GROWING BAMBOO IN THE NORTHWEST
BAMBOO, NORTHWEST STYLE
Bamboo is an extraordinary plant. It is an ancient and simple member of the grass family, but one that has no rivals in its wide range of beauty, utility, and dispersal around the world.
There are varieties that are but a few inches tall, while others soar well over 100' tall. Some have green culms (canes), while others are black, blue, red, yellow, and combinations of those colors. Some have leaves that are small and delicate and seem as if they should be on a Japanese Maple. Others have leaves long and broad and seem made for rolling into a fine cigar.
Bamboos are used for musical instruments, toys, tools, weapons and food. The plants have been used for centuries for flooring and for paper; and even before the advent of modern papermaking techniques pieces of bamboo would be used for writing on. In fact, slips of bamboo over 2,400 years old have been found in China that carried instructions to civil servants detailing procedures to be followed when examining the body of a possible murder victim.
Bamboo shoots are eaten as food, and the moisture in some varieties can be turned into cooking oil, vinegar, and even alcohol.
Despite the beauty and the thousands of uses of this amazing plant, many gardeners still view it with trepidation. It has a reputation for spreading rapidly and far, despite all efforts to control it.
As a grower of bamboo, I only wish it did grow as aggressively in our climate as its reputation suggests. The fact is, however, in our cool climate bamboo does not spread rapidly, and it is much easier to control than many other plants.
Some of the reputation for rampant growth that bamboo has earned is unfair, as it is based upon another plant that looks very much like bamboo. It goes by several names, including Knot Weed, Japanese Knot Weed, and Mexican Bamboo. It has nodes like bamboo, and large leaves like some of the bamboos. But, unlike bamboo, which is an evergreen, the leaves of the Knot Weed all fall off during the winter.
BAMBOO GROWING HABITS
Bamboo spreads in the winter time. different varieties spread underground at different rates, and send up shoots at different times in the late winter or early spring. Some varieties send shoots up in March, others not until June or July.
Bamboo culms shoot from a specialized roots called a rhizome, and because our Northwest soil is so cool during the winter the rhizomes do not grow rapidly or spread very far.
Come late winter or early spring, the rhizome growth stops, and as the soil warms up the plant stores energy as it prepares to send up shoots. When the shoots make their appearance, the growth can be astounding. Whether a bamboo is of a variety that grows 5' tall or 125' tall, all that growth takes place in eight to nine weeks. I have measured culm growth up to 14" a day in our nursery near Puyallup, and the record in the tropics is almost 5' -- yes, that is feet -- per day. Just as with rhizome growth, what drives culm growth is soil temperature. When we have several warm days in a row and the soil is warm, the culms will grow substantially faster than when we have clouds and rain and lower temperatures.
CONTROLLING BAMBOO SPREAD
When we have customers who have no experience with bamboo we always ask why they are buying it. Is it to be used as a privacy screen, blocking a view or to help cut down on noise? Or is it a plant that will be a focal point in a garden? Is it important to keep it well contained so it doesn't cross a property line or spread into another part of a garden where it would be out of place?
The answers to those questions help in deciding what variety to choose, and what containment strategy should be employed.
There are four basic containment strategies that we suggest to our customers, and they can be used singly or in combination.
The first strategy is to be an active gardener in your own garden. When the weather warms up and plants are springing to life, get out into the garden and start working with your plants.
With bamboo, look for shoots where you do not want them, break off the shoot (it's edible!) and cut through the rhizome with a shovel. Unless you have a large grove, no variety of bamboo in our climate will send out so many rhizomes so far from the mother plant that a few minutes of attention in the spring won't control the plant's spread. Bamboo does not like to send its rhizomes very deep, and a shovel is all you will need to cut the rhizome at the point where you want the plant to stop growing.
Another very effective method of controlling spread is by installing a barrier underground so the plant can't go in an unwanted direction.
Some gardeners will dig a trench and pour concrete into it; others will use metal or fiberglass sheeting. Those materials can work if they are used correctly and don't break down over the years. Concrete can crack, and metal and fiberglass can corrode and break down, giving the plant an avenue of escape.
We suggest a heavy plastic barrier that is made for containing plants. Because bamboo doesn't like to grow very deep, we suggest a 24' wide, 40-mil high impact, polyurethane barrier that can be used around the plant. The barrier provided by most nurseries will have a 20-year guarantee against failure, and is often used by cities and counties to help prevent growth of roots under sidewalks.
If the barrier is to completely encircle a plant it should be overlapped at the ends, and then several layers of duct tape used over the ends of the plastic where it overlaps. If the overlap isn't sealed off, a rhizome might find its way through that opening, defeating the purpose of the barrier.
We also suggest that about 2" of the barrier be left above ground, so if a rhizome "leaps" over the top it will be easy to see and then cut. The exposed 2" of barrier can be hidden with grass or other plants alongside it, but don't cover the top 2": with dir, or else it is harder to see any rhizome that may grow over the top edge.
Another method that works as a containment strategy is to plant the bamboo on a mound. We use mounds that are 24" high, but after a few months they have compacted down so they aren't quite that tall, and as the bamboo grows the mound becomes less obvious.
The mound does not stop the spread of the plant, but it does slow it down, making it much easier to stop its spread by simply using a shovel on the rhizomes in the spring.
Another method of containing bamboo is by building planter boxes. We have a 50' long planter box at our nursery, 24" high, and as the box fills with bamboo it provides a screen between a neighbor and us. It is a very basic box made with 2" x 12" treated boards stacked on top of each other.
At the gate of our stroll garden is a smaller and nicer planter box, this one made with landscape timbers cut to 24" and standing on end. On top of the box is a 2" x 8" board as a "cap rail" so visitors can sit down and enjoy the bamboo in the box. I lined that box with the plastic barrier so rhizomes can't sneak out through the cracks.
Some customers don't want to dig a trench 24" deep, so they go down 12" install the plastic barrier, and then build a 12" high planter box. Any number of combinations of containing bamboo can be used, and all are effective.
BAMBOO FOR THE HOME
In our climate there are at least 400 varieties of bamboos that can be grown, including some that are hardy to -20F degrees. There are many to choose from that add year-'round beauty to a garden, or provide privacy from the sights and sounds outside of your home and property.
If you have concerns about using bamboo, discuss those concerns with an experienced nursery. A nursery specializing in bamboo is likely to have more information for you than many general nurseries, and will certainly have more choices of bamboo for your needs.