No. 10
ONIONS & LEEKS
Leek - Allium ampeloprasum
Onion - Allium cepa Family: Alliaceae
Onions and leeks seed saving guide also available here as a PDF document (182Kb)
Onions and leeks share many characteristics. The main difference is that onion leaves are hollow tubes, while leek leaves are flat straps with a keel up the middle. Both are biennial, but the onion leaves die back to leave the dormant bulb while leeks are evergreen and winter hardy.
This section deals only with those onions and leeks that reproduce mainly by flowering and setting seeds. Other sorts (garlic, elephant garlic, shallots, potato onions, rocambole etc) may flower occasionally but are usually propagated vegetatively. These are dealt with in a later section, under Multiplier Onions and Shallots (Seed Saving Guideline No 15).
Allium flowers are perfect but cannot usually fertilise themselves. The male anthers open first and shed their pollen before the female stigma of that flower is receptive (protandrous). Individual flowers in ball-like heads open over a period of about four weeks, peaking in the second week.
Growing and Roguing
Onion flower
- Leeks and onions are biennials, so in the first year all you have to do is follow your normal practice for growing a fine crop.
- Onion flower stalks can reach around 150cm in height, leeks up to 180cm in height. So remember to have sufficient space and position stakes to tie them in later.
- Plant the best of your onions in the spring and they will soon put out fresh leaves and a flower stalk.
- Leeks are best left in their planting position to overwinter.
- Be ruthless about roguing any plants whose foliage is not up to scratch, or which flower in the first year.
- Susceptibility to disease, e.g. leek rust, can vary within a variety, so select the most resistant plants to save seed from.
- Only choose those onion bulbs which are characteristic of the variety.
- Avoid saving seed from ‘bull-necked’ (wide and non-rounded) or ‘bottle–necked’ (tapering up the stem) onions.
- You can slice across an onion, about a third of the way down, to check the evenness of the rings and the colouration, without any harm to the shoot inside. This allows you to check if it is true to type.
Pollination and Isolation
Bees and flies are the main pollinators, although alliums attract many other insects. Onions and leeks will not cross with one another, though varieties within species cross readily. The easiest way to maintain variety purity is to grow just one variety of each species for seed each year, allowing insects to do the work. They should be isolated from other varieties by at least 1,500 metres. You can grow others to eat, but be vigilant about removing flowers, especially from potato onions and shallots (for onions) and elephant garlic (for leeks).
If you do want to grow two or more varieties for seed you must either isolate by 1,500 metres or use one of the caging techniques. Unless you use alternate caging you will have to hand pollinate daily. Between 9.00am and noon remove the cage from each variety in turn and use a soft brush to transfer pollen between the flowers. Go round the flowers two or three times to ensure a good mix, and either clean the brush in alcohol between varieties or use a different brush for each variety. You may need an assistant to keep insects away while you are busy pollinating.
Harvesting
Allium flowers need to be watched carefully as the seeds mature because the ripe seed pods shatter easily (that is, they split and release the seeds). As soon as you can see the black seeds within the drying flowers you should cut the whole head and place it in a paper bag to finish drying. Please note: Leek seed tends to take a lot longer to ripen than onion seed.
Cleaning
Cleaning refers to the removal of chaff and debris, leaving only seed. Cleaned seed keeps better.
Most of the ripe seeds will fall from the dry flower head quite easily, encouraged by gently shaking. The rest can be removed by rubbing the flowers between your palms or across a sieve that allows the seed to pass through. The best way to clean the seed is by sieving and winnowing in a light breeze.
Storage
Onions drying
Handle onion bulbs carefully, to avoid bruising. Cure them in the sun for a couple of weeks before storing. Onions store best at low temperatures and low humidity (0-7°C/32-45°F, <40%R.H.) or high temperatures and high humidity (25-35°C/77-95°F, 60-70%R.H.). Room temperature (16-21°C/60-70°F) is the worst possible for storing onions. Storage gives another chance to reject defective bulbs, such as any that do not last for long.
Ripe onion and leek seed will store in a cool, dark place for at least two years.
Returning Seed to HSL
Seed must be completely dry and fully cleaned. Seed that retains moisture can go mouldy in transit and will have to be discarded. (It can take a few days to get to us in the post.) Pack it in breathable material (e.g. a paper envelope or cotton bag) and place it in a padded envelope or stout box to protect the delicate seed from impact damage, before sending it in the post.
Top of pageGarden Organic is the working name of the Henry Doubleday Research Association (HDRA).
We are not responsible for the content of external web sites.
Bookmark this page on: