Planting and Propagating
Plant container-grown bamboos any time of year. The more crowded a bamboo is in the container, the faster it will grow when planted out. Do not cut or spread the rootball; this may kill some canes. Best time to propagate from existing clumps is just before growth begins in spring; divide hardy kinds in March or early April, tropical ones in May or early June. (Transplanting at other times is possible, but risk of losing divisions is high in summer heat or winter chill and wet soil.) Cut or saw out divisions with roots and at least three connected culms. If divisions are tall, cut back tops to balance loss of roots and rhizomes. Foliage may wilt, but culms will send out new leaves. Rhizome cutting is another means of propagation. In clump bamboos, the cutting consists of the rooted base of a culm; in running bamboos, it is a foot-long length of rhizome with roots and buds. Plant in rich soil mix with ample organic material.
For best growth, water bamboos frequently and deeply, soaking soil around the plant to at least 12 in. deep. Established plants tolerate considerable drought but look best with regular irrigation.
Feed in-ground plants once a month, March to October, with a high-nitrogen fertilizer or lawn fertilizer. To restrict size and spread of an established bamboo, cut back on water and fertilizer.
Scale, mealybugs, and aphids occasionally appear on bamboo but seldom do any harm; if they excrete honeydew in bothersome amounts, spray with insecticidal soap or summer oil. Mites can cause yellow streaking or disfigurement of leaves; they too can be controlled with insecticidal soap.
Large expanses of concrete or asphalt won’t prevent the spread of running bamboos, but it isn’t difficult to contain them—provided you understand how they grow. Rhizomes are shallow and spread sideways, not down.
Block them. You can keep the runners from spreading by installing a 30- to 36-in.-deep, 60-mil-thick, continuous polypropylene plastic sheet around the perimeter of the planting; leave a 2-in. lip aboveground to block runners. Never place plastic under roots, as they need excellent drainage. Continuously dry soil extending 10–20 ft. beyond the planting bed also impedes runners. Or contain them by planting in long flue tiles or large plastic plant containers with the bottoms cut out.
Cut them. Equally effective but more labor intensive is to periodically insert a spade down to its full length around the plant, severing the rhizomes and isolating unwanted parts from the main plant. Break off new shoots that rise from the isolated rhizomes; they are unlikely to resprout (if they do, follow instructions for removal in the text).
Surround them with trenches. Another method is to dig an 18-in.-deep, foot-wide trench around plants. You can leave this open and remove any rhizomes that emerge, or fill the trench with loose mulch or sand, then use a spading fork several times a year to search the trench for any roving rhizomes (they’re easily severed).
These types grow in an enlarging circle and do not gracefully adjust their shape, although a barrier on just one side is sometimes useful. Plant them well away from fences and sidewalks. Once a clump has expanded to the desired size, keep it in check by breaking off new shoots where you don’t want them.