Repotting into a bigger pot

[brp7]

When changing into a much bigger pot, does anyone repot the plant keeping the old soil and roots intact? Will the plant growth pick up without any delay? I am moving the plant from a 10x8 inch pot into an 18x16 inch pot.

Thanks!
brp7

 

[RoadManDenDron]

if I have the roots out the pot I work the roots,

We only get the opportunity to work the roots at repot time and it is very important to keep the roots in order and growing where you want them

Slip potting which is what you're describing can create problems down the line, particularly the more root bound your tree is now, after a few years in the bigger pot you will still have the smaller root bound pot shape inside your roots that will be much more lignified and harder to solve.

Speaking of repot time, I'm not sure what season it is in India but I'm guessing it is out of season and that's why you're considering a slip pot?

What is wrong with the pot its currently in? you can expect much better results at the appropriate time with a proper repot.

 

[Shibui]

There are a number of problems that can be associated with slip potting.
Sometimes it depends on species so best if we know what tree you are talking about.

If the new soil mix is different from the old mix, both water and roots find it difficult to move from new to old. You may be watering the pot really well but all the water will run through the new soil and not even wet the old soil (and roots). Soon the tree dehydrates and dies.
Occasionally the reverse happens. The inner soil stays wet because the water in it cannot move past the boundary and drain out.

If your new pot is too big the roots cannot fill it quick enough and soil soon becomes toxic. Much better to upsize pots a few sizes at a time for most species. I suspect 10x8 to 18x16 is too much in one step except maybe a strong, healthy ficus.

Always tease out some roots from the old root ball when slip potting or planting potted trees in the ground. This small root disturbance helps the new soil merge with the old and encourages some of the cut roots to grow into the new soil.

The value of slip potting is probably overestimated.
For good bonsai we value good nebari - spreading surface roots. Roots in commercially grown potted trees are notorious for being tangled and growing in circles - even right down close to the base of the trunk. If those roots are not sorted early they fuse into an unmanageable mass as the trunk and roots thicken. Much better to sort out roots early while they are still a little flexible or can be cut short.
We probably don't get much extra growth between mid summer and spring by upsizing a pot but we are very likely to make roots difficult. A few months patience will pay dividends in the long run when you wait and repot properly at the optimum time.

Kerala appears to be tropical. Most tropical species can be repotted and root pruned in summer so maybe it will be better to repot properly now?

 

[brp7]

if I have the roots out the pot I work the roots,

We only get the opportunity to work the roots at repot time and it is very important to keep the roots in order and growing where you want them

Slip potting which is what you're describing can create problems down the line, particularly the more root bound your tree is now, after a few years in the bigger pot you will still have the smaller root bound pot shape inside your roots that will be much more lignified and harder to solve.

Speaking of repot time, I'm not sure what season it is in India but I'm guessing it is out of season and that's why you're considering a slip pot?

What is wrong with the pot its currently in? you can expect much better results at the appropriate time with a proper repot.

The roots have started to come out of the drain holes. This is a crepe myrtle tree about 1.2 inches thick at the bottom. White thin roots can also be seen all over the surface as well. So I thought it was time to change it at the earliest. The season is that of monsoon rains at the peak. The best time to grow cuttings. I had tried growing cuttings of Delonix regia many times to no avail, so bought some saplings. Now in this season, I tested with some cuttings and some have sprouts.

I was under the impression that the more roots the tree has, the faster it grows. So I can get a thicker trunk in less time. Many people have advised me here in this forum to plant the tree on the ground to make it thicker sooner. However I have some constraints, so I keep it in a bigger pot.

 

[brp7]

There are a number of problems that can be associated with slip potting.
Sometimes it depends on species so best if we know what tree you are talking about.

If the new soil mix is different from the old mix, both water and roots find it difficult to move from new to old. You may be watering the pot really well but all the water will run through the new soil and not even wet the old soil (and roots). Soon the tree dehydrates and dies.
Occasionally the reverse happens. The inner soil stays wet because the water in it cannot move past the boundary and drain out.

If your new pot is too big the roots cannot fill it quick enough and soil soon becomes toxic. Much better to upsize pots a few sizes at a time for most species. I suspect 10x8 to 18x16 is too much in one step except maybe a strong, healthy ficus.

Always tease out some roots from the old root ball when slip potting or planting potted trees in the ground. This small root disturbance helps the new soil merge with the old and encourages some of the cut roots to grow into the new soil.

The value of slip potting is probably overestimated.
For good bonsai we value good nebari - spreading surface roots. Roots in commercially grown potted trees are notorious for being tangled and growing in circles - even right down close to the base of the trunk. If those roots are not sorted early they fuse into an unmanageable mass as the trunk and roots thicken. Much better to sort out roots early while they are still a little flexible or can be cut short.
We probably don't get much extra growth between mid summer and spring by upsizing a pot but we are very likely to make roots difficult. A few months patience will pay dividends in the long run when you wait and repot properly at the optimum time.

Kerala appears to be tropical. Most tropical species can be repotted and root pruned in summer so maybe it will be better to repot properly now?

Appreciate your detailed response!

The roots have started to come out of the drain holes. This is a crepe myrtle tree about 1.2 inches thick at the bottom. The growth was fast in 4 1/2 months (although not as fast as Delonix regia). White thin roots can also be seen all over the surface as well. So I thought it was time to change it at the earliest. The season is that of monsoon rains at the peak. The best time to grow cuttings. I had tried growing cuttings of Delonix regia many times to no avail, so bought some saplings. Now in this season, I tested with some cuttings and some have sprouts.

As you said, we needed flat root system for the Bonsai. However, I thought I am at the initial stage and would think about pruning the tree and roots after the trunk getting around 2 to 3 inches thick.

I was under the impression that the more roots the tree has, the faster it grows. So I can get a thicker trunk in less time. Many people have advised me here in this forum to plant the tree on the ground to make it thicker sooner. However I have some constraints, so I keep it in a bigger pot.

Would you recommend pruning some roots while I move into the bigger pot? Would it make the growth rate slow?

Thanks!
brp7

 

[Shibui]

The first place roots end up is at the drain holes. That does not mean it is root bound or will slow growth. Your tree will quite happily grow just as fast, maybe even faster , in the same pot than in a larger one.
Crepe myrtle is one I would root prune in early spring - just before new growth starts but I have not tried other time of year.

A flat root system is good for bonsai but also has an influence on trunk thickness. Lateral surface roots definitely help increase basal flare which then adds to (lower) trunk thickness. Definitely do not underestimate the capacity of lateral roots to add trunk thickness.
I can only offer my experience with field grown trees as proof but find that I get more trunk thickness and better trunk shape and better trunk taper by root pruning more often. Your choice to try it or not.

Ground growing will definitely give faster trunk increase with most species but I understand that many people do not have that as an option. Larger pots is, undeniably, the next best thing to thicken trunks. We are debating the fastest way to produce good bonsai rather than thick trunks. Definitely NOT the same.