IT STARTED last week with curious footpath fruit on Dublin's Heytesbury Street. I filled a bike helmet with dozens of doll-sized apples dropped from the trees. A call to Dublin City Council and a Google image search identified them as crab apples. A scald, a boil, a makeshift jelly bag and some sugar later, I have ruby-red Heytesbury Street crab-apple jelly, a terroirfood for an urban forager.

Foraging (the newly fashionable way of saying “picking”) sounds like something requiring wax jackets and the wild expanse of a landed estate, not footpaths and housing estates. But many city trees and hedges have food on them. So I’m in Bushy Park, in Dublin’s Templeogue, to see what a forager can find.

I’m joined by the comedian Maeve Higgins, who has memories of a childhood as a reluctant blackberry-picker. Higgins has a hotline to the London home of her Aunt Mary, who is such a serious city forager that she has been known to go to the park equipped with a ladder.

The third urban forager in our group is Vinny Sheehy, a fourth-year horticulture student at University College Dublin. Sheehy spent his summer working on Søren Wiuff's farm outside Copenhagen. Wiuff supplies Noma, rated the world's best restaurant, with wild and cultivated ingredients. Sheehy can now spot chickweed and sorrel across a crowded field the way some people can spot designer labels. He's brought his version of Aunt Mary in his backpack, in the form of the beautifully produced Forager Handbook, by Miles Irving.

Sheehy doesn’t need to open the handbook to spot hawthorn berries, buckets of them, on the neatly kept hedge that borders the park. So we start by biting into the deep red haws.

“They barely have a flavour,” Higgins says, a little disappointed. “But they’re very pretty. Look how good they’d look on a roast.”

The berries are mealy and have a large pip in the middle (Miles Irving describes them as having an avocado texture), but like the crab apples (mouth-clenchingly sour when raw), I hope they’ll make a great jelly when boiled, strained and sugared. This turns out not to be the case, more of which later.

Irving’s book says you can make haw Turkish delight, which sounds like a Michelin-star approach.

Sheehy is scanning the mown grass for sorrel. Then we find acorns scattered under the huge handsome oak trees. Emboldened by the hawthorns, we all bite into a peeled acorn and then all spit out the bitter white flesh.

Among the acorns Higgins finds a walnut looking as if it has dropped out of nowhere. Minutes later Sheehy identifies two huge walnut trees. The lower branches have no nuts on them, which means others have been here before us. The windfalls look like small limes. Under the juicy green skin is the brown walnut shell. The nuts seem extraordinarily exotic to find in a Dublin suburb.

As with the acorns, the nuts inside are pretty bitter. Green walnuts are best pickled, it seems. After they have been shelled and dried, they are delicious. These are probably our biggest find. A 100g bag of organic walnuts in Listons costs €3.66.

“So is there anything here that would kill us?” Higgins asks Sheehy. There doesn’t seem to be, but in Phoenix Park on a wild-garlic hunt earlier in the year, he mistakenly ate a plant known as Lords and Ladies. The awful taste stayed in his mouth for hours. So the advice is to eat only things you know are edible.

On the London hotline, Higgins finds out that Aunt Mary picks mulberries from a tree planted in 1608 in Charlton Park. Her jams and jellies are labelled with the place of forage. She’s made sloe gin, mulberry gin and sloe-and-apple jelly, and her hedgerow jelly is a great meat glaze. She is now bletting a tray of medlars (allowing them to start to rot) for medlar jelly, which is great with cheese. And she regularly fills bags with chestnuts for a chorizo-and-chestnut soup. Much of her pantry, like a wine cellar, is future-dated for consumption at its best.

Sheehy has found some chickweed and another green leafy plant, the name of which he knows only in Danish. It tastes strongly of celery. The chickweed is green, fresh and delicate like the expensive microleaves restaurants use for garnishes.

We also try some beech nuts but decide they’re best left to the squirrels. The sliver of nut is not worth the finicky bother of getting to it.

The initial excitement of finding sweet chestnuts, resembling prickly green sea urchins, dims somewhat when we find that the contents are fibrous and tasteless, like something you’d find in a vacuum bag. We find some spectacular conkers, encased in shells like oval pears. They have whorls of fine black lines on their deep brown skins and look as though a French polisher has been working on them all summer.

At the outset I had great hopes of finding blackberries. A punnet of less than 150g of French cultivated blackberries will set you back €4.99 in Dublin’s Fallon and Byrne. At those prices Bushy Park could be brimming with black gold. But the only briar patch, near the playground, has some miserable specimens that, it emerges later, are maggoty.

I abandon an attempt to make jelly from the hawthorn berries after too many white grubs float to the top of the boiling deep purple juice. In hindsight we should have picked only the bright pink berries and not the darker ones, which seem to be past their best.

Higgins recalls how, as a child, she hated the things her parents gathered and made so lovingly, such as crab-apple jelly and rose-hip syrup.

“It all just tasted of the outdoors,” she says. “I really preferred a jar of Nutella.”

And yet some of that rural sensibility is in the blood. She knows, without remembering how she knows, that squeezing the bag as the crab-apple jelly juice drips makes it cloudy.

In the end we’ve done some fascinating but unproductive foraging, a sort of nature trail with nibbles. Elderberries, or a large haul of blackberries, would have been great.

I roast the acorns, peel them and boil them several times to get rid of the bitter tannins. They taste woody, dense and mushroomy, like nothing I’ve ever tried before. I’m going to dry and powder them to add flavour to soups.

Foraging has been food for thought about what is over our heads and under our feet. We’ve turned the school nature table into a canape tray. I’ll never look at a city park or treelined street in the same way again.

The Wild Food Calendar

MARCH AND APRIL

Wild garlic Phoenix Park has loads, but take care to rub it between your fingers and get the garlic smell before you eat it.

MAY AND JUNE

Wild elderflower Make an elderflower cordial that will taste of summer hedgerows.

APRIL TO SEPTEMBER

Wild sorrel There are two kinds: wood sorrel, a clover-like leaf, and sheep’s sorrel, a larger spinach-like leaf. They taste tangy and lemony.

JULY AND AUGUST

Chantrelle mushrooms and wild bilberries.

AUGUST AND SEPTEMBER

Wild field mushrooms and blackberries.

SEPTEMBER AND OCTOBER

Wild ceps, blackberries, elderberries, rowan berries, crab apples, sloes, rosehips and chestnuts.

On November 19th and 20th the chef Evan Doylewill host the first Wild and Slow food festival, at Brooklodge Hotel in Co Wicklow. Food producers will sell jams, jellies, pickles and other products made with wild food, and a series of workshops will show how wild-food ingredients can be prepared and used. See wildandslow.com.

The demonstrations will include chefs Derry Clarke and Ross Lewis showing how to cook wild Irish game and pheasant.

Footpath jam: Heytesbury Street crab-apple jelly

Knowing what birds and dogs leave on city footpaths, it’s best to scald street crab apples well before cutting the tough stalks off and halving them. You don’t need a jelly bag; instead, a muslin bag suspended on a wooden frame (perhaps an upturned chair with clean muslin attached by its four corners to each leg) works a treat.

To make the jelly, put the crab apples into a saucepan and fill with enough cold water to cover them. You could also add a cinnamon stick and a star anise for flavour.

Boil and then simmer for two hours or so, until the fruit has broken down into a yellowy mash. Pour the mash into the jelly or muslin bag, putting a saucepan underneath to catch the liquid. In the pan, it should turn from muddy to gorgeous bubblegum-pink juice. Purists don’t squeeze the mash (as it clouds the jelly) but leave it overnight. You can also squeeze it and then leave it in the fridge to let the sediment settle at the bottom.

Darina Allen’s recipe recommends 450g of sugar per 700ml of liquid. Bring the juice to the boil and warm the sugar in an oven before adding it to the boiled liquid. Add the juice of a lemon and boil the juice and sugar mixture rapidly for about 10 minutes without stirring, then test it on a chilled plate. If it’s ready to set, a drip will gel on the plate. Pour the jelly into scalded jars and allow them to cool before you put on lids.

The jelly is perfect on pancakes, porridge or toast. It is a great meat glaze and is good with cheese.

Footpath jam will become more of a rarity in Dublin in the future. The city council no longer plants fruit trees on or near footpaths or roads because of problems caused by roots. A spokeswoman says that fruiting trees are now only planted in parks or open spaces.

The Forager Handbook: A Guide to the Edible Plants of Britain, by Miles Irving, is published by Ebury Press