Here is a DIY project for a laidback (because it requires little effort) but patient gardener (because it takes 18 to 24 months to carry out): grow a tree-form coleus (Plectranthus scutellarioides).
Growing shrubby plants as trees may seem like an odd idea, but in fact, it’s an age-old technique, a type of topiary. The resulting plant is called a standard.
If you’re not into coleus, there are a lot of other plants that can be turned into standards by the methods described below (see Other Plants to Use as Standards below), but coleuses make particularly interesting subjects because they grow and fill out comparatively quickly. In addition, if you’re like me, you already a few extra coleuses at just about the right stage, cuttings you brought indoors before the cold season and that are now well established, so you already have a potential subject to work on!
Training a Coleus Tree
Here’s what to do:
- Start with a well-rooted coleus. Unless you want to do a mini-tree, choose one that is fairly large. Big varieties take on a treelike shape more quickly.
- Choose as straight and tall a stem as possible to serve as a trunk.
- Remove all its side branches with a pruning shear, cutting them close to the new trunk. Also remove any leaves on the lower part of the trunk.
- Insert a stake of about the desired height (2 ½ feet/75 cm for example) in the pot.
- Attach the trunk to the stake with elastic ties.
- As the plant grows, continue to attach the trunk to the stem and to remove the lower branches and leaves, leaving just a cluster of leaves at the top of the trunk. This will result in a foliage-free trunk that slowly increases in height.
- When the coleus reaches about the desired height, change tactics and pinch (clip off) the growing tip to stimulate branching in the upper part.
- This will encourage the appearance of several stems at the top. When they are about 2 1/2 inches (7.5 cm) long, pinch them too. And also pinch the growing tip of the new stems that appear after the previous pinching. In fact, the more you pinch the stem tips at the top of the plant, the denser and the more attractive the “ball of foliage” at the top of your mini-tree will be.
- Move the ties occasionally so they don’t dig into the trunk.
- Over time, the main stem will lignify (harden) and truly become a trunk. Even so, depending on the cultivar chosen, the trunk of a coleus tree may never be truly strong enough to support itself without snapping off, thus may always need a stake.
Through all this, of course, you’ll have to keep your budding coleus tree happy. Fortunately, it’s an easy plant to grow. Here’s what it needs:
- Regular watering (it’s a very thirsty plant!).
- Bright light with several hours of direct sunlight in the winter. More moderate light is perfectly fine indoors in summer… and it will even tolerate shade if you place it outside during the summer.
- Reasonably good atmospheric humidity.
- Room temperatures.
- Light fertilizing from March to October.
- Occasional repotting, probably twice a year while your coleus is growing. By the time it is tree-size, you’ll need a fairly large pot, perhaps 10 inches (25 cm) in diameter. A heavy pot (or you could double pot into a heavy cache-pot) may be necessary to keep your now top-heavy tree upright.
- Pinch off any flower spikes.
Other Plants to Use as Standards
You can use same techniques to turn other plants into standards. Among those you could try are:
- Azalea (Rhododendron simsii)
- Fuchsia (Fuschia spp.)
- Hibiscus (Hibiscus rosa-sinensis)
- Lantana (Lantana camara)
- Bay laurel (Laurus nobilis)
- Rosemary (Rosmarinus officinalis)
Most outdoor shrubs can be converted into standards by the selective pruning technique described above, although it can take longer for them to fill out. I do recommend choosing only extra-hardy varieties, such as a zone 1, 2, 3 or 4 shrub if you live in zone 5, because standards tend to bit more susceptible to cold damage than the same shrub growing normally.
Here are some examples:
- Aborvitae (Thuja occidentalis)
- Buttonbush (Cephalanthus occidentalis)
- Dappled willow (Salix integra ‘Hakuro-nishiki)
- Dwarf Lilac (Syringa spp.)
- Hardy rose (Rosa cvs)
- Ninebark (Physocarpus opulifolius)
- Panicle Hydrangea (Hydrangea paniculata)