One of the most interesting changes over recent years has been the increased interest in unusual crops. The relative cheapness of greenhouses and poly-tunnels has enabled many more tender crops to be easily grown. Foreign holidays and food programmes have all increased this trend and now a new gardener is as likely to be growing chilli peppers as their father was tomatoes.

However, gardeners are not just growing short season summer crops but they’re also planting up near hardy perennials in the belief that climate warming will bless them with crops in the near future. I hate to be a wet blanket but despite the tens of thousands of olive trees now planted in the UK the success of crops on them is pretty slight.

But that is not the whole problem- even if a crop is grown can it be processed into a passable commodity? It is one thing to grow grapes; another to make great wine. And that is the whole dilemma- it’s not that we cannot find a way to grow something. We can grow almost anything given the will, and the budget. Even coconuts given a glasshouse tall enough. No the problem is that having done so then is the result worth having? After all in France the grapes one side of the road make a grand cru, and the other side a table plonk.

I grow grapes and make wine, well and badly, but again neither tastes like any French wine as I do not have either French soils or their weather. Cheeses taste incredibly different not only depending on their method but also on where the milk was produced. The local conditions create their distinctiveness. So it’s hardly likely that your coffee or whatever, however lovingly grown and processed, will taste as good as or even similar to Jamaican Blue Mountain or even supermarket budget brand, no matter what you do.

Now don’t get me wrong, I’m not trying to be negative but realistic. It is exciting to grow all sorts of things, and educational to turn them into products. I love growing almost every crop and enjoy making every edible thing I can from each of them. But I must admit that some have not been great gourmet masterpieces. Perhaps you can do better, but be warned.

Let us start with olives. There is nothing new to growing olive trees in the UK, we always have. They are very hardy, I’ve had two for decades and they take everything the cold windy Norfolk winter weather can offer. But other than the one that came with the plant they have never cropped. For a simple reason; they flower late in the year and the olives have to swell over winter; in cold weather they drop off and never ripen. Even if a good crop was to make it through the winter it would be unlikely to ripen well and black and would have to be picked green unless we had another 1976 summer. In either case olives then need careful brining to bring out their flavour and that like great wine-making is a slowly acquired skill.

Then there’s coffee. It’s a lovely house plant for a bay window. With verdant laurel shaped leaves and white jasmine like scented blossoms coffee is worth having regardless of any crop. It makes a small tree but can be pruned back to keep it compact, and productive. Coffee is a mountain crop and can take cool conditions so although tender it does not need a hot house only frost protection. Almost always grown in the shade in the tropics it’s well suited to a life under cover here. As with a gardenia coffee likes a light position but not fierce sunlight. Although a bit prone to scale and mealy-bug coffee is quick and easy to grow from fresh seed and small pot grown specimens are often offered as houseplants. It’s even easy to crop producing the red cherries when only a few years old. Now herein lies the problem. These need picking and processing as they ripen- which they do over a long period. So at any time you never have many of them. Their processing involves pulping and fermenting the cherries in big tubs to release their bean like seed(s -the best berries have one seed, most have two.) After fermentation they are dried on barbecues (sic- the origin of the word) and then the parchment like coat is rubbed off before roasting which is in itself quite a task to get right. Indeed my home grown Norfolk ground roasted beans did make a coffee. But I must admit I’d prefer not to drink more too often. Just for the trial was fun, daily would be a punishment. Go on try your own.

Chocolate is another similar crop. I have made chocolate by hand in the Caribbean and the process is not that complicated but as with wine-making it’s hard to achieve quite the desired flavour. It’s not impossible to crop chocolate trees here; The Eden project has fruiting trees though I’ve failed so far. The plants have to be bigger to fruit than coffee and need much warmer more humid conditions. The odd sweet corn like pods are produced directly on the trunk and branches. As with coffee large quantities of beans are better processed together at one time. They come embedded in a sweet edible pulp which when fermented causes the beans to go from green to brown and changes their flavour considerably. They are then lightly toasted and ground with sugar and vanilla (and often cinnamon) to make dark chocolate. I’ll take my hat off to anyone managing all that here and getting a palatable result.

Vanilla is another crop that even if you grew it could never taste like the best Bourbon or even a poor Mexican. The raw pods like raw coffee and raw chocolate have no nice aroma or flavour until carefully processed. A straggling climber this is an orchid somewhat resembling a sick Hoya. Vanilla requires a warm greenhouse but even if the flowers were to form and be pollinated by a very off course moth they would be unlikely to swell into good pods. Then once you had those pods, in quantity again, you have to dip them in boiling water, then alternately sweat them and dry them first with blankets in the sun. Then pack them tight in a box for more sweating in the sun, then unpacking and drying in the sun, alternately for a fortnight. During this they ferment and that divine flavour is created. Difficult to get right to say the least.

An easier one is ginger which you can grow in a warm greenhouse from any bud cut off a piece of fresh root ginger from the shops. With rush like foliage the plant first makes stem ginger. The swollen stem bases are peeled and boiled in sugar syrup, cooled and repeated over and over again until they go translucent and are then bottled. If you leave the plant longer the bases toughen and form root ginger which you dry off when the leaves drop.

Black peppers are the fully ripe fruits of a climbing tropical plant and white pepper the same with their skin fermented off. The black peppercorns from the shops look as if they might grow but were dipped in boiling water before sun drying to change them from a reddy colour to deep black. Commercially the best varieties are propagated by cuttings but you can buy the seed. Requiring hot moist conditions you can grow pepper in a warm greenhouse but needing intense sun for ripening and drying it’s easier to take the unripe green peppercorns.

Nutmegs are another obvious choice for an exotic plant but not only do the nuts need to be really fresh to germinate it would also help if they had not been dried with lime to stop them moulding. And if one did germinate it could never fruit as there are male and female trees so you’d need several. This same problem also makes avocados and date palms equally unlikely croppers to say nothing of other requirements.

Or the processing may be too dangerous to practice at home. You might get a cashew to grow, it’s unlikely but we’ll assume you’ve somehow got this usually 30-40ft high tropical South American tree to crop. The cashew fruit has a fleshy pear shaped stalk from which hangs a brown nut in which lies the edible kernel. The brown shell is acrid, highly poisonous and should not be handled or any part ingested. I watched while a St Lucian roasted/burnt off cashews in their shells in a drum - the flames and fumes were apparently caustic and potentially lethal. No health and safety there then, and not something your neighbors would want you doing in your average UK garden.

Peanuts on the other hand are a cinch for anyone with a bit of warm cover. They’re tender clover like plants that flower on stems that bend over and push them into the soil where they swell into husked nuts. So they work much better in a light warm sandy greenhouse border rather than in pots! Start them off early in small pots (you can buy your ‘seed’ in their shells sold for eating -avoid roasted ones!) and plant them the same time as tomatoes, at a foot or so apart; in autumn you dig up a crop of peanuts. Shell and roast these- they’re safer than cashews.

And you could have your own cup of tea. The tea bush is a camellia no more demanding than many of our common ones. You may buy plants or grow them from the seed sold by specialist seed companies. Happier with cool moist conditions the tea plant is not hardy enough to do well outdoors in the colder drier eastern counties but thrives in the milder south and west. It would make a large evergreen shrub but is hard pruned to get flushes of tips and tiny leaves. It makes a much smaller shrub in a big tub but then you can clip a cupful off when you need it. You steam and dry the tips and leaves for green tea. Or rub and ferment then gently char them on a wok for the black. I’d stick at the green if I was you.