How to MakeT-Post Trellis Spans

By: Herrick Kimball
(click on pictures to see enlarged views)

A basic T-post trellis span in my garden 

I developed and perfected the Planet Whizbang T-post trellis span over the course of several years of gardening. It is a simple, practical support system that I'm sure you'll be very pleased with.

The trellis span pictured above illustrates the basic components. A 7' T-post is at each end of the span. The posts are driven into the soil 18," leaving 5'6" above ground. A Planet Whizbang Y-holder is attached to the top of each post. A 10' length of 1" diameter electrical conduit is cradled in the Y-holders.

The 1" diameter conduit top bar is ideally suited for this application. A 10' length will cost around $7 and is available from any home center (Lowes or Home Depot). I don't recommend a diameter less than 1."

A length of tree sapling can also serve as a top bar, as you will soon see.

The frame created by 2 posts, outfitted with Y-holders and a top bar, can accommodate different trellising options. In the picture above, I have used a 10' by 5' panel of concrete reinforcing wire. It is inexpensive (around $8), strong, long-lasting, and has a 6" grid size, which is just right. 

Another option is nylon or polypropylene trellis netting, which can be woven through the top bar, and string-tied to the T-posts down each side.

In the picture above you can see a Y-holder in place at the top of a T-post. It is held with a single hose clamp. Notice also that the concrete reinforcement panel fits over the Y-holder too. That will hold it in place while you secure the panel down the sides and along the top with some pieces of twisted wire. Once the panel is secured, it's a very sturdy trellis support.

There (above) is another view of the top bar and Y-holder. 

The picture above shows the same view of the same trellis spans seen in the picture at the top of this page. The spans are 9'6" long and I spaced four indeterminate tomato plants in that distance. I keep the bottom leaves pruned and weave the top growth into the 6" square grid. If a stem gets too long to tuck into the grid, I simply string-tie it to the heavy wire.  I prune away any stems that grow away from the trellis.

Tomato spans, like you see above, are a much better option for growing tomatoes than the usual tomato cage made of a cylinder of wire. That's because tomato plants grown along a T-post trellis span don't fall over later in the season when they get top-heavy (like those tomato cages do). The span also allows for better air circulation around the foliage (less opportunity for blight to develop).

The pictures above show the same trellis spans in late July. Notice how neat and tidy the length of the spans are. The tomatoes are green but starting to turn red...

Tomatoes on a trellis span are, of course, easier to pick. And they're not going to be soiled like tomatoes grown on the ground.

T-Post Trellis Extensions

As I've already noted, a T-post trellis span made with 7' T-posts driven 18" into the ground gives you a 5'6" high trellis. That's high enough for most flowers and vegetables, but you can easily make the trellis span higher.

 All you have to do is hose-clamp some 1" diameter conduit extensions to the side of the T-post. The Y-holder can then be dropped down into the top end of the conduit. the following pictures show trellis extensions in action.

In the picture above you can see the frame for a tomato string trellis. My standard tomato string trellis is 5' long. I plant three tomatoes in the span and prune them vigorously to grow up 9 strings. Full details about my tomato string-trellising system are in The Planet Whizbang Idea Book For Gardeners.

I cut my trellis extensions at 4' and overlap them 2' on the T-post. Notice the pan-head screw in the picture above. The screw is in the extension piece at 2' and it prevents the pipe from sliding down.

As you can see, the Y-holder fits down into the top of the 1" conduit extensions very nicely. That top bar is a section of scrub sumac tree, which I have wired to the Y-holder.
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The photo above is of the same string trellis about a month after the previous pictures. The nine strings are in place. I tie the strings at the bottom of the span to a wire at ground level, that I've stretched tight and tied to the posts.

Those tomato plants are Tommy Toe. If you want to have success with string-trellising tomatoes, stick to the smaller varieties, and I can tell you that Tommy Toe and Juliet are excellent varieties to grow.

String-trellised Tommy Toe tomatoes

String-trellised Juliet tomatoes

Ripe Tommy Toes & Juliets

Tommy Toes racing their strings to the top (click picture to see an enlarged view)

Trellised Peas

It's fun to grow tall pea varieties on a T-post trellis span with extensions, as the pictures above show. Those trellises have polypropylene trellis netting with a 7" x 7" grid. 

Keep in mind that peas grow up and hold themselves with tendrils, and tendril-growing plants don't do well on vertical strings—they need a grid with horizontals. 

On the other hand, pole beans grow by twining and they will grow very nicely on strings. Pole beans will do just as well with large-grid netting too.


Sorry but I don't have any pictures of pole beans or cucumbers or vining squashes growing on my trellises. But I have grown them all and they thrive on T-post trellis structures like I've shown you here.

And so do climbing flower varieties. A seasonal privacy screen can be made with flowers on a T-post trellis span. One of these days I'm going to try that!

This T-post Trellis Span idea is just one of many ideas that are featured in the Planet Whizbang Idea Book For Gardeners.