All Portland cement has a very fine ground sand but it won't effect your mix. I use sand in all my mixes. Remember, they add sand to Portland cement to make concrete and mortar.
Without knowing the exact recipe you used for your leaf casting it's hard to say what was the cause of the failure. Incorrect mix portions, too much/little water, too hot/cold, unmolding too soon can all make your leaf casting fall apart.
Could you tell us what recipe you are using? Exactly? Do you mix all dry ingredients together first? What's the consistency of the wet mix? How big was the leaf and how long do you let it set up before unmolding? You are using cement in your recipe and not concrete or mortar mix. The more details you can give us the better.

Thank you for answering. My leaf failure was probably 4 summers ago, so I don't remember my proportions. But now this summer since my singular tufa planter is no longer, I will make a few more. I will probably use the recipe from the handout I was given in the class when I made my first planter which was just portland, peat and perlite. I'm just left with this one question.. why add sand to a mix? I'm presuming if it's added, the purpose is to make the 3 ingredient tufa mix stronger? Sorry if my question is silly. I'm definitely a novice at this having made only the one container and subsequently the leaf failure. I've read over so many recipes but the majority don't add sand, thus my confusion on why and when it should be added.

The original recipe for Hypertufa was equal parts of Portland cement, peat moss and sand. That's the one that I use for some of my planters. I use sand in all of my recipes.
The "why"= sand adds strength to your piece. The "when"=all dry ingredients are added together and completely combined (everything should be gray, coated with cement) before adding water.

I have followed Billie's instructions and my leaf projects have always turned out great.
If you do not want to mix and can afford to pay more $$ - I have also used.
QUIKRETEî Vinyl Concrete Patcher - It is designed for a very thin application, but it will work on making leaves.
Sucess comes from practice. Thanks for all your help Billie !

the vinyl concrete patch works wonders for leaves and helps make them waterproof.