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I've done a couple of wedding cakes recently that had vining flowers on them, and that design comes with its own issues.
First, if the cake is buttercream-covered, the vines will want to dig themselves into the icing.
Second, regardless of how the cake is covered, the vines will want to move around on the cake if you put them on the cake before you transport it.
made some little "clips" from coffee stirrers.
Use a lighter and melt the coffee stirrer (it takes about 1 second, so be careful.) Hold it in place until it cools off in a "u" shape, then cut it so that the legs are about 1" long.
You can put these on the vine to hold them in place, and they're food-safe, so you don't have the issue of inserting wire into the cake. Place them around the vine to anchor it into place, usually at the base of an area where a flower is coming from the vine. That way you can bend a flower around the hook of the stirrer to hide it.
Kara Buntin owns A Cake To Remember LLC, custom wedding cakes in Richmond VA