How to pick wild mushrooms

Autumn's a bit rubbish, though we've got in the habit of pretending it isn't. Yes, the leaves are nice, and there are those mists and mellow fruitfulness, but it's basically damp and chilly and sad. In summer you lie in hammocks; in winter there are snowmen and high blue skies; in between you struggle with daddy-longlegs and wish the clouds would blow away.

But the season has one thing going for it: mushrooms. This is when woods and meadows fill with boletes and parasols and blewitts and wax caps, and only a fool would head into the countryside without a bag or a basket. As I live in said countryside, and I like a walk, I've been picking most days for a fortnight now. A week ago I came home with four or five kilos of ceps, those squat, chunky affairs sometimes known as penny buns because of their shiny brown caps. They looked and smelled as good as they tasted.

I ate a few that evening, slicing the remainder and putting them to dry above a radiator. I've now got 12 litres of mushrooms preserved in jars in my kitchen. That's enough to supply a deli, so I'll be giving a lot away. Dried fungi cost a fortune, so everyone's delighted to get them.

Except this year. This year a lot of people are saying thanks, but no thanks. Their reasons vary, but as far as I can tell they're afraid I'll poison them. I've been doing this for years, and never given myself so much as indigestion, but suddenly everyone's telling me to be very, very careful about what I collect. Wouldn't it be safer to leave it to the professionals, they ask.

It seems cruel to point the finger at someone who has suffered, but it's at least partly Nicholas Evans's fault. In 2008 the Horse Whisperer author went for a stroll in the Moray countryside and filled a basket where he expected to find ceps or luscious yellow chanterelles. Evans had picked wild mushrooms before, with no ill effects, but this time it was different. What he had harvested was Cortinarius speciosissimus, better known as the deadly webcap. He, his wife and his brother- and sister-in-law shared half a kilo or so for lunch, fried with a little parsley. Within three days, they were in hospital, their kidneys being destroyed by the chemical orellanin. They were lucky not to die, and luckier still that their children opted out of the feast. As it is, the adults were sick for months. Two years on, the Evanses and their brother-in-law have almost no kidney function. Every other day, they spend hours plugged into dialysis machines, having been on the waiting list for a transplant since early 2009. "I do not pee at all," Evans said in a recent interview. "But I dream about it – wonderful peeing dreams when I think I am cured. When I wake up and find it isn't true, it takes me a while to disbelieve it."

Webcaps are just one of the hazards you have to worry about. Also in 2008, an Isle of Wight woman, Amphon Tuckey, died a day after eating mushrooms her niece had gathered at Ventnor Botanic Gardens. They were Amanita phalloides – death caps – which are said to be responsible for the vast majority of the world's mushroom-related deaths. A single death cap can kill; in the early 20th century, a Frenchman called Girard used them to murder acquaintances and collect on their life insurance. Because Tuckey's husband had warned her not to eat wild mushrooms, and she didn't want to admit that she had, she blamed her sickness on dodgy sausages and was treated for gastroenteritis. In fact, her liver and kidneys were being wrecked by cyclopeptides, the most vicious toxin found in fungi. "You do take a risk when you eat anything that grows in the wild," the coroner told Tuckey's family. "The answer is never to do it at all."

Is accidental poisoning unique to Britain, where many people are so clueless about nature they can barely tell a crow from a cowslip? Hardly: in China, hundreds of villagers are believed to have been killed by an innocent-looking mushroom called the little white. And it's not just humans that can make mistakes. According to US vet Bari Spielman, dog owners should take care to remove mushrooms from their "yards", otherwise their best friends could end up with jaundice and seizures, or even in a coma. And yet, as any dog owner will tell you, most mutts will happily – and safely – eat fox crap or long-dead rats.

Only a few mushrooms will kill you; most will just make you wish you were dead. Species such as the destroying angel, the devil's bolete, the poison pie and the sickener get their names for a good reason. What makes things particulary tricky for foragers is that many edible mushrooms are so similar to toxic varieties that only an expert can tell the difference. The yellow-staining mushroom (Agaricus xanthodermus), for instance, which can leave you racing between basin and toilet for days on end, is easily mistaken for both the field mushroom (Agaricus campestris) and the cultivated mushroom (Agaricus bisporus), the usual white number that you buy in supermarkets. The only way to tell some lookalikes apart is to stick them on a piece of paper and check the colour of the spores that drop from their undercarriages. That's every bit as tedious as it sounds.

So if mushrooms can be so dangerous, why do I and so many other amateurs persist in picking them? It's not just for the pleasure of walking through a sun-chequered wood, trying to spot the off-white of a cauliflower fungus among the fallen leaves. If you're willing to do a little homework, the risks can be managed. They can almost be managed away.

First of all, you need to ignore every single rule of thumb that you will ever hear about how to tell a good mushroom from a bad. You can safely eat anything that an animal has nibbled? Rubbish. Cooking or drying destroys all poisons? Rubbish. Peeling a mushroom removes the poisons? Rubbish. If a mushroom is easy to peel, it's all right to eat. Rubbish. All brightly coloured mushrooms are poisonous? Rubbish. All mushrooms that smell good are edible? Rubbish. Any mushroom that turns blue when you cut it will kill you? Rubbish. Whatever the rule, it will be rubbish. As Patrick Harding, Tony Lion and Gill Tomblin put it in their book, How to Identify Edible Mushrooms, they are "dangerous superstition". The only truth in those "rules" was a partial one: cooking does destroy some poisons. It also makes all mushrooms easier to digest. Even cultivated mushrooms can make your stomach rumble if you eat them raw.

With no shortcuts to take, what can you do? Simply learn how to identify at least a few edible species and pick only them. You will also need to recognise any poisonous species with which they might be confused. For a start, you'll need a good field guide – perhaps the one mentioned above, or Mushrooms, by Roger Phillips, or Mushrooms: River Cottage Handbook No 1, by John Wright. This will tell you not only what particular species look like, but at what time of year you are most likely to find them, and in what surroundings. Some prefer grassland, others woods. Some wood-lovers prefer deciduous trees, others conifers. Some conifer-lovers prefer pines, others larches. Some conifer-lovers grow on the tree itself, others near it. Some edible varieties, such as the beefsteak fungus, grow so high among the branches you may need a ladder to pick them . . .

Book learning is not enough, however. You should also get some personal tuition, either by enrolling on a course or by going on forays with a more experienced neighbour. Unless you're positive they know what they're talking about (be very nervous if anyone tells you "I'm sure that's safe to eat, but I'm not sure what it's called" or "They don't normally look like that but that's where I found them last year"), check everything you're told against your guide. And if you have the slightest doubt about what you're looking at, leave it alone. This, in fact, is the golden rule once you feel confident enough to go picking on your own: unless you're 100% sure you have identified your mushroom as edible – ie, you can put a name to it – leave it. Cap the wrong colour? Leave it. Growing at the wrong time of year? Leave it. In the wrong place? Leave it. Better to sacrifice a thousand meals than your health.

When you get home, take another hard look at what you've picked. If anything causes you even a flicker of concern, into the bin with it.

If you want to make life easy for yourself (and why wouldn't you?), begin by searching for boletes, a family that includes some of the tastiest mushrooms there are, from the ceps that are so delicious in risotto to orange birch boletes with their bright caps and grey-flecked stalks. You'll mostly find them in or just outside woods, often beside paths or in clearings where they get a mix of sunshine and shade. Once you know what to look for, you need never confuse a bolete with a member of any other family. They have caps and stalks, like most of their peers, but the resemblance ends there. While most mushrooms have "gills" beneath their caps, radiating horizontally from the stalk like spokes on a wheel, boletes have tiny vertical "tubes", packed so closely that they seem to form a solid or slightly spongy mass. Look at your field guide if you're not sure what I mean. In fact, look at your field guide anyway. As you should have realised by now, only someone with a death wish would pick mushrooms based on a description in a newspaper.

Not only are boletes common; there aren't many varieties, so identification shouldn't be too difficult. Best of all, of all the boletes you will encounter in Britain, none is likely to kill you. Barring some freak reaction, only a handful will even make you sick, such as the devil's bolete, with its red tubes and pale cap, or the lurid bolete, with its handsome red and yellow stalk and yellow tubes. If ever there was a beginner's mushroom, the fungal equivalent of the bike with training wheels, it's the bolete.

Mind you, some people will find a way to turn anything into a dangerous sport. In Italy, at least 18 people have died gathering mushrooms this year. They weren't poisoned; they fell down mountains. Some of them had gone picking in the dark.

Send pictures of your fungi finds to the the Guardian's Green Shoots club at guardian.co.uk/greenshoots