Northern gardeners often add tropical plants to the water garden for intense color and bold, distinct foliage. But Northern winters are notoriously harsh, so the two most commonly asked questions asked about these colorful plants are: “Will they die if I leave them outside?” and: “Can I overwinter them indoors?” Of course, the answer to both is “Yes!”
Bring the Tropics Inside
Most tropical aquatic plants will winter easily indoors as houseplants. Decorative ceramic or plastic containers are widely available in many sizes and colors. They are suitable as long as they are watertight and provide a sufficient water supply to the overwintering plants. The beauty of using aquatic plants in containers any time of the year is that they require very little care and maintenance. They have their own water reservoirs that add moisture to the dry environment in a northern home in winter, and they are ideal for people who travel.
Although the containers shown are in an outdoor setting, the principles are the same when used indoors. Water can be added to fill the containers and allowed to evaporate over time. Filling should occur once every two to four weeks as determined by the size of the container and how dry the environment is. Fertilizer should be used sparingly, since active growth slows during the shorter days of winter. Once the days begin getting noticeably longer (around mid- to late February) and plants start pushing new growth, fertilizer can be added. Add it as you would for any houseplant, but apply it at one-quarter to one-half the recommended rate.
Light requirements vary depending on the plant. For example, the plants that require the most light perform best on the south side of the greenhouse or in a southern exposure window inside the home. Light levels vary from North to South in the winter months and outside factors like trees, awnings and overhangs may also come into play. A good indicator that light levels are deficient would be if plants are leaning toward the light source or growth is unusually elongated or stretched. If possible, move these plants closer to the window or to a location with a longer exposure. Sometimes turning the containers regularly is sufficient.Light Guides For Plants in the Winter) for some of the most common plants and the light levels they are best suited to. This information can be extremely helpful when assisting customers in their tropical purchases. Using this guide, customers can make an educated decision based on an available location indoors suited to the light preferences the plant will receive when the winter season approaches.
All plants need to be moved in advance of frost. Check all plant surfaces thoroughly before moving them indoors. Any pests that make it through inspection can be treated with over-the-counter indoor house plant pesticides specific to the pest to be controlled. Any deteriorating or shabby foliage should be removed as it appears. Plant energy is wasted when trying to sustain growth that isn’t healthy, so pruning keeps plants looking their best.
Canna, Colocasia (Taro) and Zantedeschia (Calla) can be dried down for winter and stored dormant. It is important for them to be exposed to cool temperatures or frost to yellow the foliage. This allows them to retract the energy they need for winter storage. Promptly after the foliage begins turning yellow and brown it needs to be removed from the tubers, and bulbs need to be cleaned so that moist conditions don’t allow rot to fester. Be especially careful to prevent cuts and bruising, as they can be contributing factors to rotting by allowing an entry point for disease. A good rinse will remove any excess soil and debris.
The bulbs/tubers should be placed in a cool area away from direct sunlight for a few days to dry. Callas may need two to three weeks to sufficiently dry. Peat moss, sand, coir fiber or vermiculite about three inches deep is ideal for nesting them. Ideally they should be spaced evenly and not touching just in case one starts to spoil. One rotten apple spoils the barrel, so they say. Ideal temperature for storage is 35 to 45 degrees Fahrenheit, like in an unheated garage that doesn’t freeze. The house wall has the most consistent temperature.
Tropical water lilies are also a prime candidate for dormant tuber storage. Once frost has yellowed the plant needs to be removed from the pond and allowed to dry slowly over a few weeks. The soil needs to be removed from the tuber and everything cleaned, trimmed and thoroughly dried. The prepared tubers can be stored in distilled water or the preferred method of damp sand or damp peat moss. Another method more recently introduced by Ken Landon is wrapping them in damp, interfacing pellen and placed inside a Ziplock baggie. They should be checked at least once a year to ensure the fabric is still damp. A target temperature of 60 degrees is ideal for long term storage.
Braving the Winter Outside
When preparing plants for winter outdoors it is important to cut withered foliage above the water level, especially on plants whose stems are hollow. A more thorough cleanup can occur in spring. Rigid, foliaged plants like Thalia are best left standing for winter. The bold foliage remains upright and collects snow, adding winter interest. Cutting back prematurely before the foliage turns can be detrimental, especially to carnivorous plants. They should only have the brown parts removed in spring since they continue to feed on the previous year’s insects. New growth will disguise the old growth and no one will be the wiser once spring growth emerges.
Finally, many still perpetuate the myth that hardy plants need to be moved to the bottom of the pond for winter. This attempt to offer added protection over the winter months often fails. If a plant is hardy in a particular zone it will more than likely survive just fine at the seasonal growing depth. The general cause for failure over the winter comes from weak plants in fall that are struggling in root-bound containers and are under-fertilized. Healthy plants survive better. Additionally, plants like lotus that are stored on the bottom of the pond have a limited reserve for emergent growth in the spring. If they aren’t brought to the surface early enough and begin to grow they will exhaust their strength trying to reach the top of the water. They are reliant on getting to the top quickly enough to gather strength from the sun to fuel new growth. Without that ability they dwindle and die.
Maintaining strong, healthy plants is key to their winter survival. Making sure they have adequately sized containers and sufficient food, good soil and the correct amount of light is critical to their success, whether indoors or out.