed to deter asparagus beetle, while asparagus roots release a compound reported to suppress root-knot nematodes affecting tomatoes. The evidence is better than most companion folklore, though not conclusive. Practically, they also occupy different times of year — asparagus is cut before tomatoes take over the space.
Basil and parsley are small, shallow and harvested by hand rather than dug, which is the real test for anything grown in an asparagus bed. They also flower and draw predatory insects.
Bad neighbours, and why.
Onions, garlic and leeks are the traditional exclusion and they compete directly for the same root zone. Potatoes fail a different test: they demand deep digging every year, and an asparagus crown sits only a few inches down. Anything that needs annual cultivation is wrong here, whatever its chemistry.
Planting crowns
Buy one-year-old crowns. Two-year-old crowns cost more, transplant worse, and do not actually fruit sooner.
Dig a trench about 8 inches deep and 12 inches wide. Mound a low ridge of soil along the bottom, set each crown on the ridge with its roots draped down both sides like a spider, and cover with about 2 inches of soil.
Then backfill gradually, not all at once. As the spears grow through, add more soil in stages over the season until the trench is level. Filling it in immediately buries the crown too deep to push through.
How far apart to plant asparagus
15 inches between crowns, 48 inches between rows.
The wide row spacing reflects what the plant becomes: by midsummer the ferns are four or five feet tall and need air moving through them. A crowded bed gets fungal disease.
Use the plant spacing calculator to work out how many crowns a bed of a given length takes. Twenty-five crowns is a reasonable starting bed for a household.
When to plant
About four weeks before your last frost, while the crowns are still dormant and the soil is workable. They go in early — the crown establishes roots before it is asked to produce anything above ground.
Autumn planting works in mild areas. The planting date calculator works the spring date out from your own frost dates.
Soil, water and feeding
Free-draining soil above everything else. Asparagus crowns rot in ground that sits wet in winter, and that is what usually kills a bed. They prefer a pH near neutral, around 6.5 to 7.0, which is higher than most vegetables — if your soil is acid, how to raise soil pH covers the correction, and it is best done before planting since you cannot work lime deeply into an established bed.
Water about an inch a week in the first two years while the root system establishes. A mature bed is fairly drought-tolerant.
Feed after the cutting season, not before. Once you stop harvesting, the ferns run all summer building reserves for next year's spears, and that is the growth worth supporting. A spring feed before cutting mostly feeds the weeds you cannot hoe out without damaging crowns. How to add nitrogen to soil covers which materials release on a useful timescale.
Harvest
From year three, cut for six to eight weeks and then stop.
Cut or snap spears at ground level when they are about 7 to 9 inches tall and the tip is still tight. Once the tip opens into a fern, the spear is woody. In warm weather a bed needs picking daily — spears go from cuttable to too far in about two days.
Stopping on time is the whole discipline. When spears start coming through noticeably thinner, the crown is running down its reserves and the harvest is over for the year. Let everything after that grow into ferns, and leave the ferns standing until they yellow in autumn before cutting them down.
Transplanting an established bed
It can be done, and it costs a year.
Move crowns in early spring while fully dormant, before any spear shows. Lift as much root as you can — the roots run much wider than the crown suggests — and replant immediately at the same depth in prepared ground. Do not let the roots dry out between lifting and replanting.
Expect little or nothing from the following season while the plant re-establishes. This is worth doing to rescue a bed in genuinely the wrong place, and not worth doing to tidy the garden.
Common problems
Thin spears. Either the bed is young, or it has been over-cut. Stop harvesting and let the ferns run — a crown rebuilds over a season or two if you let it.
Asparagus beetle. Small, dark, striped beetles that chew spears and ferns. Hand-picking is effective on a garden-scale bed; clearing the old ferns away in autumn removes overwintering sites.
Weeds in the bed. The recurring problem of a perennial crop, because you cannot dig. Mulch heavily and hand-weed, and get the perennial weeds out before planting.
Crowns rotting. Wet ground. Not fixable in place — the answer is drainage or a raised bed, decided before planting.
Asparagus shares its bed well with tomatoes, and its preference for a nearly neutral pH with cabbage and the other brassicas.