Protect young trees from freezing temps in March?

[FiggieSmalls]

Howdy folks!

This spring will be my first ever with deciduous bonsai under my care. So, I hate to ask such a basic question that I'm certain has been answered many times... But I'm looking for some "gut feelings" from those on the forums who have far more experience than myself.

Here in St. Louis, the weather has gone from temps in the 50s-60s back to freezing, and now back to high 60s once again. I'm starting to see buds emerge on some of my trees, so they appear to have mostly survived the winter! Woohoo! However, looking at the weather report a couple days ago, temps around 27 deg F were predicted for next weekend. Now the forecast is showing lows anywhere from 30-40deg over the next 10 days with highs of 46-55deg... So it kind of seems like it should be fine. The forecast has improved in this sense since I checked like 2 hrs ago... Lol. Classic St. Louis weather.

Anyway, the nature of my inquiry comes down to two questions:

1. Around what sort of temps should I consider bringing trees inside?

2. When am I okay to begin applying fertilizer?


I am in a 2nd floor apartment, with trees on my deck outside (which is south-facing, for better or worse). They get plenty of shade and are protected from wind by walls on the north and east sides, as well as some meager protection by the wooden railing (and floor) of the deck. Some of the pots are clustered toegether in large tubs of gravel.

The trees are all quite young and (I presume) fragile. They are various maple species, one purple leaf sand cherry (prunus x cisterna), and some cuttings of crabapple and satsuki azalea.

Is there any reason to be concerned about these cold temps, or no? Since they should be fairly mild and brief dips below freezing, I suppose the trees should be okay. Should I go ahead and apply fertilizer now, or wait until temps are more consistently warm?

Thanks a bunch!
Figgie

 

[Dav4]

For the trees that show no signs of breaking dormancy, no worries as far as sub freezing temperatures, but for the trees beginning to grow, you do need to be cautious, particularly if they're in small pots- age really isn't an issue imo. I'll also add that the gravel is good as it will provide some insulation from temperature swings in either direction. Swelling buds can still endure sub freezing temperatures without damage, but the root zone is likely active now and a solidly refrozen root ball could spell trouble. Frosts aren't an issue until leaves are fully opening up. Personally, I believe sun is your enemy until leaves are opening up, so I would maximize shade, thereby reducing thermal gain until leaf edges are visible.

 

[Carol 83]

I am only 30 or so miles east of St.Louis but keep my deciduous and Satsuki's in a detached, unheated garage. Listen to @Dav4 he has a great deal of experience in different climates and knows what's what.

 

[FiggieSmalls]

For the trees that show no signs of breaking dormancy, no worries as far as sub freezing temperatures, but for the trees beginning to grow, you do need to be cautious, particularly if they're in small pots- age really isn't an issue imo. I'll also add that the gravel is good as it will provide some insulation from temperature swings in either direction. Swelling buds can still endure sub freezing temperatures without damage, but the root zone is likely active now and a solidly refrozen root ball could spell trouble. Frosts aren't an issue until leaves are fully opening up. Personally, I believe sun is your enemy until leaves are opening up, so I would maximize shade, thereby reducing thermal gain until leaf edges are visible.

This is tremendously helpful, thank you!

I guess I never understood that the danger to the tree is primarily due to the freezing itself, not just the exposure to low temps...

And since you say to shade them, I suppose that is also to help the trees stay in dormancy a little longer for the protection that provides

 

[Dav4]

For a fully dormant, cold hardy tree, frozen soil and deep sub freezing temperatures shouldn't be an issue, but that all changes once growth starts. Brent at Evergreen Gardenworks has forgotten more about the physiology of bonsai then I ever knew. Here are two great articles on winter and bonsai... https://www.evergreengardenworks.com/overwint.htm
https://www.evergreengardenworks.com/frzekill.htm and many more on other subjects to peruse... https://www.evergreengardenworks.com/articles.htm.

 

[rockm]

This is tremendously helpful, thank you!

I guess I never understood that the danger to the tree is primarily due to the freezing itself, not just the exposure to low temps...

And since you say to shade them, I suppose that is also to help the trees stay in dormancy a little longer for the protection that provides

Watch these:

Read these:

Over Wintering Bonsai

Freeze Damage in Woody Plant for Bonsai

 

[Glaucus]

30F is barely below freezing. Even trees that show signs of waking up are probably ok with 30F. But make sure to check minimum ground temperatures.

Late spring freezes are generally only about trees that have woken up and are budding out. If they look dormant, they likely are. And then they aren't going to get damaged by 30F when they didn't get damaged at -5F.
Doesn't mean that a tree will be happy with -5F in March when looking fully dormant. But you get the point.

Those that have new buds, those may be killed by frost, depending on the species, depending on how moist it is, depending on the temperatures.

 

[Kanorin]

I am also in St. Louis and am not looking forward to the nights that are predicted to go below 32 F (Luckily the forecast is a little more favorable than it was a few days ago). Good advice in the several posts above me! To summarize:

• Some of my trees have already leafed out, when it drops below freezing I'll be moving those to my garage which stays a few degrees warmer (if I didn't have a garage, I'd probably bring them inside overnight and put them in the coolest part of my house).
• Some of my trees have not leafed out, but the buds are swelling and I have repotted them. For those I'll either put in garage or mulch them in (keep the roots above freezing).
• The remainder of my trees which are still dormant and I haven't touched them - I'll leave them be where they are.

 

[HorseloverFat]

Just here to appreciate your screen name with loud, guttural laughter.

 

[Gaitano]

Also remember in St Louis, the temps may dip below freezing overnight, but generally don’t stay there for more than a few hours and warm up during the day. Worry comes when the below freeze is extended for a few days and never rises above. Apartment life is tough. Like Kanorin mine generally live in the garage. My Amur, and Kashima maples have leafed out as well as the crabs. Time to start the shuffle. In at night, out in dappled shade during the day.

 

[dbonsaiw]

My favorite trees this time of year are the ones that don't need a repot and can simply stay in the mulch pile until there's zero chance of frost. Even if they are waking up and we have some 30s I'm not concerned. It's the trees that have been repotted that cause me stress. They go into the garage where its warmer and then I have to do this silly dance when they wake up. It's when I remind myself why I shouldn't be building 14x14x5 inch grow boxes out of wood.

 

[bwaynef]

I've had my greenhouse and garage packed for several days. Lows will be well above freezing, so I've unloaded what I could be bothered to unload, though nothing is back on their benches yet. We're going to dip to just below freezing again in a few days so they're going back into storage for a few days ...in a few days. Meanwhile, they'll soak up photons.

 

[FiggieSmalls]

Just here to appreciate your screen name with loud, guttural laughter.

 

[FiggieSmalls]

Thank you all for sharing so much knowledge!!!

As an aside, today I picked up a couple gems from a local nursery

And temps are going to be as low as 20 deg F this weekend...

The little maple is actually growing leaves already so I think I'm going to take it inside. I do have a bit of outdoor storage like a closet on my deck so maybe I can stick it in there. But is it really so bad to just bring it indoors for a couple days?

 

[FiggieSmalls]

Thank you all for sharing so much knowledge!!!

As an aside, today I picked up a couple gems from a local nursery View attachment 477083

And temps are going to be as low as 20 deg F this weekend...

The little maple is actually growing leaves already so I think I'm going to take it inside. I do have a bit of outdoor storage like a closet on my deck so maybe I can stick it in there. But is it really so bad to just bring it indoors for a couple days?

From the research I have done (including reading some of the articles suggested by yall!) I don't see a reason to suspect a couple days inside would do any harm to the tree(s). I'm not going to do anything stupid. Generally I will try to simulate natural conditions and avoid creating some "shock" to the trees. E.g., when I do put them back outside I'll try to do it at the warmer part of the day and do what I can to make the temperature swings gradual.

But someone at the nursery told me I shouldn't bring it inside because it will "disrupt its natural cycle." So I'm kinda wondering what specifically she is referring to that would be a disruption. Is she thinking the blue light from my TV is going to throw off my tree's circadian rhythm?

Thanks all,
Figgie

 

[Michigan Tree Murderer]

Just here to appreciate your screen name with loud, guttural laughter.

Figgie Figgie Figgie can't you see? Sometimes your words just hypnotize me.

 

[HorseloverFat]

Figgie Figgie Figgie can't you see? Sometimes your words just hypnotize me.

Notorious F.I.G.

 

[HorseloverFat]

From the research I have done (including reading some of the articles suggested by yall!) I don't see a reason to suspect a couple days inside would do any harm to the tree(s). I'm not going to do anything stupid. Generally I will try to simulate natural conditions and avoid creating some "shock" to the trees. E.g., when I do put them back outside I'll try to do it at the warmer part of the day and do what I can to make the temperature swings gradual.

But someone at the nursery told me I shouldn't bring it inside because it will "disrupt its natural cycle." So I'm kinda wondering what specifically she is referring to that would be a disruption. Is she thinking the blue light from my TV is going to throw off my tree's circadian rhythm?

Thanks all,
Figgie

Well... Besides altering light cycles and promoting flowering (which MOST LIKELY won't happen)... I think you will be ok.

It takes about a month for my ficus to "go into molasses mode for 'simulated Tropical winter'" in my rooms, here.. and that process had realistically, already been commenced by the outdoors.

About 4 weeks of temperatures pushing into it's "threshold"... (For temperates, this is 40dF, and I've found trops to be between 50-53dF to successfully "alter themselves).

I DON'T think that a week or two, with erratic light, and warmth, will throw too big a wrench in your works.

 

[leatherback]

I see that all my local trees handle an overnight frost without an issue. So my bonsai need to deal with it too. I have had japanese maples in 4-6 leaf stage in spring get an overnight frost and no damage the next day.

I feel people keep their trees too warm in winter (Shelters) and therefor they wake up very early. If you keep your trees outside normally they will only in exceptional cases be damaged. THe individual night frost will not really be an issue.

That is my view.