Sounds like too much water to me. Does it have fast drainage, it need very little water it stores it in the base of the plant. They can be made to bonsai, (stay small) You may need a change of soil, that way you can check and see if has a root problem. I hope this will direct you into solving the problem. Norma

FWIW A) worm castings provide very little in terms of nutrition, and used in any volume (in containers) they add to excess water retention. B) The problem could very well be a nutritional issue, especially if most of the leaf damage is affecting older leaves. Reason: Some nutrients are mobile in the plant (N,P,K,Mg), the rest are considered immobile or nearly so. The mobile nutrients can be moved from one location in the plant to another in order to fuel growth of new organs (leaves/ stems/ roots), while the immobile nutrients are locked into existing tissues. It is almost always the case that container media cannot break down fast enough to provide for all of a plant's nutritional needs, which creates deficiencies, even in new/ fresh plantings. When these deficiencies arise, the plant robs mobile nutrients from existing organs, mostly older leaves, which results in the plant recognizing the now compromised 'donor' leaves as a liability, which causes the plant (a shedding organism) to rid itself of the liability by shedding the leaves. C) PTs are very tolerant of droughty conditions. That is not to say they like/ prefer to be allowed to dry down completely, but drying down completely would be the lesser of two evils when the 'other' evil would be watering at intervals too short.. Ideally, you would be flushing the soil thoroughly when you water, and waiting until the soil is nearly but not completely dry to water again. IF you have been watering in sips because you think the soil is too water-retentive and are trying to avoid risking the specter of root rot, your grow medium is likely inappropriately water-retentive, not to mention the fact that watering in sips ensures dissolved solids (salts) in your tapwater and/or fertilizer solution remains/ builds up in the soil to the point where water uptake becomes difficult for the plant. A high level of salts in the soil can actually reverse the process of osmosis and pull water OUT of cells by exactly the same mechanism that curing salts pulls water from meats like ham/ bacon/ sausage. Moisture levels near the top of the soil column are relatively inconsequential. What is important is the level of moister at the bottom of the pot. I'll leave you with something I wrote about using a "tell". The "tell" will provide you with the information you need to determine appropriate watering intervals. Using a 'tell' Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant. Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor. In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water. Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'. One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue. Al

Sorry about your plants and hope it will recover. Just a note of caution about cold tolerance, guidelines generally apply to mature plants planted in ground. In my experience, even mature plants grown in pots don't have the same threshold for cold resistance than the same plant in ground. I guess they do not make as much antifreeze when in pots! Also even if the forecast can be accurate, there are many microclimates in your garden and when temps are low, a few degrees lower can make a huge difference. Maybe I am overly cautious, but for plants that have a "tropical" vibe, I protect them from frost when in pots.

What a soil is labeled or called doesn't necessarily define its drainage characteristics, even if it should. One of the worst soils I've seen for bonsai, or any plant for that matter, is Hoffman's Bonsai Soil ...... because it retains water excessively. It's unlikely that the discoloration would be from under-watering, which pretty much leaves a choice of over-watering, an excessive level of salts in the soil, or something toxic having made its way into the soil. Have you fertilized or sprayed it with anything since you became its keeper? The pot does have a drain hole, yes? Is there any chance water at the tap you used has been run through an ionic exchange water softener (one you have to charge with salt)?Not that it matters much, but this is what I use for bonsai ^^. Notice that all small particles (< 3/32") have been screened out to eliminate perched water. Al