Keep the asparagus bed weed free by hand, rather than using a hoe, as the shallow roots are easily damaged. Mulch the bed in late winter with weed-free compost to discourage weeds and to retain moisture. Consider covering the bed from autumn to winter with an opaque weed mat to prevent annual weeds germinating.
In early spring, apply 100g per sq m (3oz per sq yd) of general fertiliser such as Growmore, or fish, blood and bone. If growth is weak, repeat this application once harvesting has finished.
To avoid the top-growth breaking in windy weather and damaging the crowns, use stakes and garden twine to make a ‘fence’ either side of the row for support.
Allow the foliage of your asparagus plants to yellow in autumn before cutting it down to soil level for the winter.
Asparagus plants are either male or female. Male plants produce more and better spears, so many modern cultivars are all-male. If any female plants do appear, they will be noticeable because they produce orange-red berries. If you are growing an all-male cultivar, you will need to remove any female plants as well as any seedlings that appear.
Asparagus grows best in an open, sunny site, but will tolerate dappled shade. It is not fussy about the soil type as long as it is well drained. A pH of 6.5-7.5 is ideal, so more acidic soils may need liming.
Do not replant an old asparagus bed with new asparagus plants. Instead, choose fresh ground to avoid build-up of diseases. Prior to planting, remove any perennial weeds and incorporate at least one bucketful of organic matter, such as garden compost or well-rotted farmyard manure, every square metre (yard).
Asparagus can be grown from seed, but it is easier to plant one-year-old dormant plants, known as crowns, in March. To plant, dig a trench 30cm (12in) wide and 20cm (8in) deep. Work in well-rotted manure to the bottom of the trench and cover the base with a 5cm (2in) layer of the excavated soil.
Make a 10cm-high (4in) ridge of soil down the centre of the trench. Place the crowns on top of this ridge, spacing them 30-45cm (12-18in) apart within the row. Spread the roots evenly and replace the rest of the soil, leaving the bud tips just visible.
Leave 45cm (18in) between rows and stagger the plants between adjacent rows. Water in and mulch with 5cm (2in) of well-rotted manure or other weed-free organic matter.
Slugs and snails: These common pests can cause damage to growing tips, and can defoliate plants. They are most active at night and after rainfall.
Remedy: Protect vulnerable plants by hunting for pests by torchlight on mild, damp night, or by burying beer traps in asparagus beds. You can do this easily by half-filling a jar with beer and sinking into the ground. Chemical pellets should be used with care to prevent accidental poisoning of pets or wildlife. Ones containing ferric phosphate are especially likely to be benign.
Read more information on snails
Read more information on slugs
Asparagus beetle: 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.
Remedy: Destroy overwintering beetles by burning old stems at the end of the season. From late spring, search and destroy the pests by hand. On larger plots, use sprays containing pyrethrum.
Read more information on asparagus beetle
Frost damage: Late frosts can damage the growing tips, leading to distorted or dead spears.
Remedy: Remove any damaged growth and protect the bed with a double layer of horticultural fleece if frost is forecast.
Read more information on frost damage
Do not harvest for the first two years after planting. 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 when they are no more than 18cm (7in) tall. In warm weather, harvest every two to three days for the best quality spears.
‘Backlim’ F1 AGM: An all-male plant with good yields and fat spears.
‘Gijnlim’ F1 AGM: An all-male plant with a high yield of thin spears.
‘Lucullus’ F1 AGM: An all-male plant with a later cropping yield of medium size spears.