Harvesting

It’s vital when growing your own asparagus to allow plants sufficient time to establish before you begin to harvest. For plants bought and planted as bare root crowns, this means leaving them untouched for two years, beginning to cut spears only in year three. For plants grown from seed, add a year on to this.

Traditionally, the asparagus harvesting period starts on St Georges day (late April). In the first year of harvesting, cut spears every two to three days for up to six weeks. In subsequent years you can continue until Midsummers Day (late June). It is important not to keep cutting beyond this, as the plants need time to grow freely and build up energy reserves for the following year’s crop.

Spears are ready to harvest when they are around 18cm tall. Use a sharp knife to cut them a couple of centimetres below the surface of the soil. The best flavour comes from eating these fresh, though you can also store in the fridge for a few days.

Staking and pruning

After harvesting has finished, asparagus grow into tall, feathery plants. These are likely to need staking to prevent windy weather blowing them over and causing damage to the crown. The simplest way to do this is using bamboo canes and string to make a ‘fence’ on either side of each row.

When it comes to pruning, asparagus is very simple. Simply cut back each autumn once plants begin to turn yellow – taking the whole lot down to ground level.

Watering

Asparagus plants should be watered on initial planting, and then regularly throughout their first growing season in the ground. After this, they are relatively drought hardy and will need watering only in prolonged periods of hot, dry weather.

Asparagus in a container will need to be watered regularly throughout every growing season. Allow the top few centimetres of compost to dry out between soakings – a finger wiggled down until moisture can be felt is the best way of checking this. From mid-autumn onwards the UK weather tends to take over watering needs, though do remember to step in in the event of an unseasonably dry spell.

Feeding

Asparagus in the ground will thank you for a ready supply of nutrients – best supplied in two forms.

The first is a mulch of well-rotted organic matter in late winter, which not only adds goodness to the soil but also helps lock in moisture and prevent the germination of annual weeds (once established these are very difficult to remove from amongst the roots of asparagus).

The second is an early spring application of a high potassium general fertiliser such as Vitax Q4, used at a rate of two handfuls per square metre. You can also repeat this after harvesting in any year when growth has seemed lacklustre.

Container-grown asparagus should be fed with a balanced liquid feed once a month throughout the growing season (roughly March to September).

Cold Protection

The biggest threat to the winter survival of asparagus is not cold, but wet. Drainage is therefore key – which is where choosing a well-draining spot and planting on a ridge come in (see above).

Young asparagus spears may be damaged by a late frost. A thick, late winter mulch will help protect against this, though where it does occur simply remove any blackened, shrivelled spears at the base with a sharp knife.

Pests and Diseases

Asparagus beetle is the key pest to look out for on this plant. In larval stage it looks like a grey grub, and in adulthood it is a black beetle with yellow blotches and a red thorax. Both stages eat asparagus foliage, as well as the ‘bark’ of the stems.

Small populations tend not to cause too much overall damage and are best tolerated. Larger numbers can defoliate plants to the point of reducing their vigour and yield the following year. As ever, we encourage natural, sustainable methods of control, including handpicking the larvae off the plant in late spring, and encouraging natural predators into the garden. These include birds, frogs, ground beetles, and social wasps. Removing and disposing of pruned plant material in autumn is also advisable to interrupt the life cycle of overwintering pests.

Where infestations persist, a biological control is available containing the nematode Steinernema carpocapsae (a microscopic parasitic worm).