A 2 post trellis is installed by setting two plumb posts in concrete, then fastening the trellis panels after the mix cures.
Installing a 2 post trellis is a straight weekend job, but the steps you take before the concrete sets determine whether your panels hang straight for years. Whether you’re supporting climbing roses or training beans, the order is the same: mark, dig, set, brace, and fasten. Get the holes deep enough and the posts perfectly level, and the rest goes fast.
How Deep Should The Post Holes Be?
Dig below the frost line in freeze-thaw areas, and match depth to the structure’s height. For a freestanding trellis, holes about 9 inches wide and 2-1/2 feet deep with posts spaced eight feet apart give solid footing. Garden trellis guides call for holes 18 inches to 2 feet deep with posts 6 feet apart; arbor installations go deeper, at 24-30 inches. When in doubt, the deeper hole wins — shallow holes are the most common reason a trellis heaves or leans.
The hole width matters just as much. A 12-16 inch diameter gives concrete enough mass to anchor the post against wind load. In loose or sandy soil, widen the hole rather than assuming the manufacturer’s minimum will hold.
Setting The Posts Plumb
Run a string line between the two post locations before digging so the trellis lands exactly where you measured. Then set each post in its hole and check it with a spirit level in both directions — front to back and side to side. A post that leans even slightly at this stage twists every panel you attach later.
Fill around each post with post mix per the manufacturer’s instructions, then brace the posts so they can’t shift while the concrete sets. The fastest way is to screw a straight 2×4 diagonally from the post to a stake in the ground, one on each side. Verify the tops of both posts are at a uniform height before you walk away — a stepped installation is intentional, an uneven one is a mistake you’ll fight when capping.
How Long Until The Concrete Cures?
Plan on 24-48 hours before attaching the trellis or removing the braces. Quick-set concrete can take as little as four hours to support the posts, but the safer play is a full day of cure time per manufacturer guidance. Give it two days in cool weather; rushing this step is why posts settle and panels end up racked.
While you wait, you can pre-drill the panel attachment points. Stainless matters because it won’t rust and stain the wood the way galvanized fasteners can in wet garden conditions.
Fastening The Panels
With the posts cured and level, screw the trellis panels into place, checking that the top of each panel sits level before you drive the second screw per side. Align any top capping with the front edge of the post and screw through the capping into the panel frame.
For a T-post style trellis, the method is different: cable ties through pre-drilled holes, with at least five or six zip ties per post in one DIY example. Leave 4-6 inches from the bed edge in an arched setup so plants have room to be trained on the intended side.
Before you buy anything, it’s worth seeing which trellis designs hold up best in real yards. Our roundup of the best 2-post trellis options compares the top picks by material, height, and stated stability.
Wall-Mounted Trellis Differences
The spacing keeps the panel from bowing away from the wall where vines get heavy.
Sources differ on hardware for a reason — stainless is right for posts and panels, galvanized works for wall fixing. Match the fastener to the job and the material, and you won’t be redoing a rusted joint next spring.
FAQs
Can I put trellis posts in without concrete?
Yes, for lightweight panels in mild climates. Tamp the soil in layers around each post, packing it tight, and expect to re-tamp after the first heavy rain. Concrete is the only option that holds against wind and frost heave, so skip it only for temporary or very light structures.
Should I use pressure-treated wood for trellis posts?
Pressure-treated posts resist rot where they meet the soil, which is the failure point for most untreated posts. Cedar and redwood also hold up well in garden conditions. Whatever you choose, keep the wood clear of direct soil contact where possible and let ground-contact-rated lumber dry before painting or staining.
How far apart should the two posts be?
Match post spacing to your panel width. The sources call out eight feet for freestanding trellis spans and six feet for garden setups. Measure the actual panel or crosspiece you’re mounting and add a few inches of overlap on each side so the fasteners bite into solid post material.
References & Sources
- New Mexico State University. “Vertical Gardening.” Covers trellis post depth, spacing, and plant training guidance.