Bamboo is an attractive, fast-growing plant often used for dense privacy screens or ornamental features. Many prospective growers frequently ask if bamboo can thrive in the Pacific Northwest, specifically Washington State. While many species are well-suited to the state’s diverse climate, successful cultivation depends heavily on selecting a species appropriate for the local hardiness zone. Implementing proper management techniques from the start, including thoughtful variety selection and containment, ensures the plant remains a welcome addition rather than a garden problem.
Washington State Climate and Viability
Washington State’s climate is split dramatically by the Cascade Mountain range, creating two distinct growing environments that influence bamboo viability. The state encompasses USDA Plant Hardiness Zones ranging from 4a in high-elevation areas to 9a along the mildest coastal regions. Much of the state, however, falls within the 6a to 9a range, which is suitable for many temperate bamboo species.
Western Washington, including the Puget Sound area, experiences a marine climate characterized by mild, wet winters and moderate summers. This persistent moisture and lack of extreme temperature swings make the region highly conducive to bamboo growth, often falling into the warmer 8b to 9a zones. Eastern Washington has a semi-arid climate with hotter summers and significantly colder winters, placing it in the 6a and 7a zones. Growers must match the bamboo’s cold-hardiness rating to the specific minimum temperature expected in their local zone to ensure long-term success.
Selecting Appropriate Bamboo Species
Choosing the correct type of bamboo is the most important decision for a Washington gardener, based on the two distinct growth habits: clumping and running. Clumping bamboos are non-invasive and feature a pachymorph rhizome structure, forming canes in a dense, slowly expanding cluster. These varieties are recommended for home gardens in Washington due to their predictability.
Species from the Fargesia genus are the most popular choice for clumping bamboo in the region due to their superior cold tolerance. Fargesia nitida, for example, can survive temperatures as low as -20 degrees Fahrenheit, making it viable even in colder Eastern Washington microclimates. Bambusa multiplex (Hedge Bamboo) is another suitable clumping option, cold-hardy down to 15 degrees Fahrenheit and ideal for privacy screens in milder western zones. Clumpers like Fargesia robusta ‘Campbell’ reach up to 15 feet while only spreading a few inches annually.
Running bamboos, primarily from the Phyllostachys genus, possess leptomorph rhizomes that spread laterally underground, often traveling many feet from the parent plant. While runners create a faster, denser screen, they require proactive containment from the moment they are planted. Varieties like Phyllostachys nigra (Black Bamboo) and Phyllostachys rubromarginata (Red Margin Bamboo) are popular and cold-hardy down to 0 degrees Fahrenheit. Running bamboos are only advisable for growers committed to diligent management due to the significant risk of invasiveness.
Controlling Aggressive Growth and Spread
The greatest concern with running bamboo is its aggressive spread, requiring a physical rhizome barrier to prevent property damage or invasion of neighboring yards. This barrier should be made of high-density polyethylene (HDPE) material, 40 to 60 mils thick, to withstand the pressure of the growing roots. The barrier must be installed vertically into a trench at least 26 to 34 inches deep, since most rhizomes grow in the top 12 inches of soil.
The barrier must extend 2 to 3 inches above the soil line and be angled outward slightly to deflect any rhizomes attempting to grow over the top. This protrusion allows gardeners to visually inspect the perimeter and manually prune any escaping runners with a shovel. For established running bamboo, bi-annual root pruning with a sharp spade around the perimeter is the most effective long-term control method. This maintenance involves driving the spade into the ground to sever wayward rhizomes, which are often found just 2 to 5 inches beneath the surface.
Clumping bamboo varieties are simpler to manage but benefit from occasional root maintenance to keep them within a desired area. The dense root ball of a clumper can exert pressure on nearby structures, such as fences or sidewalks, if planted too closely. Gardeners can maintain the clump’s size and shape by performing a simple annual edging or root pruning with a spade, which cuts the short rhizomes and prevents gradual expansion. Growing any aggressive variety in a container or a raised planter also offers a reliable method of containment, provided the drainage holes are monitored.