How to Keep Your Coleuses Alive Over Winter

How to Keep Your Coleuses Alive Over Winter

By Igor Kaftan, Master Gardener

We were blessed with a wonderful, hot summer this year. The latest episodes of rain dumped sufficient amounts of water for plants to revive and look refreshed. At that time, nobody thought that the cold and wet days of fall were just around the corner. Typically, when the temperature’s reading plunges below 0°C overnight, many gardeners panic. Dozens of coleus (Plectranthus scutellarioides) cuttings will be hastily picked without keeping track of the amount and quality. Now all of these cuttings will be tightly packed up into many kinds of vessels filled with water for the roots to develop.

There is another way to manage this process that takes the edge off the rush to harvest cuttings before the frost.

Practise a pre-planned propagation of coleuses

From the middle of August onward, you can start taking cuttings from your favourite coleuses. Avoid taking cuttings from a stalk that is forming or has formed a raceme (flowering spike). These cuttings will bloom and produce seeds and eventually die out. Choose a healthy, well-developed stalk and cut off a stem approximately 5-6’’(10-12cm) in length. Flip it over and cut off all the extra leaves and axillary buds. If left behind, they will decay and can be a cause of bacterial or fungal infection that would kill your cuttings. Large leaves can be cut in half to reduce transpiration (the process where water absorbed through the plant’s roots are released through their leaves).

Label your cuttings

I have a dozen beautiful coleuses without a traceable pedigree available because I thought I would remember their name after potting them.

Take two or three times the number of cuttings you want to ensure the survival of any particular cultivar, and label them carefully. Share cuttings with your friends and family. If a cutting dies at your place, it may survive at the others.

There are two or even more methods of rooting. The first and most common is to stick cuttings into water and wait until the roots have developed. The second one, which I use, is to stick the cutting straight up into potting soil. After planting and tucking it in, you can lightly water it and put a plastic bag over to prevent wilting and drying out. Two weeks later, the plant will have developed new roots, and the plastic bag should be removed.

The benefit of the latter method is that roots are growing straight into the potting mix, therefore producing healthier and sturdier plants. The warm days of late summer promote better root development and stronger growth.

Peat pellets or an oasis block, cut into one-inch cubes, can be an alternative for rooting coleus.

In the late fall, while days are growing short, the weaker plants, with less developed root systems, are prone to damping out (collapsing and dying), especially if planted in rich, water-retentive soil.

The best way to avoid this is to plant your cuttings in an ordinary potting mix with extra perlite/vermiculite added. A few handfuls of either one, added to the soil mix, will do the trick.

Light is important for the growth and development of coleuses. Even though they are labelled as plants for shade, they still require a reasonable amount of light to thrive. Light from a south-facing window in winter is not sufficient to overwinter plants, but if a bright light is provided, it will tremendously improve their growth and agility.

Water your coleuses sparingly. As a rule, I water them every three to four days. You can judge the dryness of the soil by lifting the pot. When the soil feels dry to the touch and the pot seems light by weight, this is the time. However useful my advice is, your household may have a different microclimate, and pot checking is the best way of setting your own watering regime.

You can separate coleuses of the same variety and keep them in different rooms to increase their chance of survival.

Do not mix your coleuses with other plants to prevent the transmission of sap-sucking, pesky critters. Remember, prevention is more efficient than dealing with an existing problem.

Sly, pesky critters

I experienced the most devastating infestation of mealy bugs last winter. When I noticed this trouble on my plants, it was too late; mealy bugs were everywhere, making strains of white fluff on leaves and stems. I washed coleuses daily and started to spray plants with neem oil. Nothing helped. I was helpless and depressed. When I started to plant my coleuses in the ground, to my horror, I discovered that mealy bugs were happily living under the rim of the pots that my plants were growing in. Remember, when you bring your plants in for the winter, wipe out the pot rims with a weak solution of chlorine or alcohol pads.

By the middle of January, your coleuses will lose two-thirds of their leaves. Some of them will look wasted and tired. Armoured with human empathy, you can perk them up. I used a weak fertilizer solution of 0-0-6. I made a murky solution with this high potassium fertilizer and used it twice in a period of three weeks. Do not overdose. If you do overdose, the roots will overgrow the pots, and it will be hard to push the plants out.

Take notes and observe your plants often. Reading your notes later in the season will help you to correct and omit mistakes made in previous years.

As for any overwinter losses… have a philosophical approach to it. They died because they did not like you after all of your efforts to keep them alive.