Late summer repotting

[Forsoothe!]

When a lot of these "bonsai facts" pop up I like to compare them to how we do things at the nursery where I work. Especially since for us, doing something wrong horticulturally can cause thousands to millions of dollars in losses.

Below is a report of plants we re-potted in the past year. Note that most of these are not are-rooted but most will have at least root trimming.

FWIW, I ran this report for only "container" plants (which means no ball-and-burlap, no perennials, and no annuals).

Note: it was too big to post the exact dates and full names so here is the raw report for anyone interested: https://bit.ly/2ZEhW6T

I suspect almost all are potting-up which is even less stressful than slip-potting, and everything before April 1st in Ohio is in a greenhouse. Not exactly comparable to removing half the roots and plopping it on the patio...

 

[BobbyLane]

When a lot of these "bonsai facts" pop up I like to compare them to how we do things at the nursery where I work. Especially since for us, doing something wrong horticulturally can cause thousands to millions of dollars in losses.

Below is a report of plants we re-potted in the past year. Note that most of these are not are-rooted but most will have at least root trimming.

FWIW, I ran this report for only "container" plants (which means no ball-and-burlap, no perennials, and no annuals).

Note: it was too big to post the exact dates and full names so here is the raw report for anyone interested: https://bit.ly/2ZEhW6T

you have access to some great species for bonsai! i'd be like a kid in a sweetshop. with a bit of field growing you could have a nice little conveyor belt going there....

 

[Leo in N E Illinois]

@Igor. T. Ljubek

For the species I listed, I have higher survival rates with late summer repotting than spring repotting. This is particularly true with JBP. Long experience, near or more than 15 years, I have a better survival rate for JBP than spring. I believe it is because my long cool spring micro-climate is not acceptable for JBP.

 

[Cable]

I suspect almost all are potting-up which is even less stressful than slip-potting, and everything before April 1st in Ohio is in a greenhouse. Not exactly comparable to removing half the roots and plopping it on the patio...

Most are being put in a larger size, yes, but as I said there is often root pruning. No, most do not go into a greenhouse. Some do go into poly-houses early in the season but the plastic is soon cut off. For most of the year they're just set on the ground in full sun.

you have access to some great species for bonsai! i'd be like a kid in a sweetshop. with a bit of field growing you could have a nice little conveyor belt going there....

You have no idea. lol. I have SO MANY plants and most were free or very low cost. Of course, a lot of them will take quite a while to develop but it gives me a lot of room to experiment.

 

[0soyoung]

@Igor. T. Ljubek

For the species I listed, I have higher survival rates with late summer repotting than spring repotting. This is particularly true with JBP. Long experience, near or more than 15 years, I have a better survival rate for JBP than spring. I believe it is because my long cool spring micro-climate is not acceptable for JBP.

And what are the typical conditions when you do this? Daily hi/low temperature, sunny/cloudy skies, rH range or typical dew points.

 

[Cosmos]

I don't know...people have been doing most of their repotting in spring forever. I've done all my repotting in spring and have never lost a tree. So why would I repot at this time of year, especially considering all the warnings about how the weather has to be perfect, you can't cut any roots, etc etc?

April (and even May) is a total crapshoot here, this year is a good illustration of that. August is actually much more, much much more predictable weather-wise, fewer scorching hot days, cooler nights than July, etc. Surely it’s the same for you guys in Rochester?

And people have been sharing how much they have cut roots. Seems like a lot of conifers can take significant root reduction at this time of year.

 

[Leo in N E Illinois]

The only reason I can see is if I am unable to get all the repotting done in the spring. And that indeed happened this past spring, so I have a bunch of trees that I wanted too I wonder if he provides any extra protection for late summer repots? @Leo in N E Illinois , you say you do "appropriate" root work during late summer repottings, do you provide any additional winter protection? Would you say you've had more/the same/fewer losses on repots done this time of year versus spring?

Ultimately I think one just has to experiment and be prepared for some losses in order to fine tune any non-spring repotting, regardless of what Walter or anyone else says.

If spring repotting has been near 100% successful for you, absolutely no reason to try anything else. Seriously, don't bother to experiment.

My spring can be prolonged and cool to cold. If East wind comes in off the Lake, I can have week long periods where daytime highs will be in the low 50's. Last frost can be May 1, yet my first 70+F day might not happen until June 21. One year the east wind was so frequent that I still had a redbud in bloom 4th of July. JBP repotted in May, stalled and then failed to bud out, eventually died. Usually July I get enough heat, JBP get growing.

I found waiting until August solved the cold spring issue. I always protect JBP in winter. So root work is not an issue.

Species like Jack pine, I have not provided temperature protection in winter even after major root work. So far so good. Sample size of 2. I went with August because I felt that Vance Wood's calendar for mugo pine should work for jack pine.

Chaenomeles I had lost a few after spring repots. Switched to August and have not lost any.

Frankly, I'm busy in spring with the blueberry farm, August is my slow period. Any bonsai work I can shuffle into August is a relief to me.

 

[coh]

If spring repotting has been near 100% successful for you, absolutely no reason to try anything else. Seriously, don't bother to experiment.

My spring can be prolonged and cool to cold. If East wind comes in off the Lake, I can have week long periods where daytime highs will be in the low 50's. Last frost can be May 1, yet my first 70+F day might not happen until June 21. One year the east wind was so frequent that I still had a redbud in bloom 4th of July. JBP repotted in May, stalled and then failed to bud out, eventually died. Usually July I get enough heat, JBP get growing.

I found waiting until August solved the cold spring issue. I always protect JBP in winter. So root work is not an issue.

Species like Jack pine, I have not provided temperature protection in winter even after major root work. So far so good. Sample size of 2. I went with August because I felt that Vance Wood's calendar for mugo pine should work for jack pine.

Chaenomeles I had lost a few after spring repots. Switched to August and have not lost any.

Frankly, I'm busy in spring with the blueberry farm, August is my slow period. Any bonsai work I can shuffle into August is a relief to me.

April (and even May) is a total crapshoot here, this year is a good illustration of that. August is actually much more, much much more predictable weather-wise, fewer scorching hot days, cooler nights than July, etc. Surely it’s the same for you guys in Rochester?

And people have been sharing how much they have cut roots. Seems like a lot of conifers can take significant root reduction at this time of year.

Spring can definitely be a crapshoot weatherwise here as well. Sometimes (most of the time it seems) the large scale pattern just creates a lot of cool/cloudy/wet weather. Other times we get the same type of cold lake breeze that @Leo in N E Illinois mentions, except here it's a N wind off Lake Ontario. It can be in the 60s and 70s 10 miles south of here while we're in the 40s. So while I've never lost a tree to spring repotting, sometimes the weather forces me to do all my repotting in a short window and it doesn't all get done. Thus my interest in late summer repotting. Usually trees can wait another year but sometimes they really shouldn't. Just the other day I had to a repot on a trident group that was having trouble. I removed a large amount of matted roots from the bottom and loosened up the main root mass but didn't do much else. Put it in a slightly larger container with the plan of returning to it in the spring.

My JBPs get protected as well, I allow the temps to fall to about 26/27F for them but they are still frozen for long periods. I don't know if that is enough protection for a JBP that has had significant root work in the fall but I only have a couple of specimens so I can usually fit them into the spring repotting schedule. It's the deciduous trees that often all start budding out at once, thus creating a repotting crisis LOL.

I do wind up shuffling some newly repotted trees in and out of the barn and garage when we get cold spring nights...shifting some of the repotting to this time of year would eliminate that problem!

 

[Cable]

If spring repotting has been near 100% successful for you, absolutely no reason to try anything else. Seriously, don't bother to experiment.

My spring can be prolonged and cool to cold. If East wind comes in off the Lake, I can have week long periods where daytime highs will be in the low 50's. Last frost can be May 1, yet my first 70+F day might not happen until June 21. One year the east wind was so frequent that I still had a redbud in bloom 4th of July. JBP repotted in May, stalled and then failed to bud out, eventually died. Usually July I get enough heat, JBP get growing.

I found waiting until August solved the cold spring issue. I always protect JBP in winter. So root work is not an issue.

Same here. This year in particular I was wondering if it was EVER going to warm up. Lol.

I re-potted 30 junipers over the past couple of weeks and so far none are showing any sign of problems. I also did 20 or so back in June and they were all fine, too.

This included root work as moved from a nursery pot to a bonsai training pot. I did leave the shin intact, though.

Except one. That one got bare rooted because I wanted to see what would happen.

 

[Forsoothe!]

I think we are seeing anecdotal evidence of lots of people doing repotting in very direct contravention of the old guard's wisdom.

 

[0soyoung]

Ironically, 'old guard' doesn't equal 'old guys'.

 

[Jorow99]

Let me throw some speculation out there.

We know trees grow roots in the cooler weather of the fall. They are usually done putting out new growth by early fall in my experience, and their current root mass has sustained the tree through the summer, so they are building roots in advance of next spring's additional growth. If we root prune in spring, we have just cut off everything the tree spent resources building last fall.

When certain species thicken in the fall they are making a particular type of wood with smaller vessels and tracheids than spring wood that resist cavitation (embolism/air bubbles) caused by freezing, so cutting off roots could cut into the trees ability to add on to this new wood, which would reduce cold hardiness.for some trees (mainly angiosperms) this single new layer of fall xylem is the only thing the tree uses to transport water in the spring, as the larger vessels of the spring wood is filled with air bubbles. Also, the more sugars and starches the tree uses to build roots in the fall, the less it can use for anti-freeze.

Walters method seems to focus on not root pruning, therefore not hindering the trees ability to prepare itself for the winter much while giving it space to grow new roots.

Obviously "it depends" on the species as well. I'll share this chart from the book Applied Tree Biology.

How would I apply this if I was only using this information? Since I live in a place with pretty cold winters, I wouldn't root prune any angiosperms/ring pourous species in the fall so that they have enough vascular tissue to propel their growth in the spring and prevent cold damage. Gymnosperms are naturally more cold and drought tolerant in general partly because of the smaller tubes in their vascular tissue, and they don't depend on a half season of wood to supply their water in the spring. so let them use their stored sugars in the fall to build roots instead of cutting off their new roots next spring.

 

[Saddler]

I am wondering how a fall repotting affects the first flush of growth in spring on different trees? Possibly shorter internodes on maples? I have had various results with spring repotting and I often wonder how to get more consistent results. I have had good results with my VERY old collected in early September spruce. I might have to push the envelope on a few of my healthiest trees to start to see what happens.

 

[Forsoothe!]

Let me throw some speculation out there.

We know trees grow roots in the cooler weather of the fall. They are usually done putting out new growth by early fall in my experience, and their current root mass has sustained the tree through the summer, so they are building roots in advance of next spring's additional growth. If we root prune in spring, we have just cut off everything the tree spent resources building last fall.

When certain species thicken in the fall they are making a particular type of wood with smaller vessels and tracheids than spring wood that resist cavitation (embolism/air bubbles) caused by freezing, so cutting off roots could cut into the trees ability to add on to this new wood, which would reduce cold hardiness.for some trees (mainly angiosperms) this single new layer of fall xylem is the only thing the tree uses to transport water in the spring, as the larger vessels of the spring wood is filled with air bubbles. Also, the more sugars and starches the tree uses to build roots in the fall, the less it can use for anti-freeze.

Walters method seems to focus on not root pruning, therefore not hindering the trees ability to prepare itself for the winter much while giving it space to grow new roots.

Obviously "it depends" on the species as well. I'll share this chart from the book Applied Tree Biology.

How would I apply this if I was only using this information? Since I live in a place with pretty cold winters, I wouldn't root prune any angiosperms/ring pourous species in the fall so that they have enough vascular tissue to propel their growth in the spring and prevent cold damage. Gymnosperms are naturally more cold and drought tolerant in general partly because of the smaller tubes in their vascular tissue, and they don't depend on a half season of wood to supply their water in the spring. so let them use their stored sugars in the fall to build roots instead of cutting off their new roots next spring.

This is not clearly stated for non-biologists. Please restate for those of us who really want to understand it. Thanks.

 

[0soyoung]

When certain species thicken in the fall they are making a particular type of wood with smaller vessels and tracheids than spring wood that resist cavitation (embolism/air bubbles) caused by freezing,

The fault in this argument is that roots don't make wood, nor do they make the sugar from which wood is made.

 

[Jorow99]

This is not clearly stated for non-biologists. Please restate for those of us who really want to understand it. Thanks.

Let me try to clarify. Tracheids and vessels are the little tubes inside the wood that carry water from the roots to the foliage. Some species have very large tubes to transport a lot of water and grow quickly in the spring. Some have very small tubes to help them survive freezing and drought, but they can't transport water as quickly as the trees with the large tubes.

If the tree experiences drought, the foliage keeps trying to pull water out of the tree, and since there is no water for the roots to take up, it creates a negative pressure inside the tubes. If the pressure becomes too negative, gas bubbles can be pulled in and cause an embolism. If a tracheid or vessel gets an embolism it stops functioning and stops conducting water.

In the winter, water stored in the tubes can freeze, and when this happens gas that is dissolved in the water forms air bubbles, which can cause a permanent embolism if the tubes are too large. Small tubes are more able to redissolve the bubbles come spring.

The type of connections between the tubes also plays a major role, as they can prevent bubbles from transferring between tubes if they are small enough.

Gymnosperms (think conifers) and some angiosperms (flowering plants/deciduous) both form wood that has large tubes in the spring to conduct water quickly to compete with other trees. This wood, with it's large tubes, can get embolisms in the winter more easily. To balance this, they will form wood with small tracheids or vessels in the fall, and the difference between these two types of wood is what gives it it's rings. This wood with smaller tubes is also what gives gymnosperm wood the majority of it's mechanical strength.

That being said, the number of rings that are still capable of transporting water largely depends on the species and the individual. It can be anywhere from 1 ring in some oaks to 70 rings in red maple. Since conifers have smaller, more durable tracheids they usually have a decent number of rings that are still capable of moving water.

 

[Jorow99]

The fault in this argument is that roots don't make wood, nor do they make the sugar from which wood is made.

But aren't roots also made from the sugars?

 

[0soyoung]

But aren't roots also made from the sugars?

Indeed, as it just about all tissues in trees. Cell walls contain cellulose, a sugar polymer. Unlike starches that the tree can converted back into sugars, cellulose cannot.

The citation I originally meant to respond to is

When certain species thicken in the fall they are making a particular type of wood with smaller vessels and tracheids than spring wood that resist cavitation (embolism/air bubbles) caused by freezing, so cutting off roots could cut into the trees ability to add on to this new wood,

It is an interesting line of argument, but seemingly presented as roots are responsible for making late wood. Maybe I was just confused by the semantics you chose - it is indeed nerve wracking to pick all the right words in all the right order when one's aim is to present a simple, but accurate, picture.

 

[Jorow99]

Indeed, as it just about all tissues in trees. Cell walls contain cellulose, a sugar polymer. Unlike starches that the tree can converted back into sugars, cellulose cannot.

The citation I originally meant to respond to is

It is an interesting line of argument, but seemingly presented as roots are responsible for making late wood. Maybe I was just confused by the semantics you chose - it is indeed nerve wracking to pick all the right words in all the right order when one's aim is to present a simple, but accurate, picture.

My argument was meant to be that the tree may have to reduce the amount of fall wood it adds in order to repair and rebuild roots using it's limited amount of stored energy, if roots are reduced during a fall repot. I'm only speculating on that though

 

[sorce]

My argument was meant to be that the tree may have to reduce the amount of fall wood it adds in order to repair and rebuild roots using it's limited amount of stored energy, if roots are reduced during a fall repot. I'm only speculating on that though

If true then, one would be less likely to have wire bite in the Fall of a repot, correct?

This is good ACTUAL information to ponder.

Thanks!

Sorce