[Goosegirl]

Every year I get a lot of thick-necked onions and, though I dry them in the greenhouse before storing in the shed, they often rot. I grow from sets - Sturon and Stuttgarter this year - in raised beds in heavy silty soil improved with gritty top soil and rotted sheep manure. I feed just before planting with BFB - this year I used Growmore - then don't feed again. I water well in dry weather and lift when the tops have really bent over. They are put on the staging of a three-tier mini greenhouse without its cover which is inside my big greenhouse. I have just looked at the veg advice part on here and can't see what I need to do. Should I dig over the soil to fluff it up before planting? Any advice welcome as I just can't get onions with tiny necks you see in the shops.

[Nobbie]

Sounds like you may be feeding/watering too much leading to lush growth and thick necks. Are you getting big onions?

I think I fed too much this year as the onions are huge (Turbo and Sturon), but some of the necks are thick, so I'm not stringing them up, just leaving them sitting on wire mess so the necks can get plenty of air around them. Hopefully this will help them keep.

[azubah]

Some of mine have gone rotten at the neck. They have not been out of the ground for long.

[kosh42|EFG]

Every year I get a lot of thick-necked onions and, though I dry them in the greenhouse before storing in the shed, they often rot....

Could it be that the greenhouse is too warm and humid for them to dry properly in? Or that they are starting to grow again in there hence not storing well?

I could be wrong...

Kosh

[Trillium]

Thick onion necks are generally believed to be a shortage of phosphorous in the soil. A simple test kit would show what levels you're at.

Bone meal and rock phosphate are easily available sources. If you can find them, fish, bone meal and soy husks are other good sources.

Composted yard waste and manures generally provide all the phosphorus normally required by most plants in most soils. Some food sources have pretty high levels of phosphorus naturally - banana peels, shrimp peelings, most grains and nuts. These can be added to compost when available. Or in the case of banana peels, I often bury them right at the base of roses and other plants needing a good kick of P.

[crh75]

The OP said they used BFB so phosphorous deficiency should not be a problem. 

It can be caused by planting the sets too deeply.  The top of the set should be showing when planted then when weeding/hoeing later in the year make sure the soil does not get ridged up against the onions.

Does this sounds plausible?

[Goosegirl]

Thanks for all the useful suggestions. Maybe I did plant too deeply - only the dried stalk bit was showing; also will use bonemeal only next year. At what stage should they be lifted - i.e. how much should the leaves be bent naturally and when do the leaves and roots get cut off? Maybe I leave them on too long (as well as thick-neck problem).

[crh75]

You can harvest anytime after the leaves start to bend over.  Once the neck above the bulb goes soft it will stop growing. 

It depends on the weather really, if it is dry they can stay in the ground and then on the ground for longer to cure.  When wet like this year they need to be put under cover somewhere airy (as you did).  They may take a month to cure fully before storing somewhere cool.