There's more to onions than meets the eye, especially through a veil of tears.

You might find little difference in taste between supermarket and homegrown onions. So why give them space in the garden? easy. Homegrown onions can contain more health-giving phytonutrients and antioxidants than supermarket ones.

It's all down to the variety you choose and how you grow it. Brown onion varieties, such as Rijnsburger, probably have the strongest flavour. Essentially, the larger, milder and sweeter the onion, the less nutritious it is. The more you cry, the better the onion. Pungent, tearful onions have absorbed sulphur compounds from the soil and, as a result, the bulbs contain more phytonutrients and antioxidants. Onions bred to have a milder flavour or grown in sulphur-deficient soil have many fewer of these nutrients.

So, the best way to avoid these pitfalls is to grow your own. Check first, though, whether your ground naturally contains enough sulphur or whether you need to modify your soil. Sulphur is readily absorbed by water and leaches out of sandy, very free-draining soil, but is retained in clay ground. Pale or yellowing of new growth is a symptom of sulphur deficiency.

Epsom Salts contain sulphur compounds together with magnesium. They dissolve in water and are quickly absorbed by the onions, when applied as a foliar feed (see organiccatalog.com). Sulphur chips break down much more slowly, so aren't suitable for annual crops.

Onion sets are easy to plant, provided you follow one or two simple rules. Use good, rich, weed-free soil and water well after planting. Plant 12-15cm apart in rows 30cm apart. Sink the sets into the ground, only leaving the growing point above ground level. This prevents birds from tweaking out newly planted onions. A more labour-intensive way is to cover the onion patch with net.

Alternatively, you could sow onion seed in seed trays now. Once the seedlings are 5-7cm tall, they should be transplanted to their final position. While the plants are growing and the bulbs swelling, keep the bed weed-free and the soil damp but not soggy.

I always find room for shallots. Though a little milder, they store well and have six times more phytonutrients than the average onion. Shallots are much bigger plants than onions, so they need a lot more space. Sets should be planted 30cm apart, with 45cm between rows.

Leeks also need elbow room. When using two or three leeks per meal, you'll need a fairly large patch of ground. For decent-sized plants, space leeks 25-30cm apart, with 45cm between the rows. You might ask if leeks are worth growing; to which I would reply yes. They keep their good, strong flavour right through winter: they're in a different league to their supermarket equivalents. And your own will not have had all the nutrient-rich green leaves removed.

It's much easier to buy leeks for planting out in May or early June, but - a glutton for punishment as ever - I start sowing my leeks in seed trays about now. When the tiny grass-like seedlings are 7-8cm tall, I then line them out in rows. When they're robust little plants, usually in mid-June, they're ready for transplanting into their final positions.

Leeks need to be kept moist at all stages. When transplanting to their final positions, use a dibber to make a 15cm-deep hole. I use the top of an old spade handle, notched to show 15cm. I plant the whole leek, ignoring the couthy old advice of clipping the roots. As for varieties, Avola is a fine early-cropping specimen, lasting till Christmas. Good old-fashioned Musselburgh survives most winters, keeping well in the ground till late February/early March.