Please Help With Cold Frame Ideas

[penumbra]

I have a coldframe that is intentionally set up in the shade to prevent drastic temperature swings. I have been using it successfully with no losses for 4, maybe 5 years.
I just installed two under my largest bonsai bench that will receive some afternoon sun. I am covering them today (or tomorrow) with a 2.5 mil white frost blanket to keep them from getting too warm and to moderate temperature swings.

 

[Deep Sea Diver]

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.

Things are looking good!

Not sure what is meant by “do branch tips have any winter hardiness”. Branches and trunks do have have much better winter hardiness then the roots.

It seems these trees haven’t yet finished with breaking down the chlorophyll. It looks like the trees are still pulling out as much of the sugars and starches as possible, although the two left trees are well on the way. Also the remaining contents in the leaves is preventing freeze damage at the levels they have experienced.

My trees are in the same state here in and out of the cold frame. We are getting consistent nighttime freezing temperatures and daily warming this past couple weeks. All the trees are looking just like yours, except a lilac and a ginkgo, both of which shed their leaves as soon as the frost kissed them!

Cheers
DSD sends

 

[hemmy]

Not sure what is meant by “do branch tips have any winter hardiness”. Branches and trunks do have have much better winter hardiness then the roots.

Thanks.

I was wondering if winter hardiness of fine branching is the same for 2 trees of the same species, if one has changed leaf color and the other is still mostly green? I’m guessing not much, since it seems like the the majority of sugars within the live branch cells comes from the cell’s own starch.

For example, these 2 tridents a few weeks ago. One was head of the other and now has mostly lost its leaves, while the other is the green leaf trident from several post back in this thread.

 

[JudyB]

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.

Concrete is a wonderful heat sink, they absorb the warmth, then release it slowly over the course of the night. I have always used concrete flooring for that reason. Also water can do the same, a jug of water (I have rain barrel) will trap and retain heat, and release it slowly.

 

[Deep Sea Diver]

Your guess is right. There are differences in each tree. I have two crepe myrtles that had The same response. One lost all its leaves the other was shocking red until last week.

There are many other items that could spur one tree to drop its leaves and not another…. work done during the year placement in the yard, etc

cheers
DSD sends

 

[hemmy]

What humidity levels do you aim for in a cold frame?

Mine have been averaging 88-90% even when opened during the day. When closed they are dark, no light penetration. They’ve been averaging 40degF and I open them up when temps will stay above 45F for several hours. Mainly for light for the conifers and air circulation. The thermometers are in the hanging in the air along the back wall, so the pots buried in wood chips have less temp fluctuations and higher humidity. We have nights above 35F in the forecast but also possible rain.