Common shallots (Allium cepa var. cepa), also known as straight-leaved onions
The term 'shallots' commonly refers to the green leaves and stems of non-bulbing onions. They are grown for their whole tops, the leaves of which form long, hollow tubes and are eaten as a green vegetable. They may also be known as 'straight-leaved onions'.
These are not 'true' shallots, but rather are selections of the common onion (Allium cepa var. cepa). They are propagated using seed planted at high density. Because of the combination of high-density planting and variety, these selections tend not to produce bulbs like the onion.
There are many different varieties of shallots commercially available and adapted to a range of conditions.
True shallots (Allium cepa var. aggregatum)
True shallots (Allium cepa var. aggregatum) are grown primarily for their bulbs, although the green tops may also be consumed. Each compound bulb consists of several sets/cloves that are ideally about 30 mm to 40 mm in diameter, with brown skins and a purplish tinge inside the bulb. True shallots are used in place of onions as they have a delicate, yet distinctive, flavour that persists after cooking.
Traditionally true shallots have been propagated using bulb material, but the intensiveness of production has meant that they have only been produced on a minor scale. More recently, with changes in culinary tastes, there is renewed interest in true shallots. Seed companies have now produced varieties that can be grown directly from seed.
Note: This article uses the term 'shallots' for the straight-leaved onion type, and 'true shallots' for Allium cepa var. aggregatum.
Shallots are adapted to growing in cool mild to mild tropical climates. Seeds germinate at a temperature range of about 10oC to 30oC, with an optimal germination temperature of between 18oC and 24oC. The ideal growing temperature is in the range of 13oC to 24oC. Plantings should be timed to avoid periods when daytime temperatures exceed 27oC. In most regions of Queensland, shallot production is restricted to the winter months and stops before the hot summer months. Only in areas where summers are very mild (e.g. Stanthorpe) can they be grown over the summer months.
Shallots can be grown over a wider climatic range than the common onion because they do not have specific day length or temperature requirements. Onions and true shallots require specific day lengths for bulb initiation, and will bolt if there is a sufficient number of days below the minimum required for flowering.
The best soils for growing shallots are deep, well-drained clay loams of pH 6.5 to 7.5 that have high levels of organic matter. However, shallots have been successfully grown on a wide range of soils, from relatively shallow, low-pH sandy soils (Stanthorpe), to well-structured red volcanic soils (Toowoomba and Redland Bay) and alkaline alluvial soils (the Lockyer and Fassifern Valleys).
Liming may be necessary if the soil pH is below 5.5, as shallots are sensitive to acidic (low pH) conditions. On the acidic soils of the Granite Belt, dolomite may be better as it not only raises the pH but also adds magnesium. The rate of lime or dolomite required, and which is most suitable, should be determined by a soil test. Shallots respond very well to soil amendments of organic manures, particularly on light-textured soils with low cation exchange capacity. These amendments can be added several months before planting at up to about 25 t/ha.
Establishing and maintaining shallot crops
Land preparation is aimed at reducing weeds to a minimum. Ground should be worked to provide a fine tilth at planting. This may include a ploughing, several discings and either one or two passes with a rotary hoe or power harrow. A bed former is used to create beds (about 1.2 m wide) into which seed or seedlings will be planted.
There is one pre-emergent herbicide registered for weed control in shallots. Fumigating the ground gives some control on weeds and soil-borne diseases; however, the cost of this is relatively high.
Shallots and any other alliums should not be continually grown in the same ground, as this will potentially result in a build-up of the soil-borne diseases pink root and white rot.
Shallots can be planted from February to August in most parts of southern Queensland, and from January to September in areas where summer conditions are mild (e.g. Toowoomba). In Stanthorpe, late-autumn to late-winter plantings are not recommended. Shallots are usually grown on beds of four to six rows; however, they may be planted as single rows 20 cm apart or as three or four double rows on each bed. This is best achieved by using a precision planter, although it is not as critical for shallots as for other allium species, because a relatively high plant density is required. The seeding rate is around 8 kg/ha to 10 kg/ha, at a depth of 1 cm to 2 cm.
Direct-seeded shallots are planted dry, then followed by a light irrigation. Frequent light irrigations of about 12 mm are required until plants have emerged and developed a good root system. The topsoil should not be allowed to dry out until plants are well established. The frequency of early irrigations depends on the prevailing weather conditions at the time. After the crop is properly established, tensiometers can be used to determine when irrigation is required.
Traditionally shallots have been grown under overhead sprinkler systems, but drip irrigation is also suitable. Due to the short duration of the crop, about 2.5 ML to 3.0 ML of water per hectare is required. The true shallot is a longer season crop, requiring about 3.5 ML to 4.0 ML of water per hectare.
Shallots have similar nutritional requirements to other alliums, removing about 130 kg of nitrogen (N), 30 kg of phosphorus (P) and 60 kg of potassium (K) per hectare, as well as other nutrients that are required in smaller quantities.
On acid volcanic soils or soils low in phosphorus, 500 kg/ha of a 12:14:10 NPK fertiliser should be sufficient as a basal application at planting. Follow this with a side-dressing of 150 kg/ha urea, in two applications.
On the alkaline soils of the Lockyer Valley, lower levels of phosphorus are required. A basal application of 500 kg/ha of a 13:2.2:13.3 NPK fertiliser can be followed by 200 kg/ha sulfate of ammonia as a single or split side-dressing. On alkaline soils, responses to the trace elements zinc, manganese and boron may occur; they are best applied as a foliar application.
The best method for determining a crop's nutritional requirement is to do a pre-plant soil test followed by at least one tissue test in the early crop stage.
Harvesting and storing shallots
Shallots are ready to harvest about 10 to 12 weeks after planting, but some hybrid varieties may mature a little earlier. They should ideally be more than 25 cm long and 8 mm to 10 mm thick at the stem.
Shallots are hand-pulled, washed and bunched with the roots trimmed. Any damaged or diseased leaves should be removed. They are packaged in bunches of 10 to 12, depending on size, and either bound with a rubber band or wrapped in plastic. The tops are cut to a consistent length and pack in approved vegetable cartons. Forced air cooling is desirable to maintain freshness and shelf life.
True shallots are ready when the foliage becomes partly withered and bulbs have reached marketable size. True shallots are hand-pulled and should be stored in a cool, dry environment for about two weeks to allow curing.