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Growing Onions - Start to Finish


This is how I grew the onions on my allotment in 2020. I sowed three different varieties: Ailsa Craig (Wilko), Exhibition (D.T.Brown) and some seed I got at a lecture by a champion grower, which I believe are Kelsae.

Instructions / Diary

Click thumbnails for larger images


December 10

Fill some seed trays with finely sieved compost and bring it indoors for a few days to warm through.

December 16

Sow individual seeds in rows. This makes it much easier to prick out the seedlings later. Water with a spray bottle, cover with a propagator lid and stand on a warm windowsill.

December 31

Once the seedlings have sprouted, remove the propagator lid. Fit an LED grow-light above the seedlings. Set the timer to give them 12 hours of "sunlight" per day. Keep the seedlings well watered.

January 6

When large enough to handle, prick out the seedlings into individual pots or cell trays.
These are 7cm (7oz) plastic drink cups with a drainage hole melted in the bottom using a soldering iron. They cost a fraction of the price of plant pots, and fit perfectly in a 15-segment cell tray.

January 27

On the left, the top layer of seedlings with the grow-light, and on the right the layer below with no extra lighting. I have a board which is covered with reflective material from an emergency blanket (aluminium foil would also work). I fix this to the back of the rack to reflect as much light as possible onto the seedlings.

March 2

The difference between the two layers is even more obvious.

March 23

Place the seedlings in an (unheated) greenhouse. I felt that after the spring equinox, they should get enough natural light, and the plants were getting a bit too big to stay in the dining room.

April 8

Thoroughly weed the bed and add a good layer of compost on top. I used some spent compost that I grew potatoes in the previous year. Remove a plug of soil with a bulb planter, add an eggcup of Growmore fertiliser into the planting hole and mix it in. Transfer the onion plant, firm well and water in. The Kelsae onions I spaced at about 23 cm (9"). The others were planted in groups of four inside pop-bottle wind breaks, along with some shallots.
Click for instructions
Click for video

May 30

Remove the wind breaks before the plants get too large.

Jun 20

I left the windbreaks on too long, and they were very difficult to remove without damaging the plants.

July 16

The Kelsaes are still growing well, but a few of the others are starting to flop.


The largest Kelsae now measures 38cm (15") around

July 19

Cropped some of the Exhibition (left), and Ailsa Craig (right). Several of these had signs of white rot, which attacks the roots, and the plants were loose in the soil. This bed cannot be used to grow alliums again for 10 years. I will check the others regularly, and pull any that start to feel loose.

August 1

The largest Kelsae now measures 46cm (18") around

August 6

Cropped three more Exhibitions and three more Ailsa Craigs with signs of white rot.


Even so, they have made good-sized onions and are much larger than any I ever grew from sets.

August 24

The first of the Kelsaes has flopped. This one measured 46cm (18") around and weighed in at 1.25kg (2lb 12oz).

August 29 The largest of my show onions measured 51cm (20") around and weighed 1.96kg / 4lb 5oz

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