Answer: To grow bamboos, gardeners in the north must be willing to accept the challenge of working with a plant that normally doesn?t grow in their climactic zone. And they must also understand that the taller bamboos will not grow to the height they would reach in Zones 5 or warmer. In a particularly hard Zone 4 winter (worst case scenario: a bare ground January, minus 30?F with wind) most bamboos will act like herbaceous perennials, losing leaves and stems to ground level. For most Zone 4 gardeners, this shouldn?t be too much of a shock since this is the norm for most plants in our area.
The good news is that if you choose your plants carefully for hardiness, you will find that they tend to have double hardy root (rhizome) systems. In seven years of experimentation, I have yet to lose a bamboo completely. To manage this the gardener must consider two factors of primary importance: site and protection. Proper siting of a plant can give as much as a whole zone?s worth of protection. For example, the south side of my house is a warmer environment than the north side. The evergreen trees along the western border prevent cold prevailing westerlies from sweeping across the area, making it a micro-climate perfect for safely growing Zone 5 plants. Locating these areas on your property will give the bamboos (or any ?tender? plant) their best chance of success.
Protecting your bamboo plants is the second step to consider and this is where you can get a bit innovative. Here in our garden, protection starts with plenty of mulch from the time the bamboo is first installed. For years we have used various combinations of the following: spent mushroom compost, straw from a brood mare farm, chopped maple leaves, and pine needles. This heavy mulching makes a rich organic feeding bed for the bamboo rhizomes and gives them a friable insulated blanket against the winter cold. The second step of protection is bending the bamboo canes over so that they can be held low to the ground and then fixed in that position for the winter. Green bamboo is very supple. The live stems or ?culms? can be grasped at the base, forced down and held in place with strips of bamboo pushed into the ground perpendicular to the canes, over the canes and then into the ground on the other side, creating half hoops of bamboo to hold the culms down. (Hoops can also be made from stiff wire, cuttings from other shrubs, etc.) With the culms in this position it is easy to mulch them with straw or any sort of evergreen boughs. Don?t mulch so heavily as to block all air flow to the plant or it can cause rot during the winter. The idea of this mulch is to catch enough snow to give the plant a perfect blanket of insulation.
Even in a winter like this one, where we have had first heavy snow cover, then warm temperatures causing melting, then subzero temperatures, the live stems will remain strong with proper mulching. There may be some leaf die-back, but ultimately the plants will leaf out in the spring.
Of the taller bamboos that do well, Phyllostachys aureosulcata (golden groove bamboo) and Phyllostachys bissetii (David Bisset bamboo) are two of the best for winter hardiness. Phyllostachys nuda is also reputed to be very hardy. Medium sized species that do well are Arundinaria gigantea (canebrake, the native North American species) and two Fargesia species, nitida and murielae. Particularly interesting, these Fargesias are hardy Chinese mountain bamboos that have a clumping (sympodial) growth habit as opposed to the running habit of most temperate bamboos. This means that these bamboos do not have to be grown in a contained area. They are also quite beautiful, particularly when used as accent plants.
There are many small bamboos that do well in northern gardens. They are very effective as ground covers, border patches or in hyper-tufa planters. Though they usually will die back in winter, they actually seem to benefit from a severe prune back before they start new spring growth. Remember that these are some of the most invasive of the hardy bamboos and thus should be carefully contained. My favorites include Pleioblastus variegatus (dwarf white stripe bamboo), a beautiful green and white variegated plant; Pleioblastus distichus (dwarf fernleaf bamboo); and Pleioblastus viridi-striatus with its chartreuse/golden foliage in the spring. The smaller bamboos seem to do particularly well in shady locations as they are understory plants in their native habitat.
Bamboos respond well to lots of water and occasional feeding during the growing season.
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