The expanding trellis sold folded in a bag sags the moment a climber gets any size to it, because nothing holds the grid square. This one is fixed: a butt-jointed softwood frame keeps its shape, and the lattice is built up from pre-cut lath laid horizontal and vertical rather than ripped narrow on a saw, glued and pinned at every crossing before it goes on the wall.

A Framed Square Lattice Garden Trellis

What you need

2 length 2.4m x 32 x 20mm PAR softwood cut down for the two stiles and two rails
1 bundle 20 x 6mm pre-cut softwood trellis lath, approx. 30m total square grid infill — buy pre-dimensioned, don't rip your own
1 box 20mm galvanised panel pins or staples fixing lath crossings
1 bottle exterior-grade PVA wood glue
1 box 50mm exterior wood screws frame corners
4 20mm-thick softwood offcut blocks, roughly 40mm square spacers so the panel stands clear of the wall
1 exterior wood finish or preservative

Step by step

Cut two stiles to 1200mm and two rails to 536mm from the 32 x 20mm softwood, squaring every end on the mitre saw. The rails run short because they fit between the stiles, not across them.
20 min
Lay the rails between the stiles to form a 600 x 1200mm rectangle. Pilot-drill through each stile into the rail ends, then glue and screw the four corners, checking both diagonals match before the glue goes off.
25 min
Lay the assembled frame flat on trestles. Starting from one end, lay lath vertically across the face at roughly 100mm centres, overhanging the frame edge by at least 50mm top and bottom, and tack each one lightly with a single pin to hold its position.
30 min
Lay a second set of lath horizontally the other way, crossing the first at right angles to complete the square grid, pinning those lightly too.
30 min
Work back across the grid, gluing and pinning every crossing with a single panel pin or staple. Keep the spacing even by eye rather than measuring each gap.
50 min
Leave the glue to go off for about an hour, then trim the overhanging lath flush with the outside edge of the frame using a hand saw, cutting toward the frame to avoid splitting the last few millimetres.
25 min
Pin the trimmed lath ends down into the frame edge all round so nothing lifts.
15 min
Screw a spacer block to the back of each corner so the finished panel stands clear of the wall for airflow.
15 min
Apply an exterior finish or preservative to the whole panel, working it into the lath crossings, and let it cure fully before fixing the trellis outside.
20 min
Fix the trellis to the wall or fence through the spacer blocks with exterior screws, checking it's plumb before training anything up it.
10 min

Afterwards

Brush dust out of the lattice crossings rather than blowing it, and let an exterior finish cure fully — 24 to 48 hours is typical — before the trellis goes outside or a climber gets a grip on it. Check the spacer-block fixings each spring: a mature climber is heavier than it looks, and a loaded panel will pull loose screws before it breaks the wood.

Questions

Can I use a bought lattice panel instead of building the grid myself?

Yes. Pre-made lattice sheet is widely sold and this frame will take a panel of it in place of the built-up grid — rebate or batten the edges in rather than trimming and pinning lath.

Does the exact grid spacing matter?

Not precisely. Anything from 90 to 120mm reads the same to a climbing plant. Keep it consistent by eye rather than measuring every gap.

What will this carry?

A single vigorous climber such as a clematis, sweet pea or runner bean, comfortably. For a woody climber like wisteria, build a stouter structure — this one is sized for annuals and light perennials.