By: Penny Woodward | March 25, 2010
Asparagus (Asparagus officinalis) is a member of the Asparagaceae family and has been grown as a perennial (and eaten) for more than 2,000 years. The key to success with this vegetable is soil preparation, and given that asparagus can go on producing for 20 years, it is worth doing well. A friend who grew asparagus for more than 50 years once told me her best crop came from the bed she planted over the burial site of her favourite horse!
You may not have to go to quite those lengths, but do choose a site in a sunny position with open, friable soil and good drainage. If the soil is too heavy, then establish mounds or a raised bed. Add a barrowload of manure and compost to every two square metres of soil and sprinkle several handfuls of dolomite over the top. Asparagus likes a pH of about 7. Dig the soil well and leave to sit for a few weeks. Remove any weeds, as asparagus doesn’t like competition.
Seed, or crowns?
Asparagus can be grown by planting seed or by purchasing and planting crowns. Seed germinates fairly readily, but it can take from 2–4 weeks before the seedlings appear. I have found the best way to grow it from seed is to plant into large tree tubes. I fill these with potting mix, except for the last 2cm, which I make up with seed-raising mix.
Soak the seed overnight in warm water, water the pots well and plant two or three seeds into each pot, then water again. Line a polystyrene box with plastic sheeting and fill the bottom of the box with about 3cm of river sand. Moisten the sand. Stand the pots in the sand and move the whole box into a position out of direct sunlight. Keep the sand moist and the pots will stay moist by drawing water from the sand.
Once the seeds germinate, remove the extra seedlings so that only the healthiest remain. Leave these seedlings to grow, produce ferns and then die back.
Alternatively, crowns are generally purchased in winter and spring, and are best planted out straight away.
When to plant asparagus
The time to plant seed, seedlings and crowns depends on the climate in your area. Asparagus spears are frost-sensitive, but the plant is otherwise very adaptable and is grown from cool-temperate regions to the subtropics. It is also grown in the tropics although yields are not as prolific and plants don’t last as long.
Plant seed from late September to November in cool regions with frosts, from March to September in frost-free temperate and subtropical regions, and from May to July in the tropics.
Transplant seedlings and plant out crowns in mid-spring in frosty regions, from late autumn to mid-spring in frost-free temperate and subtropical regions, and in autumn and early winter in the tropics.
How to plant asparagus
A single row of asparagus generally results in a longer and more prolific crop, because there is less over-crowding. Dig a trench, about 20cm deep and 30cm wide, into the already prepared bed and plant the crowns or seedlings 40cm apart. Additional rows need to be 120cm apart.
For crowns, make small mounds in the trench and spread the roots over the mound so they are at an angle of about 45 degrees. Seedlings should be planted straight into the trench.
Back-fill with a mixture of soil and compost so there is about 8cm of soil over the crown, but so that the trench is still about 10cm deep. Water well, then mulch lightly with pea straw or sugarcane mulch. Mulching can delay the appearance of spears by keeping the soil cooler, but will extend the harvest at the other end of the season. This delay is actually a good thing in frosty areas, as it means the early spears are less likely to be damaged by frost.
The spider like asparagus crown and roots are spread over a small mound of soil. PHOTO: DAN COATES
Don’t harvest any spears in the first year after planting; just allow the spears to grow and fern-like foliage (called “ferns”) to develop, flower and set seed. This will return nutrients and strength to the roots and help plants establish.
Ferns can reach a height of 1.5m, so they may need protection from the wind. Every year when the spears start to appear, top-dress with blood and bone, and protect from snails and slugs. Remove weeds. It’s vital to water regularly but deeply to encourage strong root growth.
Asparagus plants are dioecious, which means they can be male or female. Female plants produce red fruit in autumn and these should be removed when they appear (unless you want to collect the seed), otherwise you may have hundreds of seedlings to weed out later in the year.
Some growers advocate removing
the female plants, believing they are less prolific than males. In reality, the spears from female plants tend to be thicker but less prolific, while male spears are thinner (sometimes too thin) but more prolific. In late autumn, the ferns will turn brown and should be cut back to a few centimetres above the soil.
Top-dress the bed with well-rotted manure and mulch with a thick layer of pea straw to keep weed growth to a minimum. My sister, who grows a lot of asparagus, lets the chooks in to fertilise and scratch among the plants once the ferns have been removed, and only mulches later in the year. She also grows other vegetables, like tomatoes, in rows beside the asparagus. The compost and manure added to the tomatoes helps to feed the nearby asparagus.
• Pests & diseases: Watch for snails and slugs, and aphids that can transmit viruses. In Queensland, Asparagus rust,
a fungal disease, has recently arrived (contact Qld DPI: www.dpi.qld.gov.au).
Harvesting your crop
In the second year after planting, spears will begin to appear in late winter and early spring, and continue right through spring into early summer. The idea now is to harvest as many as you can, but to leave enough to grow into ferns and replenish the rootstock so that you’ll have strong, healthy growth the following year.
Some growers only harvest the thicker spears, leaving the thinner ones to grow ferns, which are sometimes called mother ferns. Others harvest all the spears for six weeks to two months, and then start leaving some to grow ferns. Then, after about three months, they let all the plants grow into ferns.
In the third or fourth year after planting out, the asparagus will have reached its maximum yield and, if properly maintained, will continue to produce for another 10 to 15 years. After this, yields start to decline.
In tropical regions, you can start harvesting in mid-June and continue through to the end of August. The lack of cold to induce winter dormancy means that the plants don’t last as long as those grown in more temperate regions, although drought-induced dormancy in autumn can sometimes work as a substitute.
When harvesting asparagus, use a sharp knife and cut the spear when it is about 20cm long, cutting a couple of centimetres below the surface of the soil. During the height of the season, spears grow much more quickly, and in very warm, humid conditions can grow more than 2cm in an hour!
A powerhouse of nutrients
Asparagus is a nutritional powerhouse, containing many of the B vitamins as well as vitamin C and other anti-oxidants, potassium, and small amounts of iron. Fresh spears can be eaten straight from the garden or cooked briefly by baking, boiling, steaming, frying or even barbecuing. Finally, if you are one of about 60 per cent of people whose urine smells funny after eating asparagus, you may like to know that it comes from a chemical called asparagusic acid, which metabolises with other chemicals in your body to produce the characteristic smell.