Flexing of stems and branches stimulates releases of the alkene growth regulator, ethylene, which in turn stimulates production of the natural polymer, lignin. Lignin is what makes plants stiff/ strong/ woody and helps the plant resist laying over.
Even if your tree is staked, you can stimulate production of ethylene and lignin by flexing the trunk (as noted) or by brushing the stem with a stiff nylon or wire brush.
Ultimately, you'll gain the most traction by providing as much light as the plant can handle. High light is required to produce good amounts of secondary growth which results in thicker/stronger stems branches. Even moving the plant from it's spot indoors to a spot outdoors, just outside the large windows, will probably double the light load the plant receives, which would make a big difference in the plant's ability to resist laying over.
As noted, pruning back the length of the branches on a regular basis minimizes the the probability of lay-over because a short stick (stem) of a given diameter will be much more resistant to deflection than a longer stem of the same diameter. Pruning at appropriate intervals is a strategy that should be put into practice as soon as possible, but within the parameters of appropriate timing.
About timing: I would suggest you bite the bullet and wait to prune next June, maybe a week or 2 before the summer solstice or Father's Day. Reasons: 1) Your plant will appreciate it if you allow it to retain its leaves until the target date; this, because each leaf is a food factory in which the plant's true food (sugar/glucose) is synthesized during the photosynthetic process. Pruning now would deprive the plant of the food it needs to grow and complete its cycles and processes. You could shorten the branches slightly now, enough to prevent stems from laying over, then hard prune as you normally would next June.
Too, there is a decided advantage as it relates to eye appeal in pruning in June. If you prune now, all the growth that occurs between now and about Memorial Day will be lankier than ideal, and you don't want lanky growth. To ensure all growth on your tree has tight and compact (short internodes and as many leaves and branches as possible), do any hard pruning in June. The hard pruning will stimulate prolific back-budding. As the new buds produce new branches, you can set about pinching those branches throughout the summer. For the fullest and most compact plant, as new branches grow and the 3rd leaf on all new branches is about to open, prune the branch back to 2 leaves.
This rooted
Ficus microcarpa cutting ^^^ was pinched as the 3rd leaf was opening. The result is 2 new branches growing in the axil (crotch formed by leaf stem and branch). When the 3rd leaf on these new branches are opening, I'll pinch those as well. So from 1 branch you get 2. From 2, you get 4. From 4 - 8, then 16, 32, 64 ..... . Early next September, stop pinching and allow the tree to grow unencumbered by pruning for the entire late fall, early winter, late spring; then in June, prune hard again to remove all lanky growth and begin the cycle all over again. You'll be amazed at how well this works.
Do you have a general idea of what you eventually want the tree to look like?
Do you want to keep all the stems/trunks or would you prefer to eliminate some of them? I see a couple that appear to be crossing other branches. Removing them would add to the composition's eye appeal.
What are you doing insofar as fertilizing?
Al
