In with the old, in with the new

Sweetpea 'Cupani': the original, introduced in the 17th century

Sometimes I think there's never been a more exciting time to grow your own.

It was brought home to me when I went round the inspirational kitchen garden at Knightshayes recently. It's no showcase museum piece but a belt-and-braces, workaday sort of garden which pays its way by selling its produce, so what it grows needs to be worth growing.

Its indefatigable head gardener Lorraine is a keen advocate of heritage varieties – 104 heritage tomato varieties (she likes German beefsteaks and the near-wild species tomato, Solanum pimpinellifolium) and 10 heritage garlic, plus peas, sweetpeas and potatoes.

Pea 'Magnum Bonum': modern pea breeding has focussed on dwarf, self-supporting peas but hugely tall 19th century varieties like this one and the 'Telephone' strain are far heavier yielding and more satisfying to grow all round

There's a bed of oca next to the onions, and she's got achocha scrambling among the toms in the greenhouse. In fact, it's just like my garden (though on a spectacularly larger and less weed-ridden scale): familiar veg like carrots and cabbages rubbing shoulders with the very old and – to the UK, anyway - the very new.

Achocha in the greenhouse: this one is the exploding cucumber type (Cyclanthera explodens) not the edible achocha which is a finer, less coarse (if also less amusing) plant. The fruits of the edible one taste of sweet peppers

Until about 10 or so years ago, we had to put up with a limited range of ever-blander varieties created not for us little insignificant gardeners but for large-scale farmers and supermarket buyers. That meant they were all exactly the same shape and size, they were robust and held together well enough to be picked by machine, and they stored well for long periods of time in refrigerated lorries.

Well, as a set of criteria for choosing something worth growing in your back garden I can't think of a worse lot of reasons.

You may have noticed that there are a few things missing from the list. What about flavour? Juiciness? Explode-in-the-mouth ripeness that makes you dance round the kitchen in glee?

Babington leeks and and old Italian variety of green garlic, in the main garden

Now we've got the rediscovery of heritage veg, nostalgia veg (I'm talking samphire, scorzonera, Hamburg parsley, skirret – whole families of edibles we used to grow but don't any more) and the arrival of a whole world's worth of exotics. Joy Larkcom started it by going to China and bringing back mizuna, mibuna and pak choi; now there's Mark Diacono and his Szechuan peppers and James Wong persuading us to grow everything from wasabi to electric buttons (Spilanthes oleracea) which pop and fizz in your mouth like space dust.

It's telling that at the Edible Gardening Show earlier this year, when Suttons brought a few Danish trolleys' worth of the weirdest edibles they could think of as an experiment, they'd sold out by lunchtime on the first day. This is no passing fad: our curiosity is well and truly piqued.

And then there are all the ornamentals which turn out to be edible: Fuchsia berries (try 'Riccatonii'), flowers from sweet rocket to nasturtiums and violets, Eleagnus berries and elderflowers.

Heritage toms in the lean-to greenhouse. Lorraine says they go through a 'teenage' stage and sulk for a while when they reach about 6" tall: but they get over it, and romp away so fast they catch up with everything else around

Some argue heritage varieties aren't worth growing; well, I'll continue to swoon at the faint-inducingly gorgeous flavour of my 'Marmande' beefsteak tomatoes, if that's OK with you. Tricky as hell to grow, but you keep going just to have one unforgettable taste – and you try buying that in the shops.

And besides, heritage varieties saved by The Heritage Seed Library preserve our genetic pool of veg varieties – whether or not they're worth giving garden room to - so we don't narrow it all down so much we're breeding in ever-diminishing circles.

At the other end of the spectrum you've got the early adopters: those who say traditional veg are boring and everyone should be throwing out their spuds in favour of yacon. Well: given that all my potatoes have gone over to blight in the last week there might be something in that (though I'll mourn the loss of my 'Duke of York' should that sad day ever come).

But on the whole, for most people (certainly for me) the whole process of getting to know exotics is a series of experiments. I've tried and rejected tomatilloes – lovely plant, but not enough crop or uses for it (much as I like salsa) to justify the greenhouse room. But I now grow sweet potatoes every year, in big baskets under cover, as though the crop isn't huge it's big enough and it makes a nice change from the spuds.

And just as we thought there was time to get bored, along come yard-long beans, Chinese arrowroot and lablab beans courtesy of Sally Cunningham's Sowing New Seeds project for Garden Organic. Some will go the way of ra-ra skirts and beehive hairdos: others (my money's on the lab-labs) will be the allotment staples of tomorrow. Isn't it great?

Growing against the odds

While I was at Hampton Court I met a very nice man called Mark Diacono, who was telling me all about his olive crop.

He doesn't live in Italy, or in France, or anywhere warmer than rainy old Devon, where he has a 17-acre farm where for the last three years he's been experimenting with what you can do in a world where the climate is changing. These days, life in Devon is a good few degrees warmer overall than it used to be, allowing Mark to really push the boundaries and grow all sorts of borderline fruit which most of us wouldn't dare to try outside the greenhouse. As well as his olives, he grows apricots, peaches and pecans, all stuff we're used to thinking of as exotics here in the UK.

It's a real vision of the future. If what the government and the Met Office are predicting about the climate comes to pass, apricots and olives will become normal British fare. Mind you, like most trailblazers, Mark isn't having a straightforward time of it: the last two wet and gloomy summers did their best to bludgeon his olives into submission, and then we had last winter. It turns out, luckily for Mark, that olives are incredibly tough trees and despite losing pretty nearly all their leaves they came back again and have been flourishing in this year's heatwave. Now, if you didn't have people like Mark doing what he's doing you wouldn't believe olives could survive last winter outside in this country, would you? It makes me think I might try planting mine outside in the garden instead of making it languish in a pot all year round.

The other wonderful thing he's doing is reviving old near-forgotten English fruits such as medlars, quince and mulberries. If you want to read more about his extraordinary project, visit the Otter Farm website here, and Mark's blog which is here.