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Tozer Seeds are continuing to develop new Allium cepa salad onion varieties. The incorporation of winter hardiness into a traditional White Lisbon type was an early success. More recently Ramrod, a winter hardy variety with erect stiffer leaves was released, followed by Eiffel, an erect, stiff leaved, slow to bulb variety for summer use. Our aim is to further develop A. cepa salad onions and improve our interspecific variety Guardsman. We are also active in developing improved A. fistulosum varieties such as Summer Isle.
Disclaimer
The descriptions, advice, suggestions and vegetation cycles below are aimed professional growers and are offered in all good faith, for purely informational purposes.
Fore more information please contact us on 01932 862059 or email info@tozerseeds.com
Please use the links below for detailed technical information about Salad Onion. For further assistance please contact our Salad Onion specialist, David Leeson
The production of salad onions in the U.K. is carried out on a large scale, with several thousand hectares of the crop being grown at various locations across the country. They are also known as bunching onions, spring onions and, in Ireland, scallions.
Salad onions are all members of the Allium genus, a genus which includes some of man’s oldest cultivated crops. They are classified as low growing perennials and are noted for their characteristic smell.
Salad onions fall into three main types, or families. Allium cepa types, Allium fistulosum types, and in recent years, a cross between the two, which, in theory, contain the best attributes of both.
These are sown from early February, in succession until late July, giving crops from mid June until the end of November, depending how kind the autumn weather is. If fleece is used on the first drillings, the harvest date of the crop can be advanced by up to a week.
These varieties can also be drilled from early August until late September, for overwintering, with the crop becoming harvestable from early April into June.
Also known as Japanese salad onions, these types are not winter hardy, and are therefore only used over the summer and into the autumn. They generally have stiffer tops than cepa types, and are especially useful in the autumn, when downy mildew can be a huge problem in the salad onion crop. In the UK more and more of these types are being grown over the whole summer, rather than just late summer into the autumn, again, because of their disease tolerance.
Fistulosum types usually have a hotter, drier flavour than cepa types, and can also tend to be stringy, if really mature.
The varieties available on the market as crosses between the two above types, are becoming very popular, as they have been bred to blend the better characteristics of cepa and fistulosum. They can grow more quickly than either cepa or fistulosum types, and are often used for quicker harvest dates from drillings at the same time as cepas or fistulosums. They are not generally winter hardy, so are used in the summer months, usually at the start, and more especially for the end of the summer season, as their disease tolerance from the Japanese influence comes to the fore.
Although these cross types are very popular, and are taking more and more of the market, their germination is often slightly lower, and their root systems are very vigorous, making them more difficult and expensive to process than straight varieties of cepa or fistulosum. Their shelf life is generally longer, however, adding to their popularity.
Salad onions grow best, in light, well drained soils, and will not tolerate acid conditions. The ideal pH for the crop is 7.0, and the base dressing required for the crop, is best determined by a soil analysis. The soil index will suggest phosphate, potash and magnesium requirements, and normally, 50 kg per hectare of nitrogen is sufficient to establish spring and summer grown crops. The over-wintered crop will not, usually, require nitrogen in the seedbed.
Most growers use air drills, which place the seed quickly and accurately along the rows. Salad onions are normally grown in beds, with four double, or seven single rows to the bed. The number of seed along the row should be approx 100 seeds per metre run, on either single or double rows. Seed density should be around 2.4 million to the hectare over the spring and summer, increasing to approximately 3 million seeds per hectare for overwintering, to compensate for the inevitable mortality of a proportion of the crop due to the weather. The exact amount of seed required is determined from the germination figures of the seed, the type of drill used, time of year of drilling, and of course, the target plant population per acre. These plant populations allow plenty of air flow through the crop, helping to minimise disease problems, and give the maximum return per hectare.
All salad onion crops will require top dressing with nitrogen. The overwintered crops should not be top dressed until spring, and then, as with the spring and summer sown crops, up to 125 kg per hectare, applied in split applications to enable the crop to make optimum use of it.
Weeds
Salad onions are not very competitive, and good weed control is very important. A heavy weed infestation in the crop will take away nutrients intended for the onions, and increase the risk of attack by pests and diseases. There are a number of good herbicides on the market to deal with the weed problem quickly and effectively, but do note that weather conditions can reduce the efficacy of the chemicals applied. Note also, that these crop sprays all have a harvest interval, which must be adhered to, please consult a qualified agronomist for further information.
Bean Seed Fly
The Bean Seed Fly lays its eggs in the soil near the onion seeds, and, as the seed germinates and starts to grow away, the eggs hatch, the resulting maggots move onto the seedlings and systematically destroy them. Treating seed with Tefluthrin (Force™) is an effective preventive measure.
Onion Thrip
Thrips graze on the leaves of the onions, leaving unsightly silvery coloured lines on the foliage, making the crop unmarketable. They can be controlled by one or several applications of insecticide, please consult a qualified agronomist for further information.
Other occasional pests of salad onions are Onion fly, Cutworms and the stem nematode (Onion bloat).
There are a number of diseases which can have a detrimental or even devastating effect on the crop. Some of these diseases are more common at certain times of the year, and immediate remedial action is required, if the maximum yield is to be achieved.
Downy Mildew
Downy Mildew is one of the most serious problems to affect salad onions, generally attacking the leaves on wet autumn mornings. After infection the leaf tips will go yellow, often as spots or patches. A fine whitish brown will then develop on these patches.
Collar rot
The overwintered crops are susceptible to Collar Rot, which makes the plants collapse at ground level,
Leaf Rot (Botrytis)
Leaf rot is perhaps the most common disease of salad onions; it causes silvery lesions/leaf spotting on the leaves, and can render the crop unmarketable particularly if the attack occurs during warm humid conditions.
White Rot
Where salad onions have been repeatedly grown on the same land, or grown on the land again after only a short break, White Rot can be a major problem. The disease is first visible when the leaves turn yellow and die. Examination of the roots will reveal thread like white mycelia at the base of the stem. Onion seed can be treated with Polycote WR which is very effective in preventing White Rot, although treating seed in this way may affect its germination.
