Planting should take place as soon as possible, provided soil and weather conditions are suitable, e.g. the ground is not overwet or frozen.
Should conditions not be favourable for planting, place the asparagus crowns in a box or seed tray and surround the roots with moist peat. Store in a cool light position.
A well maintained asparagus bed can remain productive for up to 20 years. It is therefore important to prepare the ground properly prior to planting.
Asparagus prefers a deep, well drained and reasonably fertile soil that is slightly alkaline. Choose an open sunny position sheltered from late frosts and cold winds.
Since asparagus is shallow rooted, it can be difficult to extract deep-rooted weeds without causing damage to the roots. Very weedy soil therefore is best covered or cultivated with annual crops for a year or two to remove the worst of any perennial weeds which may have established, especially where you may have taken over a neglected plot.
The site should be well worked to a spade’s depth, forking the soil layer below, incorporating plenty of organic material such as garden compost, or well rotted manure. Ideally the ground should then be left to settle for a week or two before planting. Care should be taken to remove all perennial weeds.
There are two methods of planting: the single row or multiple row methods. In the single row method crowns are set 40-45cm (15-18in) apart with 1.2m (4ft) between rows. The multiple row method is a good system to use when planting space is limited as crowns may be spaced as close as 30cm (12in) each way.
Soak the asparagus crowns in water for 1-2 hours before planting. For each row take out a trench 30cm (12in) wide and 20cm (8in) deep. Replace some of the soil to form a mound or curved ridge at the bottom of the trench approximately 10cm (4in) high. The crowns are placed on top of this mound with their roots carefully spread out over the ridge; handle the crowns with care so as not to damage them. Replace the soil covering the crowns with 5cm (2in) of soil and lightly firm, taking care not to damage the crown. The crowns should be covered quickly to prevent drying out. The remaining soil is replaced gradually during the season as the shoots develop.
In the multiple row system 2, 3, or 4 rows may be planted in a bed, spacing plants 30cm (12in) apart, in the same manner described above. If more than one bed is to be planted allow a pathway of 90cm (3ft) between each bed. The close spacing of crowns in this method achieves higher yields from a given area but the spears produced will be thinner.
After planting, apply a top dressing of general purpose fertilizer such as bonemeal as per the manufacturers recommendations. Ensure the crowns do not go short of water during the weeks following planting, and water as necessary during dry spells.
Do not cut any shoots in the first year as it is important that your plant gets thoroughly established.
If the plants have established well, in the second year (12 months from planting) some spears may be harvested from mid April, through to mid May.
Harvest the spears with a sharp serrated knife when they are 12-18cm (5-7in) above the ground, cutting the stem 2.5cm (1in) below the soil surface, taking care not to disturb any developing shoots.
In subsequent years cutting can continue until the 12th June, after which allow the foliage to develop naturally. This will enable the crowns to build up resources for the following year.
In the autumn, cut down the yellow foliage to within 2.5cm (1in) of the ground. A 5-8cm (2-3in) layer of garden compost or well rotted manure can then be applied.
In the spring, apply a top dressing of general fertilizer as per the manufacturer’s recommendations. Keep the beds free from weeds by hand weeding, avoid disturbing the shallow root system which can be easily damaged.
On heavier soils, slugs can cause severe damage to the newly emerging shoots below ground level and so it is a good idea to take precautions against them. Since they are underground the best way to reach them is using parasitic nematodes ‘Slug Killer’
(Phasmarhabditis sp.) which can be watered into the soil.
Asparagus Beetles (pretty black and orange beetles) and their ugly hump-back larvae can strip the fronds very quickly. Pick them off plants when seen from late spring onwards. Burn old stems at the end of the year to destroy overwintering beetles. Where hand removal is not feasible, spray with a suitable insecticide. Any chemicals should be used strictly as per the manufacturers instructions.