My new blackberry trellises

tcstoehrNovember 2, 2008

After tasting and reading about the various thornless and/or upright growing blackberries, I was very happy to give them a try. After building an inadequate structure from T-posts and electric fence wire, I finally took a look thru GardenWeb and found out how to do it better. I built two 24' trellises. I have yet to add the horizontal support wires. Here's #1:

I used 10' long 4-by-4's sunk 2 feet into the ground. I think using 10 footers like this is the way to go. I doubt that I will later regret that the trellis is too high. The three sections are 8' wide. I should have done two 12' sections but I decided to lengthen the trellis after having built two sections, so I just added a third. Instead of the recommended 'T' formation along the top, I just used a single 2-by-4. With only an 8-foot span, I think that's adequate. I'll also likely be using 12-gauge wire instead of the recommended 9-gauge. Again, the wire will be supported at 8-foot intervals which is considerably less stress than a 16-foot span for example. And 12-gauge wire is pretty darn stout stuff.

After building trellis #1 and learning a few things, I built trellis #2:

This one has two 12-foot spans with a 'T' formation at the top to keep the posts from tipping towards each other from the strain of the (soon to come) wires. Instead of bolting them to the posts, I just supported them with brackets and sandwiched them between the posts. Seems reasonable. I will use 9-gauge wire on this trellis, although the thought of working with that stuff seems daunting.

The wires will pass thru holes drilled thru each post and anchored at each end-post with a wirevise. A wirevise anchors the wire, and allows it to slide thru the wirevise in one direction only. This allows you to tighten up any slack that may develop. They're very reasonably priced, assuming they work and last a long time. Here's a link that tells about them.


I think I'll run three wires on each trellis spaced two feet apart. Maybe only two wires spaced 3 feet apart where I'm using the 9-gauge wire.

I'm planning to put Triple Crown on trellis #2 and Kiowa on trellis #1. Yes, I know, Kiowa has major thorns but I'll live with them. I'm thinking 4 Triple Crown on one trellis and 6 Kiowa on the other, giving 6' and 4' for each plant respectively. Is this reasonable spacing? Should I spread them more? Can I spread them less?

I'll post my results with the Wirevises after installation. I think if they work well alot of folks here could make good use of them.

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Very nice trellises. I think the single beam with the 8' spacing should be OK. It may depend as much on the characteristics of the 8' beam, as it does on the stress on it. Some lumber just has a tendency to warp.

I am wondering, does it really reduce the stress on the wire by placing the posts closer together? My gut feeling is that if the wire is freely moving through holes drilled in the posts, that the stress on the wire would depend only on the total weight on the wire, and not how many posts or their spacing.

But I could be wrong.

    Bookmark   November 3, 2008 at 12:02PM
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> I am wondering, does it really reduce the stress
> on the wire by placing the posts closer together?

It does not reduce the "stretch" force applied to the wire, which is definitely a concern. You're right, that is uniform throughout. But the weight load delivered by the enormous crop of berries (har-har) will be reduced by having more intermediate supports.

    Bookmark   November 3, 2008 at 4:36PM
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glenn_russell(6b RI)

Nice job! They look nice, sturdy, etc. Being a berry fan, I always like seeing pics of other peoples' trellises

I like using the green vinyl coated wire because I try to make the hardware blend in with the plants as much as possible.

This spring, I'll be expanding my single galvanized iron pipe trellis by adding an additional 24' one.

My Chester's have 4 foot spacing between them, and that seems to work fine for me. I plan to use the same when I add my Triple Crown.

You may also want to think about adding the bird spikes. My birds just loved it up there!

Make sure to update this post in a couple years when you have tons of blackberries on there!

    Bookmark   November 3, 2008 at 6:30PM
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I'm also in Portland and am getting about 40 pounds of triple-crown fruit per 8 feet of row. Your trellis frame is plenty sturdy, triple crowns are largely self-supporting as far as fruit weight goes. Of course you want to tie them up else the whole plant would collapse. When your plants have been in 2 or 3 years, the protocanes should reach 8 feet by late july. After they are tall enough to tie off at the trellis top I would cut the top off immediately to encourage side-branching. Side branches can easily grow 15 feet.

You will have to do some climbing, though. Triple crown tends to angle its fruiting spurs at an upward angle; even the weight of the fruit does not usually bend them down below horizontal.

I have used the green-translucent coated steel wire for years and it weathers well.

    Bookmark   November 8, 2008 at 1:10AM
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Glenn, I like your iron trellis from the plumbing store. Hopefully, it will outlast treated lumber. But how did you fashion a closed square from threaded parts? You must have "cheated" somewhere.

Larry, how far apart are your Triple Crowns? I'm currently thinking 6 feet apart for mine. But I wonder if that's overkill. I'm planning the Kiowas to be 4 feet apart. But I'm just guessing.

I also got a bit worried and changed the top of my first trellis to have the complete "T" shaped top. When installing Wirevices it became clear to me how much tension would be on those wires. Although it also seems that 12-gauge wire is plenty thick and strong, when properly tensioned. I'll be using 12-gauge on the first trellis, and 9-gauge on the second. Time will tell and at least I'll learn something.

    Bookmark   November 10, 2008 at 3:05PM
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glenn_russell(6b RI)

Hi Tcstoehr-
Yep. I cheated. :-) For doing a closed loop like that, you need to add something called a "Union" instead of a regular coupling. Below is a link to an example of one. Again, this makes for a pretty expensive trellis, but I like the fact that it's very strong, won't rot, and relatively unobtrusive when painted green. I'm sure yours will work fine for many years, and when you're done making the trellis, you'll have some money left over to buy the plants! (unlike me with my expensive trellis!)

Here is a link that might be useful: Iron Pipe Union

    Bookmark   November 10, 2008 at 3:28PM
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The triple crowns within the same row are spaced close as 2 feet. Many side-branches are trained to overlap; on occasion I have bundled 6 branches and run them down the row end, cutting them off 1 foot above ground. 4-foot spacing would be less jungle-like.

    Bookmark   November 11, 2008 at 12:26AM
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