Site and soil requirements
Do not replant an old asparagus bed with new asparagus plants. Choose fresh ground to avoid build-up of diseases. An open, sunny site is best, but asparagus will tolerate dappled shade.
Asparagus grows on most soil types provided 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.
Clear the ground of perennial weeds and incorporate at least one bucketful of organic matter such as garden compost or well-rotted farmyard manure every square metre (yard).
Most gardeners plant one-year-old dormant plants called ‘crowns’ in March, although asparagus can also be raised from seed (see the propagation section below).
To plant asparagus crowns:
- Dig a trench 30cm (1ft) wide and 20cm (8in) deep. Work in well-rotted manure to the bottom of the trench and cover the base of the trench 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, with the growing points or new shoots uppermost. Space them 30-45cm (1ft-18in) apart within the row. Spread the roots evenly but handle carefully as they easily break. 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
Keep the asparagus bed weed free. Weed by hand rather than with a hoe, as the shallow roots of the asparagus plants are easily damaged.
Mulch the bed in late winter 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 fertilizer such as Growmore, or fish, blood and bone. If growth is weak, repeat this application once harvesting has finished.
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 form.
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.