Asparagus (Asparagus officinalis)

How well established is this crop?

This crop is an emerging industry. It has been grown here commercially for around 5-10 years. Commercial returns, current growers and some level of regional based research may be available to help those new to this industry.

Background

Asparagus is one of the true summer vegetables. It’s ready just in time for the barbeque season and can be eaten cooked or raw.

About half of the New Zealand asparagus grown is consumed by the local market. The export value of the 2002 fresh asparagus crop was $9.1 million, and including processed products was $16.2 million. This comes from 1,400 ha planted and total production was in the vicinity of 6,000 tonnes. The main producing areas for asparagus at present are the were the Waikato, the South West North Island and Hawkes Bay.

Climate

Asparagus will grow in most climates found in Otago. The key is to plant in conditions most likely to lead to success.

Winter Chilling and Frosts

Asparagus are dormant beneath the soil surface for the majority of the winter frosts. Spring frosts can affect the asparagus spears but more will emerge if some of the early ones are frost affected.

Rainfall and Irrigation

Asparagus is not affected by rainfall at any stage of growth. However excessive rain leading to waterlogged soil can cause the plants problems.

As the spears emerge supplementary irrigation may be required if rainfall is insufficient.

Wind

Asparagus is usually grown as a field crop without any wind protection.

Soil

The key physical requirement of the soil for asparagus is that it is free draining. The best soils tend to be deep, loose and light. Sandy loams are ideal. Asparagus roots have been known to reach a depth of 3m, and the soil should ideally allow this.

Fertility

The ideal ph for asparagus is between 6.0 and 7.5. Although the plants will grow if the pH is outside this range, the yields will be reduced.

Hills Laboratories has published a datasheet showing the optimum levels of soil fertility for asparagus production. A simple soil test followed by the application of the correct nutrients will quickly sort any problems.

Weed Control

Asparagus tends to grow slowly and does not compete with weeds very well. A number of herbicides are registered for use on this crop in New Zealand. Contact your spray professional for more information.

Varieties

There are a huge range of asparagus selections available in New Zealand. The best way to succeed is to obtain crowns from a local grower. In most cases these will be well suited to the climate you are growing in.

Recent breeding work both in New Zealand and overseas has produced purple fleshed asparagus rather than the more common green types. These seem to be selling for at least twice the amount of the common varieties.

Mounding the soil as the spears appear can be used to produce white asparagus. This is a very time consuming and expensive process. Even when cut with special long knives, the spears have to be kept out of direct light to maintain their white colour.

Pests and Diseases

Asparagus does not suffer from many insect pests, but diseases are another matter with Fusarium wilt being the main problem. Growing in free draining soil and sourcing clean stock is the best way to start, but fungicide drenches and sprays may also be needed.

Layout

Planting is usually done in beds wide enough that a tractor can be driven over the top with pickers on special platforms. Crowns are placed 2-3cm beneath the soil surface. The distance between plants is usually 10cm. The plants grow together as they mature.

General Management

Asparagus plantings are usually established after the last frost in the spring. Beds are marked out and crowns planted. In the first season weed control and irrigation is all that is needed. No spears will be harvested during this time. The plants die off in winter and become dormant. In the spring of the second year a few spears per plant can be harvested, but full production is not reached until year 4 and onwards. Regular weed and fungal control are the main tasks, with irrigation needs varying depending on natural rainfall. Asparagus fields are expected to remain productive for up to 15 years. Replanting on fresh land is recommended at this time.

Harvest

Nearly all asparagus is hand harvested, generally at intervals between 24 and 36 hours depending on the temperature. It tends to be cut with a white butt on the end that is thickened and tough. This is then removed before cooking. Snapping the spears rather than cutting them reduces the incidence of this tough end but is not a common practice.

After cutting the spears need to be chilled rapidly. If this does not happen they can continue to elongate and this causes ‘loose tips’. Butts are usually placed in water or against other moist material in the field and then transported for processing and further cooling.

Equipment

Large scale asparagus production will require a tractor, specialist equipment for planting and harvesting and spray equipment. Processing capability that can quickly reduce the heat out of a cut spear is also required. Smaller blocks can be managed with hand held gardening equipment and a backpack spray unit, although they too will need chilling capability.

Returns

Asparagus is a commodity crop with relatively low returns on the domestic and export markets. The key may be to have the crop ready on either side of the main New Zealand crop. Crop manipulation or growing on a specialist late or early site is the best way to achieve this. Local niche markets may be useful for this crop.

Contacts

New Zealand Asparagus Council
PO Box 10232
Wellington
04 472 3795

http://www.vegetables.co.nz/about/15_profile.cfm