Spring asparagus need fertile, well drained soil in full sun.  Buy them as 1 year old crowns.  Dig a trench 30 cm wide and 20 cm deep and make a 10 cm high ridge down the centre of it.  Place the crowns on the ridge about 30 cm apart, spread their roots and cover with soil.  Fill in the trench as the stems grow.  You will need to wait 3 years before harvesting but the delicious spears will become more abundant each year so it is well worth it.  Please do remember never to harvest all of your spears, tempting as it may be.  Do allow the fronds to unfold in order to feed the root system and thus lead to stronger, healthier plants.