Most temperate bamboos have the root system that is classified as “running.” This means that they have long roots that lay shallow and horizontally under the soil. These roots are called rhizomes.
Rhizomes grow just like the culms. They have the same nodes and reach full length in only a few weeks during summer and fall, just as the time it takes for the culms to reach full height in the spring. During that few week time in the summer and fall when the rhizomes are growing they can reach the same length as the culms are tall.
Bamboo isn’t entirely an unmanageable beast in the garden. It is for the most part misunderstood and often times has unreal expectations placed upon it.
Let’s use an example of a 20′ tall grove. This is the typical size of a larger temperate species you might encounter in USDA zones 5 and 6.
Let’s also say this grove is a circle with also a diameter of 20′.
This grove is made up of hundreds of culms. When many people look at this grove they see many individual “trees.” I wish the term “tree” could be stricken from every thought pertaining to bamboo. This single term is responsible for I would say nearly 100% of the unreal expectations placed upon this plant.
The most important thing to remember is that bamboo is not a tree. It will never grow like a tree and it will never act like a tree. Bamboo is a grass and it grows like a grass.
The issue is when some gardeners purchase a running bamboo plant it may be a single culm in a pot. They might expect this “tree” to remain a single growth plant. The thing is, they’re not buying a tree. They’re buying what is in fact a chunk of sod.
This is a grass and it will produce more roots and more “stems” (culms). Expecting any grass to remain “single-trunked”, as it were, is not realistic.
The assumption that bamboo is a tree is also responsible for another misconception; the extent of the drip line (root zone).
Our hypothetical 20′ tall and 20′ diameter grove has culms with branches that might extent to a radius of 2′, giving each culm a 4′ diameter branch structure. If this was a tree it might have a root zone of perhaps 6′ in diameter. This isn’t a tree and that culm is connected to every other culm in the grove by rhizomes because this entire grove is a single plant.
Photosynthesis plays a part in how big a bamboo grove’s root system can be. Remember photosynthesis? We all studied it in grade school. It’s one of the most important biological forces that keeps our planet going. Photosynthesis is the process by which plants make food for themselves from water and carbon dioxide and the byproduct of this process is oxygen for us to breath. Plants have to photosynthesize to live. Bamboo is no exception.
Thanks to photosynthesis we can calculate the root zone of a grove. The tallest culm in our grove is 20′ in height. Our grove is 20′ in diameter. That means the rhizomes can grow outward from the edge of the grove 20′ underground. How is this possible? It’s because the culm height and rhizome length are directly connected to one another. This distance is how far the rhizomes can grow outward from a grove before they have to have green tissue (leaves) growing from the rhizome to photosynthesize and give that portion of the plant life sustaining nutrients from the process of photosynthesis.
So, the #1 rule is that if you are regularly mowing off new shoots in this 20′ ring around this grove, those rhizomes can’t extend any further outward than the tallest culm is high.
The confusion that bamboo is a plant that can take over the whole world comes from people seeing new shoots produced inside this root zone, which can be 20′ out from the edge of a 20′ high grove. They then jump to the conclusion that the roots could grow to 50′, 100′, or even further and take over vast expanses. No, not if the grove is being maintained by mowing off new tender shoots above the root zone where you don’t want photosynthesis to take place.
If the grove is being mowed around, the largest this 20′ high by 20′ diameter grove’s root system could ever be is 60′ in diameter; 20′ under the grove itself, and 20′ underground on each side around it.
I recently spoke with a representative of an organization who claimed that three species were too many and were “taking over” their 40+ acre property. No. Bamboo doesn’t just take over without your permission. The maintenance crew responsible plainly isn’t doing their job in keeping new shoots removed (mowed off). Those roots can only advance further than culm height distance from the edge of the grove if those roots are allowed to sustain themselves with photosynthesis.
Here at the nursery we grow 25 species on 4.2 acres of propagation grounds. Twenty-four of those 25 species are classified as “running.”
A 60′ diameter plot of mow-able ground is plenty large enough for a 20′ tall “running” species even without using an in-ground barrier.
This root distance formula can be used for virtually all temperate “running” bamboos. The root zone would be scaled up or down depending on the species’ maximum height, or what height it would grow to in your climate under the conditions you can provide it.
Bamboo is one of the best plants at cleaning our air and providing oxygen. It removes carbon and pollution from the air better than trees and produces up to 35% more oxygen than trees. Bamboo is a fantastic plant; even the “running” ones if you care for it correctly and know what to expect of the plant.
Of course if you have a smaller area to plant bamboo, you can always put in an in-ground bamboo barrier as in the one photo shown here.
Alternately, you could plant a clumping species which advances only perhaps 3″ to 4″ per year, much like a clump of Miscanthus.