A growth regulator/ hormone (auxin) is a byproduct of the plant's metabolic processes. Flow of auxin at threshold levels across the abscission zone where leaves are attached to branches ensures the leaves remain attached. When the flow of auxin drops below threshold levels, an abscission layer forms and serves to isolate the leaf from the rest of the plant. As the layer becomes complete, water, nutrients, and all other compounds which normally move through the plant's vasculature into and out of the leaves is no longer possible.
Over-watering causes a drought response due to the fact it diminishes root function. This reduces the level of auxin and causes the symptoms you currently see. As long as the roots haven't been infected by any of the fungal pathogens on the list of damping off diseases, the plant should recover. As you already know, determining the appropriate length of the intervals between waterings is a key part of any care regimen. I'll leave you something below that will help you accurately monitor moisture levels deep in the pot, where it counts.
With the loss of foliage, the amount of water used by the plant will be reduced considerably, making watering intervals extra important.
Foliage-Pro 9-3-6 is an excellent choice as a 'go to' fertilizer for your houseplants and almost anything else you might grow in a pot. I would encourage you to use it regularly. It is a COMPLETE nutritional supplementation program from a single source and supplies nutrients in the ratio at which the average plant actually uses the nutrients. It also derives more than 2/3 of it's nitrogen from nitrate sources (helps keep plants full and compact) and none of its nitrogen from urea (promotes coarse growth and increases risk of ammonium toxicity under wet or compacted soil conditions.
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 in order 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 and 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' (more reliable than a 'moisture meter'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16" (75-85mm) works better. They usually come 48" (120cm) long and can usually be cut in half or in several pieces, depending on how deep your pots are. Sharpen both ends of each tell 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's tip comes out nearly dry. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.
Al
