If your plant can't maintain turgidity, it's because not enough water is being moved to the foliage. When that occurs, plants wilt. Two causes cover almost all cases of wilt - A) not enough water B) too much water. The not enough water thing is sort of obvious, too much water, less so. Water absorption is an energy driven process. In order that the plant can effectively take up and move water, there has to be enough oxygen in the root zone. Over-watering causes wilt because it reduces the amount of oxygen in the root zone.

In almost every case, if your plant wilts and doesn't respond when you offer more water, the underlying cause of the wilt is over-watering.

Entering the picture is the TDS/EC (total dissolved solids/ electrical conductivity) of the soil solution. TDS/EC is roughly a measure of the amount of solids (think of salts, to make things easier) dissolved in soil water. The more salt there is in the soil solution, the more difficult it is for the plant to absorb water. We see this in action when curing salt is used to dry meat. If there is enough salt, it actually pulls water OUT of the cells in the meat, drying or partially drying it in the process. The same thing can happen in plants. The scientific name for the process is plasmolysis, probably because plasma is torn from cell walls as the water is removed and cells collapse, but the common term is fertilizer burn. I'm not saying your plants have fertilizer burn, that's a symptom of extremely high TDS/EC, but it's very likely that a high level of soluble in the soil solution is contributing to your plant's inability to remain turgid. The volume of roots needed to keep the plant turgid may also have been reduced by rot - no way to tell w/o examining the roots for dark, slimy, sour smelling roots. If the soil smells like anything other than fresh earth, you probably have some anaerobic soil issues going on, rotting roots and producing noxious gases.

Last observation: If you're not flushing the soil thoroughly at every watering, a half strength dose of 20-20-20 every fortnight is a LOT. Also, plants don't USE NPK in a 1:1:1 ratio, so when using 1:1:1 ratio fertilizers like 20-20-20, the level of each nutrient in the soil can very quickly become badly skewed, which raises yet more issues.

How do the roots look/ smell?

Al

Thank you so much for your follow-up, Al. The soil smells like earth, not sour at all, and I've attached a pic of the roots, which look normal to me, although starting to get a little bound at the bottom. No slimy or black parts. The soil did seem pretty wet for my having watered the plant several days ago. There are a few strange splits in the stem, and I wondered how water would pass through. The leaves at the top are almost totally wilted now, but the ones I mentioned at the bottom are doing fine. This is the weirdest thing I have ever seen a plant do, and I have many. Regarding the fertilizer, 20-20-20 was recommended by many websites for abutilons (though I realize that not everything on the internet is true), and I do give it a thorough watering before applying the water with the fertilizer. Is that what you meant? Looking toward to hearing your thoughts. Thanks again.

Alexis

Happy birthday Alexis! :)