How to get bamboo to grow faster and bigger?

I bought some bamboo rhizomes 4 years ago and the seller told me it was the clumping type up to 25 ft tall. In 2022 the culms grew to 5-7 ft with 1/2 inch diameter. In 2023 due to late frost kill, regrown culms came down to 3-5 ft only. They are fine as privacy screens but I can't even use them for plant support.

I went to a friend's house since he got an established grove. His wasn't doing too good either. Basically all culms over 2 year old are dead and last year's canes are only half the height. The bamboos from the two locations are not related and I don't know what varieties we are having.  But maybe both are not cold hardy enough given the winter kill.

I have never pampered my bamboos: no watering, no fertilizing. Should I start doing somethingto help them grow better? How do you get your bamboos to móaturity size asap? Thanks.

Bamboo definitely has temperature ranges, and you may be experiencing "range intolerance". Average doesn't always mean plants can handle the extreme years.

That said:
1. I've read that bamboo *love* leaves on the ground - so I'd consider a little decorative fencing a good few feet out from and encircling your patch, and fill it full of all the dead fall leaves you can. This may help insulate the ground just enough from the extreme cold, that the plants would be happier.
2. Bamboo is considered a heavy feeder. The year I had the duckies bathtub drain pipe moving around my dulcis bamboo patch, the following spring it went a little berserk.
3. Item 2 notwithstanding, the ducks got moved due to a dangerous tree, and the next year I lost more culms than was typical. Was it the lack of summer water, or the extremely wet winter, it's hard to know.
4. Be careful what you wish for... if the plant grows too fast for it's roots, it may also grow less strong culms and be more prone to snow damage. I've got a pile of pruning to do on my due to the heavy snowfall we had this year.
5. I've also read that bamboo counts on its standing stems to support spring growth needs. Thus, even if you can get it growing bigger this year, I'd *really* hesitate to remove any culms that are alive. The healthier you can get the plant before harvesting any of it, the better its long term productivity is likely to be.
6. Portable fencing and a visit for a day or 2 each week by your chickens to "fertilize in situ" might not hurt either?

Thanks Jay, that's very helpful.  I did make the mistake of cutting the damaged culms down before new shoots emerged. The older culms would've provided some protection for late frost/freeze. There are piles of leaves underneath so the rhizomes are fine even at -17c but tender shoots are very vulnerable. I am wondering if the cold hardier ones also emerge a bit later in the season.
That spot is sitting on the lower corner of my property so I am digging a hole nearby to preserve some rain water and making the bamboos happy.

Can you tell me where in the world you are, and which species of the Phyllostachys genus you are trying to grow? If so I can tell you if it's a poor choice for your site, and if there is a better choice I can tell you that. I am far enough away from overload and acute bamboo fatigue to engage my bambusero* persona again. *bambusero (from Castillano: one who works with bamboo "for the people" according to Hector Gaxiola) What I see in the picture is a bamboo that got killed and struggled to recover. Bamboo is a plant, and like any plant it wants good soil and the right climate. In part cold kills by preventing transpiration, and also bursting cells with ice crystals. Phyllostachys bamboos max out at temperatures in the near zero range, + or -. You can help by having the soil moist before the cold hits, having mulch (tree chips are The Best) and in a dry summer climate, choosing a riparian site. (from Riparia, goddess of rivers & streams, if my memory from Latin class in 1967 serves me) NB: the most cold hardy bamboos are not big. The hardiest bamboos are native up into Kentucky and in the mountains of Szechwan province in China. The big stuff grows in warmer parts of Japan and China and in most tropical zones.

I am in southwest Missouri zone 6b/7a and the bamboo rhizomes were from a local Craigslist seller living 10 miles away. The canes turn from green to yellow with irregular green stripes. Seller called it clumping but new shoots have been going outwards 4ft every year.

I looked up old photos and weather records.

The bamboo leaves died when temperature went near zero F (Feb 2023, Jan 2024.
In a warmer winter (2021-2022), the leaves stayed green the entire winter.
New shoots appeared in early April after periods of rain and were very susceptible to freezing temperature. One year only a few early shoots got killed and shoots emerged afterwards were ok (2021 april).
In a bad year, killing temperature came after all shoots were high up and starting to unfurl (2023 april). Subsequent growth turned out very weak.