Asparagus is the vegetable garden’s long game. You plant it once, a couple of years, and then eat well every spring for a decade or two. It is also one of the first edible things to poke out of the ground, which makes it a fine reward for surviving another Canadian winter.
Need to Know
Life cycle | Long-lived perennial; a healthy bed produces for 15 years or more |
Height and spread | Ferns 48 to 72 inches tall, 24 to 36 inches wide |
Sun | Full sun; in shade spears grow skinny |
Water | Steady moisture for the first two years; established beds are deep rooted and forgiving |
Soil | Deep, loose and well drained; neutral to slightly alkaline (pH 6.5 to 7.5) |
Zone | Zones 2 to 8 |
Harvest time | Spring, for up to 6 to 8 weeks once established; nothing in the first year |
Frost tolerance | Dormant crowns hardy to Zone 2; emerged spears freeze at about −3 Celsius |
Good to Know
Plant family | Asparagaceae (asparagus family) |
Native status | Non-native, from the Mediterranean region; birds carry seed from female plants into ditches and natural areas |
Start method | Crowns or seed |
Planting | Crowns in early spring, as soon as the soil can be worked; set seed-grown transplants out after the last frost |
Starting from seed | Start indoors in late winter in warm soil, around 25 Celsius; adds about a year before the first harvest |
Seed depth | About ¼ inch |
Crown depth | Trench 6 to 8 inches deep, filled gradually as shoots grow |
Spacing | 12 to 18 inches apart, rows 36 to 60 inches apart |
Cultivars | All-male hybrids such as ‘Guelph Millennium’ and the Jersey series, available as crowns or seed |
Maintenance | Weed by hand, top dress with compost, leave ferns standing until they yellow |
Pests and diseases | Common and spotted asparagus beetles; Fusarium crown and root rot; rust |
Pick the boys
Asparagus plants are either male or female. Females put their energy into red berries and seed, while males put theirs into spears, so male plants generally outyield females. The berries cause other trouble too. Birds scatter the seed, and the seedlings crowd the bed and wander off into ditches. The larvae of the spotted asparagus beetle also develop inside those berries, so an all-male bed gives them nowhere to raise a family.
All-male hybrids solve all three problems. ‘Guelph Millennium’, bred at the University of Guelph, is a strong choice in cold regions. In Ontario field trials it built up its freezing tolerance earlier in the fall than a California cultivar, and it held onto that tolerance later into spring, when freeze and thaw cycles do their damage. It was also selected for rust tolerance.
Dig deep, fill slowly
Most gardeners start with crowns: one-year-old root systems that look like a pale octopus that has seen things. Dig a trench 6 to 8 inches deep, spread the roots, and cover the crowns with about 2 inches of soil. Fill the trench gradually as the shoots grow, until it is level with the ground by the end of the first season.
Depth is a trade-off. Deeper crowns send up spears later in spring, which makes them less likely to be caught by a late frost. Shallow crowns come up earlier and take their chances. Crowns also shift over the years: shallow ones settle deeper and deep ones rise, so the plant will end up where it needs to be.
Buy plump, fresh crowns from a reputable supplier. Fusarium crown and root rot is one of the main reasons asparagus beds decline, and it can arrive on the crowns themselves.
The waiting game
The first year after planting, harvest nothing. Every spear left alone becomes a fern, and those ferns stock the roots. Research on young plants found that stored carbohydrate below ground increased more than 30 times between planting and the end of the second season. Patience pays in spears, too: beds first harvested one year after planting produced less than beds left alone for two.
In the second spring, admire the spears or take only a taste from the strongest plants. Start harvesting properly in the third spring, keep that first season short, and work up to a full run as the spears stay thick.
Harvest
An established bed can usually be picked for 6 to 8 weeks. Stop sooner if most new spears come up thin and spindly, since spears shrink over the season as the roots draw down their stored energy. Stopping on time leaves the ferns the rest of the summer to refill the tank, and next spring’s harvest depends on how full it gets. Young beds get a shorter season: two or three weeks in the first harvest year, building up from there.
Spring frost is the main hazard of harvest season. In one field study, spears froze between −3 and −5 Celsius, and a night at −4.7 killed every emerged green spear. The crown simply sends up more, but if frost is forecast, pick any spears tall enough and cover the bed overnight. Frosted spears go limp and dark; snap them off and compost them.
Let the ferns do their job
After harvest, the remaining spears grow into tall, feathery ferns handsome enough for a flower border. This is where next year’s crop is made. The ferns replenish the roots after the spring drawdown, so leave them standing until they yellow in fall.
Asparagus beetles spend winter as adults tucked inside hollow asparagus stems and garden debris. Once the ferns are brown, cut the old stalks and remove them, either in late fall or in early spring before new spears break ground.
Beetles in party clothes
Two European beetles specialize in asparagus. They reached Canada by 1899, when the first specimens turned up in Queenston, Ontario. The common asparagus beetle is the bigger problem of the two: small, colourful and oddly glamorous for something so destructive. Adults and their greyish larvae chew spears and strip ferns, with up to three generations a year. The spotted asparagus beetle is orange with black spots, and its larvae feed only in berries.
When disturbed, common asparagus beetles drop to the ground and play dead, so hold a container underneath before you go after them. You have allies, too. A tiny parasitic wasp attacks the eggs and has killed up to 71 per cent of them in some fields, and lady beetles eat both eggs and larvae. Handpicking and a tidy bed are usually enough to keep the damage tolerable.
Images
References
Drost, D. (2023). Asparagus breeding: Future research needs for sustainable production. Frontiers in Plant Science, 14, 1148312.
Haynes, R. J. (1987). Accumulation of dry matter and changes in storage carbohydrate and amino acid content in the first 2 years of asparagus growth. Scientia Horticulturae, 32(1-2), 17-23.
Makus, D. J., Anderson, J. A., & Springer, T. L. (1994). Freeze avoidance in green and white asparagus spears. Scientia Horticulturae, 59(1), 1-9.
Morrison, W. R., III, & Szendrei, Z. (2014). The common asparagus beetle and spotted asparagus beetle (Coleoptera: Chrysomelidae): Identification, ecology, and management. Journal of Integrated Pest Management, 5(3), B1-B6.
Panjtandoust, M., & Wolyn, D. J. (2016). Asparagus cultivars with varying adaptation to southern Ontario differ for induction of freezing tolerance in the fall. Canadian Journal of Plant Science.
Further reading
Asparagus, Gardening at USask. Prairie-specific advice on planting, hardiness and growing white asparagus.
Asparagus, Grow with USask. A printable guide with good cautions about Fusarium and buying crowns.
Asparagus: Beyond Millennium, Ontario Agricultural College. The story behind ‘Guelph Millennium’ and the breeding work that followed.
Asparagus Beetles, University of Minnesota Extension. Clear photos of adults, larvae and eggs, plus home garden controls.
How to Grow Asparagus in Your Garden, Utah State University Extension. A thorough, practical guide from a cold-winter climate.