Growing Bulbing Onions in Tasmania.
The onion (Allium cepa) is a biennial bulb (2 year life). I often hear at market that people find onions difficult to grow, but with a little practice, most gardeners can do it successfully. There are just a few basic rules to follow in Tasmania to enhance success. They can be planted as seeds, as transplants, or as “sets” (small onion bulbs that are about to begin their second, final year of growth). In Tassie it is more common to plant via seeds due to our climate and that is the only way I have done it.
If growing bulbing onions from seeds, onion seeds are usually planted indoors at least six weeks (July to August) before outdoor planting time (September). Onion seedling transplants need outdoor temperatures above 10 degrees C before they can be moved into the garden, something that is not difficult to attain in late August and September in Tasmania. Soils are a bit cold where I am to sow seed direct.
Planting Onion seedlings
Seedling transplants should be spaced about 10 cm apart, also in rows spaced 30 to 45 cm apart. I have multi-sown onions before, ie: planted 3 seedlings to a hole. You end up with small to medium sized bulbs rather than 1 large one. Yield may be the same or even more and it depends on your goals if you plant singles or in threes. Seedling transplants tend to produce larger onions in my experience where I am, as seeds left in cold soil struggle while seedlings get a head start in growth before planting out.
Tip – Pick the correct onion variety for Tasmania and plant at the right time.
There are three types of onions. Make sure to choose the right variety based on your climate:
- Short-day onions will begin forming bulbs when there are 10 to 12 hours of daylight each day. They work well in northern states where summer daylight is comparatively short. Some common short-day onions include ‘Cipollini’, ‘early white’, ‘Gladalan Brown’. Can grow in Tas if timed correctly but I have not tried.
- Long-day onions begin forming bulbs when there are 14 to 16 hours of daylight per day. They are good for Tasmania and southern states where the summer days are relatively long. Some recommended long-day onions include Creamgold, Pukekohe long keeper, Red Sheffield, Red Rippa, Spanish Brown.
- Mid-day onions begin to form bulbs when they experience 12 to 14 hours of daylight each day. They are good for gardeners in central areas such as NSW to Vic. Possible to grow in Tasmania but I have not tried.
So go for long day onions planting in July/August
- Use as fresh a seed as you can. Ideally seed only up to 1 year old or at most 2. They don’t maintain high germination rates for that long.
- Onions need full sun (six hours per day minimum preferably in order to grow at good rates). The more sunlight the better.
- Soil is the key. You need well-drained (sandy soil is quite handy here). Adding lots of quality compost is a big advantage. Onions like a slightly acidic to neutral pH—6.0 to 7.0.
- Onions need regular water to support the swelling of the bulbs. Give them 1 inch of water per week, but don’t overwater or allow the bulbs to sit in soggy soil, since this can lead to bulb rot.
- Optimal growing conditions for onion foliage is 19 to 25 degrees C which is perfect in Tasmania in early to mid-summer. This will lead to rapid, full growth of the edible bulbs.
- Onions are moderate feeders. Fertilise them every few weeks with a high-nitrogen fertilizer to support leaf growth (Powerfeed and Seasol I use in a watering can), which will produce big bulbs. Stop feeding when onion bulbs begin to push the soil away.
The Onion Harvest
The time required for the bulbs to mature depends on the variety. But you can harvest onions at any stage—even seedlings thinned from a row can be used as spring / bunching onions.
I harvest onions when around half of the top leaves have collapsed and when the skins have a papery feel. Ideally leave the onion in the ground until over 50 % of the green tops have collapsed as this will help them store longer.
When harvesting, use a tool to help gently pull the onion up without tearing the leaf from the bulb. I them braid them like garlic and hang under the deck roof to air dry until bring them inside around early March. Creamgolds are ready around January and Red Sheffield seems to be a few weeks behind but the season dictates time to maturity.
Onions keep longer in cool temperatures (under 5 degrees C) but should not be allowed to freeze. Onions can also be stored in mesh / hessian type bags or by braiding the tops together and hanging as I do; just make sure they get good air circulation.
If they are close to ready for harvest and you see heavy rain forecast, pull them up. Generally, our weather is warmish and dry when harvest time comes but like garlic, you don’t want them saturated at harvest.
And that is it. About 4 square metres planted to bulbing onion will provide a hefty amount of your yearly intake depending on your family size. Onions may be cheap at the shop, but they will have been treated with all sorts of chemicals and fertilisers. They do take up some space in a small veggie patch, but even a months’ worth of onions is well worth it in my book.