The invitation says one o'clock. It does not say when lunch finishes, because nobody at a wine estate knows. There will be a walk between the rows, a visit to the cellar, a table set under a pergola or a plane tree, and then several hours in which bottles arrive and the light moves across the hill. What to wear to a vineyard lunch is a question with five parts: sun, shade, stone, gravel, and a chair that will be occupied for a long time.

It is an occasion with a dress code that is never written down. A vineyard is a farm, however grand the house, and anything too polished looks as though it has come to the wrong address. Equally, a host who has opened an old vintage deserves more than beachwear. The register is somewhere between the two, and it is one that linen has always occupied without effort. A shirt in certified Belgian linen is an agricultural product in its own right, grown in a field and shaped by a season, and it is at ease among others of its kind.

The day has three temperatures. The vineyard itself is open and bright; even in the weeks of harvest the midday sun on a south-facing slope has weight. The cellar is the opposite. Barrel rooms are kept cool and damp throughout the year, usually somewhere in the low teens, and twenty minutes among the casks in a thin shirt is noticeable. The table, finally, is in dappled shade that cools as the afternoon goes on. One long-sleeved layer, worn rolled and then unrolled, answers all three.

For him, that layer is the Laos Long Sleeve Linen Shirt in Beige Cream or Oyster, colourways that sit close to dry earth and pale stone. The seashell buttons are the only ornament it needs. Where the lunch is more formal, at a château in Bordeaux, say, or a quinta above the Douro, the Monte-Carlo Male shirt in Vanille brings walnut buttons and a slightly dressier line. Below, the PP Casual Linen Trousers in Oatmeal are the natural choice. Vanille and white linen are handsome among the vines and will be worn by the confident. Those less sure of their neighbour's pouring arm may prefer Roosewood Pink, a colour with little to fear from a glass of rosé.

For her, the Amelia linen dress shirt is the most complete answer. In Dubarry it has the depth of late-season foliage; in Oyster, with walnut buttons, it is closer to the pale stone of the cellar. It is easy across uneven ground, cool at the table, and substantial enough for the cellar. The PP linen blouse in Orchid, long-sleeved and cut to the hip, makes the same argument more simply. On the warmest days, at an estate in the Cape winelands in February or a Provençal domaine in July, the ladies linen set in Dubarry or Lemon is entirely in keeping.

Footwear deserves a thought, because the ground decides. Gravel courtyards, cellar steps worn smooth and grass between the rows all favour a flat, firm sole. A heel belongs to another kind of lunch. So does anything heavily scented; a winemaker pouring something delicate will be grateful for a guest who arrives smelling of nothing in particular. These are small courtesies, and a vineyard is a place where they are noticed.

The setting changes the palette more than the garment. In Chianti and the hills south of Siena the ground is ochre and the cypresses nearly black, and warm neutrals look native. In the Douro, where the terraces drop in steps to a green river, deeper colourways hold their own: Dark Blue for him, Dubarry for her. Napa in harvest is gold and dry, and takes white and Oyster well. Stellenbosch and Franschhoek, under granite mountains, have a brighter, cleaner light that is kind to Sky Blue. None of this is a rule. It is simply what the eye observes when a table of twelve is seen from the far end of a row.

And then there is the matter of sitting. Three hours at a table will leave its record on any natural cloth. The crease across the lap and at the elbow is simply what linen does, and at an estate where the barrels are stained and the secateurs are hung by the door it reads as evidence of a good afternoon. Linen softens through a day like this one. By the time the cheese arrives, the shirt has settled into its wearer in a way that no morning pressing can arrange.

The host will be remembered for the wine. The guest is remembered, if at all, for having looked comfortable: unhurried, appropriately dressed, plainly glad to be there. The journal's guides to Tuscany and the Douro Valley take the same thought further, for those planning to stay on after lunch.

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