Have you noticed anything about your onions this year? Do lots of them have thick necks? I’ve seen plenty of this – at village shows and gardens that I’ve visited during the summer. And, as anyone who has grown this kitchen staple will tell you, it’s the bulbs with a broader, flatter shape and a thin neck that will store for longest, while the thick necked ones are prone to rotting, drying out or the formation of brown skins inside the bulb.
Simply speaking an onion is made up of overlapping leaf bases and the ‘neck’ is the point where the leaves join onto the bulb. Thickening at this point is usually due to the formation of a flower stalk or a nutrient imbalance that causes fleshy, coarse leaf bases to form. Both of these conditions prevent the efficient drying of the bulb, this producing the papery coating that helps exclude air and fungal infections.
So why are there more thick necks this year? Well, invariably the performance of a crop is influenced by the prevailing weather conditions and the nutrients available to it from the soil. Onions benefit from a couple of months of consistently cool conditions early in their growth cycle – preferably not exceeding 10C for prolonged periods – if they are to produce the best bulbs. But for many of us, last winter and early spring were unusually mild with little in the way of frost, not ideal for the development of dense, closely packed leaf bases that form the basis of a good onion.
Meanwhile in much of the UK, late spring and early summer were consistently wet which caused more problems for our onions by washing nutrients from the soil. Thick necks are also caused by a lack of potassium and calcium, both of which are needed to conteract the vigorous growth induced by nitrogen, and which are needed as the bulbs start to form – you’ve guessed it, in late spring and early summer. It was at this stage that the wise grower would have top-dressed their onions with wood ash, the traditional standby for top-notch onions – with elegant, thin necks.