Do you have a cat?

I do but most of these plants are truly inaccessible (several are hanging) so I don't think that's it.

I think there is a single cause underlying the variety of symptoms, and it isn't insect herbivory or disease pathogens. If you want to open a discussion about what that cause might be, we can almost certainly determine a strategy, even if it is multi-pronged, to resolve the issue if you determine suggested accommodations to be reasonable.

In my experience, the cause will be related to what cultural factors might be interfering with normal root function. There is also potential for some of the damage to be nutritionally related, but nutritional issues can be caused by too much or too little of various nutrients, or they can be caused by seemingly extraneous cultural factors inhibiting uptake of key nutrients. Examples: If someone adds a little extra a shot of Epsom salts for the magnesium content, the excess can cause a Calcium deficiency. Too, over-watering can cause a 'cultural' deficiency of Ca, which would account for symptoms presented on plants other than the F. elastica. The necrotic leaf margins on the F. elastica are likely from over-watering or a level of dissolved solids (salts) in the soil solution at levels greater than the plant is programmed to deal with, unless the leaf is an older leaf located low on the plant.

Al

Thanks Al, I would love to continue troubleshooting with your expertise! For some additional context on my plant care, all of these plants are 1-5 feet away from southwest facing windows. They are in a chunky soil I mix myself with 1 part peat soil, 1 part perlite, and 1 part pine bark fines. I feed "weakly weekly" with the Dyna-Gro Foliage Pro fertilizer. I test with my finger to make sure the soil is dry an inch down before watering, and water until it drains (and make sure the pots don't sit in the drainage water). I have tended towards under-watering in the past and am trying to check the plants at least once a week so they don't dry out too much.

The affected leaves on the F. elastica are indeed the two lowest leaves, if that helps. What else would you need to know?

The leaves on the Ficus are likely in the process of being shed due to normal senescence (aging), or because they are being shaded by leaves higher on the plant. A reduction in light levels reduces the flow of a growth regulator/ hormone (auxin) which essential to keep a layer from forming (abscission layer) at the base of the leaf stem where it attaches to the branch or stem. Once the abscission starts to form, the flow of water/nutrients to the leaf is walled off from the rest of the plant and the flow of photosynthate (sugar - the plant's true food) is gradually reduced. Essentially, the change in the plant's chemical messengers alert plant central that the leaves have become a liability, and that starts the irreversible shedding process.

I sounds like you've done a good amount of research on your own, and are definitely on the right course insofar as your your journey toward a green thumb. There really isn't much to critique about your care regimen, but maybe some answers to questions will reveal something that leads to improvement in your plant's vitality.

*Can the plants most affected by the symptoms you've shown be said to be in deeper pots than those less affected? Using the digital tester Mother Nature gave you (a finger or thumb) works fine for testing moisture levels deep in the pot if the soil is 5" deep or deeper. For deeper pots, a wooden tell stuck all the way to the bottom of the pot will give you a better read on moisture levels, and keep you on track insofar as determining appropriate watering intervals. if you use a finger in deeper pots, the tendency will lean toward over-watering in a high % of cases.

To keep track of when each plant should be fertilized, drop a marble, button, bottle cap, ...., into the pot when you water. That way, you need only count the objects to know when each planting needs fertilizing. When you fertilize, remove the objects and start over.

* Are you sure the entire soil column is getting saturated when you water?

*Does your home make use of a water softening system that requires recharging with salt as the ionic exchange medium?

* How weak is the fertilizer solution you customarily apply? If you are fertilizing at every watering, you should be flushing the soil with each watering and using somewhere around 1/2 tsp/gal. It would probably be better to tie your nutritional supplementation to the number of times you water instead of the calendar. I grow under LED lighting, use FP 9-3-6, and I used to water with 1/4 tsp/gal at each watering. I changed that so I'm fertigating (fertilizing + irrigating) plants in smaller volumes of soil more often because the nutrient levels in the soil solution are more affected by flushing than plants in larger pots. I have plants in pots that hold less than an ounce of soil all the way up to plants that hols several gallons of soil. You might try using 1/2-1 tsp/gal and fertilizing every 3rd or 4th time you water. You can do the same in summer, but increase the fertilizer strength to adjust for the increase in light/ growth rate/ increase in temperatures. Would I be right to guess your home temps range from 65-75*? Do you have an idea re what the relative humidity (R/H) % range is? I grow in my basement where I keep temps at 66-68* nights & 72* days. R/H is kept as high as I can w/o moisture forming on basement windows, so from 55-62%. Low R/H is usually more of a contributing or exacerbating factor when it comes to spoiled foliage due to leaf hydration issues, and longitudinal tears in foliage occur frequently as a result of low humidity levels while the leaf is unfurling.

* Did you add any supplemental liming agent to the soil when you made it?

Have you used anything other than FP 9-3-6 as part of your nutritional supplementation?

* Do you get the sense that the soil might be holding too much water? If yes, I can share some tricks that will reduce the volume of water the planting will hold after a thorough watering. Some remedies are passive, require little to no effort on your part, others require a slight effort when its time to water, but nothing most would consider to be seriously off-putting.

I feel like there is something I'm missing, but it's late and I'm getting tired. If I think of anything, I'll add it later. I do think though, that you've put most of the things most growers don't consider behind you, so it's more about tweaking your routines than reordering them entirely.

Al