The weather is playing havoc with them they do not like the swings in temperature and this is how they react. I would just keep them alive untill spring then feed them and repot at that time if needed. Keep uniformly moist and I expect by spring that they will grow out beautifully. Also, they love and i mean LOVE coffee grounds.
Great! because I love and I mean LOVE coffee. Thanks.
Gail, where do you have them located? Do the pots have good drainage? When did you first notice the leaf issues?
The yellow leaves are not so much a red flag as the dark dried leaves. Older leaves on Gardenias will go yellow, usually in the early spring. The dark dried leaves indicate a problem though. Check the pot for moisture. Also check the leaves for signs of pests on the back side and in the crotch where the leaf meets the stem. Next what type soil do you have them in? How big are they and how big are the pots?
They're in a spot that gets sun a couple of hours a day. I noticed yellow leaves weeks ago, but now there are black leaves. The pots are 15" wide by 11" tall, with drainage holes. The soil was pretty dry, so I watered them thoroughly today (hope I'm not too late). About the possibility of pests: some leaves have a bit of what looks like white powdery stuff on top that won't rub off, but on the back of the leaves, there's black powdery substance that comes off when I rub. On one plant, about 1/4 of the stems and leaves look black, and are brittle - dead. The rest of the plant looks good except for the white and black I described. Soil: I used jungle growth potting mix with some perlite and soil conditioner. I'm going to attach pics (if I can figure that out). Thanks!
Here are the pics.
My advice it to spray them with a good fungicide & insecticide coating both tops and bottoms of the leaves, maybe some neem oil. Also I would Insulate the pots with some mulch or wheat straw for the winter. The roots may get a little too cold in the pots if you are in zone 7 especially if we have a winter like last years.Keep a good eye on your water over the winter, not too wet, not too dry. I don't think you have totally lost them, but it will be next spring before they recover fully. Right now you just want to keep them from going down any further. Give them some fertilizer (maybe some Espoma plant food )I hope it turns out well for you!
Won't know for sure till next spring, but I'm taking the advice offered. Thanks.
Gail, you have gotten good advice but I wonder if they didn't get dried out in the current pots, also do your pots have drainage holes in the bottom?
I just ask because I grow gardenia in a pot outside and you have to make sure they don't dry out too much. I also agree you will probably want to repot them in the spring. You may not need to spray with anything if they revive after watering.
Anne's gardenia pot sits in a saucer for water so she knows it does not dry out. It if rains for a day or so the saucer gets dumped. I found the plant seems to do better when you keep it moist. The secret is not to let water stay in the saucer. When it gets watered I let the saucer fill with water. If the water is still in the saucer the following morning it gets dumped. I am also a fan of horticultural oil to help control black sooty mold and over-wintering insects.
I'm revisiting my post and the answers I received - which I appreciate very much. I plan to repot the two gardenia plants in the spring. Right now the green parts look very good - and those are the majority of the bush; the leaves and branches that were looking bad are black and dead, but no more seem to be getting that way. I guess I should prune the black ones away.