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,
Asparagus is harvested for about eight weeks in spring and early summer, when little else is cropping, making it all the more special. Asparagus spears are also quite expensive to buy, so are well worth growing if you have the space. An established plant should produce about 10 spears per season.
After the harvesting period, shoots should be left to grow into tall ferny plants over the rest of the summer. Then simply cut them down to the ground in autumn, and they will re-sprout in spring, ready for harvesting again.
Month by Month
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.
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.
What and where to buy
Seeds can be bought in garden centres and from online seed retailers.
Preparing the Ground
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.
Planting asparagus crowns
Dig a trench 30cm (1ft) wide and 20cm (8in) deep. Fork garden compost or well-rotted manure into the base, then cover with a 5cm (2in) layer of the excavated soil. Make a ridge of soil along the centre of the trench, 10cm (4in) high.
Place the crowns on top of this ridge, with the growing points or new shoots uppermost, spacing them 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, then 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 suppress weeds. The bed needs to be kept weed free, as asparagus grows best without competition from other plants.
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.
Weeding and removing female plants
Keep the asparagus bed weed free, as asparagus grows better without competition from other plants. 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), weed out any seedlings they produce. If you’re growing an all-male cultivar, you may still find the occasional female plant, which you should remove.
Water new asparagus plants regularly throughout their first summer. Once established, asparagus plants are drought tolerant, so only need watering in long dry spells.
Mulch the bed in late winter to discourage weeds and hold moisture in the soil. Consider covering the bed from autumn to winter with weed-suppressing membrane to prevent annual weeds germinating. It is important not to let weeds get established.
In early spring, apply a high potassium general fertiliser, such as Vitax Q4, at a rate of two handfuls per square metre/yard. If growth in spring is weak, repeat this application once harvesting has finished.
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 Sowing and planting, above), with the buds visible at the soil surface.
To harvest, cut individual spears with a sharp knife 2.5cm (1in) below the soil surface when they’re no more than 18cm (7in) tall or about finger thickness. In warm weather, harvest every two to three days for the best quality spears – they grow quickly and soon turn woody. Regular harvesting also encourages more new shoots to be produced. Expect an established plant to provide about 10 spears over the harvesting period.
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.
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