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montreal_gw

potted dwarf conifers

17 years ago

Hi,

Last spring I bought 4 dwarf Thuja Occidentalis and planted them in pots (approx. 16"x16" plastic pot inside a bigger ornamental resin "wicker" pot). They sit on my balcony. They did well but now I'm worried about insufficient insulation for the planters during the winter. I live in Montreal, Quebec, Canada and our winters are quite cold and long.

I have put all 4 planters together to form a square. I've wrapped the perimeter of both inner and outer pots with bubble wrap. I've mulched the top of each planter. I've built a wooden frame for the 4 pots which I am using to support rigid polystyrene insulation boards and burlap around the perimeter of the frame. I've also put wooden boards on the sides of the frame to prevent wind damage.

I'm not too worried about the wind as the boards protect the little shrubs very well. What worries me most is the degree of insulation needed to keep the roots from freezing over and dying. Since there is a lot of air leaking through the insulation boards, I was thinking I should buy some insulation batting to cocoon the planters. This is their first winter.

The planters are sitting on a rigid polystyrene insulation board (R-12).

I am willing to do the work if someone is willing to guide me as to what works for this particular situation and zone.

Please help... I don't want to lose them...

Comments (19)

  • 17 years ago

    MY GOD .... you wont fail for lack of trying.. lol ...

    in my zone 5 .. thuja occ... freeze solid in the ground every winter.... no problems there ... so get it out of your head that you need to protect the roots from freezing ...

    i think you took care of freeze drying winds.. and i think you took care of keeping the pots out of winter sun.. so the pots/roots don't thaw and freeze repeatedly ...

    T. occ should be fully rated for your zone.. unless you can give us ta specific cultivar name and research shows us otherwise .... what do you mean when you say 'dwarf' thuja occ????

    make sure they don't freeze the roots into an ice cube.. let them enjoy the cold.. and DO NOT KILL THEM WITH TOO MUCH LOVE ....

    good luck

    ken

  • 17 years ago

    Thank you for your reassuring words Ken!

    The exact name of my conifers is Thuja Occidentalis "Hetz Midget" Dwarf Globe. They are rated for zone 3.

    Yes, they are well protected from the wind and sun.

    Just a few days ago we had some colder weather mixed with freezing rain and the next day, I noticed some ice around the edges of the planters. So out of curiousity, I took a knife and tried to dig into the soil along the edge of one of the pots and it was practically frozen! So this has me a little worried as our Montreal winters get much colder than this...

    As you put it, I don't want the roots to freeze into an "ice cube"... hence, this posting :)

  • 17 years ago

    link below to the ACS website.. as you note.. fully zone 3 ....

    keep the roots from thawing and freezing repeatedly all winter .... and protect from drying wind.. and winter sun... and you should be all set ....

    if you have access to the pots... I HAVE HEARD... but never tried... an ice cube or snowball in each pot.. will add some water if the temps come up a bit.. a way of adding some potential water in the great white north. ... in mid winter ...

    in january or so .... try rooting some cuttings.... some little greenhouse.. some perlite .. some rooting hormone .. ask for more info in a new post in january ... i am sure you have a few branch ends to try ... what the heck.. eh???

    i cant tell from your facts.. but i would not cover them completely .... they shouldnt care about the level of cold ... and a little air movement is better than a cocoon ...

    and forget about the roots freezing... its irrellevant .... as noted.. they live through such down here ... and quit digging around in the roots.. your base line should always be .. DO NO HARM .... i just meant dont water them anymore .... frozen soil.. is NOT an ice cube.. there is still air in there .... no air in ice ...

    say a prayer.. and let them be... you are borderline on the verge of trying to kill them with too much love ....

    you are welcome .. and.....

    good luck

    ken

    Here is a link that might be useful: ACS database

  • 17 years ago

    Thanks again Ken. I'm a novice at this so I really appreciate your feedback.

    I've read about the ice cube idea before... I think it might be a good route to take. Yes, I have full access to the pots.

    I don't know about the root cuttings though. I'm really new at this and live in a condo... think I'm going to focus my efforts on what I have at the moment. But, maybe in time, I might get a little more "adventurous" ...lol

    They are well protected on all sides but are completely open on the top so they are definitely getting a lot of fresh air. In fact, they have browned a bit but I'm not too worried about this. I might use a temporary (partial) burlap cover for the top on really sunny, windy, or snowy days... when the winter has fully set in.

    The "cocoon" I was referring to initially was soley in relation to the perimeter of the pots... for root protection.

    If you have any other suggestions, please let me know!! Thanks again for all your input Ken. It's put this beginner at ease :)

    I'll keep you posted on how they're doing. And thanks for the link!!

  • 17 years ago

    While Kens information is great and very informative, keep in mind hardiness ratings for "container" plants are referanced for the roots normally...not a plant in the ground. You live in an area where a plant will most likely reach a true, full dormancy....but most container winter protection is focused on the roots, not the top...plants evolved to have their roots in the ground...not a container...they as a "rule of thumb" are the most sensitive.

  • 17 years ago

    Adding insulation will not help. Insulation only works to trap warm air in (or out), and since there is no heat source at the plants, there is no heat to trap.

    Keeping wind and sun off is useful.

  • 17 years ago

    Thanks everyone! I appreciate your feedback.

    In fact, I was doing some reading today and came across a scientific study confirming that insulation around a potted plant does indeed affect the temperature of the soil/roots... so I think I've done something right (lol).

    Please get back to me if you've had experience with potted conifers in colder zones... this is a great site!

  • 17 years ago

    For what it's worth I think insulation around or over the roots might help. Sure, the soil will likely reach the air temperature, but it might be a slower more gradual adjustment making the plant more able to tolerate it.

    As for potted conifers, I had a thuja occidentalis 'smargd' growing on the deck in a ceramic pot. For winter I placed the pot in an unheated dark shed. The plant came through winter very well. Not sure how cold it got in the shed (it is sort of against the side of the house) but when we experience -35C mornings it's likely in the -20's celsius in there. But here too, the temperatures probably do alternate but more gradually than, say, if the plant was outside exposed to the elements.

    Good that you wrapped the plants in burlap too. Winter damage from wind and sun is a concern, particularly in late winter.

    Good luck,
    Glen

  • 17 years ago

    Thanks Glen!

    My hetz midgets are supposed to be hardy in my zone. That, plus the fact that I've added fibreglass insulation around the containers (which are grouped together) should help keep the roots from from freezing over and dying. I'm not worried about sun and wind though. The green is very well protected, yet still gets a lot of air. I should try to add a photo but I'm still not sure how to do that. I'm new here!

    If your conifer survived in -20C with no insulation around the pot, then I think mine should be alright. The insulation I've used around the planters ranges from R-20 to R-32. Our temperatures are already around -10C. Is there any way of knowing they're in trouble during dormancy?

    Unfortunately, I live in a condominium so I have no shed. I do have some storage space in the garage area, but it's heated (about 15C), and has flourescent lights which are on continuously. I don't think this would be a good option for my dwarfs. I believe they need a period of dormancy.

    By the way, I'll try to find the link of the scientific study I stumbled upon. It was extremely informative. They grouped several potted plants together and over the course of the study they found that the roots in the middle planter were almost 10C degrees warmer than the edge of one of the outside planters. I was amazed...

    The information from members on this site is also extremely helpful :)

  • 17 years ago

    Since evergreen plants continue to photosynthesize and thus transpire during winter, they themselves are a heat source, albeit tiny :-)) That is the concept behind grouping containerized plants together in the winter to form a small microclimate - transpiration expends calories which equals heat. Bubble wrap is an extremely efficient insulation material as the sealed pockets are dry and remain so and the clear plastic absorbs and transfers any radiant heat received during the day. Just make sure the plastic is not in direct contact with the foliage as well as the sun.

  • 17 years ago

    The major benefit of insulation in my opinion is that it moderates the nighttime low temperatures. I do the snowball trick with my japanese maples I overwinter in my garage. Works great and virtually no effort, plus it adds insulation.

    Bill

  • 17 years ago

    Well... we had plenty of snow in Montreal today, so I was able to put quite a bit on top of the mulch. I'm using nature as my reference. In-ground shrubs were almost buried in snow today. I managed to get about 6 inches of snow on top of the soil (and surrounding insulation) of my planters. Hopefully, this will not only protect the roots, but also provide water when the temperatures go above freezing. Does this seem alright?

    As a beginner, I'm relying on your feedback to guide me.

    By the way, I found the link to the study I was referring to in earlier messages. It compares various overwintering methods. Some people might find it useful...

    http://www.jeffriesnurseries.com/ow_.pdf

  • 17 years ago

    Incidentally, Montreal is a solid zone 5, not 3.
    Most of the island and surrounding area to the north are Z5a, while to the south is Z5b - until you hit the Adirondacks in NY state....

    Miniature conifers hardy to only Z6 & 7 do quite well here, mostly because they pass winter under a cover of snow.
    This includes such things as cultivars of Cryptomeria, Cunninghamia, Thujopsis, etc.

  • 17 years ago

    You are correct. I obviously didn't get the right information when I started researching zones, but luckily, being in zone 5 works in my favor.

    Thank you:)

  • 17 years ago

    Hi montreal. I'm new to these forums myself.

    I have two dwarf Alberta spruce in containers I keep outside in winter, my biggest concern is that the containers will crack.(Honestly, there's already a small crack in one where I bumped it driving in/out of the garage!)

    I am also more concerned with the effects of drying (dessicating) winds, that is where the snowball "trick" comes in handy! It is very important to water evergreens well before the ground/soil freezes and temperatures drop. If the plant goes into dormancy without sufficient water reserves it will quickly be depleted and suffer/or die.

    Sounds like you've taken good care of yours so that is not of particular concern.

    Also, plants in ground have the ground to insulate them, so I don't think you're wrong to wrap yours, and to keep the foliage from sunburning with the burlap screen.

    BUT, I have seen miniature evergreens used in outdoor containers in the city of Chicago, oh they are pretty, with twigs of dogwood branches, and curly willows and sparkly ornaments, and obviously they endure quite a bit. Perhaps they are not meant to last?

    Anyway, it sounds to me like you are on the right track. :)

  • 17 years ago

    Hi Prairiegirl,

    It sounds like you'll be needing some new planters next year! lol..

    I'm wondering how old your evergreens are and how big their containers are at the moment. If they've survived a couple of winters, then that's reassuring.

    Can you please tell me what the "snowball" trick would be? I thought it meant piling some snow on the planter to protect the roots and provide water but I'm not 100% sure that I've got it right.

    I did give them plenty of water before freezing weather kicked in, but I also worry about root rot. Although I don't think it would be too much of a factor when the weather is below freezing?

    These planters are so well protected that if they don't make it through winter I'll be extremely surprised. Sun barrier, wind barrier, fibreglass insulation, the works! lol... and topped off with several inches of snow...

    I'll try to take some photos this weekend and post them here. If nothing else, it might be helpful to others.

    It would be easy to do nothing... but I really do want mine to last... I've kind of gotten attached to the cute little things :))

  • 17 years ago

    Hi Everyone,

    Well, it's now April in Montreal and temps are finally above zero. Not sure how my conifers have done but they still have a lot of green so I'm hoping they pulled through their first winter.

    Any suggestions on what I should do at this point in time to encourage their health?

    Thanks!

  • 17 years ago

    hi

    green is good ...

    keep the black pots out of the sun ... we dont want the roots to become too active.... on a warm day .. and then get frozen on some freak april night

    anything you can do to keep them from wild spikes is preferred ....

    other than that.. dont give them too much water which might freeze.. but dont let them dry out...

    do not trim any brown out until late may ... you never know what might re-sprout .... if there is any damage ... you can always take it off later.. you cant put it back on ...

    continued luck

    ken

  • 17 years ago

    Thanks Ken... your advice has served me well.

    We're hitting 20 degrees during the day now so I took the top (layer of burlap) off the shelter I'd put together. I'll be removing the insulation from the perimeter of the 4 pots this weekend. I'm thinking of leaving the frame of the shelter (4 posts) and the burlap around the frame because it may serve to protect them from any winds for the next few weeks.

    The soil in the pots is cool and moist but the leaves are very dry and crumble when they are handled. Is this normal?

    I'm thinking of repotting in the same planters with new soil... would this be recommended?

    I'm also considering adding some Miracle grow to their water at this point... good idea or not??

    Not sure when to expect the first buds... I'm eager to see some new growth... just so I know they've survived. They all have green but the brown branches have left me with some doubt. I guess it's all part of the learning process.

    Many thanks... Irene