A bigger squash: Mammoth marrows, whopping radishes and killer carrots. Anna Pavord enters the small world of giant fruit and veg

To the outsider, there is a magnificent lunacy about giant vegetables and the wildly competitive shows at which they are pitted against each other.

Carrots are turned into Gorgons' heads, whirling nests of bright orange snakes. Pumpkins look like mounds of slowly sinking dough. All giant pumpkins have the same saggy, flattened, run-out-of-steam look, the look of a vegetable that has been pushed to the limit. In the process of getting big, most giant vegetables also get ugly. Only giant onions retain their svelte sleekness. And there are sometimes wondrous cabbages - symmetrical, grand, carved - although they may be four feet across. At the Bay Tree Nurseries in Spalding, Lincs, which used regularly to hold giant vegetable events, I once saw a cabbage that weighed 116lbs. It was almost as heavy as its owner, Ken Dade of King's Lynn.

The growers at these shows stand round in knots, arms folded, sleeves rolled up, leaning back slightly from the waist, the stance of men who know where they fit in the great scheme of things. The conversation is only of vegetables. 'I've not done it on the sub-laterals. That's where I've slipped up.''I fancy he's lost a bit of weight overnight. I'm not happy about him.'

Only the novices look at all nervous, worrying that at the last minute an unexpected parsnip or tomato might turn up on the show bench and smash their dreams for ever. The old hands know who has won long before judging has even started. At the tail end of the season, many of the vegetables - onions, marrows, parsnips, giant radish - are already old troupers. They have done shows in Scotland, won prizes in Wales, travelled the pubs of the northeast where the leeks and the onions gather.

Wherever two or three growers of giant vegetables gather together, you will find arguments about rules and standards. Forget CAP and the Single Farm Payment. Nothing that goes on in Brussels could be more serious and impassioned than an onion grower's plea for standardisation of the neck-trimming procedure re: onions. 'It's a minefield,' says Bill Rogers, an old hand. You can lose an all-important quarter ounce with a bad trim.

'Why do you do it?' I once asked a trio of growers, rudely interrupting a conversation which had consisted entirely of tales of onions past, dreams of onions future. I may as well have asked, 'Why sleep?', 'Why eat?'. 'Well,' said one of them eventually, scratching the knitted back of his cap, 'I was looking for something to do.' Courtesy demanded an answer and these are kind, courteous people.

The expertise needed to produce these monster vegetables, the love and care lavished on them, is self evident. But why is bulk so much more interesting than quality? Because it is measurable, say the people who grow them. Incontrovertible. It's a mine-is-bigger-than-yours situation. No argument.

Of course you won't find men like these poncing about with courgettes or petit pois, though it is surprising that no one has yet found a way to persuade a potato to abandon its sensible way of life and take its place among the giants. Anything these people take on has to have the capacity for mammoth growth: swedes, leeks, beefsteak tomatoes, beetroots, watermelons, cucumbers. They have been quick to see the possibilities in mooli, the Japanese white radish. I've seen radishes that could double as truncheons.

And I like being amongst people who have expertise, however esoteric it may be. I liked watching Ian Neale of Newport, Gwent, when he presented the world with its biggest ever beetroot, 40.5lbs of inedible fibre, which he lifted as a shot putter might, the vegetable balanced menacingly in his huge hand. It was forty two and a half inches round the waist, he told me proudly. Two years ago he also took the UK record for the heaviest watermelon - a monster of 165lbs.

Unfortunately, I was always destined to be an onlooker rather than a participant. The recipe for success is so daunting. First take 40 tons of muck and dig it in well ... I was thinking this while planting seeds of squash earlier this year. None of my Spalding heroes would be bothering with a butternut such as 'Avalon' (Thompson and Morgan, £2.09 for 12 seeds). But it suits us because you can bake it, roast it, make soup with it or use it in risotto and vegetable lasagna. It ripens early and stores for up to six months. The fruit is small and sweet.

Seed is best sown one to a 3in pot. Set them on edge on the surface of multi-purpose compost and cover them with vermiculite. None of our seeds gets extra heat. They all germinate in the cold frame, so I don't sow before May. Provided the pots are well-watered and the night temperatures isn't too severe, you can expect the seeds to germinate within a week. The plants grow fast; since they can't be set out until the end of May, there's no point in being in too much of a hurry.

If you are growing in a cold frame and opening the frames every day, the plants gradually harden themselves off. If you are starting off seeds in a greenhouse or on a kitchen windowsill, you'll need to acclimatise them gently to the real world. Either way, it's worth digging a decent pit and filling it with compost or muck, before planting your squash on top. It will need plenty of water. You can build a little wall of earth round the plant to retain any water you have available for it, or sink a flowerpot by its side and pour your water in that. It will then be delivered straight to the roots.

Though the plants were slow to get going this year, the first fruits had set by early July and we picked the first squashes recently. They need plenty of room. Leave at least three feet between plants when you set them out and remember to gather in all the fruits before the first frosts arrive.

The Baytree Nurseries, Spalding, no longer holds competitions for mammoth vegetables. The action has moved down to the southwest, where the National Giant Vegetable Championships are now held at the Amateur Gardening Show, Bath and West Showground, Shepton Mallet, Somerset. Last year the world record for a giant marrow was broken by 22-year-old Dorset grower Mark Baggs, who is hoping for even better results this year. The show runs from 1 to 3 September (9.30am-5pm). Admission £11 on the gate, £9.50 if booked in advance on 01749 822222. For more information, visit www.bathandwest.com