looks and feels like jello

[stuff]

I friend of mine recently went to London, England on a visit. She stopped off at a store that had colored soil for plants. It's not really soil. It looks and feels like jello. The substance can be a variety of colors. They are these little pebbles I guess you would say. The size of fish food. You put some of them in water and after 4 hours it thickens and feels like jello. Plants grow in this and it's suppose to be good for it.

My question is do you know what this is called? She forgot to ask for the name.

Thanks