Few free lunches are as generous as a British hedgerow in late summer. From mid-August into September, the bramble tangles along a quiet country lane are heavy with fruit, and the cost is nothing more than patience, long sleeves and a careful eye on the traffic.

Blackberries are the classic gateway forage: abundant, easy to identify once you know what you are looking at, and forgiving provided you pick above the height a dog can reach. Here is how to gather them safely, legally and without stripping the hedge that wildlife depends on.

Know your season and your route

Blackberries (Rubus fruticosus aggregate — hundreds of microspecies, which is why no two hedges taste quite alike) ripen from July in the south-west and reach a glut by early September. They are sweetest after warm, dry weather; after heavy rain the fruit swells and tastes thin, so wait a day or two.

Ripeness is easy to judge. A good blackberry is dull black, gives slightly when squeezed and slips off the stem with a gentle roll of the fingers; anything that fights back is not ready. The first to ripen are those at the top of the hedge and on south-facing edges where the sun strikes. Brambles flower from June, so you will often find white blossom and ripe fruit on the same bush.

Avoid the busiest roads

The most important decision of the day has nothing to do with fruit: choose your lane carefully.

• Favour quiet lanes and bridleways with a wide verge. However laden the hedge looks on a fast A-road, it is not worth standing inches from traffic with your back turned.
• Park in a lay-by or village car park, never in a gateway or on a bend.
• Wear something light-coloured or high-visibility, especially at dusk, and keep facing oncoming traffic if you have to walk in the road.
• Listen out for cyclists, horse riders and tractors on narrow lanes.

There is a contamination question too. Berries within about two metres of the tarmac catch spray drift, exhaust particles and grit, and the lowest 50cm of any hedge is where dogs and foxes mark their territory. Pick at waist height and above, even if the fattest fruit is hanging right over the road.

Identifying blackberries and their lookalikes

A bramble is unmistakable once you have met it: arching canes armed with curved thorns, leaves in threes or fives with serrated edges, and fruit that ripens from green through red to black.

If your fruit is red and pulls off the plant hollow, you have found a wild raspberry — smaller, softer and every bit as good. A ripe blackberry comes away with a pale pithy core still inside it. Dewberries, the trailing relatives with a waxy blue bloom, are also edible and often sweeter.

The berries you must leave alone grow in the same hedge, but they have no thorns and no bramble leaves:

• Ivy berries — dull black clusters on glossy evergreen leaves; mildly toxic.
• Privet berries — small, shiny black, borne on a shrub with opposite oval leaves; toxic.
• Black nightshade — a soft-leaved plant with small white flowers and shiny black berries; toxic.
• Dogwood and wayfaring tree — black or blackening berries; unpleasant and not worth the stomach ache.
• Black bryony — bright red berries on twining stems that scramble through hedges right beside brambles. The whole plant is highly toxic, so look before you reach.

The rule that keeps you safe is simple: if it has no thorns and no bramble leaves, it is not a blackberry. Never eat a berry you cannot identify with certainty.

Pick responsibly, leave plenty behind

Picking wild fruit for your own use is perfectly lawful. The Wildlife and Countryside Act 1981 makes it an offence to uproot a wild plant without permission, but not to pick fruit, and the Theft Act 1968 treats fruit gathered for personal consumption as outside theft. On nature reserves or sites of special scientific interest, ask the warden first.

• Take no more than a third to a half of the ripe fruit from any one bush. Birds, badgers, foxes and dormice are eating from the same larder.
• Stay on the path side. Do not snap canes or trample the verge — hedgerows are a priority habitat, and birds may still be nesting into August.
• Leave gates and fences as you find them, and take all litter home.
• Carry a shallow tub rather than a bag, so the fruit does not crush under its own weight.

Kit, scratches and aftercare

• Long sleeves, trousers and gardening gloves. Bramble scratches on the back of the hand heal slowly.
• Check yourself for ticks afterwards and remove any attached tick promptly with fine-tipped tweezers.
• Rinse the fruit in cold water before eating or freezing, to shift dust and bird droppings.
• Take water, a charged phone, and tell someone your route if you are heading somewhere remote.

From hedge to kitchen

Deal with a full tub the same day. Freeze the berries loose on a tray before bagging so they stay separate for crumbles and smoothies, or cook them straight away into jam, cordial or a fool. Blackberries pair beautifully with apple, and a splash of gin over a jar of fruit makes a decent winter tipple.

Then enjoy the walk home. A warm lane, a laden hedge and purple-stained fingers are one of the small, free pleasures of a British summer — and with a little care, the hedge will be just as generous next year.