Spring bonsai shuffle

I remember Ryan has said this before, but what is the minimum temperature that would trigger us to protect trees like a normal deciduous in the spring? Thinking of trees that have leafed out specifically.

Was it 34 degrees F? Bonus points if you can name the video that it is in. There are so many videos that it is hard to dig in to find this one piece of knowledge.

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I don’t know the temperature or video, but will comment that you can get frost of surfaces at air temperatures well above freezing. If the sky is clear and the humidity level is fairly low, radiation cooling to space will result in frost. I have seen it at temperatures in the 40-45 F (4.4 - 7.2C) range. That is one of the reasons frost covers are used with early spring crops (in addition to preserving a small amount of ground heat). As a result, protecting your delicate trees from the open sky on cool evenings is also a good idea.


for me, if the tree is climatized to full exposure, frosts on boxwoods, azaleas, pines, firs, junipers and other evergreens are ok down to 30 degrees for a couple hours as long as they haven’t been repotted that season. I generally put my repotted trees on a heat mat under a structure for 3 weeks then off the mat for 2 before getting the full exposure.

Deciduous trees that have bud swell are also left out to that overnight temp.

Larch are fine until I see the separation of the needles - then I typically put them under an unheated cover structure that has 2 fans to circulate air for sub-30 overnight temps.

Once the buds on the deciduous trees open up, they will get moved under cover when overnights forecast to below 32 degrees depending on my read of my own microclimate vs what the phone weather app says. larch, crab apple, and others can take a couple hours of sub-freezing temps fine, but if that temp is sustained for 3+ hours well before dawn, I protect when possible.

all my trees for the past 5 years have overwintered in an open sided hoop structure to protect from all the Seattle rain, but as overnights creep into the upper 30’s i will bring my pines and needle evergreen trees out and they will stay unless we get a cold snap in the mid-lower 20’s.

I haven’t lost any trees from spring frost that I can recall – the more cold they experience the better to keep them slowed down, but I have had way more issues with letting things leaf out in a protected enclosure then burning from sun/wind, so I try to let them get as cold as I dare depending on the overall health.

best rule of thumb I used when starting out was if I was worried about something and I had the time to do something about it I would do it – better safe that sorry. if that meant and emergency tarp over the trees, or rolling down the sides of the hoop and putting a heater in there I would do it. Over the years of that I have modulated my response and now I move trees less, but part of the fun is handling the trees as they start to wake up!

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great insight! I am in the situation right now where a trident has swelling buds, but the temps are expected to go well below freezing this weekend. Its currently in the low 30s and I still have it outside. I think I will be moving it to overnight cover for the next week, though. Since there are supposed to be freezing temps in the day time, should i put the tree back to over-winter mode until the cold weather passes? Or will the swelling buds need more sunlight than that? What a weird spell of weather for our trees!!

if the daytime highs are that cold, i would consider putting them back in overwinter mode through the weather anomaly. fans are great at keeping air circulation going, so as to prevent any specific area getting too cold.

we had a week like that about 3 weeks ago (overnights high teens, low 20’s with daytimes just hitting mid 30s) and i moved everything but my largest trees back under cover with the sides down until it normalized. buds don’t need sun and wouldn’t be harmed by a few days without in a spring shuffle context.

prolonged sub freezing temps, or deep spikes in cold temps are what does the damage IMO.

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this is very helpful @Jhunsperger

I really appreciate it! Back to winter mode it goes for the low temps.

Hi all,
all I know is, if there are freezing temperatures you have to protect your trees. The trees have only two modes during the winter. From autumn to winter the trees turning into winter mode by reacting to temperature and daylight length. There are in this mode until the temperature rises up for a longer time and the days have passed a limit of daylight length. From this point on the tree can’t return into the winter mode. Now the tree has not winter protection by its own and you have to protect.

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Ok, wow. The internet may be ones and zeros, but the real world isn’t that binary. Weather isn’t linear, and if trees were that locked into growth than any weather anomaly would…… nevermind… out. Do what u like, I do just fine!

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