It can be normal for the lower leaves to drop, especially if the environments changed recently. The lower leaves are the older growth so if they're the ones dropping then there isn't too much to worry about (in my experience). The misting won't do all that much to be honest, sometimes it does more harm than good. I like to give the leaves a good wipe every once in awhile to keep the dust off etc. I would just keep it up. It sounds like you've been good with watering based on how the soil feels (water when soil is dry, and water until it runs through the bottom, assuming the pot it's in has a drainage hole). The light conditions sound ok, mine does well in bright, indirect light. The strange marks look like damage, probably from the store it was at. Always hard to tell in photos but it doesn't look like it was caused by pests. Honestly, your plant appears to be in pretty good shape, just keep it up and hopefully she'll perk up for you soon. Good luck!

It's good to hear that it probably isn't from pests. That was my main concern!

Do you think the yellowing leaves could be from a nutrient deficiency?

These plants need a lot of water especially in hot months. They are crazy about water on its leafs. I would put plant in a sink with enough water to submerge whole plant container. Let all air bubbles escape. Release water after a couple of minutes in this bath. Let plant drain thoroughly. Put back in pot. Check and drain any sitting water. Keep out of direct sun but some indirect light is good. See how it does. It probably only needs this bath treatment once a week. If leafs start to droop back to the bath. Tepid water is good. Not hot and not too cold. Hope you can save this plant. I think you can.

I just watered it pretty thoroughly today, so should I wait until the next time it's dry to do this?

Yes. Overwatering is what does many plants in! Good clarification.

im so sorry to see your plant suffering my friend daxeek. hope it gets better soon. some times you just need to give it time...

Thanks, Mike. :)

Mysterious. There are more yellowing leaves on my Dieffenbachia today, and MANY yellow leaves on my Marble Queen Pothos as well. Do you guys think this could be from cold air, maybe? I don't overwater them, for sure. They're both in pots with drainage holes and I water them when the soil is dry. They're both potted in a mix of 40% potting soil, 60% perlite.

We've been keeping the windows cracked at night here, and it's gotten down to 30 degrees most nights. Could it just be the temperature for both of them?

oh noooo not the marble queen!

these are tropical plants they dislike temps below 65F and 55F is winter for them and at those low temps they are usually dry in habitat.

so stop cracking your windows! they are wet and cold - that can easily cause leaf-yellowing and drop.

in the house you should keep them somewhere without cool drafts in cold season and where it never drops below 60F. also they need humidity at least 40% or you'll get a bad case of spider mites on dieffs.

in general they like temps of 75-85F and at those temps they need plenty of water.

and then you should never let them fully dry out - drying in hot temps will cause leaf drop and yellowing too.

If yr winter temps hover around 65F mark then you should water them much less then in summer. it's ok then to allow the top half of the pot to dry out before you water. but not more then that.

I'm keeping it in a warmer part of the apartment now. We'll see if this helps!

from my personal experience: i had a very nice robust dieff that i lost last year due to root rot (and it did drop most of it's leaves while at it :)) 'cause i left it on water-wick (hence moist) closer to the winter window then i should've.

i put it there to get better light :). My aglaonemas don't mind the spot and they are prone to root rot when cool and slightly moist. they were totally fine.

but dieff just dropped most of the leaves and 1 cane even rotted, the 2nd had just 2 leaves left on top. the temps there were prolly around 60-62F for a month.

the other one in the middle of the room was at 65F and it did perfectly ok.

you might want to gently pull out the rootball to have a look at the roots, to make sure there's no rot and they are not overly damp.

when you re-potted did you bare-root? did you break off some or many roots? that can also be the cause of leaf yellowing.

Pothos had rotting roots due to soil not drying out because of the cold air. Different circumstances. My Dieffenbachia is always in a warmer part of my apartment, and its roots are perfectly fine.

So, I was thinking about what else I could possibly be doing wrong for this Dieff. And then it hit me.

COLD WATER.

I water all of my plants with cold tap water (I'm thinking now that this probably isn't great for any of them, but is particularly bad for this plant). I cannot believe I didn't realize this sooner. Of course the plant that hates cold drafts/air would hate cold water on its roots. Duh. *facepalm*

Just dunked this guy in some room temperature water for 2 hrs. FINALLY looking good! No drooping leaves. Standing up nice and big.

FINALLY.

Wow! Great thinking!

Thanks for the tips, Flo. You were a huge help!