I am making a fondant covered cake and piping grass accents in select areas. I have an amazing buttercream recepie that I use on my cakes but it's very light and doesn't keep it's shape well. Is there something i can add to make it hold the grass shape after I pipe it?

I have made a number of cakes using the grass tip to create grass and fur. I just use American buttercream and it comes out great! I use an equal ratio of butter and crisco. Hope that helps!

Just add a little more ps to it to stiffen it up a little.

As the others have said, add some powdered sugar to thicken up you b'cream OR if you are making it fresh, cut down on the liquid used.