Unlike most vegetables, onions can be grown in the same spot several years running, given careful soil preparation well before each. One of the secrets of growing good onions is that the soil must be made very firm for sowing, and for transplanting also, if the latter is done. They prefer a medium soil and a sunny open . But before then the soil has to be prepared, for though the onion itself matures on the surface, the fibrous go deep and consequently well-drained soil is required, deeply dug and well manured the previous autumn, putting in matured and hop manure if animal manure is scarce. After filling in the top spit work up into ridges (if the soil is really heavy) and then leave it to the frost and weather. As soon in the New Year as the ground is fairly dry, usually in February, level out the ridges and get a fine tilth by raking and apply a dusting of soot, which must be not less than 12 months old. A complete fertiliser can be worked into the top inch or two of soil, just before sowing or when the onions begin to form bulbs, usually about 6 weeks after sowing. At any favourable time from late February till the end of March do the sowing, only covering the soil and thoroughly firming with the foot (it is quite unnecessary to use a roller), the drills being 1 ft. apart. By sowing under glass in January in gentle heat earlier results are obtained. For autumn sowing the best time is early August in the north and towards the end of August in the south. The are then planted out in March. The procedure is the same as with spring sowings, except that can be sown rather more thickly, especially in cold districts. Note that //» oz- °f onion usually covers a 25 ft. row (there are approximately 7,000 onion to the ounce).
The spring sowing should be sufficiently forward by mid-April to plant out 6 in. apart, or thin out to the same distance, allowingto go down their length, not spread out, and putting the bottom of the young bulb only l/4 in. below the surface. Thin out when the onions are a couple of inches in height, and again when double that height, which should leave the 6 in. between. During August bend over the , so that they touch the ground, thereby hastening ripening (the back of a rake is a good tool for this job). Loosening the bulbs in the soil is also helpful. Lift the crop when the are obviously dead. A rather easier alternative to bending over is to run the hoe along each row 2 in. below ground to break the roots; this hastens ripening without the trouble of bending over. In any case lift within 3 weeks, putting the onions to be sun-dried on sacks or boards, the roots facing the sun. When dried, they can be strung in ropes for storage till wanted. Alternatively they may be stored in trays. Always choose a cool, dry shed or other place which is reasonably airy. Should any of the onions start for seed, pinch off the seed shoot; the bulb will then continue to grow. Onions can also be ripened by spreading the bulbs out under cloches. Turn them over occasionally. Cloche-raised onions are less liable to stand still for a while when planted in their permanent quarters. In the south sowings can be made at the end of January, but in the north early February is best. Place the cloches in position 10—14 days beforehand to warm up the soil. For spring or salad onions make a sowing of White or White Spanish (Lisbon) in August and protect from frost. The ordinary thinnings from general sowings are also quite tasty as spring onions. For pickling onions, fairly thickly any time up to June, and thin to about 2 in. White Portugal and Paris Silverskin are suitable varieties. Rich soil is unnecessary.
Choice of Varieties:. Onions differ considerably in colour. For example, there are varieties with yellow, brown, red or white skins. They can be flagon-shaped, spherical, flat etc. Some, like Unwin’s Reliance, James’s Keeping and Sutton’s A 1, have exceptional keeping qualities whereas, on the other hand, the Italian varieties like Giant Rocca and White Tripoli do not keep for long.
Varieties for spring sowing include Bedfordshire Champion which sometimes bolts when sown in August. The large globular bulbs have light brown skins, a mild flavour and keep well. James’s Keeping or James’s Long Keeping is another globular onion with a reddish-brown skin and a rather stronger flavour than Bedfordshire Champion. Rousham Park Hero makes very large straw-coloured bulbs, flat and with a mild flavour. It does well on light soils. For autumn sowing Unwin’s Reliance (also known as Reliance, Big Ben, Isleham and Okey) is hard to beat. It makes a large, flattish bulb sometimes described as chestnut copper, is happy on dry soils and probably keeps as long as any variety. Sutton’s Solidity is another excellent keeper.
The Welsh or perennial onion is evergreen, succeeding on most soils without special preparation. The leaves andare used for flavouring. Increase by division of the clumps in March.
Insect Pests and Fungus Diseases:
Onion Fly. A widespread pest which is fortunately fairly easy to control by timely application of modern insecticides. The first generation of the onion fly appears in May, eggs being laid near the seedlings. They hatch out andon the base of the plants. Infected specimens can be detected by the limp, yellow appearance of the leaves, especially at the tips, also an unpleasant smell. Such plants are unfit for use and should be burnt, with the maggots in the soil. Onion flies often breed in fresh manure, hence the advisability already emphasised, of manuring land intended for onions as long as possible beforehand. A firm seed bed makes it harder for the fly to lay its eggs. Autumn-sown onions, as with broad beans, seem less liable to attack than spring sowings. Sowing in boxes and planting out in showery weather are also claimed to keep down attacks. Thin sowings undoubtedly help since handling the seedlings increases the onion smell which attracts this pest. Calomel dust and gamma-BHC (lindane) are often dusted along the rows when the onions are in the ‘loop’ stage. Alternatively, aldrin dust can be incorporated in the seed drill or applied as a band about 4 in. wide along the rows when the seedlings have emerged. A further dressing may be given in July as there are three generations of onion fly.
Onion. Most varieties of onions and shallots are susceptible to onion . Symptoms can be observed as early as March, especially in damp weather, although the disease is generally noticeable after the bulbs begin to form. Light, greyish-mauve patches appear on the leaves which may later shrivel up. The often spreads into the bulb and overwinters on the scales, as well as in the soil. It is more common on low-lying badly-drained land.
Diseased plants must be burnt and if the entire crop is infected, rest the land from onions for two or three years. Spraying with Bordeaux mixture or a proprietary copper fungicide in spring and again as necessary may give some control but onion mildew is often less responsive to fungicides than many diseases. Note that Bedfordshire Champion and James’s Keeping are decidedly susceptible.
Onion White Rot. Often troublesome in the north, as it thrives in a moist atmosphere. The foliage turns yellow in summer and a white, fluffy growth is found at the base of the bulb. This subsequently develops into black ‘pin-heads’ which are the sclerotia or resting-bodies of the fungus. Unless diseased bulbs are immediately burnt, the sclerotia will contami- nate the soil so that onions cannot be grown for up to 8 years. There is unfortunately no infallible chemical control and a long rotation is normally the only practicable remedy. In recent years, however, it has been found that a fairly good crop can be raised by the use of calomel dust (already mentioned as a control for onion fly). About 4 oz. will suffice for an 18 ft. row, the dust being applied to the open drill before sowing. This treatment seems to be most effective for spring sowings as when applied to autumn sowings growth may be retarded. Note that Ailsa Craig, Premier and White Lisbon are very susceptible. Bedfordshire Champion, Rousham Park Hero, Sutton’s A 1 and White Spanish show some resistance.
These are small onion bulbs about the size of marbles (raised from seed sown the previous summer). Where onion fly is trouble some onion sets are often preferred, as they usually escape the attentions of this pest. The older types of onion sets had a tendency to ‘bolt’ but present-day sets seem less liable to this trouble. They are planted in early spring in the same way as shallots, I.e. shallowly so that only the tips of the bulbs are visible above the surface (like shallots they tend to work loose from the soil). Space the sets 9 in. apart in rows 1 ft. apart. Stuttgarter Riesen is a good variety, resembling Unwin’s Reliance. Dobie’s Giant Globe is also excellent, yielding nearly 70 lbs. of onions from 1 lb. of sets. Onions grown from sets die down and ripen earlier than those grown in the normal way from seed. They are therefore particularly useful for northern gardeners as a cooler atmosphere and a heavier rainfall delay ripening of bulb onions.
Weeds are invariably a major problem among young onions. Promising results have been obtained with a new pre-emergence weedkiller known as S. E. 2 which is applied before the seedlings come through. It is claimed that all weedgrowth on the surface layer of soil is destroyed. This means clean ground for about 6 weeks, ensuring that the newly sown crop derives the maximum benefit from light, moisture and plant nutrients in the soil.
A flame gun can also be used 7—10 days before sowing. This will avoid any risk of damaging the seedlings. See WEEDS for particulars of this technique.