How To Grow Asparagus

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Asparagus spears ready for harvesting. Photo by Dusan Zidar

Often the first vegetable in the garden to herald the arrival of spring, asparagus provides a delicious welcome to the coming season. While it can take some patience, there is little that comes close to the taste of your own asparagus plucked straight from the ground. Once established, asparagus plants can produce for over 20 years.

A member of the lily family, Asparagus officinalis is a perennial plant with fern-like fronds growing to 1.5 m high. It retreats to dormancy in the cooler months, with quick-growing shoots emerging from the ground in early spring. It is these shoots that we recognise as asparagus spears, and when they start to emerge, they will need to be picked every day or two to get the sweetest, most tender asparagus for the pot. If left to grow, the spears continue skyward and the tightly bunched scales on the tip loosen and elongate, eventually becoming branches on the tall, ferny plant.

Once established, around eight to twelve plants will provide a family of four with a good amount of asparagus for two or three months over spring. Nutritionally, it’s a great addition to the vegie garden, containing B vitamins, vitamin C and potassium, as well as a number of antioxidants. It also contains the compound asparagine, which gives asparagus its ‘umami’ flavour, the savoury fifth taste that’s also found in tomatoes and mushrooms.

Varieties

Common varieties of asparagus in Australia include Mary Washington, an open-pollinated garden staple with high productivity; Fat Bastard, a hybrid variety known for fatter spears and high yields; and several beautiful purple varieties, which are generally more tender (due to a lower fibre content) than green asparagus.

Interestingly, white asparagus, prized for its delicate flavour, is not a separate variety of asparagus at all. It’s green asparagus that has been protected from exposure to sunlight, so the spears do not photosynthesise and therefore do not turn green.

Climate

Asparagus is typically a temperate plant, but it can grow quite happily in subtropical environments. It is thought to originate from the Mediterranean region and likes full sun (or part shade in very hot areas) and plenty of water throughout the growing period. When cold weather arrives, the plant will start to decline and go into dormancy, waiting for warming soil temperatures and longer days to start the cycle once again. In subtropical areas this may not happen until winter, while in temperate areas it may happen much earlier. Asparagus doesn’t tend to do as well in tropical environments, as it needs a cooler dormancy period of at least a couple of months.

Soil

Asparagus likes a deep, rich soil with a pH of 6.5 to 7. When preparing your bed, dig in plenty of compost and well-rotted manure, correcting the pH if necessary. Feeder roots for asparagus can grow up to 2m long once established, so it is important for the soil to be loose and not compacted. It hates competition, so make sure your bed is free from strong perennial weeds, and keep it clean and mulched coming into spring and throughout the growing season.

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Photo by Elena Moiseeva
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Photo by Bec Shann

Clockwise from left: Asparagus spears emerging; Asparagus crown root length; Asparagus ferns.

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Photo by Maryna Ges

Growing From Seed Or Crowns?

You can grow asparagus either from crowns or seed. Both are easy, but using crowns will give you a year or so head start.

To grow from seed, sow into trays in early spring. Germination should take around three weeks, after which you can pot them up and plant them out when the plants have matured.

When planting out asparagus crowns, dig a hole or trench just wider than the crowns and deep enough to allow the top of the crown to be below the soil level. Make a small mound in the bottom of the trench or hole, and drape the asparagus roots over the mound. This maximises soil-to-root contact and avoids leaving an air pocket under the crown itself.

Asparagus needs plenty of space: plant them at a minimum of 30 cm apart, but up to 60 cm spacing is good too. Backfill until the crown is covered by a few centimetres of soil, then water in well to settle. The addition of seaweed solution to the water will promote root growth, especially if it is towards the end of winter, when the plants will be waking up.

Harvest And Storage

During the first spring after planting out the crowns, you should leave any spears that emerge to grow and produce ferns. This will feed the crown and help them establish; remember, growing asparagus is a long-term game! In the second spring after planting, you can harvest lightly, leaving the smaller spears to grow on, and look forward to a full harvest the following spring. Growing from seed will add a further year onto this process.

In the third or fourth year, you will be able to harvest asparagus for eight to twelve weeks after the spears first appear. Only cut those spears that are pencil thickness or greater – anything thinner should be left to keep growing.

When the spears reach around 20 cm in height, cut or snap them at ground or mulch level to ensure you don’t damage the crown below. Asparagus deteriorates quite quickly after picking, so is best eaten on the day it is picked. You can tell if cut asparagus is older by looking at the pointy end of the spear: if the scales have started to pull apart, it’s a sure sign that the asparagus is past its eating prime, becoming more starchy and less sweet over time. Leave these to grow up and turn into ferns.

Plant Maintenance

Wonderfully, asparagus does not have too many pest or disease issues. Thrips, aphids and the usual suspects of snails and slugs can be easily managed if they become a problem, with the best defence always to focus on having strong and healthy plants, as stress may make them more susceptible to attack.

To promote growth, keep the plants well-watered throughout the hotter months. Asparagus plants in full foliage are photosynthesising and feeding the roots and crown; it is this reserve that will give you a harvest in the following year, so don’t neglect them once you stop harvesting.

Asparagus plants are dioecious, meaning they have both male and female plants. If your asparagus plant sets bright red berries in summer, you know it is a female plant as the males do not produce berries. If you let the berries fall to the soil you may notice self-seeded asparagus growing the following year. Remove these seedlings to avoid overcrowding in your bed: pot them up or compost them. Some people advocate removing any female plants altogether, as generally the best spears will be harvested from male plants.

Once the ferns have yellowed off in autumn, it is time to cut back the above-ground part of the plant. The fronds can be put in the compost bin, but just as easily laid on the ground at the base of the plants. During winter, it pays to top dress around the asparagus with well-rotted manure or compost and mulch to suppress any weed growth. With a little upfront effort and some patience, you could have many years of happy asparagus harvests in front of you!

Cooking It Up

Asparagus is a versatile ingredient, featuring in risottos, pastas and quiches. However, to fully appreciate its fresh flavours, asparagus is best cooked simply and with minimal fuss. To roast it, preheat your oven to 200°C; pop the stems in a lined tray; drizzle with olive oil and a little salt and pepper; then roast for approximately ten minutes. To serve, drizzle with lemon juice and lightly grate some fresh parmesan over the top. Alternatively, you can pan-fry for a few minutes until lightly browned; steam for three minutes; blanch in boiling water for two minutes; or barbecue.

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