Thinning out older small culms to promote larger new shoots.

[stevelau1911]

On most of my moso seedlings, I have cut out all of last year's growth because they seem to just take up space, crowding out space that could be used for newer larger shoots so they seem to be a liability. When there are close to 30 culms, all so close together in a 3 or 5 gallon pot, new shoots don't even have much of a chance to leaf out properly.

Since most of my moso seedlings seemed to have met a plateau in up-sizing my experiment is to get rid of all smaller culms that were produced last year and leave a few good larger culms to let them branch out and get thicker. The idea is that the root-ball is already established and rhizomes are already forming so therefore it won't stress the plant to cut out the small stuff. The foliage exposed to sun will be decreased by a bit after the thinning, however the larger culms should leaf out more and fill in that space. Less culms total means that the energy produced by the plant should be consolidated into fewer, but larger new shoots. On average the plants started out with 20-30 shoots, half of them shorter than 1ft, and I have cut them down to the 5-10 that were produced this year which average around 18 inches tall, some up to 2ft.

The ideal situation is that in another 2-3 weeks, the remaining culms will bush back out and larger shoots will be produced, hopefully hitting the 3ft mark. Here's an example of a couple that I thinned out.


Does anyone thing this is a really bad idea? If they start looking better than the un-thinned ones I might have to cut out some of the smaller shaded culms on my in-ground moso which has approximately 140 culms varying in size from 3ft to 6ft tall in approximately a 7 square feet area. Some of these culms get almost no sun.

[Matt in TN]

Yes, this is a bad idea. Thinning (especially this young) will stunt the growth. I thin my older (5 yrs) rubro because I like the way it looks, but I understand in doing so I'm probably slowing further upsizing. I don't trim anything on plants younger than 4 yrs or so.

But they're your plants - experiment to your heart's content and document your results here

[Alan_L]

Steve -- doesn't make sense. You went through a lot of trouble to make these plants retain as many leaves as possible over the winter, then you removed a lot of them intentionally? On young plants it *is* important to keep as much leaf mass as possible if your goal is to get the plants to size up.

[stevelau1911]

Here's a moso from the same batch so it is also 15 months old having been thinned before and getting up to 3 1/2 ft. It seems that having too many culms in general promotes the production of more culms with less upsize, but when smaller ones are thinned out leaving the biggest ones there, they still have the same root ball to work with so those culms should get bushier and eventually still be able to pull in a lot of energy, but the difference is that it should be in fewer and larger culms.

I liked the idea of retaining a lot of leaves, but when there are so many so that new shoots have to fight to grow through the clump, and can't leaf out properly, it seems like the smaller and older ones need to go.

[Bamboo Conne'isseur]

I have noticed and have heard from others that thinning tropical clumpers does help to get larger shoots and culms. In fact my favorite style of timber size bamboo is to keep it to around 5 to 7 culms no matter what size except when it is young. I have seen this done to D. asper and B. vulgaris and the vitatta, and everyone of those plants had larger than usual culms. I have also seen this practice in thinning out large areas of running bamboo that is mature and established and the shoots seemed to be larger, and the grove looked better as well.
I believe thinning groves and clumpers is an artform and a science, as well as simple maintenance.
Of course you have to have enough water for the upsize as well. Bamboo simply cannot support the large culms without enough rainfall or supplemental water to reach those sizes.

[stevelau1911]

After only 1 week, I am noticing that many of the thinned ones are starting to put out upsized shoots, not all as extreme as my heteroclade which nearly upsized by around 5X, but it also looks like the ones that have 20 something culms don't want to put on any more since it looks like they are at maximum culm capacity for their either 3 or 5 gallon pots. If this trend continues for another 2 weeks, I'll thin out the rest of them.

Another question is on when they should be thinned since I have one of my 3-4 month old mosos which is already has 14 culms however the plant itself is only about 12 inches tall from the base to leaf tip while my tallest one from this batch has only 6 culms and is up to 22 inches tall with a rising shoot that should break 30 inches and it seems to be upsizing way faster on each shoot. I'm not sure if this is based on each seedling's genetics, but the ones that are putting on lots of shoots don't seem to upsize as fast as the ones that concentrate their energy into fewer shoots.

I thinned out my in-ground moso grove too, taking out approximately 1/2 the culms which were all too short to get light anyways leaving approximately 75 of the best culms. The grove doesn't really look any different, but on the interior, it is much less congested now.

[Matt in TN]

Just imagine what would happen if you cut down ALL the culms!

[Jerry Hamilton]

I can't see cutting down any clums on young bamboo. I would let it grow up and become a larger bamboo before I start to thin out. More there the more it can put into the rihzomes.

[stevelau1911]

The 3-4 month old ones should probably just be left alone until they reach the 1 year old mark which will likely put them at 10-30 culms at 2ft tall on average and I'll probably give a small thinning in early spring to leave like 5-15 culms. Sometimes they can get so congested that it reduces the shooting capacity since there is no room to grow.

I have tried cutting down all the culms on one of them prior to shooting season and surprisingly, it came back except only with smaller culms and this moso is currently at around 15 inches tall. I didn't expect it to come back that strong, but I guess there's a decent amount of energy stored in the base.

As far as the big one, taking out around 75 culms when there are 150 total which are tightly packed together is not much because here's the before and after pictures.

July 19th before thinning.


August 4th after thinning. The lower branches get more sunlight and each individual culm gets a chance to leaf out a little more.


All my other groves will likely need to be thinned out next year once they go onto their 3rd year. The yellow groove is putting out surprisingly very little rhizome activity probably because I didn't load a few hundred lbs of manure on it yet, but I'm hoping for a 20 footer off this grove since it created an 11ft one this year. It also is not leafing out completely like most other phyllostachys, maybe because its location is too dry, but it should still have the largest culms for a couple years.

[Alan_L]

All my other groves will likely need to be thinned out next year once they go onto their 3rd year.

I'm pretty sure they won't *need* to be thinned, but it sounds like you *want* to thin them to get the look you want.

[bambooweb]

At the WSU research groves they have 4 rows of 7 species replicated randomly in each row. Each plot is 25 feet square and started with plants planted on 5 foot centers. For the first 4 years the same two rows were thinned then in the 4th year all the rows were thinned. The next spring shoots were harvested and measured and weighed and they found no statistical difference between the plots that were thinned and the ones that were left to grow.

So the conclusion was, for that climate, you can thin out the small culms after the new ones have leafed out if you think the plant looks better but it will not change the size of future shoots.

Bill

[Alan_L]

Bill -- what about number of shoots? Did thinning result in fewer shoots each year?

[bambooweb]

Bill -- what about number of shoots? Did thinning result in fewer shoots each year?

No, the number of shoots in the thinned and unthinned plots were close to the same.

I looked over some of the information from the grower that did the harvesting & record keeping and on his farm he waters and fertilizes in the fall to get larger buds and larger shoots the next spring.

Bill

[stevelau1911]

I'm about to do my fall application of manure/compost in about 1 week and by that time, I will have a good idea about where all the rhizomes are growing because I have noticed that it really increases the feeder root activity by having organic material in the soil mix. I knew nothing about the larger buds for larger shoots, but that makes sense if the rhizomes produces more roots.

As far as the idea about fertilizing with too much nitrogen late in the year and getting them more prone to winter damage, is there any hard evidence on that? I think most of my groves are large enough to where that shouldn't be an issue unless it makes them put out a full flush of shoots in November which I really doubt.

[stevelau1911]

Some of my moso seedlings have sent up decent shoots aiming towards the 3ft range, but it appears that most of them have switched over to rhizome/ whip shoot mode after the thinning 3-4 weeks ago. The ones that I still haven't thinned are starting to look noticeably shorter probably because there's no room to larger shoots to emerge out of the crowded pots. I always thought that more culms was better with more photosynthesis, but my latest observations disprove this idea.

This one should get up towards 3ft once the shoots are done elongating, but still seems to have too many culms at 12 even after I took out over half of them. Most of the thinned ones have sent up shoots at least over 2ft tall. They grow new leaves to get bushy again pretty fast after a good thinning.


Here's the results my neighbor has gotten with the latest culms over 40inches high and it seems like he doesn't let it get up to too many culms either given that there are only 6 and the rhizome activity seems to be way ahead of any of the ones I have. More than likely he'll get rid of the 4 shorter ones to bush out the 2 big culms and get a big jump in size again.