Unless you have a conservatory, your best bet with larger tropical plants (like caladium, elephant ears and bananas) is to store their root/storage organ in a dormant state over the winter. Coleus (Solenostemon sp.), on the other hand, can't be overwintered in a dormant state. In order to save coleus from one year to the next, you have to take cuttings of your existing plants to create new, smaller plants that you grown indoors during cold weather.
Luckily, if you can provide enough light and water, coleus is an easy plant to grow indoors. Here's the process I use for taking cuttings.
You'll need the following:
- Small plastic cups, with 3-4 drainage holes punched in the bottom.
- Potting medium (I use MiracleGro potting soil so I don't have to deal with fertilization over the winter.)
- Rooting hormone (I use Rootone.)
- A pair of small hand pruners
- Flat trays (enough to hold all the plastic cups)
- Coleus plants (You can use the coleus you've grown in your garden, or even discounted plants that still may be available at your local garden center.)
First, pre-moisten the potting medium in a large bucket and fill each plastic cup with soil to about 1/2-3/4 inch of the cup rim. Filling the cups to full will make watering the coleus a more difficult and messy process throughout the winter. Once you have the soil medium in the cups, you'll then need to select the branches from your coleus plants.
The best branches to choose are those with multiple side shoots that terminate in a multiple leaf cluster. If the branch doesn't have side shoots, you'll only get one cutting per branch. If you cut more than one or two branches at a time, be sure to have a vase of water in your prep area. Coleus rapidly dehydrate after cutting, so it's important to keep them in water if there is any significant delay between cutting and transplanting.
Using your hand pruners, cut each side branch off the main stem, leaving about 3-4 inches of stem down from the terminal leaf cluster. The same can be done for the leaf cluster at the top of the branch.
Carefully prune the side leaves off the stem, leaving at most four leaves at the top of the stem. The goal is to have enough leaf surface to help feed the new plant, but not so much that it's impossible to keep alive during the rooting process.
Dip the bottom inch of the cutting into the rooting hormone, making sure it is thoroughly covered. Be careful to avoid eye or mouth contact with the rooting hormone, as most contain a fungicide that is toxic if ingested.
Gently insert the cutting into the potting medium, one cutting per cup. Coleus stems aren't very sturdy, so it takes a bit of practice to slide the stem into the potting medium without breaking it.
On some varieties of coleus, the terminal leave cluster includes two larger leaves. On these varieties, I tend to pinch half of each of the larger leaves off to reduce the amount of plant material the cutting needs to support.
Continue this process until you've inserted all your cuttings into the potting media. Make sure to water the cuttings lightly, and continue to do so as necessary. In the beginning, watering is required every day or so. Once the plants have established new roots, watering can be scaled back to about once a week. Be sure to monitor them regularly, as the coleus will droop almost instantaneously when they reach a critical moisture threshold.
Coleus also need bright light to thrive. I grow mine under timer-controlled fluorescent plant lights that provide 12-14 hours of light each day. If you had a sunny window and just a few cuttings, you could probably avoid the need for plant lights.
This year, I took 105 cuttings, including the following:
- 'Religious Radish' (18)
- 'Rustic Orange' (8)
- 'Aurora Peach' (8)
- 'Trailing Dark Heart' (27)
- 'Big Red Judy' (8)
- 'Pat Martin' (7)
- 'Trusty Rusty' (9)
- 'Henna' (8)
- 'Alabama' (5)
- 'Twist and Twirl' (1)
I'm hoping to add a few more cuttings from my own garden to this list, as well as a few new varieties from gardening friends. Last year was my first year overwintering coleus, when I took nine cuttings. These cuttings grew so well, I had to take two additional sets of cuttings during the winter. As a result, I ended up with about 70 plants by spring. With 105 cuttings (and more to come) this year, I'll probably have coleus to spare for next year's garden.