Some people say the premixed just-add-water cement powder may not be as strong as the one you mix yourself. Another issue when making the concrete posts is the steel rebar inside. Will they get rusted & affect the plants? Let's see how to make strong, good sturdy poles may just outlive us.
Round or square shape
Some growers prefer square posts because they provide a good flat surface to lean the dragon fruit plants on. On each of the four sides, we can plant 4 cuttings of dragon fruits. For shipping & handling, it's easier to stack square posts on each other than the cylindrical ones, which may roll & create empty space in between.
The downside to square posts is that they're almost never square. The edges, or 4 corners, of the posts are slightly rounded when taken out of the concrete mold. So there's always a bit of concrete left over. Which creates waste. Choosing a shape from the start can help you choose the right mold to make the post.
Height & width
A good height for dragon fruit post is around 5-6ft (1.5-1.8m). The diameter for a square shape post is around 4-5 in. (10-12 cm). For cylindrical post, the minimum recommended diameter is 4.7-5.9 in. (12-15 cm) for good support.
When you're planting the pole in ground, take into account the depth of the hole. If it's about 1-1.5ft (30-45 cm), then the part of the 6ft pole from the ground up will be 4.5-5ft.
The weight of the post usually anchors itself well in the ground. Some make extra cement footing right inside the hole. You can pour some concrete around on the top soil surface to anchor it more securely. With the dragon fruit roots grabbing on as they grow, the pole will stand even more sturdy in the ground.
Premix or self-mix concrete
Ready-mix concrete is good if you're busy & don't want to spend more for a concrete mixer of some sort. You can use a wheelbarrow or any container to mix. A 90-lb bag can be had for less than $5. The downside to this is that it may not be as strong as you like or strong enough to support the plants as they grow bigger.
If you use premixed concrete, half a bag (or 45lb) would be enough for one 6ft post. Some add more water than instructed on the package so it's easier to mix.
If you mix your own stuff, try the 123 ratio. Mix 1 part concrete, 2 parts sand, and 3 parts gravel or aggregate. Similarly, you can try the 4:1 ratio of 4 parts aggregate & 1 part concrete. A finished post can weigh about 200 lbs. It's ridiculously heavy.
When letting the concrete cure, tap along your mold to make the air bubbles pop. If the post doesn't set properly, you may see something like honeycomb on the surface.
After pouring the concrete in, if you have an air pump, use it to pump air inside the concrete. You can use a trowel to poke in & out. This helps burst the air pockets inside, making the concrete more compact & stronger. Concrete with empty air pockets inside are weaker.
After about 48 hours minimum, you can take the post out of the mold. If you take it out too early when it's still wet, it might crack. For the first 2 weeks after the release, pour some water around or hose down the post. Moisture helps the concrete cure & strengthen it. After 28 days, it will fully set.
Choosing rebar for reinforcement
Rebar or some steel rod in the core can help strengthen the overall post. If your posts are about 6ft tall, a 5.5-6ft (1.6-1.8m) rebar will work. The ones with diameter around 3/8-1/2 in. are good enough.
You can use the 1/2" one as the central spine. And three 3/8" ones as the supporting bars. Wire them using 17-gauge bar ties into a triangle prism like this or any structure that you see fit.
Some people raise the question of whether the rebar will rust? Well, the part covered with concrete will get protection from corrosion or environmental factors. The only concern is the exposed tips or antennas for supporting the top platform. They look a bit like these:
From growers experience, these exposed steel bars will rust over time. If you don't like this, then use shorter rebar or just don't let it expose out. Alternatively, you can use something like a Zinc Gal or any cold galvanizing spray as a protective coating.
A single 1/2" rebar would be okay for supporting the pole. Doing it this way, you may need a different top design to support the branches. Some top platform that you can remove & replace after some years is also a good option.
The mix location
When you mix & pour concrete into the mold, do it near the holes where you're going to plant it in. It's a point many overlook. If you do it somewhere far away, you're gonna have a hard time dragging that 200-lb monster to where it's going to sink in. The near-by location makes it a whole lot easier on you & your back.
Making the mold
Wet concrete is very heavy so choose a mold material that can withstand such weight & pressure. If the mold is too flimsy, the concrete may bend it and you'll end up with a curved post. Materials like steel, wood or thick PVC work well as molds for concrete.
If you want to make multiple poles at once, try the multi-post mold:
Basically, they have this 6ft (1.8m) steel mold with 3 dividing steel planks. Both ends have steel cap–it's all in one piece. There are 3 bars across the mold to keep it in place. You can see the 2 long handles on the side. Those help the builders lift the mold up.
To make the post, first they lay a layer of newspapers down. Place the rebar on & put the mold on. Then, they pour concrete in. After 15-20 mins when the surface of the posts dries, they lay another layer of newspaper on, put the rebar in, place the mold in & pour concrete. Layer by layer, we can see a stack of poles like these.
The builders put newspapers as liners on the ends for easy release. The weight of the newer posts can help compact down the older ones. A downside to this method maybe the new concrete spilling down to the older posts. But if you're mass producing, it helps you speed up the production.
This YouTuber has a great video series on making multiple cement posts:
Single-post square wood mold
To make a wood mold, use thick wood for this purpose. You can try the open topped box mold with braces so the sides don't bow out. A basic construction can be something like this:
|Part||Thickness x width x length|
|Bottom plank||1" x 8" x 6'|
|Side planks||1" x 6" x 6'|
Screw the side planks to the bottom plank with some nails. For both ends, screw on some big enough piece of wood. Use braces or wood bars to secure the top open surface. Deck screws also work. And you're basically good to go.
Single-post plastic cylindrical mold
If you have PVC storm water pipes, you can utilize those to make the posts. We don't need to oil it or use any releasing agent. But you can if you want to. Old engine oil will work fine. It will release out of the mold & won't stick.
Some people prefer this cylindrical style because it looks nicer. The minimum diameter around 4.7-5.9 in (120-150mm) is good for this type. A 3-inch drainer pipe also works.
You may need to plan a good space for this because you'll be pour the concrete from the top of the tube down. Again, do it somewhere near the pole so you won't need to drag it to the destination afterwards.
Estimate total cost per post
- 45-lb concrete: $2.5
- 4 rebar: $12
- Molds, water, screws: $10
Roughly, approximately $24.5 for a post that lasts 60-70 years. This varies very much depending on where you live. In some places, there are dragon fruit planting services. They go from A to Z. If you have a piece of land & want to start a dragon fruit farm, call them & they'll come dig the holes, plant the cuttings and cement posts & set up everything needed. All you gotta do is taking care of the plants & get the fruits. Sort of like a turn-key solution with a lifetime warranty.
Let's take some tours around the dragon fruit post production site:
Have fun DIY!
Now we know the dimensions of the posts, some good & bad points of each material and some little tips & tricks in the making. Hope this was helpful. Have fun creating your projects, thanks for visiting & enjoy!
Share or pin this post!