Please Help With Cold Frame Ideas

[hemmy]

btw prepared for critters in each space?

Nope and I’m terrified about them. The rodents and rabbits were my welcome party this summer. The rodents gnawed on my 1/4” irrigation lines and the rabbits went after some trunks. I’ll lay enough traps to look like a cartoon, but I’m not real big on baits if they impact higher predators.

Anyone have good trunk wraps? Maybe just aluminum foil?

 

[Dav4]

Nope and I’m terrified about them. The rodents and rabbits were my welcome party this summer. The rodents gnawed on my 1/4” irrigation lines and the rabbits went after some trunks. I’ll lay enough traps to look like a cartoon, but I’m not real big on baits if they impact higher predators.

Anyone have good trunk wraps? Maybe just aluminum foil?

I just use snap traps and check them every day. At the beginning, I'll kill a mouse or two nightly for 2-3 days but eventually the vermin traffic decreases... but keep those traps primed right through the winter. Also, don't fill the cold frame until late November or else the mice will overwinter with your trees.

 

[hemmy]

Also, don't fill the cold frame until late November or else the mice will overwinter with your trees.

Well that didn’t work! We are forecasted for 10-20degF colder lows than our average. I couldn’t wait any longer. I know mice can make it through very small openings, but my box is pretty tight. It is filled and traps are set!

 

[hemmy]

Comments and criticism welcome. Cold frame box is built and loaded. If we get a warm snap, I’ll paint it to match the house. It is partially on concrete and a gravel bed. Still needs a ground anchor it is not tied to the house. Not pictured is the 2” rigid foam base under the 1/2” AC2 plywood. All wood is AC2. Footprint is 4’x8’, 5’ tall in back to 3’ in front. Small door on side.


There is 1/2” rigid roam against the house, then plywood, studs, 1/2” foam inside back wall of box. All the other foam is 2”.

 

[hemmy]

Unfortunately there is no power on this side of the house, so heat won’t be an option this year. Box was loaded during 35degF and overnight outdoor lows hit 25degF, while the box only got to 32.7degF. I have about 1ft of wood chips, but probably need another 1ft or more?

For those below 0deg arctic blasts, I was going to cover it with plastic and stack concrete blocks or little square straw bales(?) around it. Can I keep it above 15-20F if the outside is below 0deg for 12hrs?

 

[ShadyStump]

Thermal mass is the general idea here. The more mass, the longer it takes to be change temperature. So, your construction looks great, but I wouldn't have insulated the bottom, just put down some gravel for drainage. The mass of the ground would radiate residual heat into the box.
What's done is done, though, and I think you'll be ok. Once you mulch around the pots, you'll have a good deal of mass and insulation.

Frankly, the best way to deal with harsh winters is simply to expect some level of loss. Monitor your temps closely this season, maybe make some notes, and apply lessons learned next year.

 

[Dav4]

Unfortunately there is no power on this side of the house, so heat won’t be an option this year. Box was loaded during 35degF and overnight outdoor lows hit 25degF, while the box only got to 32.7degF. I have about 1ft of wood chips, but probably need another 1ft or more?

For those below 0deg arctic blasts, I was going to cover it with plastic and stack concrete blocks or little square straw bales(?) around it. Can I keep it above 15-20F if the outside is below 0deg for 12hrs?

The KISS approach is so important here and I think your trees will be fine with what you've done already, assuming they're cold hardy to your zone as landscape material. If anything, I'll agree with Shady and say I think the insulation is overkill... without it, you're still providing much more protection than I will and I'm in a colder zone. The key is protecting the roots from temp extremes and you've done that with the mulch. The canopies of your trees, even though they've been in SoCal forever, should be able to handle temps in the teens or even colder without issue, particularly since wind won't be a factor. I'd water the mulch down then encourage everything in your cold frame to freeze and try to keep it that way as long as you can. Healthy trees that are cold hardy to your locale will happily sleep through winter there if they stay cold long enough. Be vigilant with vermin patrol!!!

 

[JudyB]

Yeah looks pretty good, I would say if you do get some insane long term cold windy temps, you could do a run of outdoor christmas lights in there, that will give you some spread out warmth. Or a small heat cable on a thermostat would work. I always just used a bare bulb when I had an outdoor mulch bed with some sides, but that looks too tight to do that with your box.

 

[hemmy]

but I wouldn't have insulated the bottom, just put down some gravel for drainage. The mass of the ground would radiate residual heat into the box.

Thanks for the feedback. That makes a lot of sense. I was just concerned because half of it was on concrete and I thought it would lose heat to concrete.

 

[hemmy]

cold hardy to your zone as landscape material.

Thanks. But of course, I’m pushing that zone envy. JBP and JRP should be good. The valley oaks are pushing it. But they are just 2yo and no big loss.

 

[Deep Sea Diver]

Well done!

Experimenting is a good thing. imhe starting with overkill is much better the underkill. We started with underkill, now it’s all about keeping the trees a healthy as possible all winter with little to no damage. So we take pride in ensuring our trees are well cared for throughout the winter. That way we are certain to have healthy trees that can be worked for a full bonsai year instead of seeing exposed, tender and weaker trees dying back..

That said I concur insulation on the flooring could be a hindrance to proper drainage and enhance fungal issues. Likely the time to be concerned would be the “bridge times”. (In fall and spring or when temperatures inside never get down to freezing at night and above 45 during daytime... or during warm snaps.) Opening the covers will do a lot to help keep this issue at bay.

Once the trees go through a couple winters you will learn a lot to help inform your future modifications.

btw: Do you have a crawl space under the house or is it slab built? If the former I can see a future fun time commando crawling a run of Romex 12-2/g to the cold frame needing electrical service. Been there done that too many times to count!

Looking forward to seeing how the trees come out of winter next year.

cheers
DSD sends

 

[ShadyStump]

Thanks for the feedback. That makes a lot of sense. I was just concerned because half of it was on concrete and I thought it would lose heat to concrete.

I had this same sort of concern last year, and learned the hard way. NOT light losses.
Concrete might not be solid earth, but it's the next best thing. It'll hold temperature allot better than you're pots.

 

[hemmy]

(In fall and spring or when temperatures inside never get down to freezing at night and above 45 during daytime... or during warm snaps.) Opening the covers will do a lot to help keep this issue at bay.

Thanks. I’m expecting to have to open it most days when it gets warm as you said. But now I have to open it since a trident and a cedar elm are barely turning color.

 

[Vinnie Charity]

I always put my trees huddled together onto a concrete slab each year to overwinter them and I don't use mulch, though I do pack leaves between the pots to keep the wind from blowing in between them.

The key is to keep the wind off of the pots and trees because that will dry them out and can cause the water in the pot to freeze almost instantly if it's cold enough outside (think wind chill).

The trees are not covered with anything and I'm in zone 7. I've never lost a tree while overwintering using this method.

 

[hemmy]

The trees are not covered with anything and I'm in zone 7.

Richmond sounds very nice! Almost sub-tropical sounding after I was outside raking leaves all day! I looked our record lows and even just going from 6b to your 7, the average winter lows are 10F colder and the record lows are even more extreme. Our record lows are all below negative 20F for Dec. to Jan. there are only 3 months of the year that have never seen a hard freeze!

 

[Vinnie Charity]

Richmond sounds very nice! Almost sub-tropical sounding after I was outside raking leaves all day! I looked our record lows and even just going from 6b to your 7, the average winter lows are 10F colder and the record lows are even more extreme. Our record lows are all below negative 20F for Dec. to Jan. there are only 3 months of the year that have never seen a hard freeze!

Richmond isn’t too bad. It got as low as 17°F last winter and my trees didn’t skip a beat. I have experienced temperatures as low as 0°F and it hurt to breathe. I can only imagine that I would need better protection for the trees at those low temperatures, so they’d go into my unheated woodshop for protection.

In my opinion, my partially buried concrete slab has a more consistent temperature than the air, so with the trees huddled together, and the leaves packed between the pots, a lot more of the ground’s warmth helps create slower fluctuations in the pot’s temperatures.

This would probably work even better on the ground, but I think the pots would stay too wet. The concrete slab provides far more superior drainage.

 

[hemmy]

btw: Do you have a crawl space under the house or is it slab built? If the former I can see a future fun time commando crawling a run of Romex 12-2/g to the cold frame needing electrical service.

Unfortunately, no crawl space or basement. Slab house and vaulted ceilings. I’m not super excited to be back in tornado alley without a basement. On the electrical, the panel is just on the other side of the garage wall. So it will be an easy fix to get power to that spot.

 

[bwaynef]

Is that a drier vent I see in the back corner of your cold frame?

 

[hemmy]

Here’s another question on winter hardiness. One Trident Maple, a Zelkova, and a Cedar Elm all still have pretty green leaves. They stayed out for ~32F, but went in for sub-25F and I’ve been opening the top for sunlight. If the trees haven’t broken down the chlorophyll, but have experienced cold temps down to short freezes; do the branch tips have any winter hardiness? I assume so, since the leaves didn’t wilt and fall off. I had a gingko that was only slightly greenish-yellow and those leaves wilted with the freeze.

 

[hemmy]

Is that a drier vent I see in the back corner of your cold frame?

Yes, a dryer vent. But it is outside the frame and ~3ft from the cold frame. The only building code I could find was 3’ from doors and windows to the house for moisture and lint. I believe the current space provides sufficient airflow to take away the heat. I ran the dryer with my thermometer in that corner of the frame and didn’t see a temp change.

I briefly entertained the idea of making it so I could run the hose into the frame for those polar vortex, artic chills. But besides being against code, probably also wouldn’t be good for the trees with moisture and hot blowing air.