I will be doing a vegan wedding cake (6') thank god and I'm worried that the vegan buttercream will not harden in the fridge since it requires margarine. She also wants it with fondant so i'm really nervous also that the fondant may sag. Any suggestions? THank you

what kind of fondant are you planning to use? They are not all vegan. You can also make "buttercream" using nothing but vegeatable shortening

I totally forgot about the fondant not being vegan to.  I really dont know which to use. Would the shortening harden with out butter?
 

AShortening does harden and has a higher melting point than Katherine/butter. What yor actually want it to do is crust not harden and that is dependent upon your sugar/shortening ratio. There are vegan fondants but you need to do the research. MMF is not

ASatin Ice fondant is vegan.

I recommend experimenting with your vegan recipes to see how they hold up to refrigeration, ideally before committing to making a vegan wedding cake. Especially a 6' cake, that sounds like a monumental task.

I did a vegan cake for my daughter's baptism. It was absolutely awful. I used all vegetable shortening (crisco) for my buttercream and it was a disaster!!! That's what I get for not doing a practice cake ahead of time, but I didn't have time.

I'd recommend using SmartBalance instead of margarine for your buttercream; it has a wonderful buttery flavor and is nice and creamy. There is a soy-based version and a soy-free version. I think they taste the same, although I'm not sure if one has an advantage over the other in terms of using it to make buttercream. If I have to do a vegan buttercream again I'll be using this instead of vegetable shortening.

Satin Ice is vegan, also FondX is too, I believe. When you settle on a recipe, be sure to do a practice cake with it to be sure it will hold up when tiered and covered in fondant.

Also, be aware most powdered sugars are NOT vegan. Cow bones are used to process the sugar. If the customers want truly vegan powdered sugar, consider this when giving them a price. A 1 lb bag of vegan powdered sugar is $5 at Fresh Market!!!! 

A

Our vegan buttercream frosting uses Sweetex Z high ratio shortening (essentially palm oil with emulsifiers) and Earth Balance vegan buttery sticks (soy-based margarine). It has an excellent taste and texture (although it is a little temperature sensitive due to the zero trans fat shortening) and in our tests most people prefer it to butter-based BC.

Also, be aware most powdered sugars are NOT vegan. Cow bones are used to process the sugar. If the customers want truly vegan powdered sugar, consider this when giving them a price. A 1 lb bag of vegan powdered sugar is $5 at Fresh Market!!!!  :o

This is actually true of most cane sugar, not just powdered sugar. If you are looking for vegan sugar you can buy organic or raw sugar (which is usually more expensive) or beet sugar, which is not processed with bone char.

http://www.vrg.org/journal/vj2007issue4/2007_issue4_sugar.php

Oops! Jason is right! I meant Earth Balance, not SmartBalance! I'm a little sleep deprived over here!
 

Wow! I never knew that about sugar. Great info!

I recently made a dairy free/alcohol free cake and for the icing I used a combination of the New Balance and the Palm oil shortening from Whole Foods.  Jason is right as far as temp sensitive and it will be softer than reg. butter cream.  You will find you have to add more flavoring than usual.   I can't stress enough to experiment.  I personally had a hard time with flavor but after a couple of tries it was pretty good - but I got to use raspberry flavoring (Frontier) which made it easier :)