Asparagus is normally grown from a crown rather than from seed. Seed can be sown, but it takes two years for it to form a crown that must then be transplanted into a permanent bed. So purchasing asparagus crowns from your local nursery will save a great deal of waiting. While it will grow in almost any kind of soil, asparagus does better in friable light loam with a good depth. If your soil is clay, the beds should be mounded and gypsum used to help break it up. The PH of the soil should be 6.5-7, so add lime if necessary.
Prepare the bed for asparagus crowns by digging the full depth of the spade and incorporating a great deal of well-rotted manure and compost. Once this has been done, trenches 8 inches (20 cm) deep and 12 inches (30 cm) wide must be dug. The crowns should be 18 inches (45 cm) apart and placed onto a slight mound formed in the centre of the trench. This allows the roots to be gently coaxed out and placed at an angle of 45 degrees into the trench.
Once placed into position the trench should be backfilled with compost to 3 inches (7 Â½ cm). As the crowns grow, the trench can be gradually filled in. The first harvest should be restricted to just a few shoots to allow the plant to build up plenty of strong roots. The second year can be a slightly heavier harvest, but full harvest should wait until the third year. The ferny top growth of the asparagus plant will grow up to a meter high or more when left alone.
Once the frost hits, all the top growth will brown off. This should then be cut back to about 3 inches from the ground, lots of compost and manure added and the whole covered with a thick mulch of hay. The in the spring when it shoots up again there will be plenty of fertilizer at hand to feed those tasty shoots.
Cut the spears when they are about as thick as a pencil and before the tips have developed any ferny growth. Asparagus is the only plant to have male and female flowers on separate plants. If the female plants are left with seed it is likely to all germinate and choke the rest of the bed, so try to cut that all off before the seeds are ripe enough to fall.
Once asparagus is properly established it will last up to 20 years. In sub-tropical climates it can often be harvested twice a year due to the drenching rain. Asparagus is usually grown in cool to temperate climates and has no pests or diseases.