Hardy as far north as USDA hardiness zone 4b but generally best grown in zones 6 to 11, Musa basjoo, Japanese hardy banana, is an eye-catching tropical often used as a specimen plant or as a foundation planting in tropical-themed gardens. This cold tolerant variety succeeds where other, more tender tropicals will not. The plant is an ornamental, which means it does not produce edible bananas, but no one seeing the beautiful foliage of this plant will notice. Planted outdoors, Musa basjoo requires some winter protection, even in its hardiness zones. Indoor plants need only a few accommodations to weather the winter successfully. Musa basjoo can withstand temperatures as low as minus -12.2 degrees C, though the plants may die back and stay dormant until spring.
Growing to about 18 feet tall, Musa basjoo is not a real tree, but a pseudostem. What appears to be a trunk is actually tightly wrapped leaves that will eventually unfurl as new growth appears to replace it. In some areas, the pseudostem, or part of it, will remain intact and upright after a hard freeze, even if nothing else survives. The stem protects the corms below ground, which will begin producing new growth as soon as the soil is warm enough in spring. Leaves of the Musa basjoo can grow to impressive sizes, often 2 feet wide and more than 5 feet long.
Cut back on the amount of water your Musa basjoo receives during the winter, whether the plant is kept indoors or out in the yard. In the yard, choose a planting site that drains quickly and well, so moisture does not collect around the roots and freeze in winter.
Mulching Outdoor Plants
Heap piles of mulch as high up the banana plant as possible to insulate the plant's interior from the cold. This will not protect the foliage, however. In temperate zones where freezes happen rarely or only occasionally, cover the foliage with a light blanket or plastic, then mulch heavily to protect the stem and hold the cover in place. Use bark chips or any other type of mulch that does not retain moisture.
Pruning Outdoor Plants
Musa basjoo is one of the largest and fastest growing tropicals available. The plant can grow 15 feet in a single season and can eventually reach heights of 20 feet or more. Since covering a plant this size is impractical for most homeowners, the most effective way to overwinter an outdoor ornamental banana is to cut the stalks down to the ground before the first frost occurs in autumn. Cover the stubble with a heavy layer of mulch about 2 feet thick. Alternatively, you can remove all of the leaves and stems and cut back the pseudostem. Gardeners in the Ryukyu Islands wrap the stems thickly to protect them. You can either wrap the stems or let them die back naturally.
Before planting an ornamental banana in the garden, consider the damage wind can do to the large leaves. Musa basjoo foliage shreds in high winds. Although unsightly to some, the shredding protects the plant by keeping the large leaves from being ripped away and causing severe damage. The shredded leaves allow more cold air to penetrate the plant, however, which may shorten its growing season. Plant Musa basjoo in an area that receives plenty of sun in winter, and where some protection from wind is available. The walls of the house, a shed or a sturdy fence (without open links) can help protect the plant from both wind and cold.
Moving Plants Indoors
If the Musa basjoo is small enough, you may opt to dig it up and keep it in a container indoors for the winter. Musa basjoo already growing in containers are easier to transport. Move them to a bright, warm spot in the house.