Every vegetable gardener has a clutch of trusty favourites to sow, but it would be tedious to restrict yourself to just that.

I'm always keen to experiment with varieties - they might fare unexpectedly well or might be new on the market, with improved disease resistance, yield or flavour. Or they might just look a little different.

When an old favourite starts performing poorly, it's time to chuck it. Unlike most folk who grow broad beans, I find dwarf varieties are much easier: they don't need staking and produce a decent harvest. Until recently, Sutton was the only dwarf in town, but I was tiring of it - germination rates were declining and not a few plants performed badly. After trying out Robin Hood for a couple of years, I knew I had found my bean.

It's always worth ploughing through seed catalogues for fresh ideas. Admittedly, some varieties may simply be "new" to the seed company, but you might occasionally stumble upon a gem such as flower sprouts, a cross between kale and brussels sprouts. They grow like sprouts and you harvest what look like blown sprouts - often described as tiny blown cabbages. But don't be put off: they remind me of sprout tops and are absolutely delicious. I grew Petit Posy Mixed last year, but there are others, like Autumn Star and Snowdrop.

Not all varieties that are "new" to the UK are necessarily winners. I greatly admire James Wong's Homegrown Revolution because it encouraged us to experiment. Unfortunately, many of Wong's examples were tender and slow growing, so could never reach maturity in Scotland. Callaloo and New Zealand spinach sound delicious but have little chance this far north. Cucamelon, on the other hand, a tasty, lemon-flavoured baby cucumber, is an outright winner in a polytunnel.

It's always tempting to try fruit and veg with pretty red or purple fruits, rather than the more pedestrian shades of green. With more health-giving antioxidants, who could resist? I, for one, did. I always found red sprouts, kale, purple carrots or stripy beetroot deeply disappointing. They were never as robust or produced as good a harvest as their traditional counterparts.

Luckily, though, things are changing. Breeders are producing tougher coloured varieties. In the past, few of my purple carrots have reached maturity, but I will be trying Purple Sun F1 this year. It's described as a "striking purple carrot with a superb sweet flavour and intensely dark colour right through to the core". It's crammed with antioxidants. We'll see how it performs.

Like many new varieties, Purple Sun reputedly has good disease resistance. This is a vital selling point. Late blight on tomatoes is becoming a major problem, so the new variety, Romello, could be worth trying. Club root is another and much more serious disease, but a few varieties now have some resistance. They include the sprout Crispus, the cabbage Kilaton and the cauliflower Clapton.

These new varieties, often F1s, solve many problems, but I like trying old or heritage varieties too. Admittedly, many have been superseded by more reliable specimens but some do have advantages. As I've said, Garden Organic's Heritage Seed Library has built up an impressive collection.

A similar organisation, L'Association Kokopelli, was established in France in 1999. Members of the association maintain and grow 2,500 varieties, which are now sold throughout Europe. Kokopelli have been actively involved in promoting sustainable organic agriculture in developing countries by donating seeds and establishing seed-saving workshops and networks.

I'll be trying some of the Kokopelli seeds this year, including the leek, Bleu de Liege. Pandora's been my favourite, but let's see how this one does.

Much closer to home, The Real Seed Company (realseeds.co.uk) and Plants with Purpose (plantsandapples.co.uk) offer a broad selection of more unusual veg and herbs.