Onions and their relatives belong to a group of vegetables that have evolved a rather specialized growth habit results in the formation of bulbs at the end of their growing season. A bulb is a swollen storage organ that allows a plant to survive climatic extremes in its natural environment. The great advantage to us is that the bulbs keep exceptionally well in the kitchen enabling us to have onions all year round.
Onions and many of their relatives (such as garlic) are thought to have originated in central Asia or the Middle East and as such are one of the oldest vegetables in cultivation. Their cultivation can be traced back to Egyptian civilization, as early as 3200 B.C. From there they have spread around the world and, not surprisingly, local varieties have been selected for different climates, making it important to choose a variety that is well adapted for the area they are to be grown in.
Another interesting aspect of this group of plants is that most derive from species belonging to the genus Allium that belongs to the lily family. As well as producing the many edible plants that are featured here, the genus also contains many interesting ornamental members that have purple, pink or white globe-shaped flower heads that can be featured either in the garden or as cut flowers. Indeed onions and garlic will produce pleasant but small flowers if allowed to grow to maturity.
This ‘onion’ group generally follows a similar pattern of growth with seeds being sown in the spring and rapid growth occurring through the warmer months. As the days get longer and temperatures increase the formation of bulbs is triggered. The bulbs then form in late summer and fall when they are ready for harvest and storage. Some members of the group such as shallots are harvested before bulb formation occurs and the immature shoots are chopped up and used in cooking.
Growing requirements are very similar for the entire group with well-drained, fertile soils in full sun giving best results. If your soil conditions depart from the ideal then building up a raised bed 10-20cm above the existing soil will solve the problem. Use some recycled bricks or railway sleepers to enclose the bed and fill it with a suitable soil mix that can be delivered in bulk from your local garden centre or landscape supplier. Such a bed will be ideal for a wide range of vegetable crops other than the onion group.
As a rule the ‘onion group’ prefers a Mediterranean-type climate with hot dry summers that are ideal for bulb formation as well as mild spring weather during the establishment phase.
Salad onion in the garden
Onions – Red, white and brown
There are hundreds of different varieties worldwide but all originally have arisen from the species Allium cepa. Over thousands of years of selection various skin colors such as the familiar brown, white and red have arisen but all are alike in their growing requirements. It is simply a matter of selecting a variety that has the color and flavor you desire as the different colors have similar growth habits generally speaking. They can be easily grown from seed sown directly into the garden or from seedling punnets. Plant them as early as possible in spring and do not be afraid to plant them close together as they can be thinned out with the immature plants suitable for garnishing salads as one does with chives.
A characteristic feature is their ability to induce tears in the kitchen due to a sulphur compound that is converted to sulphuric acid when in contact with water causing the characteristic stinging of the eyes. Chilling your onions in the fridge makes the offending chemicals less volatile and will help considerably to keep your eyes dry.
These are special varieties of onions that have been selected for rapid early growth that makes them particularly well suited to being harvested when immature before bulb formation has occurred. They are often incorrectly referred to as shallots that are actually an entirely different Allium species. Spring onions can be grown from seed sown right through the warmer months and harvesting can begin as soon as they are big enough to cut. Sow them thickly as the entire plant is removed from the ground when they are harvested.
Shallot (also known as eschalots or green onions)
Shallot is also a specially selected variety of onion that is harvested either as a small pointy bulb or immature as a green shoot (hence the name green onion). The shallot bulb has a tapered shape and a fine-textured, coppery skin, which differentiates it from onions. It also produces many small bulbs as opposed to the large bulbs formed by most onion varieties. True shallot as opposed to spring onion has a milder flavor and also grows better in hotter climates. Seed is difficult to obtain and so it is grown from small bulbs that should be planted in spring. Bulbs can be saved from a previous crop but initially they can be difficult to find. If all else fails bulbs purchased from a vegetable retailer can be used to get started.
Botanically known as Allium sativum, garlic is very similar in its growing and climatic requirements to onions. Its habit of growth is rather different as it forms clumps of small bulbs (cloves), rather than one big bulb as for onions. The easiest way to get started is by planting healthy looking cloves in early spring directly into their final position about 19-15cm apart with the nose of the clove just protruding through the soil.
The entertaining botanical name Allium ampeloprasum variety porrum indicates that leeks are fairly closely related to onions. They are, however, rather different in that they do not normally form large bulbs in cultivation. The leaves differ also in being long and flat, forming into a tight cylinder. Leeks are harvested for their long, white stems and swollen bases. They have a milder flavor than onions and garlic and are excellent as a cooked vegetable or in soups. Leeks are more adaptable to climate than onions and grow more quickly.