Growing Asparagus

Asparagus officinale

Garden asparagus has been derived from the wild plant of the same name and is recorded as a cultivated plant in Britain from the early seventeenth century. It is a hardy perennial which is grown for the young, tender shoots or ‘spears’ which are cut when they are 15 to 25cm (6 to 10in) long. These green shoots have either a green or, more usually, a purple tip and a white base where the light has been excluded by the soil. Asparagus, when grown traditionally, is blanched. Soil from the pathways is continually thrown over the developing shoots to produce a long tender white area at the base. This is laborious and, more recently, crops have been grown ‘on the flat’.

Asparagus beds can have a productive life lasting many years provided they are managed correctly and grown on a suitable site.

Asparagus is not difficult to grow if you follow the recommendations and the rewards are great. The ‘spears’ are ready for cutting from late April until mid-June. They are tied in bundles and then cooked standing upright in a little boiling water or steamed and served with melted butter. It is quite suitable for freezing as long as over-mature ‘spears’ are not used.

Soil and fertilizer requirements

Pre-planting preparations for asparagus, as for all other perennial vegetables, must be thorough since the crop will, it is to be hoped, be with you for up to 40 years. Deep digging and incorporation of well-rotted organic manure or compost are essential in the autumn before planting and, at the same time, all traces of perennial weed must be removed. The ideal soil is a light, easily worked and well-drained loam but heavier soils can be used if they are lightened before planting—by adding peat or compost—and used with the raised bed system of culture. Quite a large area of asparagus bed will be needed to meet the requirements of an average family so careful planning is necessary to determine if, and where, it is to be sited. Apply a general purpose fertilizer at 100g per m2 (4 oz per sq yd) and rake it in during the final pre-planting preparations in the spring.

Plant raising

Asparagus can either be started from seed— which is a cheap method but takes 2 or 3 years before crops can be harvested—or from 1 to 4-year-old crowns which is more expensive but less time consuming and more instantly rewarding. Leave plants raised from seed in the seedbed for 2 years—during which time the less productive female, fruit-bearing plants should be rogued out—before the young crowns are transferred to the permanent bed. Sow the black seeds, from the red berries, thinly during April in a well prepared seedbed. Drills should be 1.5 to 2cm (about |in) deep and 30cm (12in) apart. The young seedlings will need plenty of room if they are to develop into strong crowns so thin them to 30cm (12in) apart in the rows. Weeding, watering in dry periods and top dressing with a general purpose fertilizer will all encourage leaf growth which will, in turn, lead to the production of well developed crowns.

Asparagus crowns are available from a number of stockists. A uniform bed will be established more quickly from one-year rather than older material. You may get a number of female plants, which are less productive than males, but they can be rogued out later if their performance is poor.

Planting

If you grow asparagus ‘on the flat’ no earthing up will be needed but the ‘spears’ will have very little blanching. Plant the crowns 40cm (16in) apart in single rows with 60-cm (2-ft) pathways between rows. On heavy soils raised beds should be made before planting. Make them 15 to 30cm (6 to 12in) high and 45cm (18in) wide by taking soil from the pathway areas. Again, leave 60-cm (2-ft) wide pathways between raised beds. Asparagus is then grown on the flat tops of these beds without further earthing. Earthing up asparagus—in order to produce blanched stems—is possible on light, easily worked soils and crowns should then be planted in double rows. Space the two rows 60cm (2ft) apart and leave a 1.5-metre (5-ft) path before the next double row.

Once again the crowns should be 40cm (16in) apart within the rows. Plant the crowns so that the tops are 5 to 10cm (2 to 4in) below the soil surface. Make the holes large enough to take all the roots when they are spread out and work loose soil around them during planting. Leave a slightly ridged surface over the crowns to prevent water settling into their centres. Do not expose the thick, fleshy asparagus roots for too long at planting time or they may dry out. Plant in March or early April when the soil can be easily worked.

Crop management

Weed control is very important but particularly if you grow asparagus ‘on the flat’. Cultivations prior to and during earthing up will help to keep down weeds but when soil is not put over the plants the weeds must be pulled out by hand. Damage can be caused to emerging ‘spears’ if hoeing is done before harvesting finishes. Apply a top dressing of a general purpose fertilizer at 50g per m2 (2 oz per sq yd) in the spring before growth is obvious. Begin earthing up blanched crops as soon as the shoots appear through the ground. Cultivate the soil in the pathways and carefully build up vertical-sided beds over the double rows. The beds should be 1.25 metres (4ft) wide and earthing up should allow 25-cm (10-in) long ‘spears’ to be harvested.

Leave the shoots that emerge last to develop into the 1 to 1.5-metre (up to 5-ft) tall branched stems of fern. These produce the plant food which goes to build up the strength of the crowns. Pieces of fern can be used in decoration and flower arranging provided not too much is removed. Draw-away the soil from the earthed-up plants at the end of the season and cut back the stems, when they turn yellow, to within 2cm (1in) of ground level. Apply a mulch of rotted organic manure or compost in autumn.

Harvesting

Newly planted beds should only be sparingly cropped in the first year but once they are fully established—after 2 or 3 years— cutting can continue from late April until mid-June. Cut the ‘spears’ from flat beds when they are 15 to 20cm (6 to 8in) tall. Use a sharp knife and cut 5 to 7cm (about 3m) below the soil surface taking care not to damage the crown or other ‘spears’. Earthed-up crops are more difficult to harvest since the knife must be pushed in from the side of the bed. The tip of the ‘spear’ will just be visible through the top of the bed. Hold this with the fingers of one hand while carefully pushing the knife with the other. You will feel the ‘spear’ move when you touch it with the knife and it can then be cut—about 25cm (10in) from the tip. Be very careful not to cut other concealed but developing ‘spears’. A very sensitive touch is required! Stop cutting in mid-June to allow sufficient vegetative growth during the rest of the summer.

Pests and diseases

Adult and larval forms of the asparagus beetle feed on developing shoots and emerged foliage. The beetles have a black cross on an orange background on the back. Violet root rot fungus produces the tell-tale purple threads on the roots.

Suitable cultivars

‘Perfection’, ‘Connovers’ Colossal’ and ‘K.F.B.’ are long established cultivars while ‘Purple Argenteuil’ is the traditional French asparagus. ‘White Cap’ is an early cultivar with a white, rather than purple, tip.

01. June 2013 by admin
Categories: Tips and Advice | Comments Off on Growing Asparagus

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