Asparagus

Start from crowns: July-August

Optimum soil temperature for germination (if growing from seed): 15-30°C

Plant crowns or seedlings: July-August

Plant spacing: 30-45 cm in rows 1-1.5 m apart

Days to maturity: first harvest 3 years after planting, then 8-10 weeks harvest period annually

Introduction

Asparagus (Asparagus officinalis) is a perennial, herbaceous plant, in the family Asparagaceae, that grows up to 2 metres tall. Unlike most vegetables, asparagus plants can produce crops for 15-20 years once established, making them a valuable addition to any garden.

Asparagus has been cultivated for over 2,000 years, originating in the eastern Mediterranean region. The Romans were particularly fond of asparagus and cultivated it throughout their empire. Today, it’s grown worldwide for its tender spring shoots.

The edible portion of asparagus is the young stem or spear that emerges from the underground stem, called a rhizome, in spring. These spears can be green, purple, or white. All spears are white until they reach the surface and chlorophyll starts being produced. Thus, white asparagus is grown by excluding light. Rich in vitamins A, C, E, K, and B vitamins, as well as minerals like folate and chromium, asparagus is not only delicious but also nutritious.

Site and soil

Asparagus is a long-term investment in your garden, so site selection is crucial. Choose a permanent location with full sun and good drainage. Asparagus won’t tolerate competition, so select a spot where it won’t be disturbed by other garden activities.

Prepare the bed thoroughly before planting since asparagus will occupy the space for many years. Double dig the soil and incorporate plenty of compost and well-rotted manure. Asparagus prefers a slightly alkaline soil with a pH between 6.5-7.5. If your soil is acidic, add lime to raise the pH.

Asparagus can be grown in raised beds, which is advantageous in Canberra to improve drainage during wet winters. The beds should be at least 30 cm deep to accommodate the extensive root system.

For details on preparing soil and pots, including the use of lime, dolomite, gypsum and fertilizers, please refer to the COGS guide to garden bed preparation.

Planting Crowns and Seedlings

While asparagus can be grown from seed, starting with one-year-crowns will give you a head start. In Canberra, the best time to plant crowns is in July and August. Crowns are generally sold bare rooted.

Dig a trench 20-30 cm deep and 30 cm wide. Create a 10 cm high ridge along the centre of the trench. Place crowns on top of this ridge, spreading the roots down both sides. Space crowns 30-45 cm apart in rows that are 50cm-1 metre apart.

Cover the crowns with 5-10 cm of soil initially, then gradually fill in the trench as the spears grow, until the trench is level with the surrounding soil. Water thoroughly after planting and mulch with straw or compost to suppress weeds.

If growing from seed do this in spring or autumn. Soak the seeds overnight to soften the tough seed coats then sow in seed or cell trays. The tiny feathery seedlings will look delicate, however, they transplant well when they’re about 10-15 cm tall. Seedlings will take an additional year to reach harvestable size compared to crowns.

Cultivation

During the first two years after planting do not harvest any spears. Let them develop into ferns. The aim is to let the ferns photosynthesise and send energy to the rhizomes which are the underground storage organs. Strong rhizomes are necessary to produce a good crop.

Water deeply on a regular basis, ensuring the soil stays moist but not waterlogged. Asparagus has deep roots that can access water, but young plants need regular watering during establishment.

In autumn, the ferns will turn yellow and then brown. After the ferns have died back completely, they can be cut back to ground level and the debris removed. This is a good time to apply compost or aged manure and a balanced organic fertiliser. A layer of compost applied annually will provide nutrients, feed the soil biology, and improve soil structure. A monthly foliar spray with seaweed solution; a mix of worm juice, seaweed and compost tea; or trace elements will help boost growth and resilience to pests and diseases.

Asparagus has separate male and female plants. Female plants produce bright red berries which are not edible. Male plants have a tendency to produce thicker spears than female plants because they do not expend energy producing seeds leaving, Thus more energy can be diverted into the rhizome. Therefore, some people remove female plants in favour of male plants to get thicker spears. Alternatively male cultivars can be purchased.

Weed control is essential, as asparagus doesn’t compete well with weeds. Hand weed carefully to avoid damaging the shallow crowns, and maintain a thick layer of mulch to suppress weed growth.

Harvesting

Patience is key with asparagus. Do not harvest any spears during the first two years after planting crowns (three years if grown from seed). This restraint allows the plant to establish strong rhizomes and roots.

In the third year, you can harvest spears for 2-3 weeks. In subsequent years, extend the harvest period to 8-10 weeks, usually from September to November in Canberra.

Harvest when spears are 15-20 cm tall and before the tips begin to open. Use a sharp knife to cut spears just below the soil surface, or snap them off at soil level with your fingers. Stop harvesting when the diameter of most spears becomes pencil-thin, allowing the remaining spears to develop into ferns.

Problems

The best approach is to have a reliable Australian reference book to identify problems. Garden Pests, Disease and Good Bugs by Denis Crawford is recommended.

A general strategy to follow with any problem is to observe the plant carefully before taking action. Identify the problem then carefully consider the course of action. For example, with pest insects, you often can see a predator nearby. If you watch and wait the predator may deal with the problem for you. Beneficial predatory insects which feed on pest insects can be purchased from suppliers such as Bugs for Bugs. If the problem needs further action the above recommended book has suggestions.

Practicing good garden hygiene, crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention.

While asparagus is generally resistant to many pests and diseases, there are a few issues to watch for:

Asparagus Beetle: Both common and spotted asparagus beetles can damage spears and reduce plant vigour. Control by:

Handpicking beetles and larvae
Removing plant debris in autumn
Applying organic insecticides if infestation is severe

Slugs and Snails: Can damage emerging spears. Use beer traps, copper tape, or organic pellets (iron EDTA) to control.

Crown and Root Rot: Caused by fungi in poorly drained soils. Prevent by:

Ensuring good drainage
Avoiding overwatering
Planting in raised beds if soil drainage is poor

Rust: A fungal disease, causing orange-brown pustules on ferns. Control by:

Ensuring good air circulation
Removing and destroying affected fronds
Avoiding overhead watering

Recommended Varieties

All-male hybrids generally produce higher yields since they don’t expend energy producing seeds. However, heritage varieties offer excellent flavour and may be more adapted to local conditions. Several asparagus varieties perform well in Canberra’s climate:

Green Varieties:

Mary Washington– traditional variety with good disease resistance
UC 157 – productive hybrid with good cold tolerance
Jersey Knight – all-male hybrid with high yield and rust resistance
Atlas – cold-hardy variety with thick spears

Purple Varieties:

Purple Passion – sweeter than green varieties with purple spears that turn green when cooked

White Varieties:

White asparagus is not a different variety but is produced by mounding soil over green varieties to exclude light as they grow

References

Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023.
Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.