Onion growing from sets - Onions how to grow, tips, varieties, cooking.

For the time pressed gardener onion sets are a godsend. Onions seed can take a long time to germinate; it transplants poorly, and needs a long season to attain a kitchen ready bulb size. So it usually makes more sense to grow your onions from sets instead.

Sets are just one-year-old onion seedlings that were dug up whilst the bulbs were still immature. The bulbs are then gently dried, stored for the winter, and arrive in garden centres the following spring. I suppose you could say the sets are in hibernation at this time and you reawaken them by sowing them into your gardens soil.

Common names:
Onion, garden onion, Spanish onion, red onion, cooking onion, or bulb onion

Botanical name:
Allium cepa

Area of origin:

Brief description:
Onion plants comprise vertical hollow shoots, usually green in colour, atop a swelled underground stem know as a bulb. These bulbs depending on the variety grown will vary in colour from white, to yellow to red. If left to flower (inadvisable for kitchen use), the onion plant will produce a ball-like cluster of white or lavender flowers.

Are they easy or hard to grow?:
Reasonably easy to grow once soil is suitable. Growing onions from sets is certainly easier than growing straight from seed.

Varieties suitable to grow in Ireland:

Rijnsburger 5 (large globe onion with pale yellow to straw coloured skin, white flesh, good taste, stores till May the following year)

Ailsa Craig (medium-sized globe onion with pale yellow to straw coloured skin, white flesh, excellent mild flavour, popular exhibition variety, stores till March the following year)

Stuttgarter Giant (bulbs are less round and more flat, excellent mild flavour, bolt resistant)

Sturon (medium-sized globe onion with light brown skin and juicy yellow flesh, bolt resistant)

Note: Onion sets that have been heat-treated have less chance of bolting or running to seed, so I suggest you ask for heat-treated when dealing with your supplier.

Irish stock.

UK stock.

When to grow:
Onion sets are usually sown from the middle of March until the end of April.

Where to grow, and soil conditions required:
Onions grow best in an airy sunny location on fertile soil that drains well. Avoid at all costs soil that waterlogs or conversely dries out rapidly. Onion sets are slightly more forgiving of poor fertility than onions grown straight from seed.

Onions don’t grow very well in a strongly acid soil preferring instead neutral to slightly alkaline soils (6.0 - 7.0 approx). If the pH (relative acidity or alkalinity) of your soil is not suited to the vegetable, then soil nutrients such as Nitrogen, Phosphorus, Potassium, iron, boron, copper, manganese and zinc start to become unavailable, leading to poor crops.

You can use a home soil test available in most garden centres to determine your soils ph. By taking account of the test results you can then decide how much if any amendments are required to bring the to pH of your vegetable garden soil in line.

The application of ground lime will be helpful in countering the acidity. As a rough rule of thumb an application of 250g of ground lime per metre squared the autumn before planting/sowing will commonly increase your ph by about one point. However as lime is available in different formulations, I advise also consulting the rates set out on the pack.

Food reserves required:
For long term feeding of your crop, every 10m2 of growing area should have one wheelbarrow load of well-rotted homemade compost or farmyard animal manure spread over its surface sometime during the autumn/early winter before planting/sowing. Dig this in to a spades depth all over the proposed growing area to enrich it for your crop. Whilst digging, remove any stones and other obstacles that might obstruct roots.

As a rule of thumb, well-rotted manure/compost will be over six months old, and tend to be dark brown will little if any smell. You should not be able to distinguish individual pieces of straw, hay, vegetable peelings, grass etc., as it will all be rotted down.

A week or two before planting/sowing you should also lightly rake into your growing area a well-balanced fertilizer. Growmore or fish blood and bone (organic option) are both suitable for this purpose. Apply according to the rates on the pack.

How to plant or sow:
Onion sets can be sown by simply pushing the bulbs down into soft crumbly soil leaving the tips of bulbs just above the soil surface. If you fear your soil is not soft enough or that you may possibly damage your bulbs by planting this way then you can always sow them into shallow drills instead.

At 12 inch 30cm (30cm) spacings create flat-bottomed drills 1 inch (2.5mm) deep, then lightly press your sets into the base of these. After sowing close the drills with soil, lightly firm around the sets, water well and label.

Caring for your crop:
Keep the soil around the onion plants weed-free. Take care when weeding because the roots and bulbs are easily damaged.

During a prolonged spell without rain (week or more) you should water gently but deeply once a week. As a rough rule of thumb apply approx 10 litres per metre squared of soil area. Carry out this watering in the morning and try to avoid splashing the leaves, watering the soil instead. Forget about manual watering altogether once the onion bulbs have swollen to full size (usually late summer or early autumn), as at this time dry conditions are an aid to the eventual harvest

One option to conserve soil moisture in a dry summer is to spread a one to two inch thick layer of grass clippings on the soil around the plants. Ensure the clippings are weed killer free and that they do not directly touch the plant stems.

At about the ninth or tenth week after sowing and while plants are growing strongly you can apply a second application of a well balanced fertiliser. Although not essential, a further scattering of Growmore or fish blood and bone can increase the vegetables vigour and make them less susceptible to plant ills. Once scattered the fertiliser should be lightly scratched into the soils surface followed by gentle but deep watering of the soil.

If you notice any set lifted by frost or birds you can resettle them back down into the soil. Should any flower stem/heads start to appear you should snap these off. Take note of which onion plants these appeared on and use these in the kitchen first as they will be useless for storage purposes.

Pests and Diseases:
Bird attack tends to be one of the main pest problems encountered by onion set growers. These pests tend to pull up young setts root and all. Bird protection in the form of netting should be used. Fine netting draped across a few twigs will provide protection against these birds. This protection measure is especially important if pigeons are a problem in your area.

Other troubles of onions include…

Onion fly,
Stem and bulb eelworm,
Neck rot
White rot/Mouldy Nose
Root rot
Downy mildew
Set Division
White Tip
Bull/Thick Neck
Leek Moth

You should not encounter major problems with this fungal disease on onions if you follow the soil preparation, plant spacing, feeding and pH rules mentioned earlier. With any cases of this disease, when you are watering you should try to avoid splashing the leaves which can spread the fungal spores.

Harvesting, when and how:
Once your onions display swelled bulbs and stems beginning to yellow and topple (at about 18 weeks), then they are close to harvest. This can be encouraged along by manually bending over the stems once the leaves start to yellow.

After a further two weeks you can begin on a dry day to carefully lift your crop with a hand fork. Lift them completely out of the soil onto trays, boards or some other dry surface that allows them season through sunlight and air movement. Any bulbs that are damaged or soft should be discarded, whilst all bulbs with thick necks or those which produced flower stems/heads should be used the kitchen first as they will be useless for storage purposes.

If the weather is warm and dry then outdoors will be fine for drying your crop, otherwise it can be carried out in indoors on a shed windowsill or on shelves in the greenhouse. Drying should take about two to three weeks, throughout which time you will have turned the bulbs around a few times so as to allow light to season the skin all over.

I find it beneficial when drying my onions to have the bulb section slightly elevated compared to the drying stem. I feel it helps prevent rot by stopping any trapped water within the hollow stem from flowing into the bulb.

For short-term storage (one week) of bulbs with thick necks or those which produced flower stems/heads (one week), place them in the salad crisper compartment of your refrigerator.

All onions that have been allowed to dry for two to three weeks can then be stored in a cool dry place for approx six or seven months. Trays, slatted boxes, net bags or tied off pantyhose are ideal for storing the onions whilst allowing airflow. Some gardeners even go for the decorative and practical option of onion ropes, where the bulbs are strung up a length of cord using their dried stems.

Onions are a cooks most adaptable vegetable. As accompaniment to the main course they are incomparable. Use them to flavour stews, casseroles for instance. Garnish your salads with thin onion rings from mild varieties, or fry the stronger ones to top off liver or beef burgers. Pickled onions are untouchable when teamed with crusty bread and cheese for a “farmer’s lunch”.

More debate about this topic on our forum,
click The Irish gardeners forum.

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