Q: My bamboo is headed straight for a neighbor’s house. What kind of barrier will keep the clump inside my garden? — Gitta Morris, Madison, Conn.
A: For a bamboo of the running sort, which spreads rapidly via rhizomes or stolons (underground stems), the most effective barrier is a band of heavy plastic, installed about 3 feet deep all around the clump to contain that subterranean expansion. Nurseries that specialize in bamboo sell heavyweight black polyethylene (40 to 80 mil) and stainless-steel stakes for fastening the ends of the flexible plastic together. Two stakes are bolted together on either side of the plastic to hold the seam shut. Use the heaviest-gauge (80 mil) plastic, overlap the ends at least 6 inches, and take care that there isn’t so much as a pinpoint puncture for a runner to poke through. Bury all but an inch or two of the plastic collar to leave a narrow rim above ground.
In Japan, where bamboo is revered, the law requires that a landowner obtain neighbors’ permission before planting a clump and that he swear to keep it within bounds. It is essential anywhere to monitor all running bamboos, even those confined within a strong, deep subterranean barrier. Wherever mulch or tall weeds create a moist, dark area near the top of the barrier, runners will sneak over and out. Inspect the rim carefully each fall, looking for wayward runners; prune them back and pull out any that have rooted beyond your bamboo zone. If you regularly prune out older canes in the center of the clump, large new canes will fill in, making the bamboo less inclined to break out. Install a barrier as soon as you can. The odds are good that you have yellow-groove bamboo, Phyllostachys aureosulcata, which in the early years after planting may seem controllable by occasional pruning and mowing. After 10 years, however, it will start to run aggressively, and a bamboo as vigorous as yellow-groove will be hard to confine to a patch smaller than 100 square feet. Most of its runners travel within the top 6 inches of soil, but they can reach down 22 feet, hence, the 3-foot barrier.
If you have at least 30 feet of lawn on all sides of your clump and mow regularly, you can probably hold it in check without a barrier. However, you’ll also notice little tufts of bamboo foliage hiding in the grass, just waiting for you to stop mowing for a season. That’s why a barrier is almost always essential for peaceful coexistence. For future plantings, you may want to try a “clump-forming” bamboo, which spreads very slowly: a few inches a year, versus 5 or more feet a year for yellow-groove. The hardiest kind in your region that offers varieties similar in height to yellow-groove are those in the genus fargesia. Graceful, delicate-looking plants, they are nonetheless as hardy as the running sort, and they won’t make you feel like a horticultural prison guard.