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A word about first overwintering of variegated seedlings

A word about first overwintering of variegated seedlings

I still can't snap a photo which shows the true orange color of the culm
I still can’t snap a photo which shows the true orange color of the culm

Winter is finally coming to an end. Days are getting longer, snow has almost melted and mild spring-like temperatures are on our way. This winter was quite cold with temperatures down to -16°C and strong north-eastern wind that emphasized the windchill index. Luckily, we’ve also had quite a large amount of snow during the cold weather. It was not hard to protect bamboos using snow this year, so I expect minimal damage on my larger bamboos, moderate damage on my Moso seedling and no damage on my Phyllostachys arcana seedlings.
I can only hope we don’t get hit by severe freeze in late spring like we did the last few years. It did not affect the bamboo much, so I’m more worried about other plants and fruits around the garden.

Interesting variegation on one of the culms
Interesting variegation on one of the culms

I’m keeping my variegated seedlings in a raised bed. To keep the bamboos protected, I covered the whole thing with a PVC tunnel. It did OK throughout the mild first part of winter, but as it got really cold, I’m not sure the seedlings would be able to survive without better protection. Lucky for us, the polar blast brought some snow, so I was able to pile it up around the raised bed. There was enough snow to cover the bed completely. Later, we’ve got quite a lot more snow and tunnel finally collapsed under thick snow cover. When the worst was over, I removed the snow and found the seedlings completely unharmed. They were in better shape than I hoped they would be. I hope to see a decent upsize this spring. Last year, there were hardly any new shoots, all of them seemed to be survival shoots. They managed to grow long rhizomes in all directions, though, so I expect them to upsize… eventually.

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Protecting bamboo during the winter

Protecting bamboo during the winter

Most of temperate bamboos are quite cold hardy, but there are exceptions and every plant’s cold hardiness has its limits. To prevent damage during the cold months of winter, it’s often best to offer your plants at least some protection to prevent loosing your bamboo.

Most common causes of winter damage

Drought stressed Moso got severely burnt during the cold weather
Drought stressed Moso got severely burnt during the cold weather

Beside the cold itself, sometimes there are other causes of winter damage. In late fall, bamboos go through a preparation period in which their cold hardiness improves considerably. Their growth and transpiration halts to a minimum, some can even shed some of their leaves. When soil is cold, sometimes even frozen, water mobility from roots towards the leaves is extremely difficult process which can even completely stop if the soil or any part of bamboo culm gets completely frozen. At that point, each additional leaf that requires water, means that the plant loses more water than it can replenish. It is also good Idea to mulch the soil around the bamboo with layer of dry leaves, grass or wood shavings. Mulch does attract rodents, which can sometimes cause more damage than the mulch prevents. If you fertilize in late autumn, there is a possibility that bamboo fails to enter the winter preparation and continues to actively grow. During growth it’s much more delicate and can be damaged by either drought, heat or cold. Plants that were already stressed during previous growing season are often more prone to cold damage.

How cold is too cold?

Snow covered Borinda fungosa. Late fall shoots are toasted since first frost
Snow covered Borinda fungosa. Late fall shoots are toasted since first frost

There’s no answer to that one. Cold damages plants, but it usually doesn’t “work” alone. If it’s cold and the weather is overcast or if there’s fog and no wind, there will be much less damage, compared to clear sunny windy and frigid day. Wind can dry out even the most prepared leaves that are coated with thick layer of wax. Sun warms up the dark green foliage that heats up readily, transpiration rate goes up and the roots can’t supply enough water. When you combine all three, cold, sun and wind, the effect is by far the worst. I’ve lost several bamboos in those conditions.

Piled-up snow – best winter protection

Raised bed covered with PVC tunnel and snow insulation. PVC tunnel collapsed due to snow cover weight. Plants were completely unharmed.
Raised bed covered with PVC tunnel and snow insulation. PVC tunnel collapsed due to snow cover weight. Plants were completely unharmed.

When snow falls over bamboo, it will easily bend and soon, snow covers the bamboo completely. That is bamboo’s natural defense against winter extremes and it works extremely well. If there is at least some snow before the cold hits, it’s best you use it! By tarping the bamboo down to the ground, it is easier to cover it with snow. I usually just shovel up a pile of snow over it, and hope enough snow falls before the bitter cold arrives. Tarping bamboo to the ground is necessary when the plant gets larger, but usually gets impossible as the plant matures. Snow covered bamboo makes the air around bamboo leaves warmer than the air above, regulates moisture and prevents desiccation. It is also dark and keeps only minimal transpiration.

Thick layer of snow effectively protects the plants below
Thick layer of snow effectively protects the plants below

All the snow covered bamboos survived the cold blast completely intact. Soil did not freeze under snow insulation and my protected bamboos only suffered minor culm and branch breakage. The much taller and robust bamboo culms that remained exposed got damaged. My Moso seedling that got drought and heat stressed during the summer is going to show substantial winter damage. Tender Phyllostachys aurea is fried up to 50% and Phyllostachys aureosulcata ‘Spectabilis’ (Lamatempel) with no damage whatsoever. All my smaller other bamboos got protected by themselves – snow laid them flat and since the snow cover got thick enough, they remained safe during the severe winter weather with temperatures down to -16°C and powerful dry wind.

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Borinda fungosa winter damage 2016/2017

Borinda fungosa winter damage 2016/2017

This winter was quite brutal. Temperatures did not plunge lower than normal, but it got cold enough for the soil to completely freeze down to 0.5m and even deeper. With no snow cover to protect the delicate Borinda leaves, it stood little chance to survive the winter.

The cause

Top killed Borinda fungosa
Top killed Borinda fungosa

During early winter, there was no visible damage on any of my bamboos, even Borinda fungosa (gaolinensis?) fared much better than I expected. But then came a period when we received no snow, only freezing temperatures that remained below freezing even during the day. Combined with cold north eastern winds, soil cooled off considerably and it froze much deeper than usual. It remained frozen for quite some time, even when temperatures rose above freezing.

The damage

When temperatures got back to normal and after some “warm” rain, leaves lost their green color and it became evident that bamboo ended up completely top killed. Culms were all noticeably bleached, green culms had the darker green, somewhat watery appearance. At that point, I was sorry I didn’t tarp the bamboo and try my best to protect it. It all seems now, that no protection could have save it this winter – the weather was just too much for a marginal bamboo like Borinda to survive intact.

The awakening

There is still some life in it...
There is still some life in it…

In early spring, we’ve had a period of extremely warm weather which had awaken all the bamboos, including the badly damaged Borinda fungosa. I have completely removed the dried out culms and I soon noticed a couple of survival shoots, pushing out from the base of dead culms. Until now, there are no regular shoots that would prove that the bamboo is going to recover. I hope there are healthy rhizomes with undamaged rhizome buds below ground. Usually the first shoots appeared around mid May, hopefully they will push out this year as well.

The conclusion

Some small survival shoots started to emerge
Some small survival shoots started to emerge

Borinda fungosa I’ve been growing from seed for 6 years somehow managed to thrive in this marginal climate. It got damaged during the winter and didn’t like the heat in the summer, but it managed to grow and upsize into a very decent bamboo. This winter was not typical for us. At least not statistically. It’s sad that the same climate pattern started to repeat itself almost every year. Almost no winter precipitation, cool northern wind and sunny weather can dry out even more winter hardy bamboos. As if the winter was not bad enough, we were recently hit by a nasty late spring freeze. My Borinda doesn’t have the best growing conditions in my garden. It may perish in a year or two even if it survived this winter.

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Broken winter dormancy …

Broken winter dormancy …

Swollen buds on bamboo seedling
Swollen buds on bamboo seedling

We’ve had quite cold and very dry winter so far. Most of the pots outside dried out completely during the dry, cold and windy weather. I needed to thaw some of my bamboo seedlings that were completely dry. Temperatures plunged below freezing even during the day, so I placed the containers into the basement. My initial plan was to keep them in somewhat warmer place, water them, and take them out when the weather warms up at least a little bit. It did not warm up soon enough for them. I noticed elongated leaf buds and branches on most, if not all my bamboo seedlings. Bamboos and my blueberry cuttings decided to leave the winter dormancy behind and start actively growing.

Awakening buds on blueberry cuttings
Awakening buds on blueberry cuttings

If I would not water them, they would dehydrate completely, but when I took them inside, I unintentionally broke their dormancy cycle. They only needed about a week of warmer temperatures to start showing signs of growth. When I wanted to finally take blueberries out, I’ve noticed their swollen buds that were already green. They were just waiting to burst open and start flowering. The fast growing Phyllostachys arcana ‘Luteosulcata’ seedling from last year was also fully awaken.

Temperatures outside will remain below freezing for quite some time, and I’ll not be able to place them outside until at least late March. They will have to remain in the basement for at least a couple of months with only minimal available light. I intend to take them outside whenever weather allows me to. If it warms up enough, I’ll leave them outside as long as possible, until it cools off well below freezing again. Breaking dormancy, not the best thing to do during such a cold winter…

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