Grow & cook
Asparagus is unlike any other vegetable you’ve ever grown, and yet so undemanding that it should be in all kitchen gardens with cooler climates in South Africa. This highly nutritious perennial will keep on producing for years, but off the shelf the spears usually come with a hefty price tag and an even heftier carbon footprint.
Although it belongs to the lily family, asparagus grows as a fern. The fern is a modified stem that photosynthesises to provide energy for the rhizomatous root ball or crown. The spear we harvest and eat at its most tender and tasty is the immature part that is formed by the crown. If left unharvested, a spear unfolds into the woody inedible fern of up to 1,8m high.
Battle of the sexes?
Asparagus is a dioecious plant, which means that it has separate male and female plants. The males produce more and thicker spears than females and are therefore preferable. It’s easy to distinguish between male and female plants: males produce a small pale yellow flower and females a bright red berry about 8mm in diameter.
The berries, when fertilised, contain two or three black seeds each. The ripe berries can be harvested and the seed collected for sowing again; if left unchecked they will readily self-sow. This is another reason why it’s better to plant male plants as they aren’t as likely to cause overcrowding in the asparagus patch.
How to plant
Establishing asparagus requires little more than patience…
SOWING If you grow them from seed you need to wait two years for the crowns to mature before you can start to harvest the spears. In the third year you can start to harvest for about a month of the growing season before allowing ferns to mature and strengthen the crown. From the fourth year a proper harvest of two to three months can be made. The good news is that a plant will keep on producing its highly nutritious bounty for many years.
The best time to sow is at the very start of spring. It is advisable to sow asparagus in 15cm pots and only transplant it at the start of the third spring. For the average family >
20 to 25 plants should be enough – but because you’ll select only the males for transplanting, you’ll need to sow at least 30 pots. Use a mixture of potting soil and vermiculite. The seeds can take up to 10 weeks to germinate. Again, patience is key.
By the second autumn you’ll be able to distinguish between male and female plants and select the more productive males. Sowing in pots first and transplanting later also allows you to plant the crowns deeper than it would have been possible to sow the seed.
It is important to plant asparagus in a spot that receives full sun as most of the problems that a plant can experience stem from conditions that are excessively damp. Remember that the area you select will be its home for at least a decade!
Planting depth is very important.
If the crowns are too shallow, you’ll get a large number of thin spears; plant it too deep and you’ll only have a couple of very large spears.
SOIL Having selected the location, prepare the soil for planting by digging a trench of 20cm to 30cm deep. Mix the material from the trench with an equal amount of rich compost. If you know the soil is acidic, some lime can be added. Using the mixture, fill the trench halfway before placing the two-year-old crowns about 40cm apart. Cover the crowns with 5cm of soil at first, then fill the trench with the remainder of the compost-andsoil mixture as the plants grow.
Asparagus can tolerate brackish or alkaline soil and will even grow in coastal areas, but prefers sandy soil. It will be necessary to improve the drainage where soil is more dense. This can be achieved by raising the bed through digging the trench a lot shallower – only 10cm – before planting as described above. A layer of compost and mulch should be added at the start of spring every year.
MULCH A layer of straw or similar mulching material about 10cm deep should be applied to assist with moisture retention and temperature regulation – but, more importantly for asparagus, it will also help combat weeds. Bear in mind that this will have an impact on how much water reaches the roots. It is therefore recommended that drip irrigation is installed before mulch is applied over the surface. Alternatively you can water by hand once a week using a hose or watering can with the nozzle removed.
Asparagus requires regular watering throughout summer. It is best to water less often but more thoroughly to encourage root growth. One or two deep waterings per week should suffice.
Varieties and companions
It is relatively easy to come by the green and purple varieties in South Africa now. The white spears are simply green ones that have been blanched. This is achieved by raising the bed above the crowns using a very light soil mix such as compost and sand, or straw mulch. The spears remain white for as long as they are kept away from sunlight.
Comfrey makes a good companion to asparagus and can be planted along the edge of the bed, interspaced with the crowns. Comfrey leaves can be cut and laid down as mulch on a regular basis – as it breaks down it acts as a good source of potassium.
Harvesting from the third year entails carefully removing the material around the young spears and cutting them at the base with a sharp knife early in the morning. Be sure to harvest only about 75% of the young spears, leaving the other 25% to mature and supply energy to the crown for the next season’s harvest.
By the first frost the ferns will have died and browned. They can now be cut at ground level.
Pests and problems
Very few pests and diseases affect asparagus in South Africa. Take care not to overwater plants as this could cause root rot and other fungal disease. Aphids are often a temporary annoyance but can easily be sprayed off with water or washed off after harvesting. Pretty asparagus beetles may feed on the tips of spears or lay their eggs there. These bugs don’t like the smell of tomatoes, so if it isn’t possible to plant some tomatoes close by, simply pick some tomato leaves, and crush and scatter them in the asparagus patch to deter the beetles.
ABOVE, FROM LEFT A male asparagus plant in flower; female plants can be identified by their red berries. OPPOSITE The green spear that ends up on your plate is in fact a modified stem that supplies energy to the root ball or crown below the soil surface.
Sowing asparagus in pots to transplant them later allows for selection of the more productive male plants, and you’ll be able to plant their crowns deeper than you’d be able to sow the seed.
Allow approximately a quarter of the spears to mature so that they can provide energy to the crowns for the following season.