I've got some Red Baron onions sets but the ground is far too wet and cold for me to plant them out at the moment. Will I gain much in terms of their ultimate size if I plant them into individual cells in my mini plastic greenhouse now? Will their ultimate growth be held back by any root disturbancewhen I plant them out? I'm not much of an onion expert so don't really know how early and how much cold weather they can take.

Primrose ..I have done exactly the same with my red onions , in fact most of my onions..It works wells and gets them off to a good start, just try and avoid disturbing the roots when you plant them out..keep them cool , mine are outdoors in the cold frame.

Thanks. That's very helpful. As a matter of interest, what size cells do you use? I suspect that the one inch square ones might not contain sufficient compost/nutrition to keep the onions going for too long ?? Or do you plant them in bigger trays?

Hi Primrose,

I used the module method last year. I used 15 cells to a full size tray modules, and had great success with them. Once planted out they raced away Out of about 120 sets, only 3 or 4 of the reds bolted.

In previous years I have started sets off in root trainers - the 5" ones are ideal for this. There is enough compost in each cell to allow quite sturdy little plants to develop. With their upright growth onions are well suited to root trainers.
Onions have long weak roots and when grown in pots, the roots will tend to knit round each other into a tight tangled mat.

John

Peat pots are pretty good as well, also loo rolls cut in half , filled with compopst , one onion set per each and off they grow !!

I use 8cm round continental pots which are really little more than half pots and as John quite rightly says the roots will curl in the bottom of the pot but I have not found this a draw-back in any way and gives the onions a really good start in life. With pots, when planting out, I use a pot of the same size as a former and then when de-potted the plants fit snug into the hole and they then gallop away! (poetically speaking!)
JB.

He's right! I've used that process fro some years now and it hasn't failed.