You can thin them whenever you want, but bamboo is not like a lot of other plants. I don't think you will gain much from thinning. Culms that are coming up will reach the height they are intended to get, and existing ones will not grow bigger as a result of thinning. In addition, with every culm you take out, you remove leaves that help the plant grow as a whole through photosynthesis.

If you thin out your bamboo, I would suggest waiting until after shooting season when new shoots are fully grown, hardened off and have leaves. This way you won't affect the size or the vigor of the following year's shoots.

At some point down the road, thinning, according to a couple of experienced growers, will encourage fatter culms on average because you are selecting out weaker rhizomes and letting the stronger rhizomes get all the attention. That's at least the explanation I've heard. Once your bamboo fills out the intended space, they say you cull out one fourth or one third of the culms anually for the best grove. In victorian times, the rule was thin out the grove so as a lady could walk through and still hold her parasol. I thinned out rubro at three years, and although I got fewer culms the next year they were all nicely upsized from the previous year. I guess there is a balance point where too much thinning would be deleterious, and just enough thinning, will at the least, do no harm.

Mackel

Healthy bamboo will upsize each year without human intervention, until it reaches the maximum size for that species.

Well said Kudzu, my feelings exactly and I also agree with your other point about taking out small culms. The way I figure it is if you take out any except the dead you are actually setting the plant back, I mean after all the plant is smart and it knows what it needs. This plant does some of the craziest things I've ever seen. Thats one of the reasons I like it so much because its so different from anyother plants I grow. Bamboo is my favorite plant to grow, It makes me money, that keeps me happy. It grows extremely fast, that makes me real happy. It keeps my stress level at an alltime low, and it looks great all year round that keeps my family happy. Its great for the environment both wind and water, by producing more oxygen and stopping erosion. And thousands of uses for the canes, my favorite part. The only ones I have trouble growing are the ones I spend the most money on, dont matter what species. If I spend alot on it it gives me problems everytime. Finally got me a couple small groves of P. Nigra going after spending $225 or better on 3 failed pots. Someone gave me a pot and its doing great. Then I bought another pot and its doing well.

In my clay, bamboo gets so dense that most of the smaller culms get no light at all. It doesn't make sense to me, how these smaller culms, after a number of years, do anything for the colony except for create dead weight, extra transpiration with no real concomittant photosynthesis to speak of. Like I said, there were less shoots where I trimmed out some of the rubro, but each new culm was as large as the rest of the new culms that shot within the colony. These new culms get more light than other new culms, so the plant has spent less energy in this part of the colony to get the same amount of light. If the plant spends less energy getting the same amount of light, it would seem to me that this is not a bad thing.

Perhpas the microclimate has something to do with how thinning effects eventual starch production, and whatever the limiting factor on growth in different locations may be. Some locations, the limiting reagent is heat, some places the length of growing season, some places the amount of rainfall. In our climate, there's lots of heat, a long growing season, and rainfall is the limiting reagent. In our type of climate, photosynthesis is near a max at all times, if the soil has enough moisture, and cutting back smaller culms may have a very different effect than say a location with excessive rainfall, where the plant has limited heat and growing season. If you cut out some culms in that type of climate, where photosynthesis rather than rainwater is the limiting factor, no amount of irrigation will make up for the loss. But we don't have photosynthesis as a limiting factor, here. So why would I worry about cutting out some totally shaded culms? The answer may appear to be less than cut and dry, than conventional wisdom has informed us.

I know that Jan over in Europe uses thinning to get huge canes in northern Europe in a limited space enviroment. He says it is the essential secret to getting oversized canes. Thinning should be explored more as a tool of bamboo management, it's an interesting and integral topic.

Mackel

Interesting set of opinions. What really needs to happen is to have someone do a controlled experiment. Pairs of identical clumps with identical siting and environmental conditions, where one clump in each pair is the untouched control bamboo and the other one keeps getting pruned.