Cold weather protection for JWP.

[Rgw66]

Hello all. I was recently gifted a Japanese white pine bonsai. It is a pretty mature tree. Pictures of it are attached.

I live in Washington DC (zone 7a), and we are supposed to be getting some very cold weather early next week. Lows in the single digits down to 3°F, and highs not reaching above 20°. I live in an apartment and the tree is on my neighbors deck. Because of this, I don't have the option to bury the base or cover in mulch, and I don't have access to a greenhouse. I have a makeshift cold frame that I made out of PVC pipe and plastic, and I have rolls of burlap I was planning on wrapping around the pot and tree for a few days, but I'm not sure that will be enough. Any suggestions on what I should do with it? Is bringing it inside for 2-3 days and leaving it in a very cold area an option? Or would that shock the tree worse than the cold weather?

 

[MaciekA]

Just a fun thought experiment: What if your tree just happened to be at a 2 or 3 day bonsai exhibition during that specific cold weather period? Happens all the time, it's happening in Japan as we speak for example (though I think they don't heat their interiors to boiling hot like we do in the US). So, technically within some range of reasonable not-too-hot temperatures, we know it's not an issue for 2 or 3 days.

If you have a room that'll stay below 50 and dark, it's probably fine. I'd get it back out after the deep cold passes, though.

 

[JudyB]

The major issue with a tree being inside during dormancy is that it might try to break that dormancy. Unless the tree has reached its dormant hour requirements, it will not break dormancy and start to move. I don't imagine at this point, it has reached the requirements, and a couple days inside will not make it wake up so to speak. I would try to get it into a cold area that is not actually inside though (like a garage or a shed). If you leave it outside, you could do the makeshift cold frame, and do a heat cable or heat mat under the tree to keep it warmer. Even a bare light bulb inside a structure like that or old school incandescent electric christmas light strings can add enough heat in a simple structure to take the edge off. I'm sure that even at 3 it's probably fine as it's a conifer, but I don't like taking chances with my trees, so I do protect on the side of caution.

 

[penumbra]

The Japanese White Pine is a very cold hardy tree. It is rated zone 4 to zone 7, so you are close to the southern terminus. Just make sure it is not dry and just pile a few burlap squares over the pot. This is probably more than it needs. I have a few of them sitting on the ground and I am not at all concerned though I live 60 miles west of you in the Shenandoah Valley where you can take a few degrees F off what you will be experiencing. I have one in a wood planter that is about 4-1/2 - 5 feet tall that has been in the same spot in my yard for 34 years. It has been down to minus 14F with no harm.

 

[Japonicus]

A light weight cold frame and plastic wrap
can take flight in a wind. Plastic wrap can
beat the new apical buds in a wind, so take that
into consideration if you do use that and
make the construction in a way that overcomes wind.
Edit
Also open the construction by day once
the cold snap has passed and water to overcome transpiration.

 

[River's Edge]

Hardiness Zone ratings are based on trees planted in the ground. Bonsai practitioners need to concern themselves with safe temperatures for roots in a pot. The temperatures you are expecting are dangerous for JWP. I would place inside in a cold area if possible. Some research has been done on a table of safe root temperatures for containerized plants. In Bonsai Heresy by Michael Hagedorn there is an excellent discussion on how plant hardiness zones compare to root hardiness of containerized plants. Pages 84 to 95. I would reference the research of Oregon State university in the list published by species that provides how the root kill temperature relates to hardiness zone temperature rating. In short we need to understand that Hardiness zone relates to the top of the plant not the roots in a pot. The root kill temperature is much warmer than the hardiness zone rating. For example : the root kill temperature for Pinus Parviflora is listed at 10 F the hardiness zone temperature is listed at -20F.

 

[Kanorin]

I'd try out your temporary cold frame idea and buy a wi-fi enabled temperature probe to go in there. This will give you the data you'll need to make the call.
Taking it inside for 1 or 2 nights is certainly an ok backup plan. It's less likely to easily break dormancy now compared to if this same situation happens in mid-February.

 

[penumbra]

You are overthinking this, but do what you are comfortable with. I have I believe 8 JWP that are sitting on the ground with a little mulch around them. As I have stated, My largest and oldest one survived 14 below zero without and problem. And it is in a wood planter.

 

[JudyB]

So there is your answer, it depends on what you're comfortable with risking or being safe with. I would not want to risk any tree in my care, I did that for a few years before we built the storage house, and I lost some key branches on a couple. And if I remember back that far, one whole tree might have died.

I'm a huge believer in heat mats for root protection.

 

[River's Edge]

I live in an apartment and the tree is on my neighbors deck. Because of this, I don't have the option to bury the base or cover in mulch, and I don't have access to a greenhouse.

The OP mentioned this information which is important.
Penumbra mentioned a wood planter experience that has some benefit.
Wood is an excellent insulating material and of benefit in short cold spell situations where the temperature swings quickly.
Factual information is available to assess the risk.
One of the larger nurseries with a lot of experience connected to containerized plants has a manager with professional bonsai training and also has a reference list for root kill temperatures that can be compared to the research list of Oregon State University. The Nursery is Iseli and the manager is Joe Harris !!!. Many of you will recognize the name from workshops and conventions.
I( may not have explained it as well as this quote from Michaels book. Myth #13 is that plant hardiness zone corresponds to root hardiness.
" Roots are far more susceptible to cold than trunks and branches"

 

[Bob Hunter]

I always bring my JWP in a unheated Garage for temps under 20F then bring them right out over 20F. You could bring it in your house for a couple days.

 

[Dav4]

My JWP are up against my house on a concrete patio, pots covered in wood chip mulch with added snow for insulation. Next week, they'll see several mornings where the temperature is well below zero, and they might see close to three straight days where the temperature doesn't break ten degrees. The combination of essentially being on the ground with the mulch/snow insulation protecting the roots from extreme temperature swings means they will be fine. If they weren't on the ground with pots insulated, I'd be much more concerned. If you can't get the pot on the ground and insulate it, bring it inside for a few days.

 

[River's Edge]

One small experiment revealed that there can be a 7 degree difference ( warmer) under a pot placed on the ground as opposed to left on a bench. Placing mulch has an extra insulation effect. Avoiding windchill also makes a differrence.

 

[Rgw66]

OK, well thank you everyone who has replied. Lots of conflicting information here, but for the most part, it seems like the tree will probably be fine, though I will take protective measures anyway. The projected temperatures are slowly going up. Lows on the coldest day are now 8° with highs in the 20s. I am not worried if it drops below 10° for a few hours as long as it gets up into the 20s in the afternoon.

I will wrap the base/pot with a few layers of burlap to help insulate it a bit more. It also still has some snow on it from the last snowstorm we had, so I will likely just leave that on as well for more insulation (and to water it as it melts). I am hesitant to use my PVC cold frame because we typically have pretty strong winds in the winter and I don't want it to blow away or have the plastic whip against the branches. I don't have a garage or shed I could put it in temporarily, and while there might be some cold areas of my apartment, I doubt they're as cold as 50°. If the temperatures drop any lower than what they are projected to be now I will likely just bring it inside at night and then put it out again during the day.

My neighbor's deck is on their roof, so I also plan is to measure the temperature of various places on their roof to see where it is warmest and leave the tree there (as long as it's still protected by the wind). I imagine the heat radiating from the top of the building would be enough to keep the pot from getting way too cold.

 

[Rgw66]

I just wanted to share with everyone what I came up with. Ended up taking the tree in last night. But I put it in this 26 gal bin I had laying around to help it retain some of it coolness from outside while it was inside my apartment (which worked. The soil in the pot was still frozen when I brought it back out in the afternoon).

I had the realization that if the pot fits inside of the bin, then I could pack mulch around the sides and bottom for extra insulation during the winter. I put a layer of burlap between the pot and the mulch and left the base of the tree exposed so I can continue to water it and so the moss that is at the base can continue to get sun. I put some snow on it so it will water itself as it melts. Once spring rolls around I will take it out of the bin.

I thought this was a good idea to protect the roots from extreme cold, but also to keep the temp generally more stable once we will start getting the random days of warm weather. I am surprised I have never seen anything like this in these forums before. Is there any reason I shouldn't do this? It seems like a no brainer as long as I don't over water it and saturate the mulch.

 

[Japonicus]

You should update your profile
To include your location.

Once spring rolls around I will take it out of the bin.

Is there any reason I shouldn't do this?

I think it's fine for the quick overnight indoor storage.
Outdoors the lack of breathability, and the accumulation of moisture can lead to problems.
Assuming this bin is without drainage holes and the fact that most conifers despise wet feet, rain then becomes a greater issue.

I would've packed a bag of ice or snow in it for the night indoors, but frozen is frozen.

 

[Paradox]

I just wanted to share with everyone what I came up with. Ended up taking the tree in last night. But I put it in this 26 gal bin I had laying around to help it retain some of it coolness from outside while it was inside my apartment (which worked. The soil in the pot was still frozen when I brought it back out in the afternoon).

I had the realization that if the pot fits inside of the bin, then I could pack mulch around the sides and bottom for extra insulation during the winter. I put a layer of burlap between the pot and the mulch and left the base of the tree exposed so I can continue to water it and so the moss that is at the base can continue to get sun. I put some snow on it so it will water itself as it melts. Once spring rolls around I will take it out of the bin.

I thought this was a good idea to protect the roots from extreme cold, but also to keep the temp generally more stable once we will start getting the random days of warm weather. I am surprised I have never seen anything like this in these forums before. Is there any reason I shouldn't do this? It seems like a no brainer as long as I don't over water it and saturate the mulch.

I would make sure there are holes in the bottom of that so it doesn't accumulate water

 

[Rgw66]

Outdoors the lack of breathability, and the accumulation of moisture can lead to problems.
Assuming this bin is without drainage holes and the fact that most conifers despise wet feet, rain then becomes a greater issue.

I guess I didn't think this was much different than burying it in the ground, but I suppose water has somewhere to go other than just stay in the bin.

I took the mulch off the top of the pot so it can breath more and so I can pull it out easier and check how wet it is underneath.