Construction should be straightforward if the ground is pegged and marked out using sand, string and stakes. Constantly check measurements and lay out components to check nothing has been forgotten.
Pathways should be at least 100cm (40in) wide although wider is preferable. Where space is limited a narrow paved path can be edged with pea or ornamental gravel bounded by 15 x 2.5cm (6 x 1in) treated boards or brick edging. Grass often disappoints due to shade, wear and damage in wet weather.
Set uprights firmly using metal spike fixings or concrete. Ensure that 20-25% of the total length of the uprights is embedded. Use a 60cm (24in) deep hole for a 15 x 15cm (6 x 6in) timber pergola upright of 2.7m (9ft) length, giving a 2.1m (7ft) above ground. Lighter 10 x 10cm (4 x 4in) timbers may be used in sheltered sites.
Keep the hole no wider than a spade's width and place a half brick or large stone at the bottom. Half fill the hole, around the upright, with tightly packed hardcore (continuously checking the vertical aspect of the post with a long spirit level) and top up with concrete. Use temporary supports to steady posts while the concrete sets.
Check measurements and take a step back occasionally, to ensure that the structure is being accurately assembled and that it looks right.
Attach crossbars, support trusses and trellis panels when the uprights are truly solid in set concrete. Use the right sized galvanized wood-screw rather than nails. Preformed brass or steel brackets can save large amounts of joinery work or angled pre-drilling but can be unsightly when used on visible surfaces.
Further information
Choose plants to train over an arbour