How to Grow Your Own Overwintering Onions

Following on from 10 reasons why you should grow your own onions, here's how to grow overwintering varieties (planted in the Autumn).

50 Senshyu Yellow Onion Sets

Something to remember if you're aiming for a year round supply of alliums:

Overwintering onions will not be ready to harvest until early to mid-summer and don't tend to store as well as onions that are sown in the spring (although they can be diced and frozen).

They will however, fill the gap (spring planted sets are usually ready late summer to autumn and will store until mid-spring the following year if stored well). Some people grow shallots to fill any gaps as they store particularly well.

1.  Find a supply.

Luckily with the trend in grow your own building, finding a supplier is getting easier.  I bought two varieties (Radar and Senshyu Yellow) in a local garden centre ( Morgans in Carlow) who were selling a few varieties.  Priced at just €1.75 for 50, sets are generally considered easier to grow and less prone to disease (although they often bolt or run to seed).  Sets are also available on line (see http://www.greensideup.ie/ for links).

2.  Prepare the ground.

Avoid planting onions in soil that's been freshly manured or they will be too lush. I've planted mine in the patch that I'd manured for potatoes at the beginning of the year. Onions also prefer soil that has a fairly neutral pH of 6 to 7 so test it with a pH kit (easy to do, just follow instructions on the packet) and add lime if it's very acidic. Avoid planting them where onions have grown in the last three to four years to prevent pests and diseases.



Use a marker to measure distance.

3. Place the onions in position.

I find it easier to place all the onions in position and then plant them.  I usually follow the recommended planting depths and distances on the packet but if I don't have a packet usually plant them about 7-8in apart each way.  The two packs I planted today recommended 5in apart. 

I then use a marker snapped to the correct length and a rake handle (or bamboo cane) laid across the bed as a marker.

(spot the health & safety hazard!)

From experience I've found it easier to place all the bulbs before planting so that I can see where they all are! It also gives me a second chance at checking that they're the right way up.  The bottom of the bulb is usually flatter and the tip pointed.

4.  Plant the sets.

Onions are sown quite high in the soil, about an inch deep, as opposed to garlic which is planted deeper.

If your soil is quite firm avoid pushing the bulb into it as you may damage it.  Use a dibber or a stick to loosen the soil first.

5.  Label.

Once you've planted all your sets, label them with the variety and date and watch them grow.

6. Looking after the crop.

Keep an eye on the sets and re-plant them if birds dislodge them.

Ensure the soil is kept watered if there's a dry spell.

Keep the soil weeded (which is much easier at this time of year as they're not growing as quickly, if at all).

In the spring you can add a seaweed-based feed (example here from The Secret Garden)which is full of nutrients and minerals to give your plants a boost.

7.  Pests and Diseases

If you're prone to onion fly (where small maggots attack the seedlings), you can grow them under fine netting. Unfortunately you wont know you're prone until you've experienced them!

There are no organic remedies for mildews and rots of onions (which will be worse in damp weather) that I'm aware of.

All that's left of our summer crop, oh no!

8.  Harvesting

You can lift and use the onions as you need them once they're a reasonable size.  If you're hoping to store them, wait until the foliage dies down and the tops bend naturally (see blog in September).

Good Luck!