Crop Focus: Onions
Why Grow onions?
We were first inspired to grow our own onions after visiting Les and Bev Blackwell’s garden about 14 years ago. Les had a beautiful framed bed in which fitted exactly his year’s needs of onions! And now, having grown our own onions the last several years, I can say it is such a worthwhile crop to grow. Most of us probably start cooking each meal by gently sauteeing an onion or two. That’s 360 onions already! Then there’s chutneys, relishes, pickles and kassundi which use lots of onions too!
Onions don’t take a huge amount of space as they are closely planted, and if well mulched need very little attention.
They are a great storage crop – once harvested, they can be plaited and hung in a dry cool spot ready to use as needed. They usually store til around November when they start to sprout.
Growing your own means you can eat organic onions! Why is that important? Non-organic onions are pretty cheap to buy, but there is a nasty side to them (see below). On the other hand, organic onions are free of all the nasties, but 3 to 4 times the price of non-organic (and for good reason!). So if you want to be able to partake freely of one the most health giving vegetables in the world, GROW YOUR OWN!
Why are non-organic onions not so desirable? Commercially grown onions are planted pretty close together, in huge mono crop fields – a perfect situation for insect pests and diseases to breed up fast. So they are regularly sprayed with…
Insecticides, including organo phosphates and synthetic pyrethrum (which kills all insects whether beneficial or pest), mostly to control thrips, which is a common insect pest for onions, and with
Selective herbicides for weed control.
onions take around 5 months from planting til harvest, so they receive a lot of different sprays over their lifecycle. And all of that is absorbed into the green onion leaves, which swell to become the onion bulb (which we eat), plus the skins and into the soil.
So if there is one crop worth growing yourself it is ONIONS!!
Time from Sowing to Harvest: Longkeeper types: 6-7 months; smaller types like Purplette, 3 months
Onion seedlings are slow growers. They take around 8 weeks from sowing to being large enough to plant. Once planted, the larger long-keeper varieties will take around 5 months to grow to harvest size (September to January). They do most of their leafy growth in winter/spring and then bulb up when it starts to heat up.
Soil Needs: onions are fairly light feeders so a light dressing of compost will be enough. Foliar feed with seaweed spray made from kelp.
Water needs: Onions need damp soil to keep growing and avoid stress. The critical time for onions is when they start to bulb up. If denied water, the onions will be small, and the stress could attract thrips and black fly. The key is to mulch them well once they are big enough to grow above the mulch layer - about 15-20 cm tall. A 10-15 cm layer of dry bamboo leaves/chopped banna grass make fantastic mulch for onions. The mulch will also make it super easy to keep on top of the weeds. If you have a good water supply, a good deep water every few days in the heat of summer will be worthwhile.
Pests: Thrips is a tiny long insect which LOVES onions (and spring onions). Thrips scrape the leaves and leave long whitish marks on the leaves. The lesions on the leaves can lead to fungal diseases, especially if conditions are wet, and reduce the size of your onions. Thrips multiply fast so checking and observing your onions each week is a good idea. We use predatory mites which are a very effective, natural biological control to keep the thrips from damaging the onions. (Available from BioForce).
Black onion fly is a small black aphid that sucks the juice out of the plant. It breeds super fast being an aphid. It is attracted by the smell water-stressed onions (or chives/spring onions etc) give off. If you keep your plants damp and mulched they won’t bother you.
Favourite Onion Varieties that do well on Aotea
Storage Onions: Pukekohe Longkeeper (Egmont seeds) yellow storage onion can be large if well watered - keeps very well
Red onions: Red Rambo and California Early Red - red onions are tricky they don’t always bulb up for me!
Purplette (Kings seeds) - small red/purple salad onion (fast growing by comparison)
Walla Walla (kings Seeds) - a very large white onion, very crisp, sweet/mild and juicy. Wonderful in salads, sandwiches and burgers.
Banana Shallots: Zebrune (Kings Seeds) Banana shallot seed NZ grown (Trade me)
Banana shallots are like a long, large very sweet onion. Incredible roasted and used in chutneys etc, or used raw
Sowing Onions and Banana Shallot seeds
Deep Seed Trays
The thing to bear in mind when sowing onions is that they are going to be in their seed tray for several weeks. Like around 8! So they need to have room for their roots to grow. If you don’t have deep seed trays like the ones in the pictures (about 5cm internal depth), you can sow them into a shallower tray and when the roots start to hit the bottom put another tray of potting mix underneath them so the roots can keep going. When you plant onions out, it is good practice anyway to trim to the tops and the roots, so you can run a knife along between the two trays at planting time.
Fresh Seed
It also pays to have fresh seed. Onion seeds lose their viability (ability to germinate) within 1-3 years. And the expiry date on the seed packet doesn’t actually tell you when the seeds were harvested, as this is not a requirement in NZ. At least one major seed company I know of simply rolls over the expiry date to three years ahead of the packing date, no matter how old the seeds are! So be warned!!
Space for seedlings
Avoid overcrowding the onion seeds. Aim for around 1 cm between seeds so you get healthy plump seedlings. In the seed tray in the photo, I have placed around 18 seeds per row (rows are about 25 cm long in these trays). So in this one tray I have about half a year’s worth of onions ! (At one onion per day). I usually sow three such trays to allow for losses along the way, and to have extra for pickles, chutneys and preserves.
A small bamboo twig makes a useful marker for straight rows of seedlings, pressed into the potting mix. Sow seeds into the groove then cover with seed raising mix and press down flat. Water lightly and keep damp til seedlings emerge – usually in around 10 days (depending on temperature) - then water daily. We keep ours in our greenhouse.
