1. The ground on which they are planted is not firm enough. This might be my problem (although I doubt it). I fork over the ground just before setting out my young seedlings, which I sow in a frame. Then I take care not to firm them in too much, because my soil is a silty clay and compacts quickly in the kind of heavy rain we experienced this spring. Apparently it is better to fork over well in advance (very early spring), and then just allow it to settle. When you plant, you don’t fork it over again, but simply pop the youngsters into the ground. When the sprouts are swelling in early autumn, you can also try earthing up the base of the plants. To hedge my bets, I'll fork the ground over at least a month in advance next year.
2. Lack of fertiliser. This could also be my problem. Because my garden is so young, I’m finding it hard to make all the compost I need (most of my gleanings from the ground so far have included pernicious weeds - creeping buttercup in my case - which you cannot add to a compost heap). I’m going to be setting up a fertiliser 'factory' using comfrey and nettles (and describing how I do it in future post), but for the time being I’m relying heavily on artificial fertilisers. Fertilisers of any description are shockingly expensive in France (and I prefer organic methods in any case), so my sprouts get one dose of feed when I put them in the ground and that’s it.
3. Lack of available nitrogen when the sprouts are starting to swell. Looks to me like the most likely answer. This year we had a deluge of rain in the early autumn (washing available nitrogen from the soil). Since my plants were very late in the ground, that weather coincided exactly with the time the plants were budding up.
4. High temperatures (over 24 °C) when the sprouts are forming. Also a possibility, given that my veg patch is on a south-facing slope. The only solution here is to plant later, so that the sprouts are maturing in the early autumn. But, since I planted them a bit late in 2012 and 2013, all I can do is pray for bad weather in August and September. And I'm not that fond of sprouts.
My favourite solution is 3, so I’m going to try a liquid nitrogen fertiliser when the buttons are forming (and make a note in my diary to get that little nettle factory into production). All ideas welcome!
I should add that I’m going to eat them anyway, because those little sprouts still look pretty tasty, even if they resemble small cabbages.
Or perhaps, since I’m half way there anyway, I should try the new ‘Flower Sprout’ from Tozers next year? A cross between cabbage and kale, the company claim that the taste is much more subtle than the Brussel. I’m definitely not one of the ‘supertasters’ discussed in this BBC Science article, but you never know who might come to dinner!