I would like to know if it is possible to encourage new leaves to sprout from bare thicker branches (as in the following photo):
If you lived in Florida, SoCal, or the tropics, or the tree was any other Ficus than benjamina, the answer would probably be 'without a doubt'. Since you live where you do, the answer is maybe ..... if you have the guts to do what it will take. Of all the Ficus species, benjamina is one of the most reluctant to back-bud reliably on old wood. It's very possible that after your repot, you'll start seeing a break or two here & there on old wood, and the chances of that increase significantly if the plant is outdoors in good light and moving air. The recipe for forcing a significant number of breaks would start with a repot, so you're on schedule there. Then, let the plant grow entirely unfettered by pruning, in all the light you can give it, for the rest of this year, feeding heavily until growth slows; then, follow a maintenance fertilizing program. When spring arrives & night temps are reliably above 13*, acclimate the plant to full sun & resume heavy feeding. In the first or second week of July, remove all foliage from the top 1/3 of the tree, and reduce every branch on the lower 2/3 of the tree to no more than 2 leaves. It would be ok to pot up the year you do this, but not repot. If the plant is going to break back, it will do it with that treatment.
Essentially, you're building the trees energy reserves as much as possible, then, by the tip pruning and defoliating, you're cutting off the polar flow of auxin almost completely. Auxin is the growth regulator that suppresses backbudding. This gives dominance to auxin's 'antagonist', cytokinin, the growth regulator that stimulates back-budding. Backbudding should be profuse, but whether or not the tree will break back on the old wood is a question that you won't know the answer to until you try.
About the only noticeable effect from trying it will be some stalled branch extension while the plant pays out it's energy to put on a new flush of growth, but that won't be a big deal because branch extension is already beginning to slow by the summer solstice anyway.
I completely defoliated a large F nerifolia (willow-leaf ficus) in mid-June (prolly 1,500-2,000 leaves) so I could use it in a bonsai (wiring) demonstration at an art studio that chose Japanese art as the theme for their annual fundraiser. Within a week, I was rubbing off dozens of new branches that were popping all over the large branches & trunk. Just a month later, it's flushed out completely so you'd never know it was defoliated, and I'm still removing unwanted branches.
This is a newly established cutting, but see how old it looks just because the trunk tapers so quickly from fat at the bottom to thin at the top?
Thank you for detailed explanation. I think I have guts to try...
I have few questions:
Then, let the plant grow entirely unfettered by pruning...
- I pruned almost all branches in top 1/3rd to 3 leaves approx. 2 weeks ago, seeing lots of new leaves growing already. Would that interfere with storing as much energy as possible?
.. night temps are reliably above 13* means 13 degrees Celsius, right?
... for the rest of this year, feeding heavily until growth slows... - how much fertilizer would that be? I am using MG 12-4-8 with micros (yellow jug), about 1/8th of recomm. amount with every watering.
In the first or second week of July, remove all foliage from the top 1/3 of the tree, and reduce every branch on the lower 2/3 of the tree to no more than 2 leaves. It would be ok to pot up the year you do this, but not repot. If the plant is going to break back, it will do it with that treatment. - If the tree does not break back, what will happen then? Would it just grow leaves on same branches/same places? (I am not sure if I am using correct terminology, you know that I am new to this...)
Since I did such an extensive root prunning, I thought that potting up next year should be enough anyway.
And the final question: I did air layering on a thick branch that I want to cut off anyway. Would that interfere with building trees energy?
You said it is a newly established cutting in the photo you posted. How was it rooted? I thought that it is difficult to root such a thick branch (that is the reason I tried air layering - branch is much more than pencil thick). Or it depends on the tree?
Thank you for your time, again.
I pruned almost all branches in top 1/3 to 3 leaves approx. 2 weeks ago, seeing lots of new leaves growing already. Would that interfere with storing as much energy as possible?
Whenever you remove foliage or reduce the amount of solar energy the leaves receive, you inhibit the plant's ability to make food. This means a larger fraction of current photosynthate is used for the plants daily business, so there's less to store. The biggest run up in energy reserves will come next year though, after temperatures warm up and days start to approach their maximum length. Your plant will probably be at its most robust, in terms of stored energy, in mid-late August, but you need to temper when you can cut back with the consideration of how long it will take the tree to recover after nearly being defoliated, so we come up with a July hard pruning in compromise. Your tree has plenty of recovery time, about 6 more weeks, so no need to be concerned about the shape it will be in entering winter.
13* = 13*C = 55*F That was for your benefit (Canada).
... for the rest of this year, feeding heavily until growth slows... - how much fertilizer would that be?
I would try 1/2 tsp/gallon at each watering if you're flushing the soil every time you water. See if it tolerates it - that might be on the heavy side for a plant indoors - depending on the light. In winter, half that should be good.
If the tree does not break back, what will happen then? Would it just grow leaves on same branches/same places?
Since I did such an extensive root pruning, I thought that potting up next year should be enough anyway.
It WILL break back - for sure. We just won't know how extensively it will break back on old wood until you try. Plants aren't regenerative organisms, in that they don't regrow their parts in the same spatial positions, like animals. The plant will start to grow new BRANCHES from the axils of the petioles you left behind, and will also start new branching from immediately distal to some of the old leaf bundle scars (where leaves used to be attached). The end result will be a much fuller tree with a LOT more branches.
I did air layering on a thick branch that I want to cut off anyway. Would that interfere with building trees energy?
Yes, but not significantly. If you ring cut the branch (all the way around the branch) in layering it, the tree can still move water and nutrients from roots to shoots via the intact xylem; but since you disrupted the continuity of the cambium, all the photosynthate (food) produced by the foliage on the branch you're layering hits a dead end in its downward journey when it gets to your layer. If all goes according to plan, all the food/carbohydrates produced in that branch will accumulate in the cambium immediately above the layer, along with the auxin (growth regulator) that can't complete its journey to the roots, thus providing the energy and stimulus (auxin) required for root initiation.
The cutting in the picture was rooted in my high-tech intensive care incubator, seen here.
If you're careful about what you do, you can root some rather large Ficus cuttings if the timing is right.
Thank you Al, that is encouraging.
I'll follow this regime, already looking forward to next spring! It will be long winter...waiting :)
I did layer ring-cutting (since I tried it once & was succesfull; mind you it was a palm tree, not ficus B.)
I like your high-tech IC incubator! What is right timing? and what would I have to be careful about?