I made a planter roughly the same as what you are making 60 odd cm by 60 cm roughly..with 3 inch width to the sides approx as I filled it by eye. I got a box of wood for the outside and filled the centre with polystyrene box think they are dry ice boxes. this was about 8cm/10 cm smaller then the bigger box on all sides. This area I filled wit the mix. (i hope I am making sense to you ). Once it had dried I gouged out all the polystyrene and that gave me my planter space. I used plastic hose pipe between the mix at the base of the planter so it would drain and I removed this after the planter had dried.

Is this too big a project to just form fit it to the out side of a form?

I find it's easier to do it that way. Does not mean it's the best or the right way :). The weight of the cement is what to be careful of, doing one of the planters even the wood could not handle the weight ..it exploded all the mix went everywhere and I was running and panicking like a deranged chicken! You learn by your mistakes :)

Thanks I handn,t considered the weight of the project while being made just the finished weight and how to get it over to where its going to be used.

Something this size is best made in place unless you have a tractor or lift to move it.
For something this large it best to work inside a mold. You would use a box inside a box mold. For working in place the mold should be bottomless. The outer box is bottomless and staked to the ground. You place your hypertufa mix directly on the ground. Then center the second box on top of the hypertufa mix. Use several bags filled with sand to weight down the inner box. It's easier to remove smaller bags of sand rather than filling that inner box.....I know. Then start filling the space between the two boxes with hypertufa. Fill all the way around in layers and tamp the mix to compact it to remove any air pockets. Something this size needs rebar that's been coated with a rust inhibitor.
If it's taken you years to work up the nerve this is not the project for you. Start with something smaller.

Thank you for your helpful tips. You mentioned several things I would never have thought about until after it became a explosion;) The plants are already up and looking good so I was intending to do the project away from the spot intended then move it over there and plant it out after it aged for the winter. Now I think I will just have to do it in place and transplant the plants in pots until the planter is ready for use.

The best advice you got was Billies last sentence. Start with something smaller. We have all been where you are - and made many mistakes.
There are many things that we have all learned from trial and error that you cant read about on the web.
Find a bowl, and use that as a mold. Place the damp mix in the bowl, wait 24 hrs and then remove the mold. Learn about the importance of curing ( keeping damp) the hypertufa container.
And if it does break, you only have a small project to dispose of.

Also - buy an Elephant Ear Plant. It is easier to grow and much easier to do a concrete leaf.

Mike

Let me suggest you go to my friends' web site; www.almostancientpots.com She has made a pair of VERY big hypertufa planters and gives some info on how she did it. Good luck,
Cora

http://almostancientpots.com/index.html

the first link did not work for me