Growing English spinach in Western Australia

Introduction

Spinach is a generic term for certain vegetables and may refer to plants from five different families including English or common spinach (Spinacia oleracea), silverbeet or Swiss chard (Beta vulgaris), French spinach or orach (Atriplex hortensis), New Zealand spinach (Tetragonia expansa), Chinese spinach (Amaranthus gangeticus), water spinach (Ipomoea aquatica) and Indian spinach (Basella rubra).

English spinach and silverbeet belong to the plant family Chenopodiaceae. In Western Australia, the term spinach normally refers to English spinach. This is less vigorous with smaller leaves than silverbeet. It is also softer and has a green rather than white midrib. English spinach is less heat tolerant than silverbeet.

Spinach is a minor crop in Western Australia that has traditionally been consumed as a boiled or steamed green vegetable. As a cooked vegetable it has now been largely displaced by Asian vegetables. Demand has increased recently since it is more commonly consumed in pre-prepared salad mixes.

Spinach is a useful source of vitamins A, B and C and calcium. It contains oxalate and should not be eaten by people suffering from kidney stones.

Climate, soils and varieties

In Perth, best quality spinach is produced from May to October but it is marketed all year. In summer, some varieties quickly produce flower stalks. For summer production, choose a variety with good bolting tolerance.

Spinach is fairly resistant to frosts while high temperatures cause yellowing of older leaves.

Soil

Spinach can be grown on a wide range of soils, providing they are well-drained. It is very sensitive to acid conditions. To correct this, add lime where soil pH in calcium chloride is less than 6.0.

To avoid disease, rotate crops to give more than four years between spinach crops on the same ground. This is rarely achieved commercially as spinach is harvested at an immature growth stage (baby leaf) for the salad market. Turnover times are much quicker than in the past and many more crops can be grown on the same land in a given period.

Varieties

Commercial vegetable varieties change constantly with changing consumer preferences. Before planting, check with seed company representatives and your destination market for current varieties.

Planting

Planting may be conducted all year but March to August will produce the best quality spinach.

Spinach is rarely transplanted. It is sown directly into a well-prepared level bed. For ‘baby leaf’ production, sow seed 1 to 2cm deep in rows 10cm apart to achieve a final stand of about 40 plants per metre of row. In a commercial bed layout of 15 rows in a 1.5m wide bed, this equates to about 600 plants per square metre. Spinach for culinary purposes is sown at about one sixth of this density and the crop allowed to fully mature. It is not economic to thin spinach after emergence. However, too high a density may increase problems with leaf disease.

Hydroponics

Some growers have successfully grown spinach in a hydroponic lettuce-type nutrient film technique system. One of the advantages is that it is marketed with no sand in the leaves. There have been problems providing sufficient aeration to the roots and the nutrient solution must be replaced more regularly than with other hydroponic crops.

Irrigation

Spinach growing in sandy soil will need daily irrigation at most times of year and twice or more daily in hot weather. It will not tolerate waterlogging.

Comprehensive information on the principles of irrigating vegetable crops in WA can be found on the vegetablesWA website. Irrigation rates for your specific location and circumstances can be calculated by using the irrigation calculator.

Spinach has a higher salt tolerance than most other vegetables and can be grown successfully with water of an electrical conductivity (salinity) level as high as 270mS/M. It can tolerate water up to 635mS/M.

Fertiliser

Spinach has a high demand for nutrients. Apply the following rates of magnesium and trace elements (per hectare) every 18 months.

Spinach has one the highest requirements for phosphorus of all vegetable crops. Your program needs to take account of this but also recognise that the crop is often harvested as little as 30 days after planting. Phosphorus present during this short time needs to be immediately available to the crop, but not so excessive that large quantities are left in the soil after the crop is removed, potentially to be leached away and wasted.

If soil test P levels are less than 40mg/kg Colwell P, broadcast a high phosphorus product such as triple superphosphate at 500kg/ha before planting and incorporate to 15cm. Immediately after sowing, broadcast 100kg/ha MAP fertiliser.

Spinach also has a high demand for nitrogen and potassium. Starting three days after sowing, spray urea at 20kg/ha plus potassium nitrate at 20kg/ha in 1000L/ha of water. Repeat this every 3-4 days until the crop is ready for harvest. To avoid foliar damage, these applications should be washed from the leaves as soon as possible with no more than 3mm of irrigation.

Salad processors, the main buyers for baby spinach, have almost no tolerance for damaged leaves.

If these rates prove to be insufficient, fertigation with urea at 50kg/ha or calcium nitrate at 150kg/ha may be required after 21 days. The downside of doing this is there is often overspray on adjacent younger plantings, leading to fertiliser waste and leaching.

On alkaline soils, a foliar spray of manganese sulphate at 5g/L may be required in the first 14 days after emergence if the leaves show a mottled yellowing and don’t go green after nitrogen is applied.

Diseases, pests and weeds

Spinach can be affected by a range of diseases or insect pests.  It is susceptible to attack by root knot nematode and beet cyst nematode. It may also be attacked by aphids, grubs, snails and weevils.

The fungal disease Fusarium root rot may be a problem in summer resulting in plants wilting and dying. A good rotation will help to control this disease.

Weeds can be a problem when cropping first commences with baby leaf spinach, but regular cropping and short harvesting cycles do not allow most weeds to flower and set seed. Baby leaf is a high value crop and can usually sustain the cost of limited hand weeding. Weed seed burden can be reduced prior to planting by deliberately irrigating the site a number of times after cultivation and then spraying with a contact herbicide or cultivating before weeds grow too big.

The registration and availability of chemicals for pest, disease and weed control changes regularly. Consult a trained and experienced horticultural agronomist or the Australian Pesticides and Veterinary Medicines Authority (APVMA) website for chemicals which are currently registered or have a permit for use on this crop. The information on the label or permit for a chemical must be followed including the directions for use, critical use comments, withholding period and maximum residue limit. Quality assurance (QA) schemes for horticultural crop production require producers to have current information on chemical registrations and permits readily available.

Harvest and market

Spinach is sold on appearance. Any problems with leaf yellowing, caused by poor fertilising, or cosmetic blemishes will affect the appearance of the crop and decrease its value. It may even be unsaleable.

The market destination determines when and how it is harvested.

Baby leaf used for mixed packaged salads is usually machine harvested when immature and only the leaves are taken. The time from planting to harvest is around 30 days. The harvested product is washed in chlorinated iced water by the processor.

For a bunched culinary product, the crop is allowed to mature to 8-12 fully grown leaves and a time to harvest of 40-50 days. Bunched spinach plants are hand pulled with roots attached. They are washed and tied into bunches of 10 plants, weighing 500 to 1000g. Yield may range up to 4000 bunches per hectare.

Market

Spinach may be packaged into about 20 bunches per 36L plastic container. Produce should not be sprinkled with water in summer as this may cause the leaves to stick together. If required, store at 0^oC with relative humidity of 90 to 95% for 10 to 14 days. For distant markets, it may be packed in sleeves and top-iced.

Acknowledgement

The original content of this page was authored by John Burt.