I've wanted to build a few large planters for a while now, and I've considered using concrete, wood, etc. I don't know what other cheap material to use.

Initially, I wanted to make them out of pre-mixed concrete, but realized that a square 24" concrete planter would just be too much weight for my rooftop. Each paver would be minimum 60-lbs each, so that's 300 pounds for one planter. Four planters would easily be over 1,000 pounds.

I then considered using wood, but untreated wood would rot and treated wood would poison the plant. So that's also out of the question.

So my question: for someone like myself with very extremely limited DIY skills and tools, how do you recommend I build a lightweight large planter?

I would like to try and build it because the cheapest 24" x 24" plastic planter is $35, and they're very ugly.

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    Treated wood doesn't poison plants (at least since CCA was discontinued). I have two raised gardens in treated lumber and millions of people have flower and vegetable gardens and lawns in treated landscape timbers. – isherwood Aug 27 at 20:04
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    Cedar might not last as long as treated lumber, but it's all natural and is rot and insect resistant. Also much lighter than treated. There's tons of instructions online for cedar planter boxes. – JPhi1618 Aug 27 at 20:23
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    Modern building facades are made of concrete coated styrofoam held in place with "chicken wire" and wood ribs. You can also simply mix a lighter aggregate into the concrete; pearlite, vermiculite, and polystyrene pellets (bean bag fill) come to mind. You can "mud" over the surface a 2nd time if needed to make it indistinguishable from solid concrete, except when you go to lift it... – dandavis Aug 27 at 20:25
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    @AlaskaMan, for the project at hand, cedar planks for fencing can be very affordable. Nice cedar for certain projects can be pricey, but fence grade is all this needs. – JPhi1618 Aug 27 at 21:23
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    you are concerned about the load on your roof .... have you considered the weight of the soil? – jsotola Aug 29 at 1:57

Animal watering troughs make for low cost and easily implemented "instant" planters that are (or start out) light weight for the strength they provide. You can cut down on the weight of the soil by putting in a layer of crumpled soda cans or plastic water bottles in the bottom. I like the looks of the plain galvanized metal ones, but you can paint them if you don't, or there are plastic versions that come in colors.

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  • Any large container which needs to hold dirt cannot be "inexpensive". How much are you willing to spend ? – Retired Electrician Aug 28 at 2:20

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