How to grow asparagus

Asparagus is a long-term crop, with plants lasting up to 20 years. They are usually grown from crowns, or one-year-old dormant plants, but can also be grown from seed. They need a sheltered site with free-draining soil, ideally in a bed just for asparagus. If you’re lucky enough to already have an established asparagus bed, then little maintenance is required, apart from weeding,

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

Asparagus is usually grown from ‘crowns’, or dormant roots – this is the easiest and fastest option, as little maintenance is required and harvesting can begin after two years. Asparagus can also be grown from seed, but seedlings need more looking after and take longer to get established, so you should wait three years before harvesting. Still, seeds are cheaper than crowns.

Asparagus plants are either male or female – male plants produce more and better spears, so many modern cultivars are all-male. Most crowns offered for sale are all-male F1 hybrids.  

Older, non-hybrid cultivars produce both male and (less productive) female plants. The female plants also produce seedlings that need to be weeded out to prevent competition with the existing plants. Even all-male F1 seeds can produce the occasional female plant. 

As asparagus plants can crop well for around 20 years, it’s worth choosing your planting site carefully and preparing the ground well.  

This long-term crop needs a dedicated, permanent bed of several square metres/yards, depending on how many plants you want to grow (space them up to 45cm/18in apart). It’s best not to grow other plants or crops among asparagus, and don’t replant an old asparagus bed with new asparagus plants – choose fresh ground, to avoid any build-up of pests. 

A planting site in full sun is preferable, but asparagus will also tolerate dappled shade. Most soil types are suitable, as long as they’re well drained. If you have heavy soil, make a raised bed to provide better drainage. A pH of 6.5–7.5 is ideal, so more acidic soil may need liming. 

Weed the bed thoroughly before planting, then dig in at least a bucketful of organic matter, such as garden compost or well-rotted manure, per square metre/yard. 

Sow seeds indoors in February at 13–16°C (55–61°F). Fill a modular tray or several small pots with seed compost and sow one seed into each. Keep the seedlings warm and well watered, in a bright location. Start to harden them off after the last frost and transplant into their final positions in early June – see Preparing the ground and Planting asparagus crowns, above.

Alternatively, sow outside in March or April, in drills 2.5cm (1in) deep and 30–45cm (12–18in) apart. Thin the seedlings to 15cm (6in) apart and protect from slugs and snails. Transplant them to their final positions, into well-prepared ground, the following March  – see Preparing the ground and Planting asparagus crowns, above, for full details.

To grow well, asparagus plants should be fed well and kept weed free. Plants may need supporting as they grow quite tall, and should be cut down at the end of the growing season - allow the foliage to turn yellow before cutting all the stems down to the base.

Asparagus is generally trouble free, cropping reliably every spring. However, there are a few pests that can damage plants and lead to reduced harvests, the principal culprits being slugs, snails and asparagus beetles. Late frosts can also damage young shoots in spring, and plants are prone to rotting in damp soil.