A headstone saddle wreath is a flower arrangement made out of silk or real flowers that rests on top of a tombstone in honour of the deceased. The metal part of the saddle wreath is a bracket that straddles the top of a headstone like a saddle straddles the back of a horse. Attached to the wire bracket is a piece of styrofoam that usually comes already attached to the bracket. The flowers are affixed to the styrofoam block.
Set the gravestone saddle on top of something similar in shape to a headstone to hold it upright in place while you attach the flowers. Perhaps the back of a chair or a real headstone will be available.
Push 6 long stem flowers such as carnations, gladiolas, roses, irises, etc., into the centre of the styrofoam on top of the gravestone saddle.
Arrange some greenery around it, pushing the ends of the stems into the styrofoam to hold them in place.
Cut the rest of the flowers down in size a bit and arrange them around the middle 6 flowers in an aesthetically pleasing manner.
Add more greenery around these shorter flowers.
Arrange fake moss on top of any remaining gaps of visible styrofoam.
If you want your flowers arrangement to last much longer, select silk flowers. But they will still get dirty fairly quickly due to the outdoor nature of these arrangements so consider that when trying to decide whether to go with real flowers or artificial ones.