When is the best time to plant onions?

Does it matter when you plant onions? Do you get bigger onions if you plant them earlier? 

In theory, planting earlier should give them more growing time and therefore they should reach a larger size, but is that how it turned out? 

My onions certainly won't win any prizes for size or looks, but they do taste good, and it's always extremely satisfying to grow your own.

They are incredibly easy to grow. I plant them and leave them, simple as that. But I've been trying to work out whether they will be a bit bigger if I plant them earlier. Here's how it went...

When is the best time to plant onions? 

There are in fact varieties of onion that are suited to planting in autumn and many people do this. The reason I don't is that my plot is rather wet in winter and I think the risk of them rotting is too high. 

I wait until spring. But which bit of spring, that's the question.  

In past years I've simply followed the directions on the packet and planted at the recommended times. These usually say "February to March" and I have tended to wait until March when the soil gets a bit warmer.

But my onions never get that big, and having only 80 minutes a week, I tend not to feed or water them. So would planting earlier, even if it's a bit colder, give them time to grow bigger? This year I tried to find out.

Growing Your Own Onions is Easy

All my onions were grown from sets. These are miniature onions prepared for planting before you buy them, and is quicker and easier than growing from seed.

I planted them in rows 2 metres long, with a generous spacing of 6 inches/15cm, in the hope that this also would allow maximum growth. I didn't worry about being too precise but this meant that each row contained about 14 onions.

This comparison is of four different batches of the white onion variety Sturon.

Every year is different, and this year we've had some difficult conditions, with weeks of snow on the ground through March which was very cold, and later no rain and temperatures of 30C from early June to the end of July. 

My onions haven't been watered or fed, and were all lifted in early August.

Does planting onions early make them grow bigger?

The earliest batch were planted in the first week of February. It stayed pretty cold for a while and it was six weeks before their shoots even appeared above ground.

Of the 14 planted in this row, 13 ended up being lifted, with one presumably nibbled by pigeons or slugs, or rotted before growing. Only 3 were of a good size, which to me means an onion will fill the palm of your hand when you are holding it. Most were just a bit smaller than that.

   

My early planted onions

Altogether this batch weighed 666g (average 51g per onion). It certainly doesn't feel like the early planting paid off.

Which batch of onions produced the best return?

The 2nd batch of sets I planted was of 2 rows in late March. From these 2 rows of 14 I harvested 18 onions. More were lost to slugs, birds etc and none grew as large as the biggest in Batch 1, but they were more consistent, with 7 good sized onions, and none of the rest being too small.  

The second batch were more consistent in size

This batch weighed in at 860g (average 47g), on average smaller than Batch 1, but with less variation.

Is it worth planting onions later?

My 3rd batch (of one row) were planted in early April. Despite benefiting from extra manure added to this part of the plot in February, it produced a measly return. Only 9 onions survived to be worth harvesting, and none were of significant size, weighing a combined 294g (average 33g).

The later batch was disappointing 

My 4th batch was a bit of an after thought. In mid April, I decided there was space to plant 2 rows of any of the onion sets that were left over at that point. These will have benefited from much warmer weather immediately after planting, but had less time overall to develop and grow.

They didn't appear to grow well at all, produced little foliage and died back quicker than the other rows planted earlier. I put this down to having a less well established root system having had a later start.

19 survived, but some were not much bigger at harvest time than when they were planted. They totalled 449g (average 24g). Though this is better than having thrown the sets away, the return is not a good one. I wish I'd planted these earlier.

Batch 4 didn't grow much at all

Onion planting times results

Every year on The 80 Minute Allotment is slightly different. Our climate is such that you do not reliably get the same weather at the same time of year each year. This unpredictability is what makes the UK such an interesting place to grow your own.   

My early planted onions suffered from unusually cold and wet weather in March this year. 

I think this affected the chances of growing larger onions this year.

Consequently my early planting didn't pay off in that respect. But the relative yields from different batches cause me to think that with slightly more helpful conditions it might have done so. The earliest batch did produce the largest individual onions. 

Though planting earlier may not increase your total yield too much, it seems that delaying planting will certainly decrease it.

My advice is whenever you do start planting your onions, get them all in as early as soil conditions allow, as the earlier ones are much more likely to grow well than the later ones.  

From left to right, batches 1, 2, 3 and 4

Happy growing,

Paul 

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