As the old saying goes, if we didn’t have weather what would we talk about?
A customer asked me if his bamboo would “ever be perennial.” Well, bamboo is always a perennial. It comes back year after year from the previous season’s growth (roots). That’s what a perennial is.
Specifically what he meant was, would his bamboo ever have culms that survive winter. Or would it always die back and then re-shoot from the roots.
Unfortunately, the answer isn’t a simple yes or no. It depends… on a lot of factors. Right off the top, grove age. In this case we’re talking about plants that are only about three years old. It’s going to take a little bit for them to make a sizable root system to sustain top growth through harsh weather. The more roots a grove has, the more water it can take up both before and after severe low temperatures.
More of a factor are:
Severity of winter low temperatures
Duration of sustained extreme temperatures
and Available (thawed) moisture in the soil.
The bottom line is that the temperatures can’t be colder than what a species is rated for, or known to withstand. Those low temperatures that border on what it can withstand come with a time limit as well. Experiencing -10F for a few hours overnight and then thawing enough to take up water within the next day or two is different from a temperature of -10F that’s sustained for a whole day, two days, so on, with no thawing temperatures that allow the plant to take up water to replace what was lost from being nearly more or less freeze dried.
Wind is a huge part of top kill. It desiccates the plants in no time when the temperature is below freezing, particularly when it’s below 0F.
This past winter of 2018/ 2019 was terrible. We had -20F with 50 mph winds on January 30th and we had below 0F temperatures for days on end prior to and following that. While wind chill doesn’t affect plants in the way it does warm blooded lifeforms, it does still affect plants through its drying capabilities.
For the past several years our bamboo has top-killed at least to the snow line. It’s not a big deal. It grows back from the roots in the spring. The winter of 2014/ 2015 was bad. We lost top growth on Phyllostachys nuda that was over 20′ tall. For a few winters prior to that we had some good winters where nuda didn’t top kill. Each spring it put up larger and larger shoots until it had reached to over 20′.
Then came the winter of 2014/ 2015 and it top killed. As I recall the winter of 2015/ 2016 was better and it didn’t completely top kill. Since that time most of our bamboo has top killed.
The exception was the ‘Macon’ clone of our native Arundinaria. We’ve had it since around 1998. It had never completely top killed for us until this winter of 2018/ 2019. It top killed to the soil line. We set a 53 year record for extreme cold here. Let’s hope that’s the last of that for at least another 53 years!
Bamboo culms aren’t the only thing to suffer from winter extremes. The Indiana DNR sent out a mailing saying that certain flowering plants such as quince and a few others wouldn’t flower well this year due to the extreme cold experience this past winter. Sure enough, they were right. Our quince bushes that usually put on a spectacular show each spring are very sparsely flowered this year. I have one large quince bush that I counted about four flowers on this spring.
Willows, Zelkovas, and Maples all took a hard hit and have a lot of die back. One willow tree I have that was close to 8′ tall died back to the snow line. The entire trunk down to a few inches of the ground is dead.
This spring hasn’t been so great either. We’re way below in temperatures where we were last year. Our high today is supposed to be 71F. Last year on this date our high was 79F. Tomorrow’s high is supposed to be 55F. It’s staying in the 50s with lows in the 40s until next week. Then in the 60s.
At least we haven’t had a late freeze like we did on May 8th, 2017. That was a killing freeze. There are trees here that still haven’t recovered from having their new growth frozen off two years ago.
We live in a northern climate and I’ve come to accept that. We push the limits with some of the plants we grow here, but we never know what winter will bring. Every winter is different.
To say yes or no your bamboo will or will not top kill isn’t something that can be guaranteed. We can say that it will re-shoot come spring. Ours always has since 1997. There have also been winters where our most cold hardy species haven’t top killed. Phyllostachys bissetii and nuda have both had several winters where they haven’t. ‘Macon’ had a track record of not being top killed for twenty years here, until this winter.
Bamboo still makes an awesome screen when compared to evergreen trees. If evergreen trees have freeze damage they can take years to recover. Add to this the threat of Dothistroma needle blight in conifers and bamboo starts to look even better. Dothistroma is a fungal infection that is becoming more widespread and is killing conifers from coast to coast in the U.S. Austrian Pine seems to be most severely impacted; at least here in the midwest.
There was a time when I thought that our native white pine could be resistant and over the past five years I’ve witnessed Dothistroma kill off areas of this species as well. I also used to believe that spruce could be resistant to the needle fungus. This year brought reports and photos by the Indiana DNR’s plant pathology division showing that Dothistroma has been found in spruce trees as well.
Deciduous trees make a nice screen during the warm season, but they don’t hold green leaves through December and January like bamboo does even during the worse winters. After that, the straw colored dried leaves hang on until spring, still providing screening. Even if completely top killed, bamboo comes back to screen in only a few weeks in the spring. Bamboo still gets my vote over trees for privacy because of these factors, even if it does top kill several winters in a row until we get a more mild winter.
The below chart shows the approximate green leaf coverage season of each screening option for northern Indiana.