Danny, is your allotment in an area with artificial light? or perhaps you should put your plants in a week or two later.

hi there Danny. I have had the same problem. The only thing that i can put it down to is the soil not being firm enough. I grow my veg on a raised bed. Everything grows well but the sprouts are pants. They really need firm soil around the plants, so treading the plants in when young is very important, but my soil never even gets dug or walked on. Hope this helps.

But do not despair the blown sprouts are still edible, just treat them like small cabbages.

Try to pick them sooner even if they are smaller.

Danny, have got just the same problem, started off fine but have nearly all opened up.

A quick check in one of my references says always plant sprouts in a sheltered site if possible to stop wind rock thereby reducing damage to root hairs so the plants can take up maximum food (especially Nitrogen). Planting deep up to the young plants first large leaf goes some way to help. Nitrogen uptake appears to be part of the problem concerning your blown sprouts.

If at all possible, try not to apply fertiliser and lime (if needed) in the same season together as they react albeit mildly in a negative way in the soil which can sometimes effect the plants growth in the short term.

Remember to plant in another prepared site next year (crop rotation).

Hopefully your soil is naturally ph7 as this is the best compromise ph level if you want to grow both brassicas and potatoes, the former preferring alkaline, the latter slightly acid.

I surspect that you are feeding them, if you are rotating your crops the manure you gave your spuds will be ampel for the following sprouts ,or plant were there has been no manure for a time, manure will will bolt them ,which is what has happend hear,