"They grow so easily, don't feel embarrassed knocking on a door to ask for a few cuttings," Cornwall says.
Make sure any old bottom leaves are removed, then leave the cuttings on a tray in a cool, shaded area for a few days to form a "scab" on the ends before planting.
Set the frame mesh-side up on a table and fill with soil, using your hands to push it through the wire mesh openings.
Be sure to use cactus soil, which is coarser than potting soil for better drainage.
Some vertical gardeners place a layer of sphagnum moss under and over the soil to hold moisture in when watering.
Fill in with plants
Now comes the fun and creative part.
Lay out the succulent cuttings in the design you want on a flat surface, and poke them into the wire mesh holes in your frame.
You can start either in one corner or by placing the "focal point" cuttings in first and filling in around them. Waves or rivers of color are popular living-picture designs, although Cape Cod-based landscaper Jason Lambton has gone bolder with spirals of green and purple.
"We painted the pallet different color stripes to go with the color theme of the back of the house," says Lambton, host of HGTV's "Going Yard." "It looked like a cool piece of living, reclaimed art."
Using just one type of succulent is also a simple yet elegant option, says Kirk Aoyagi, co-founder and vice president of FormLA Landscaping.
"Collages with some draping and some upright plants can create a more dramatic look and feel," he says.
Care and maintenance
Keep the living picture flat and out of direct sunlight for one to two weeks to allow roots to form along the stems, then begin watering.
"If you hang it up right away or it rains a lot, that dirt will just pour right out. ... I made that mistake once," Lambton says.
Mount your living art once the succulents are securely rooted, which can take four to eight weeks, depending on climate.
After that, water every seven to 10 days by removing from the wall and laying it flat. Be sure to let the water drain before hanging your living picture back up, to avoid rotting.