Building a Two-Wire Thornless Blackberry Trellis on T-Posts with a Clip Tool: Wires at 3 and 5 Feet, Posts Every 20 Feet, and Five Plants on a 40-Foot Row

Thornless blackberry trellis with galvanized wires on green T-posts over mulched soil

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For a 40-foot row of semi-trailing thornless blackberries, drive three 8-foot T-posts 20 feet apart, run 14-gauge high-tensile wire at 3 and 5 feet, and close the clips with a T-post clip tool. Five plants set 8 feet apart fill the row, and 6 clips hold the wires on the posts.

What wire heights work for a two-wire blackberry trellis?

Put the lower wire about 3 feet above the ground and the upper wire at 5 feet for erect and semi-trailing blackberries. The low wire shapes the plant, the top wire carries the fruiting canes, and you tip new canes once they reach the top wire.

NC State Extension's home garden blackberry guide recommends a two-wire system with wires at 3 and 5 feet for erect and semi-trailing types. It says to tip canes at the top wire, prune laterals on erect types to 12 to 16 inches in winter, and keep 6 to 8 canes per square yard.

Clemson Cooperative Extension's blackberry factsheet builds its V-trellis on 8-foot T-posts set in pairs every 20 to 25 feet, anchored at the row ends, with 14-gauge high-tensile wire. It spaces semi-trailing plants 6 to 8 feet apart in rows 10 feet apart and keeps a weed-free strip 2 to 3 feet wide on each side.

Parts List for a 40-Foot Row

Item Count Detail
8-ft. T-posts 3 in the row At 0, 20, and 40 ft.
Anchor T-posts 2 Angled out from each end post
14-ga. HT wire About 100 ft. 2 x 40 ft. plus end wraps
T-post clips 6 used One per wire on each post
Plants 5 8 ft. apart, 4 ft. from each end

The 100-foot wire figure is 80 feet of run plus about 5 feet of wrap at each end of each wire.

Materials and Tools

  • T-post clip tool for wrapping the clips around the wire
  • Five 8-foot studded T-posts, a T-post driver, and a box of matching T-post clips
  • About 100 feet of 14-gauge high-tensile wire and one in-line wire strainer
  • Lineman's pliers, a tape measure, a level, and soft plant ties

Trellis Steps

  1. Mark the row. Stake a string 40 feet long, ideally running north to south.
  2. Drive the line posts. Set T-posts at 0, 20, and 40 feet, studs facing the same way, with about 6 feet above grade.
  3. Add anchors. Drive one T-post at an angle a few feet beyond each end post and wire it to the end post's top.
  4. Mark the heights. Measure 36 inches and 60 inches up each post and mark them with tape.
  5. Tie off the start. Wrap the top wire around the first end post at the 60-inch mark and twist it back on itself five times.
  6. Run and strain. Pull it to the far end, add the in-line strainer, wrap the post, and tighten until the wire no longer sags between posts.
  7. Clip the middle post. Hook a clip around the center post under a stud, then use the clip tool to wrap both clip ends around the wire.
  8. Repeat low. Run the 36-inch wire the same way and clip it, then plant the five canes 8 feet apart.

As new canes pass the top wire, tie them loosely to it and tip them, following NC State's timing.

Trellis Mistakes

  • Skipping end anchors, so the end posts lean in once the canes load up
  • Setting the top wire higher than you can easily reach for picking
  • Wrapping clips so tight they kink high-tensile wire
  • Crowding plants closer than the variety's spacing

Raspberries use a similar two-wire setup in building a two-wire raspberry trellis with 12-gauge galvanized wire. The clip-closing motion is shown step by step in clipping 4-foot welded wire to studded T-posts with a clip tool.

To keep rabbits off young canes, see the barrier sizes in the hardware cloth mesh size and gauge guide.

For hard ground at the post marks, follow driving 6-foot and 8-foot T-posts in clay and rocky soil.

FAQ

Do erect blackberries need a trellis?

Not always. Clemson notes erect types can stand alone if summer pruning keeps canes at 3 to 4 feet, but a trellis makes picking easier.

Can trailing types use this trellis?

Yes. Instead of tipping, weave trailing canes down to the low wire and back up, as NC State describes.

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