Down in the Garden: Growing Onions

Now that tomato season has left us, one crop you can pop in and successfully grow after this heavy feeder is onion (Allium cepa).

The best time to plant onions on The Coast is from March until May and while it is true that you do need a bit of space, you can plant out successive crops over a few weeks of heirloom varieties or favourites to add a bit of interest to your harvests.

Onions have three types that are related to the amount of daylight hours available: short, intermediate and long day-length.

Here on the Coast, at this time of the year, you can grow most types but will do far better with early varieties for this time of the year.


Onions are a biennial plant that are grown as an annual for culinary use.

As with all vegetables, there is a far greater range of seed varieties than seedlings.

Germination of seeds can be a little bit of an issue with onions, so it is far better to get them started in seed trays and then plant out at about 4 weeks after germination.

Another way to start your crop is with seedlings or seeds sets (small bulbs).

General disease resistant varieties include ‘Marco’ and ‘Golden Bear’ while both ‘Feast’ and ‘Norstar’ being rather good at withstanding downy mildew.

‘Gladalan Brown’ is mild onion very suitable for the Coast, as is ‘Lockyer Early White’.

An heirloom variety that you really should try is ‘Barletta’.

It’s quick to harvest at just seven weeks if you are after baby onions to pickle or it’s sixteen weeks to a mature harvest.

As they grow, you will notice that onion bulbs push up out of the ground. This is normal and you should not cover them with soil or mulch.

Growing Notes

Position: All onions need lots of full sun they do well after leafy crops like tomatoes and also lettuce and cabbages. You can grow onions in large pots but the yields will be a lot smaller.

Soil: Your soil will need to be non-acidic with a pH level sitting at 6.5 so add lime if needed.

It also needs to be well-drained and the reason it makes a very good crop after plants like tomatoes is because they use up a lot of nitrogen which you don’t need for onions (in fact excess nitrogen is not a good thing at all).

They need potassium and so adding potash or wood ash prior to planting is a good practice to ensure healthy yields.

Water: The problem most people have with onions is ‘bolting’. This is not your onions running away, but rather sending up seed heads as they think that life is coming to an end for them.

To avoid this, water regularly and do not allow them to dry out, but don’t overwater as they will rot. When newly planted, watering around two or three times a week is good and then you can cut back to around once a week after three months.

Fertiliser: Just a light general feed with a low nitrogen all-purpose fertiliser every couple of weeks will do.

Pests & Disease: The thing that onions hate most is weeds, so keep them under control. Other problems you may encounter are onion thrips, onion maggot and downy mildew.

Onion thrips can be deterred by ensuring even watering but look out for them in the throats of the foliage, treat with an organic pesticide.

Onion maggots move in when you have too much organic matter in your compost mixture that has not broken down. Make sure Ph levels are also correct in your soil and you will also need to spray with an organic insecticide.

Downy mildew looks like cotton wool developing around plants. Make sure spacing is adequate for your variety to avoid it an if you find it occurs, you could try this organic mixture:

Place a handful each of nettle, seaweed and comfrey leaves in a container, cover with water and a lid for 48 hours. Strain and bottle and then use 1 part mixture to ten parts water. Spray on bulbs to prevent and to stop mildew.

Harvest: Onions can be harvested at any time, it all depends on what you want to do with your crop.

They can be pickled or simply cooked whole as ‘baby onions.

You will need to lift them once their growing period has ceased and this is indicated by the wilting of leaves.

Whenever you harvest, pull gently from the soil, trim leaves to within 3cm of the bulb and then leave in a sunny place to dry out.

They are ready for use or storage once the skins and roots have dried out.

Onions are best stored in a cool, dry, dark place and I find mesh bags that I hang somewhere are best.

You may notice advice saying that onions can be left in the ground to dry out and while this is true for some places, I’ve found that on the Central Coast, is can be a little wet in most areas to successfully do this.

Companion Planting: Onions are happy neighbours with carrots and beetroot but not with peas, beans or potato.

Onion Folklore & Facts

The Ancient Egyptians ate onions but they also used them in their mumification process.

Long being regarded as an excellent antiseptic (due to their sulphur content), they have been used throughout history to dress wounds.

Don’t quote me on this, but I have found references to onion juice mixed with honey being a cure for baldness and placing an onion in each corner of a ‘bad vibe’ or even haunted room will send that unwanted energy packing.

If you want to rid yourself of cold or flu you might try placing a thick slice of onion to the sole of your foot and then wear socks over them to bed.

Apparently, according to this old folk remedy (below grey box), you should reduce symptoms overnight.

While onions have a long growing period of up to six months and so are perhaps not suited for smaller gardens, they are worth the space as they require little effort once they are established. A last little trick: if you tie the all the leaves into a knot, 16 weeks after germination, this will accelerate the bulb growth.


This week you could plant: onions, artichoke, Asian greens, beetroot, broad beans, broccoli, brussels sprouts, cabbage, carrot, cauliflower, celery, chives, coriander, endive, English spinach, alyssum, calendula, carnation, delphinium, everlasting daisy, godetia, hollyhock, lobelia, pansy, primula, stock, wallflower.


Ultimate Fungal Wizardry April 10th Join Urban Kulture for this in-person workshop in gourmet and medicinal mushroom cultivation. Learn how to grow your own mushrooms in only 2 hours. Gosford Regional Gallery and Edogawa Commemorative Garden. Saturday at 9:30am, 11:30am, 2:30pm or 4:30pm


School Holiday Program: Autumn Adventure Woy Woy Library, Monday, 12th April 10:30am to 11:30am

Decorate you own plant pot, construct a leaf press decoration, create leaf artwork and more. Ages 5-8 years.


Cheralyn Darcey is a gardening author, community garden coordinator and along with Pete Little, hosts ‘At Home with The Gardening Gang’ 8 – 10am every Saturday on Coast FM.

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