When the foliage turns yellow cut the stems back to about 2.5cm above the soil level and mulch the crowns with well rotted manure to protect them from frosts.
When growing asparagus, it is important to resist the temptation to harvest the spears during their first season, but instead allow the plants to develop foliage. A limited crop of spears can be harvested in the second year during April and May when they reach 15cm (6") tall. By the third year, the crop can be fully harvested. It is recommended to stop cutting from the end of May to allow the shoots to develop into foliage. Later harvests can be made but these will risk weakening the plant.