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Onions (from seed)

Allium cepa

INTRODUCTION

Although Onions are readily available in the supermarkets, they are very easy to produce yourself and really are an essential part of any allotment or kitchen garden set-up.

Cultivated for centuries, Onions come in a range of colours and shapes and with careful planning and storage will give you a year-round supply.

Onions from seed are slightly more tricky than growing from sets, but you will have access to a much wider range of varieties.

Soil Preparation

Onions from seed are a relatively straightforward crop to grow but good soil preparation is essential for the best results.

The growing site should be in a sunny position with organic material added well in advance of sowing.

The ground should be light, fertile, free-draining and stone free. Heavy clay soils are not ideal.

Onions do not appreciate wet soils, especially if growing overwintered crops.

Onions also dislike acidic soils. Correct soil pH if necessary. 

Don't grow Onions in soil that has had Alliums grown in the last two seasons. Always practice crop rotation.

Sowing & Planting

The main advantage of growing Onions from seed is that you have access to a much larger range of varieties and types than you do with Onions grown from sets.

Onions produced from seed fall into two main categories -Autumn sown (Japenese types) and Spring sown. Each has its own specific selection of varieties.

Autumn varieties should be sown during August and September and Spring Varieties during March and April.

Each type shares the same sowing requirements.

Prepare the seedbed by removing stones and weeds and rake to a fine tilth and gently firm soil.

Take out a drill (shallow trench) 2.5cm (1 inch) deep and sow seed thinly.

Leave 25cm (10 inches) between individual rows.

Cover and water well.

As an alternative method, sow seed into modules and prick out into 9cm pot for planting out when weather permits.

Growing & General Cultivation

When Onion seedlings are large enough to handle, thin out to about 15cm (6 inches) to enable bulbs to reach their full potential. Closer thinning will result in smaller harvests. Thinning can be carried out in two stages several weeks apart.

Keep growing area weed-free but take care not to damage roots when hoeing.

Keep watering to a minimum as Onions do not like to be overly wet. 

Feed once or twice during the growing period.

Pests & Diseases

Onions are in general, a relatively trouble-free crop but the occasional issue may arise:

Bolting is the process where the Onion bulb prematurely flowers and runs to seed. It is caused by fluctuating growing conditions and temperatures. Try to keep growing conditions as constant as possible. If this becomes a regular problem, try growing Onions from heat-treated sets (The heat treatment removes flower embryos).

Onion White Rot is a soil-borne fungal disease and a serious problem if you have it. It will affect all members of the Allium family and can persist in the soil for twenty years or more. Avoid growing any Onion related crops in the same soil. 

Onion Fly will result in plants collapsing. The larvae eat roots in early summer, particularly during very dry weather. Cover susceptible growing areas with fleece.

Downy mildew which shows as yellow patches on foliage and affected leaves should be removed. To prevent, ensure good air circulation and low humidity. It is more prevalent in new growth. You could try growing a resistant variety such as 'Santero' 

Harvesting

Autumn sown Onions should be ready for harvesting during mid-summer and spring-sown crops during late summer.

Bend over foliage as it starts to go yellow and leave to die off naturally.

When foliage has died down, lift Onion bulbs and allow them to dry in situ. Finish drying and curing in the greenhouse or shed.

Properly dried Onions should store well into the new year if kept frost-free.

Store in Onion nets or tied into Onion strings.

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