I use mostly copper and bronze for the leaves, stems, and bark of my sculpture. Copper is a relatively soft metal, particullalry when hot worked, and lends itself quite well to the organic shapes of plant structures. Copper and bronze can be turned different colors using various patinas, applied with a torch, that give durable green, brown, and red tones that are perfect for plant colors.
The components of each scultpure are joined with silver braze and designed to allow wires to pass through the different sections. Stainless steel fittings are often used to reinforce areas that need high strength, and I use steel lattice structures to support climbing and vining plants.