Timing of repotting and moving outdoors

[Steinar]

I'm into my 5th month as a bonsai owner (and I'm thoroughly hooked)

The learning curve has been steep. I have two trees that are currently indoors (living room temperature, as that's all I can offer them). I will move them outdoors as soon as the conditions allow (it's currently -4C (25F) here, so expecting at least May before they can go outdoors without too much of a temperature shock). They are an elm (ulmus parvifolia) and a pepper tree (zanthoxylum piperitum). Both were sold as indoor bonsai, but I have of course later learned that they are not. They are in a southwest-facing window so they get some good hours of sunlight each day when the weather is good. The rest of their days are spent under artificial lighting, so they're averaging 15-16 hours of light each day.

If I understand correctly, plants gauge the seasons by increasing or decreasing hours of daylight, but for these guys it's pretty constant, so they might not know what season it is, or do they?

The thing is, they both need a repot (both are very root-bound and in potting soil). The pepper tree is currently finishing off a major growth spurt (loooots of new foliage), and the elm is currently growing new shoots and leaves all over the place.

So I'm looking at both a repot, and moving them outdoors, but I am wondering about the timing. "Repot in spring" I see everywhere, but that would imply that they have been dormant, which these two most definitely have not been.

When should I repot? And when should they be moved outdoors?

 

[JudyB]

As they are having growth spurts right now, I would not do any repotting until the current spurt has hardened off. And if they are really growing so well, maybe hold off repotting until the next repotting window, fall or spring after next winter. They can start going outside when frosts have stopped. Many people wind up shuffling their protected trees outside in the daytime to start the acclimatization process, then back in for nights that are too cold before frosts are over. In a window is still not full sun, so be careful to expose them too much all at once. I don’t know pepper trees, but the elm is pretty bombproof to rootwork, so you could probably do repot on that one late spring as long as it’s before your climate reaches a heat stoppage of growth. Most trees will stall growth when temps get too hot, and you don’t want that directly after a repot. Sorry for such a long post!

 

[Steinar]

As they are having growth spurts right now, I would not do any repotting until the current spurt has hardened off. And if they are really growing so well, maybe hold off repotting until the next repotting window, fall or spring after next winter. They can start going outside when frosts have stopped. Many people wind up shuffling their protected trees outside in the daytime to start the acclimatization process, then back in for nights that are too cold before frosts are over. In a window is still not full sun, so be careful to expose them too much all at once. I don’t know pepper trees, but the elm is pretty bombproof to rootwork, so you could probably do repot on that one late spring as long as it’s before your climate reaches a heat stoppage of growth. Most trees will stall growth when temps get too hot, and you don’t want that directly after a repot. Sorry for such a long post!

Hi Judy, and thanks! Not too long at all

Temperatures here rarely get very hot so that's not a problem I would think. Over 26C (77F) is rare.

So if I repot the elm in late spring, how long would it need to settle before being given the extra stress of moving outside?

 

[JudyB]

You can move the tree out whenever the weather is right for it to be out there, no matter when you repot. Just make sure to wire the tree in the pot so the wind wont move it around and break those little new roots.

 

[Paradox]

I'm into my 5th month as a bonsai owner (and I'm thoroughly hooked)

The learning curve has been steep. I have two trees that are currently indoors (living room temperature, as that's all I can offer them). I will move them outdoors as soon as the conditions allow (it's currently -4C (25F) here, so expecting at least May before they can go outdoors without too much of a temperature shock). They are an elm (ulmus parvifolia) and a pepper tree (zanthoxylum piperitum). Both were sold as indoor bonsai, but I have of course later learned that they are not. They are in a southwest-facing window so they get some good hours of sunlight each day when the weather is good. The rest of their days are spent under artificial lighting, so they're averaging 15-16 hours of light each day.

If I understand correctly, plants gauge the seasons by increasing or decreasing hours of daylight, but for these guys it's pretty constant, so they might not know what season it is, or do they?

The thing is, they both need a repot (both are very root-bound and in potting soil). The pepper tree is currently finishing off a major growth spurt (loooots of new foliage), and the elm is currently growing new shoots and leaves all over the place.

So I'm looking at both a repot, and moving them outdoors, but I am wondering about the timing. "Repot in spring" I see everywhere, but that would imply that they have been dormant, which these two most definitely have not been.

When should I repot? And when should they be moved outdoors?

I dont know much about pepper trees so I cant really advise on that but the elm should never have been inside in the first place.
It needs dormancy in the winter like all temperate trees. The fact that it is leafing out is a concern. It is going to be a very delicate procedure to get it outside when the temperatures are high enough.
You are going to have to expose it to full sunlight gradually because those leaves are not adapted to full sun right now and putting them out in full sun will probably cause them to burn.

If the leaves are fully out, its not a good time to repot. We repot most temperate trees as buds swell in spring, once the leaves are out, its too late. The reason is, repotting disturbs the roots which effects how well they take up and transport water. When a tree is in full leaf, they need the most water so compromised roots can cause a decline or even death of the tree.

So I would try to get them outside once the temperatures improve. Use this summer to plan for a better method to overwinter them than inside your house. The elm tree will only take so many years of that without proper dormancy and then it will die.

 

[Steinar]

I dont know much about pepper trees so I cant really advise on that but the elm should never have been inside in the first place.
It needs dormancy in the winter like all temperate trees. The fact that it is leafing out is a concern. It is going to be a very delicate procedure to get it outside when the temperatures are high enough.
You are going to have to expose it to full sunlight gradually because those leaves are not adapted to full sun right now and putting them out in full sun will probably cause them to burn.

If the leaves are fully out, its not a good time to repot. We repot most temperate trees as buds swell in spring, once the leaves are out, its too late. The reason is, repotting disturbs the roots which effects how well they take up and transport water. When a tree is in full leaf, they need the most water so compromised roots can cause a decline or even death of the tree.

So I would try to get them outside once the temperatures improve. Use this summer to plan for a better method to overwinter them than inside your house. The elm tree will only take so many years of that without proper dormancy and then it will die.

Thanks Paradox.

I am well aware that they should not have been inside, but that's too late to change now. Also, they are going outside when it warms up, and will of course stay there forever after.

I will be very careful to gradually expose them to sunlight.

Are you then saying that I should not repot this year? Especially the elm is in a really small pot, with poor nursery soil, so I imagine it will be a pain to water it properly during the warmer period. JudyB said the elm is bombproof to rootwork, so are there mixed opinions?

 

[Paradox]

Thanks Paradox.

I am well aware that they should not have been inside, but that's too late to change now. Also, they are going outside when it warms up, and will of course stay there forever after.

I will be very careful to gradually expose them to sunlight.

Are you then saying that I should not repot this year? Especially the elm is in a really small pot, with poor nursery soil, so I imagine it will be a pain to water it properly during the warmer period. JudyB said the elm is bombproof to rootwork, so are there mixed opinions?

You could do a slip pot, being very gentle to not disturb the roots. Doing a root reduction while the tree is in leaf is a bad idea IMO.

 

[Lilliput]

Don't think you should keep the pepper tree outside in Norway during the winter. The elm should be fine with protection, mine are. I also had no problem with a spring repot when in leaf, just gave it some extra care after. But I am no expert.

 

[Steinar]

Don't think you should keep the pepper tree outside in Norway during the winter. The elm should be fine with protection, mine are. I also had no problem with a spring repot when in leaf, just gave it some extra care after. But I am no expert.

The hardiness zones that I have found say USDA 6-8, so my zone 7ab should be covered. Do you have experience with this species?

Og hvor i Norge bor du?

 

[Steinar]

You could do a slip pot, being very gentle to not disturb the roots. Doing a root reduction while the tree is in leaf is a bad idea IMO.

I was certainly not thinking to reduce the roots (the pot is very small as it is), just give them better conditions (meaning a bigger pot). Thanks for your help!