Asparagus is easy to grow, producing tasty new shoots from mid-spring to early summer – a seasonal treat to be savoured. These large perennial plants need to be grown in the ground, rather than in containers, where they will crop annually for many years. However, new plants take a couple of years to settle in before you can start harvesting, so patience is required initially.
Jobs to do now
- Cut down growth when stems and foliage turn yellow
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Asparagus is usually grown from crowns, but can also be grown from seed, these plants take one year longer before you can start cropping – three years as opposed to two years grown from crowns.
It is best to choose an all-male F1 hybrid cultivar, as these tend to produce better and stronger spears. Non-hybrid seeds produce female as well as male plants, and these will in turn produce seedlings that will need to be weeded out to prevent competition with the existing plants. Even F1 all-male seeds can produce the occasional female plant.
Sow seeds indoors in February at 13–16°C (55–61°F). Sow them singly into modules filled with seed compost. Harden them off and transplant into their final positions in early June. Prepare the planting site by weeding thoroughly, then dig in at least one bucketful of organic matter, such as garden compost or well-rotted farmyard manure, every square metre/yard.
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 the following March.
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 season.
Weeding and removing female plants
Keep the asparagus bed weed- free, as asparagus plants grow better without competition from weeds. Weed by hand rather than with a hoe, as they have shallow roots that are easily damaged.
If you have any female plants (which produce orange-red berries), you will need to weed out any seedlings. If you’re growing an all-male cultivar, remove any female plants that appear.
Mulch the bed in late winter to discourage weeds and hold moisture in the soil. Consider covering the bed from autumn to winter with a weed-suppressing membrane to prevent annual weeds germinating.
In early spring, apply 100g per sq m (3oz per sq yd) of general fertiliser such as Growmore, or blood, fish and bone. If growth is weak, repeat this application once harvesting has finished.
Asparagus grows into a tall, feathery plant over the summer. To avoid the stems breaking in windy weather and damaging the crown, support plants using stakes and twine to make a ‘fence’ either side of the row.
In autumn, allow the foliage to turn yellow before cutting it down to soil level.
To make more plants, you can divide well-established crowns in late winter or early spring. Do this no more than every three years, as asparagus plants can be slow to settle back in afterwards. Dig up the crown, handling it carefully. Gently prise it apart into several smaller sections, each with several growing points, taking the strongest parts from the edge of the crown. It may be necessary to cut some roots if they can’t be pulled apart. Discard any old, woody parts. Replant the new sections straight away (see Sow and plant, above), with the buds visible at the soil surface.
Asparagus are usually grown from dormant roots, called crowns, available in garden centres and online. Plants are either male or female – male plants produce more and better spears, so many modern cultivars are all-male.
There are several varieties to choose from, producing different flavours, colours or sizes of shoots, and sometimes only male plants.
Look in particular for varieties with an RHS Award of Garden Merit (AGM), which shows they performed well in trials, so should grow and crop reliably – see our list of AGM fruit and veg.
Growing asparagus from crowns
Asparagus is usually planted as one-year-old, dormant plants called crowns. These are widely available in garden centres and from online suppliers in spring. They should be planted straight away, ideally in March. Plant them a dedicated asparagus bed, rather than mixing them with other crops.
It’s best to choose a planting site in full sun, but asparagus will also tolerate dappled shade. Most soil types are suitable, as long as they are well drained. On heavy soils, consider creating raised beds. A pH of 6.5–7.5 is ideal, so more acidic soils may need liming.
When planting asparagus, choose fresh ground to avoid any build-up of pests – don’t replant an old asparagus bed with new asparagus plants.
Weed the ground thoroughly before planting, and dig in at least one bucketful of organic matter, such as garden compost or well-rotted farmyard manure, every square metre/yard.
Then dig a trench 30cm (1ft) wide and 20cm (8in) deep. Fork garden compost or well-rotted manure into the base of the trench and cover with a 5cm (2in) layer of the excavated soil. Make a ridge of soil, 10cm (4in) high, along the centre of the trench.
Place the crowns on top of this ridge, with the growing points or new shoots uppermost, spacing plants 30–45cm (12–18in) apart. Spread the roots out evenly, but handle carefully as they break easily. Mix organic matter into the excavated trench soil, gently return this enriched soil back into the trench, leaving the bud tips just visible. Space rows 45cm (18in) apart and stagger the plants between adjacent rows.
Water in, then mulch with a 5cm (2in) layer of well-rotted manure or garden compost to help supress weeds which can be a problem.
Asparagus is generally easy to grow and crops 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. Frost can also damage young shoots in spring, and plants are prone to rotting in damp soil.
Slugs and snails
These feed on the young seedlings and you'll see the tell tale slime trail on the soil around your crop, as well as on the leaves.
There are many ways to control slugs and snails, including beer traps, sawdust or eggshell barriers, copper tape and biocontrols.
Adult beetles and their larvae strip the outer bark and leaves from the stem. Damaged areas become yellow-brown and dessicated. The black beetles are 6-8mm long with a red thorax and six yellow blotches on the wing cases. Larvae are grey-black in colour, 1cm (½in) long, with three pairs of legs.
Destroy overwintering beetles by burning old stems at the end of the season. From late spring, search and destroy the pests by hand.
Late frosts can damage growth, leading to it dying or being distorted.
Remove any damaged growth and protect the bed with a double layer of horticultural fleece if frost is forecast.
Resist the temptation to harvest newly planted asparagus for the first two years, to let plants get well established. In the third year, harvest spears from mid-April for six weeks. In subsequent years, you can harvest for eight weeks from mid-April.
To harvest, cut individual spears with a sharp knife 2.5cm (1in) below the soil surface when they are no more than 18cm (7in) tall. In warm weather, harvest every two to three days for the best quality spears.
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