Please Help With Cold Frame Ideas

[hemmy]

This is my first winter in over a decade and the first with a serious amount of trees that all lived out year round in SoCal.

I’m looking for ideas and feedback on a DIY cold frame for overwintering JBP, JRP, and tridents in zone 6a. I have a space that already has a 12x12 wooden plaform with picket fence on north side a former hot tub platform. It is on north side of house with shielding by house on west and partially on south. I’m thinking about a PVC or metal conduit hoop frame covered inside and out with plastic sheeting. Then some type of wood frame with sheeting or polycarbonate sheets on the ends. I’d like the center to be at least 6ft tall. With our wild temp swings in winter, I’d expect to have to cover with shade cloth. Budget is ~$600 and I’d like to convert it to partial shade structure in the summer.

Challenges are that the current platform is a made from a treated 2’x6’ box frame resting on a concrete slab on one corner and concrete blocks on the other. It is not anchored and is a couple inches off the ground. It is also not level. I do have a nearby outdoor outlet to power fans or heating cables.

My original thought was a gravel bed floor with heating cables to keep the bed and pots above 36F. I’d like to avoid repeated freeze thaw cycles on my substrate and pots. It doesn’t get cold enough here to have snow for insulation. I am already battling squirrels, rabbits, mice and rats so it needs to be tight and I figured on setting traps and wrapping trunks.

 

[hemmy]

Questions include, should I build the heat bed on top of the treated wood decking, by putting down fabric and filling with haydite (I can get it by the yard)?

Should I pull off the decking and put the gravel bed in existing frame? It has a gap at bottom, so I’d need to insulate it on the sides. But I’d have added heat from ground. I’d probably need to create a hardware cloth cage on the bottom for vermin and then line with fabric.

PVC or Metal frame?

How to affix the plastic? Pre made clip systems?

Should I think about polycarbonate sheets and frame it as a raised side, partial A-frame?

Recommendations on exhaust fans?

How much hotter than the ambient temps could I expect it to get with 50% shade cloth? Do I need higher %?

I know I’ll get a lot of ‘just put them on the ground with mulch’, but I’d really like to step up my game for a couple nicer JBPs and to preserve eventual fine twigging on deciduous. Plus with -20F here a few years ago and my lack of winter in 12 years has me a little freaked out.

THANKS IN ADVANCE FOR ANY INPUT

 

[hemmy]

This is my current inspiration.

How to Build an Inexpensive Hoop-Style Greenhouse | Alberta Home Gardening

How to build an inexpensive 12 by 32 foot hoop-style greenhouse made from pvc pipe for under $400

www.albertahomegardening.com

 

[sorce]

Build an invisible one!

It's real easy!

Sorce

 

[Paradox]

IDK. I think you are over complicating it.

I don't like the idea of putting plastic sheathing on a structure that is supposed to stay cold. That is a greenhouse and it won't stay cold. Then you have to vent it which is a delicate balance to get enough air flow. Forget the heating coils, just asking for trouble with that. Both venting and heat coils use electricity. Let the radiant heat from the ground do the work for you.

Honestly I would just keep it simple and build a true coldframe. Solid walls to protect from wind, solid cover in case you need it and just tall enough for the trees to fit so that when it is covered it takes advantage of the heat from the ground.

I built mine from concrete blocks that forms a box along the north side of my house. The house is the 4th wall. It's 3 blocks tall for most of its length then one end has a section that is 4 blocks tall for taller trees. It takes advantage of radiant heat from both the house and the ground an usually stays above 30F when it's covered.

The blocks along the wall are to support the covers when I need to close it. It's simple, low tech and works great.

 

[penumbra]

JBP, JRP, and tridents in zone 6a

I have small coldframes, and a couple of hoop tunnels, but I would not waste the place therein on the species you have mentioned. Not only do that not need this level of protection, but they would likely resent it. I have all three of these species and they get mulched in at most.

 

[ShadyStump]

I agree that you're worrying too much about it, but I'll throw in my 2 cents on a cold frame anyway.

I was stationed in Ft. Riley back in the day, so I'm familiar with what KS can throw at you.
If it were me, I'd pull out that entire wood deck and cannibalize it for materials. Your trees will do better directly on the ground with that thermal battery being more help than atmospheric protection. Maybe put down a bed of gravel to keep mud down. Use the wood to enclose the rest of the space, or at least for framing.
You'll want some southwestern sun protection with the huge temp swings. This is something we also have to worry about here in Colorado. A single digit night rolls into a 60F+ afternoon, and everything with southwestern exposure gets shocked to death. You'll want to have a solid wall there.
The rest you can enclose with the heavy clear plastic sheeting. Build a decent door, but your walls can all be in sections so you can take them down come spring. Your roof, just a few boards across the top to support your plastic, but you will want a slant to aid in runoff. This could also be modular.
If your building all your walls and roof as modular panels, you might think about connecting them with hinges so you can open different sections. This allows for ventilation and easy access in a short structure.

 

[hemmy]

Thanks for all the replies. I am certainly panicking about my 1st winter in over a decade.

I don't like the idea of putting plastic sheathing on a structure that is supposed to stay cold. That is a greenhouse and it won't stay cold. Then you have to vent it which is a delicate balance to get enough air flow. Forget the heating coils, just asking for trouble with that.

This makes a lot of sense, as I knew if I covered it with plastic then I'd also have to cover it with shade cloth. But even with shade cloth in that direct sun until about 2pm, I bet it would get pretty warm inside (+20Fto outside air?). The idea make a structure was also to keep out varmits. But obviously that's not going to stop a rat or mouse if they really want in.

Honestly I would just keep it simple and build a true coldframe. Solid walls to protect from wind, solid cover in case you need it and just tall enough for the trees to fit so that when it is covered it takes advantage of the heat from the ground.

Maybe I should go this route, but I don't have a good run of space on the north side. I only have 3ft of length up against the house. I also have the NE corner which has ~6ft of north wall space, but has this 5x10ft concrete pad that stretches along the east facing wall. The very back corner has the dryer vent, which can't be blocked but I guess would pump some heat and moisture in the cold frame. lol.

I'm thinking the concrete pad would not retain as much heat as the ground. But would it actually get too cold if I set down mulch and then mulch in the trees on the pad surrounded by concrete blocks? Thanks!

 

[Dav4]

I'm thinking the concrete pad would not retain as much heat as the ground. But would it actually get too cold if I set down mulch and then mulch in the trees on the pad surrounded by concrete blocks?

I overwintered trees on the concrete slab of an unnattached garage in zone 6 MA for 10+ years, and I recently overwintered trees on a raised(but in contact with the ground) concrete block patio in zone 6 MI, pots placed together and mulched in place. I measured the temps below the pots- on the concrete- several times through the winter in both locations... the temps never fell below 32 F. The key is the concrete being in full contact with the ground and the pots being mulched.

 

[hemmy]

I also may want to include a gingko, Elaeagnus multiflora, chojubai, and juniper outside in the cold frame.

My shohin sized trees; elms, japanese maple, and apple were all going to winter in the garage. But I'd like to avoid the shuffle when they start early bud break. I'm just freaked out about leaving the little trees out with possible mammal damage (the 4 legged kind), after I had summer mouse, rabbit, and squirrel damage in the first 2 months after moving back to the Midwest.

I also have to get building on my tropical grow room in the garage (maybe by next Friday) and I was going to put up another garage tent for "Mediterranean" climate type trees like olives, pomegranate, satsuki azaleas, and a redwood that I'd like I'd like to keep above freezing. But that is a subject for a whole other post.

 

[Canada Bonsai]

I don't know if this document suits your needs, but it might be useful to read through simply to help generate your own ideas and and raise considerations

Winters in Canada

CLICK HERE for our 'Winters in Canada' handout

canada-bonsai.myshopify.com

 

[rockm]

Thanks for all the replies. I am certainly panicking about my 1st winter in over a decade.


This makes a lot of sense, as I knew if I covered it with plastic then I'd also have to cover it with shade cloth. But even with shade cloth in that direct sun until about 2pm, I bet it would get pretty warm inside (+20Fto outside air?). The idea make a structure was also to keep out varmits. But obviously that's not going to stop a rat or mouse if they really want in.


Maybe I should go this route, but I don't have a good run of space on the north side. I only have 3ft of length up against the house. I also have the NE corner which has ~6ft of north wall space, but has this 5x10ft concrete pad that stretches along the east facing wall. The very back corner has the dryer vent, which can't be blocked but I guess would pump some heat and moisture in the cold frame. lol.

I'm thinking the concrete pad would not retain as much heat as the ground. But would it actually get too cold if I set down mulch and then mulch in the trees on the pad surrounded by concrete blocks? Thanks!

View attachment 457564

I would not cover the structure. It will heat up too much, provide shelter for rodents who can eat your trees at their leisure without fear of weather or predators. You are overestimating your needs in fear of winter. IN keeping the snow out, you also keep out a great source of not only insulation for your trees' roots, but a source of constant moisture for them that doesn't require thawing out a hose.


I'd take the suggestions to use ambient ground heat and mulch as a primary protection. SKIP trying to make some kind of greenhouse or structure, as that entails proper venting when needed. With a greenhouse even a "cold" greenhouse, you will get extremely early bud break on your trees--like full leaves in Feb., which would then have to be taken inside to avoid death until mid-spring. Don't put the set up in an area that gets sun. Keep it shaded. Sun will also accelerate early bud break.

FWIW, I mulch all my trees on a paver brick patio out under open sky, with six foot fence for a windbreak.

 

[ShadyStump]

I'm thinking the concrete pad would not retain as much heat as the ground. But would it actually get too cold if I set down mulch and then mulch in the trees on the pad surrounded by concrete blocks?

I was asking this same question last year because I wouldn't trust my gut on it.
Yes, concrete won't hold as much heat as the ground, but WILL HOLD PLENTY ENOUGH. Don't set the pots on mulch, except maybe the thinnest layer if drainage is a concern. If you do you'll be insulating them from the heat in concrete that you want. You're aiming for direct temperature condition, not convection. Questioned this myself last year and lost some trees for it.

Positioning, just worry about NOT south or west in your climate.
If you really can't let go of the idea of a structure, just build a windbreak around them. Probably a good idea in a KS winter anyway.
So anything north, anything east, and a windbreak is all you really need to worry about, then mulch them in.

 

[hemmy]

Thanks all, I’m coming to terms with the idea of a block structure with no covering. That would solve for those occasional 70deg winter days! I'm still sticking on the idea of soil cables because it sounds like a great failsafe to keep the tree's roots above 20F in case of the artic blasts like 2021.

We average 13 inches of snow per year, but practically we could have an entire season with no snow. So that eliminates it as a cover.

I read that wood chips have an "R" insulation value of 1.0 per inch. While sand & gravel have 0.6 per inch. I think haydite (expanded shale) would probably be around that either higher or lower. I had originally thought of using the soil cables in the shale aggregate. But I guess they would work equally as well in wood chips?

 

[hemmy]

Plus any thoughts on how trees acclimate when they have been grown from seed in mild climates and never experienced a freeze? I would think that each year is a complete reset and they should be good as long as they are gradually exposed to cold to build up the necessary sugars. I don't want to loose my awesome JBP from @Housguy. But the cork oak is going into the garage under lights!

Bonsai Club of Santa Barbara Annual Show, Santa Barbara, CA, USA, May 21-22, 2022

After a 2 year hiatus for COVID, we are back! elm forest Please Join Us on Saturday and Sunday May 21 and 22, 2022 Fellowship Hall at Trinity Lutheran Church 909 La Cumbre Road, Santa Barbara at the corner of Foothill Road 11:00 a.m. to 4:00 p.m. Saturday Noon to 4:00 p.m. Sunday What we’ll...

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[ShadyStump]

Plus any thoughts on how trees acclimate when they have been grown from seed in mild climates and never experienced a freeze? I would think that each year is a complete reset and they should be good as long as they are gradually exposed to cold to build up the necessary sugars. I don't want to loose my awesome JBP from @Housguy. But the cork oak is going into the garage under lights!

Bonsai Club of Santa Barbara Annual Show, Santa Barbara, CA, USA, May 21-22, 2022

After a 2 year hiatus for COVID, we are back! elm forest Please Join Us on Saturday and Sunday May 21 and 22, 2022 Fellowship Hall at Trinity Lutheran Church 909 La Cumbre Road, Santa Barbara at the corner of Foothill Road 11:00 a.m. to 4:00 p.m. Saturday Noon to 4:00 p.m. Sunday What we’ll...

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This being their first REAL winter, you may very well expect some die back but not total losses. I don't think the heater cables are an awful idea in that regard, but I wouldn't bet everything on them, and wouldn't use them all season. Only turn them on when the weather man tells you to, which would only be a handful of nights all winter, and monitor the soil temps in your pots when you do.

 

[Dav4]

Plus any thoughts on how trees acclimate when they have been grown from seed in mild climates and never experienced a freeze? I would think that each year is a complete reset and they should be good as long as they are gradually exposed to cold to build up the necessary sugars. I don't want to loose my awesome JBP from @Housguy. But the cork oak is going into the garage under lights!

Bonsai Club of Santa Barbara Annual Show, Santa Barbara, CA, USA, May 21-22, 2022

After a 2 year hiatus for COVID, we are back! elm forest Please Join Us on Saturday and Sunday May 21 and 22, 2022 Fellowship Hall at Trinity Lutheran Church 909 La Cumbre Road, Santa Barbara at the corner of Foothill Road 11:00 a.m. to 4:00 p.m. Saturday Noon to 4:00 p.m. Sunday What we’ll...

www.bonsainut.com

If the tree species are cold hardy to your local climate and have been there for more than a few months, you'll be fine. My poor trees got dropped in Southern Michigan the 4th week in November after spending 13 yrs- or their entire existence- in GA. Low temps in GA prior to the move around 40 F- 2 days after getting unloaded in MI, it fell to 22 F and never got out of the 30's until March. For all intents and purposes, they remained mainly in frozen soil through the winter and did fine this year. I did lose a decent trident I started from seed but I'm convinced it was underwatering that did it in as many of my deciduous trees went crispy mid October... they weren't getting watered enough by me and it really didn't rain.

With all that being said, a really nice JBP or trident in my care here will get extra protection in the form of spending the winter in a cold room kept in the mid 30's from mid/late December thru March... at least here, I've heard we can get infrequent but significant arctic fronts that can briefly drop the temps close to -20F and that would wreak havoc with the JBP and Trident.

 

[hemmy]

With all that being said, a really nice JBP or trident in my care here will get extra protection in the form of spending the winter in a cold room kept in the mid 30's from mid/late December thru March... at least here, I've heard we can get infrequent but significant arctic fronts that can briefly drop the temps close to -20F and that would wreak havoc with the JBP and Trident.

I'd love to have a cold room facility like JudyB. It is definitely a goal in the next decade when I get too old to shuffle these trees all around. My concern is keeping the roots above 20F and the branches above 0F. I saw once source listing -10F as the damage temperature for JBP. I think I can protect from that with the block cold frame with temporary solid cover and the soil heating cables or a heat bulb if we get an artic blast.

This is my first year growing bonsai with a garage. So once I get experience with how it cools and warms during winter, I should be able to build a simply cold room with ventilation in the garage. I just have no idea how warm it will stay in winter.

I also realized that I won't have trees on the benches this winter (duh!). So the benches under partial pergola shade against the house could be stacked to use as a cold frame.

Thanks!

 

[ShadyStump]

If there's room in your garage that's definitely your better option. It will protect against temperature extremes and weather.
It should never warm up inside enough to break dormancy, especially if you have your pots sitting on the floor. Same with cold.

I've heard that pines and many other conifers do better with some sun in winter, though there seems to be allot of conflicting anecdotal evidence for this.
Anyone have any thoughts on this?

 

[Dav4]

I'd love to have a cold room facility like JudyB. It is definitely a goal in the next decade when I get too old to shuffle these trees all around. My concern is keeping the roots above 20F and the branches above 0F. I saw once source listing -10F as the damage temperature for JBP. I think I can protect from that with the block cold frame with temporary solid cover and the soil heating cables or a heat bulb if we get an artic blast.

This is my first year growing bonsai with a garage. So once I get experience with how it cools and warms during winter, I should be able to build a simply cold room with ventilation in the garage. I just have no idea how warm it will stay in winter.

I also realized that I won't have trees on the benches this winter (duh!). So the benches under partial pergola shade against the house could be stacked to use as a cold frame.

Thanks!

Placing the pots on the ground and mulching around and over the top of the pots will keep soil temps way above 20 F all winter. As far as mitigating severe damage to the canopy from severe cold, you could fashion a cold frame out of concrete block that could be temporarily covered in the event of extreme cold. A sheet of ply wood would work, as might a canvas or plastic tarp. I'd plan on leaving it open for most of the winter and plan on covering only if the temps are expected to fall into the single digits or lower. Fwiw, I left- and plan on leaving again- lots of JBP and tridents out on the patio, open to sky all winter simply mulched into my "poor man's" cold frame made from retrofitted wooden benches. I've kept evergreens inside cold rooms and garages now for 11 or 12 winters... no light to speak of from mid December until March when they might get moved outside... my new cold room does have grow lights now but they don't get turned on until the room starts to warm. All my shohin JBP were de-candled twice this summer, so no issues with vigor here.