While tropical marginal plants do require more work than their hardy cousins, they can add a spectacular splash of colour to your water garden, making them well worth the effort. Many of the tropical varieties listed here may be kept indoors as houseplants during the winter, while others should be treated as annuals.
Tropical marginal water and bog plants are available in 4″ nursery containers, but they should be transplanted into 8″ pots or baskets to encourage vigorous growth. Keep in mind that wide based pots are more stable for tall plants. Fill the 8″ pot half full of moistened, tamped soil. Don’t cover the holes at the bottom, as they allow for the roots to grow out into the water. Place the plant into the centre of the pot. Then add more soil so that the roots are well covered. Leave the crown of the plant, from which the leaves grow, protruding from the soil. Push 2-3 fertilizer tablets into the soil around the crown. Tamp soil down gently. Cover the soil with a layer of gravel and soak with pond water before placing the pot into the pond to prevent muddying up your pond water. Fertilize monthly to encourage growth and bloom. They can be divided and transplanted in the same way at any time. However, we don’t recommend planting tropical marginals directly into your pond as this creates more work in the fall when it’s time to bring them inside for the winter. Recommended planting depths should be respected to produce good foliage growth and blooms.
Tropical marginal plants must continue to grow during the winter months. Growth will be reduced considerably as daylight hours diminish. Umbrella Palm, Dwarf Papyrus, Little Giant Papyrus and White Arum lilies will survive the winter indoors and make excellent houseplants. Other varieties are best treated as annuals.
Remove tropical plants from the pond before the first severe frost and bring indoors to a heated greenhouse or sunroom. Plants must remain in water and be kept at a temperature of approximately 18°C (65°F). Remove old growth if it yellows. Return to the pond in spring when there is no risk of frost. Small amounts of fertilizer may be required to encourage plants to keep growing during the winter.
Many people treat tropical marginal plants as annuals due to the cost and effort required to overwinter. Simply compost plants in the fall and restock the pond the following spring.
Water gardeners in Canada frequently use the previous overwintering methods for plants. These suggestions can be used alone or in any combination to best suit your own situation. There is no guarantee that your plants will survive the winter however, by trying these commonly used methods your chances of success will be increased. We would be glad to hear from you if you have found other successful ways to winterize your plants.