I stumbled upon this forum while searching for large pots. I inherited some very large round concrete pots (terra cotta coloured) that are too wide for my deck. Finally found some narrower pots and need to sell my 2 lovely but large planter pots. They are 25" diameter at top and 22" high. I gather from this forum that these puppies are very hard to find. Big enough to accommodate a small tree or shrub. Light enough that I can drag them around and sturdy for winter. Not sure how to post a pic here yet but I think it worked below. Looks like this forum will be helpful to learn the ins-outs of gardening in BC for this Ontario transplant. Thanks !
Generally, buy and sell isn't something we want on these forums, but this seems pretty innocuous. Try Craigslist as well.
Large pots are beautiful things, especially when you put beautiful plants in them. This situation is a lot like aquariums, the bigger you want them, the harder they are to obtain. Just as fish-keepers often make their own aquarium a home-owner/gardener with some space and light may want a huge pot as a feature, as a "book-end" or just to hold something that has grown too large for lesser pots. The materials needed to make one are rather simple, except for chicken-wire. Not many of us raise chickens at home these days... Anyway, you need something that's thin but with tensile strength. Concrete is very strong in compression but it can't stand forces that pull it apart or bend it. You need some thin reinforcement. Some kind of steel wire mesh is good but it mustn't be too thick or you will get excessive cracking. The wire is meant to prevent cracks from opening up seriously. If the next step is intimidating, hire a kid. Tell them to wet some sand and make a "sand-castle" with a shape like you want for the interior of the pot. Put it on a sheet of plywood or something you can lift the pot away cleanly. You could put down a sheet of plastic over it to prevent damage to the plywood. Contractors sometimes grease wood to allow concrete to "release". Use whatever works for you. Draw a circle on the wood to start and build up the sand just like you used to do at the beach. This sand core will have no strength if it dries out so immediately apply a thin layer of stiff concrete. The concrete needs to be made from Portland cement and sand only, no gravel or pebbles. You just want a layer of concrete over the sand, something that will hold its shape and perhaps 1cm thick. This concrete has to be really stiff so it doesn't "slump" or slide down. While it's still damp, apply a layer of chicken wire over all the exposed surface. This will help it hold still too. It will help to have some helpers as the wire is springy and you can't apply much force anywhere or you will damage the work of art beneath. Use heavy scissors or shears to cut the wire. You don't want any gaps and overlapping areas a bit is good. If you can't get the concrete to stand up to suit your needs, you could try adding a fibrous thickener like fibreglass. This can be dangerous to skin, respiration and eyes so don't use it unless necessary. Adjusting your design is a better option. Even dry sand will stand a 30 degree slope. Damp sand or stiff concrete can get to 90 degrees with care. Now, stand back and admire your work for a while. The concrete will gradually stiffen. Before it's hard but after it has stiffened noticeably (yes, go ahead and poke it to see), perhaps an hour or two later, use a paring knife or similar gadget to open drainage holes. You may want a bunch for a large pot but you want at least one hole about the size of the openings in the chicken wire. For three days, keep the concrete moist and covered with plastic so it doesn't dry. Water is essential for the hardening process. Then you have a concrete pot but it is too fragile. Apply one or two more layers of concrete and chicken wire each about 1cm thick until you have a good thickness. For the last layer, you want just concrete, no wire, because this surface will be visible. When it's all done and dry, you may want to paint the outside of the pot. Some people embed nice rounded pebbles or coloured stones as ornamentation. It's also possible to colour the last layer of concrete so the colour will be more durable. Let the finished pot sit still for many days before tipping it. The concrete is pretty hard after a few days but reaches maximum strength after weeks. The pot will be incredibly heavy because of the sand inside. You can try to lift the lip just a bit and wash the sand out with a garden hose. Then you will only have the shell to lift. Lifting is definitely a job for a team of strong fellows or some kind of hoisting machine. Roll the pot gently onto its side and then on to its bottom. Edges can chip so be careful to distribute forces. Lift it onto a wagon to put in final position. Other shapes are more challenging as the concrete will slump at too great a slope. To make a box this way, you probably have to use forms just as contractors do for a basement or swimming pool, plywood sheets holding the concrete in place against gravity and its tendency to flow. You can pour the concrete in stages so a weaker form will do. The greater the depth of concrete that is fluid the stronger the form has to be to restrain the pressure. To make very deep pots, you can use cardboard forms called "Sonotube" a smaller one nested in a larger one. Plywood can be bent more if it scored on the inside. If these techniques are not adequate for a huge pot, consider making it of masonry/brick and building it up incrementally. Don't forget reinforcing such work with a layer of steel-reinforced concrete between two layers of masonry. For thicker layers of concrete you can and should use heavier wire. We used to use "page wire" for concrete a few inches thick. For thicker stuff use rebar just like contractors. It can be easily bent to shape and secured with wires into position for casting/pouring. Stir deep concrete a bit to eliminate voids in corners and such. As with any new technology, practice on a smaller project before scaling up for something big so mistakes will be smaller during the learning process.
