Most of the containers that I make look like containers. It will be a little harder to make it look like a rock. Search this forum for suggestions . Start with making hypertufa , placing inside the mold , like a bowl then place the tufa on the outside of the mold. As skills develop then try creating a wire form. Making a rock will involve making a form with chicken wire and then covering the wire with hypertufa. Others may have different approaches.

You can plant anything you like - using different potting soils will impact what you can plant.
Good luck and welcome.

Mike

Here is a link that might be useful: Some photos of containers

How large of a plant? It can be very heavy.
You can do like Mike said, and make a mold out of wire or work on the outside of a bowl. You can stuff a cardboard box with newspaper (that's to help it hold it's shape once you put on the wet cement mix) then turn the box over and bash in the bottom of the box to give it an irregular rock shape. Drape the box with a plastic dry cleaner bag and apply the hypertufa mix. After you get one thin layer on go back and add details to make it look like a rock. I've also made slab rock with shallow cutouts for bonsai. The slabs have a wire mesh center. You work on one side, let cure overnight then flip it over and work on the back side. Depending on the size, you may need someone to help turn it over.

billie ann, I thought hypertufa was pretty lightweight. I was thinking of flowers, petunia, pansies, that type of thing. I was thinking of a rock that was not a boulder size able to hold these type of flowers.

The weight depends on the size of the rock/planter and what hypertufa recipe you use. Even then these are not lightweight. The lightweight comes in comparison to a concrete planter which is made from portland cement, sand and gravel. A hypertufa planter is made from portland cement, sand and peat moss (or vermiculite or perlite or other concoctions).
As Mike said you can plant anything in these containers.

dj95, I just joined to learn more about hypertufa. As to your idea of a ht rock planter, I've made a few small ones that I really like and are in great shape after about 5 years outside, year round.

I used foam- mostly from printer cartridge shipping boxes, but any kind and shape will work. I like to use, at least on the "bottom", 1/4 hardware cloth (a.k.a. hail screen) and sometimes all around.

Also, for great ideas, do a search for "fake rock background" and you'll see many ideas used for aquarium, vivarium, terrarium displays like zoos have. Great ideas in those.

I ran into this article on making "faux rocks" out of hypertufa while doing some research that might be of interest. The "rocks" in the picture sure look like rocks to me! I'm going to do my first hypertufa project this spring.

Does anyone know where to find large bags of vermiculite? I plan to use it instead of sand, so the hypertufa is lighter.

Also, it would be great to see pictures of some of the projects people in this forum have done - for inspiration.

Here is a link that might be useful: The Artistic Garden - hypertufa faux rocks

I purchase 40 lb. bags of vermiculite at our local Seed and Feed Store. It comes in course or fine granules. I was getting the small bags at Lowes but whew did that run into money as I was using quite alot.

Betnee, we have some farm supply stores, i.e. feed and seed. Why do they stock the large bags of vermiculite? Which is better; the coarse or fine?