Most of the vegetables we grow are annuals. They grow quickly, are ready for harvest in only a few months, and then we replace them. But there are some perennial vegetables, which will live and produce for years, and perhaps the most popular of these is asparagus. An asparagus plot can produce for over 15 years once established.
Asparagus (Asparagus officianalis) is a member of the lily family. The fern-like foliage grows to about 1.5m if it is not harvested for consumption as a young shoot.
This is a nutrient-rich vegetable, high in folic acid and a good source of potassium, fibre, vitamins B6, A and C and thiamine. It contains no fat, no cholesterol and is low in sodium. It tastes delicious, and, because it can be expensive to buy, it’s a great crop to add to the home garden.
It’s incredibly easy to grow. Plenty of room and plenty of patience are the main requirements, as it takes a couple of years for an asparagus bed to become productive.
The best way to grow asparagus is by planting crowns, which are established root systems with dormant top growth. Crowns are available for a brief period in winter. Asparagus will also grow from seed, but crowns will produce more quickly, because they are already about two years old. You need to plant at least 6 crowns to get a decent crop in the first few years, but plant more if you have the space.
Because asparagus will remain productive for many years and doesn’t like to be disturbed, you must choose a position where it can be left alone. A sunny, well-drained position is essential.
Dig the soil deeply and add plenty of organic matter. Asparagus performs best when the soil pH is 6.5-7.5, so you may need to add some lime too.
Make a trench about 25cm deep, and make a little mound at the bottom of the trench. Plant the asparagus crown on this mound, spreading the roots out. Plant the crowns about 40-50cm apart, each on its own little mound. Cover the crown with 5cm of soil. Fill in the trench gradually as the shoots emerge, taking care not to cover any foliage. In a few weeks the trench will be level with the surface of the soil. Asparagus is hungry stuff, so feed it regularly during the growing season.
To let your asparagus bed become really productive, don’t harvest any shoots in the first year, and pick only a few in the second. In the third year, cut the spears just below ground level when they are about 15-25cm high, for 2-4 weeks in spring. In subsequent years, take all the finger-size spears you want for about 10 weeks. Stop harvesting when the shoots become thin, and let these ones grow into ferns to feed the crowns for next year’s crop, fertilising them every now and then with a complete organic plant food.
In autumn when the ferns start to turn yellow, cut them down and use them as mulch over winter.
Asparagus shoots grow really quickly – as much as 25cm in 24 hours. Once your bed is established, you will need to harvest every day. Watch out for slugs and snails, and mulch to prevent weed growth.
While green asparagus is the most common, there is a form that produces purple spears. Eat it fresh and raw if you want to retain the purple colour, as, like purple beans, it will turn green when cooked. If you want to grow white asparagus, then cover the shoots with something (an upturned bucket would do) to exclude sunlight.