Introduction
Silverbeet (Beta vulgaris) belongs to the Chenopodiaceae family and is closely related to beetroot and true spinach. It supplies useful amounts of carbohydrates, fibre, vitamins A and C and riboflavin from the fleshy green cooked leaves.
As a wild plant, silverbeet is a biennial and produces flowers and seeds after the winter of the second year after planting. Under cultivation, it is treated as an annual and is harvested before the plants ‘bolt’ into flower.
Most production is in the Perth Metropolitan Area where it is usually grown under frost-free conditions. A slightly acid to neutral soil is preferred (pH 5.8 to 7.0), well supplied with organic matter.
The crop is grown throughout the year but cold conditions in winter may cause the plant to run to seed in spring. Plants will produce fairly well during summer but must be kept well watered to prevent wilting and leaf burn. There is no consistent seasonal effect on production and prices, which fluctuate throughout the year.
Growing the crop
Varieties
Red, pink, yellow and orange-stemmed varieties are available but these are not as popular as the white-stemmed varieties and are sometimes grown as ornamental vegetables. Check with seed and nursery suppliers for preferred varieties.
Seed often contains a small percentage of off-types, which produce poor quality plants.
Planting
Plantings may be made at any time in the year. Plants will crop for many months so that replanting is only needed at four-monthly intervals. In practice, sowing in December, March and July should give good results for establishment, growth, yields and quality throughout the year.
Seed may be direct sown in the field at 6 to 9kg/ha and thinned. Rows are spaced at 40 to 80cm and plants are thinned to 20 to 40cm apart in the row. Several plants often arise from each seed and these must be thinned. The use of transplants is increasing, either home-grown or purchased from a commercial nursery.
Fertiliser
Apply the following rates of magnesium and trace elements to the soil before planting:
- 50kg/ha magnesium sulphate to supply magnesium
- 20kg/ha manganese sulphate to supply manganese
- 18kg/ha borax to supply boron
- 18kg/ha ferrous sulphate to supply iron
- 18kg/ha copper sulphate to supply copper
- 18kg/ha zinc sulphate to supply zinc
- 2kg/ha sodium molybdate to supply molybdenum.
Compost applied at up to 50 cubic metres per hectare before planting or to other crops in the rotation will supply organic matter, add nutrients and help to retain moisture in the soil.
Apply fertiliser to supply 105 kg/ha of phosphorus before planting but reduce the rate on old vegetable ground and if compost is used.
After planting, apply weekly topdressings of nitrogen and potassium (Table 1) preferably through the irrigation water.
| Season | Nitrogen | Potassium |
|---|---|---|
| Summer | 40kg/ha urea | 20kg/ha muriate of potash as solid fertiliser or 25kg/ha potassium sulphate through irrigation water |
| Winter | 30kg/ha urea | 15kg/ha muriate of potash as solid fertiliser or 20kg/ha potassium sulphate through irrigation water |
Supplementary nutrients, preferably applied through the irrigation water, may be needed (see Table 2).
| Nutrient | Time of application | Rate/ha | Effect |
|---|---|---|---|
| Boron (as borax) | Two and six weeks after planting | 20kg/ha | Prevents cracks across the stems and distorted leaves and stems. |
| Manganese (as sulphate) | Monthly | 15kg/ha | Controls stunting and mottling on young to fully emerged leaves, especially on alkaline soils. Can also be applied at 8g/L to leaves. |
| Magnesium (as sulphate) | Monthly | 50kg/ha | Prevents yellowing of older leaves. |
Analyse soil and irrigation water for nutrients before planting, plus one to two analyses of the youngest mature leaves after planting. This will provide information on nutrients that are deficient or toxic and let you adjust your fertiliser program accordingly.
Some of the suggested nutrients may be deleted or reduced if they are sufficiently high in the irrigation water and soil, including sources from compost and fertilisers from previous cropping.
Do not apply excess fertiliser because nitrogen, phosphorus and potassium are easily washed through sandy soils by rainfall and irrigation. This may lead to pollution of groundwater, rivers and estuaries.
Irrigation
The crop is not suitable for areas with a high level of iron in the water supply as this will result in browning of the stems. Silverbeet may tolerate slightly higher levels of water salinity than most vegetables.
Plants must be kept well watered, with one watering per day in early morning from April to October, dependent on rainfall, and two waterings per day, half between 7am and 9am and half between 2pm and 3pm from November to March. Table 3 is a guide for watering, but no research has been done with silverbeet to obtain the precise needs of the crop.
| Month | Average evaporation in mm/day at Medina Research Station | Average water in kL/ha/day at 140% evaporation replacement | Average minutes/day for a typical butterfly sprinkler | Average minutes/day for a typical knocker sprinkler |
|---|---|---|---|---|
| January | 8.6 | 120.4 | 32.5 | 89.0 |
| February | 8.1 | 113.4 | 31.5 | 86.0 |
| March | 6.2 | 86.8 | 25.0 | 66.0 |
| April | 3.8 | 53.2 | 15.0 | 40.0 |
| May | 2.3 | 32.2 | 9.5 | 25.5 |
| June | 1.8 | 25.2 | 7.0 | 19.0 |
| July | 1.7 | 23.8 | 6.5 | 18.0 |
| August | 2.2 | 30.8 | 8.5 | 23.0 |
| September | 3.1 | 43.4 | 12.0 | 33.0 |
| October | 4.5 | 63.0 | 17.5 | 47.5 |
| November | 6.2 | 86.8 | 25.0 | 66.0 |
| December | 7.8 | 109.2 | 30.0 | 82.5 |
Data from Medina Research Station, Perth, Western Australia represents average conditions and adjustments must be made for changes in temperature, humidity, effective rainfall and wind speed. Use evaporation data from the nearest meteorological station if your property is not situated near Medina.
Typical butterfly sprinklers are spaced at 277/ha with an output of 15L/minute or 4.15kL/ha/minute. Typical knocker sprinklers are spaced at 69 per hectare with an output of 22L/minute or 1.52kL/ha/minute. The irrigation time has been adjusted to compensate for the efficiency rating of butterfly (85%) and knocker (80%) sprinklers.
Pests, diseases and weeds
Silverbeet may be seriously affected by rootknot nematodes and may also be damaged by sugarbeet nematodes. A range of other pests may also attack it, including snails, slugs, webworm, cutworm, budworm, loopers, weevils and two-spotted mites.
A number of diseases have been recorded on silverbeet, but they are usually of minor significance. These include leafspot and various root-rotting diseases.
Weeds may be controlled by hand weeding or by using herbicides.
The registration and availability of chemicals for disease, pest and weed control change 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.
Harvesting and storage
A crop may take from two to three months to mature. Size of the plant and leaf development are the guides to maturity. The outer two or three leaves are twisted off from the base of the stem, leaving five to six leaves on the plant. Sometimes all leaves are stripped off and there is a longer interval between picks.
In the field, tie about 20 leaves into bunches of about 750 to 1500g, the weight depending on the age of the crop, the size of the leaves and the length of the stalk. The stalk may be 400 to 500mm long after trimming.
Crops may be picked for four to six months. Eventually, plants show pronounced stems devoid of lower leaves and leaves become smaller. The number of plants which ‘bolt’ into flower may also increase. At this stage, the crop is finished and the remaining vegetative matter is incorporated into the soil.
Wash the bunches in a bath of clean water or hose them down, especially with silverbeet grown in sandy soil. Pack into plastic crates.
Yields vary from three to seven bunches per plant over the life of the crop.
Acknowledgement
The original version of this material was authored by John Burt.