Creating a coleus topiary causes me to garden contrary to my usual standards. When I grow plants from seed, or from cuttings, I want them to bush out and develop branches. To grow a topiary I need them to grow tall and leggy. The best way I’ve found to accomplish this is to put the plants in a shady area where they must grow upwards to reach the brighter light.
Recently, I dug up and transplanted into potting soil several of the coleus volunteers from the front garden. Now they are growing in a shady nook of my outdoor porch, below the screened window. The coleus get enough light to live, but nothing direct, this causes them to shoot upwards toward the light. At this point their colors fade, and the growth becomes leggy, but this is exactly what I want from them.
As they grow upwards, I clip off their side shoots with small manicure scissors, leaving only a set of leaves at the top and the growing tip. The coleus will continue to grow toward the light, and I will continue to clip until each reaches a height I want. Even as small as they are I might have to begin staking to support the stem. At this point, because of their size, I would use a coffee stirrer, or another small slender support.