My mature gardenia had a full bloom in both early summer and now again in early October! Will it have time to set buds and bloom again next spring/ summer? Some leaves are yellowing, too. But, I think that is not uncommon. This is my first year at this house to observe this plant...
I just purchased a gardenia a week ago, and it's also full of buds. I wouldn't worry about having blooms now, just enjoy! I don't think it will affect next year's flowering. Unless I'm mistaken, gardenias set flower buds on new growth, and it will certainly have new growth next year.
I guess you're in zone 8. They are said to do fine in zones 8-10, but if you know you have worse weather, maybe some mulching would help, or moving it in a protected area. Do you have it in the garden? I have mine in a pot.
This is just what I have planned, but this is my first gardenia, so not too much hands-on experience here...
prune it gently (remove weak growth and crossing branches) in late winter (I don't really have winter, I'll do it when the temperatures will be around 60F) and fertilize it or move it in a bigger pot when the weather starts to get warmer (really, for me this is about 1 month time-frame). It likes the acidic soils better, so I will use fertilizer for azaleas. I read also (I think in Logee's catalog) that a very inexpensive way of ammending its soil is to give it some coffee (diluted, and cooled off, of course). I wouldn't mind having a coffee now and then with my gardenia!
You can also try to look it up in Plant Files here,on DG (it frequently helps me). You can learn a lot from other DG members that wrote reviews. http://davesgarden.com/guides/pf/go/198/ . You might find comments from your zone neighbours, and those are your best!
I think after the scorching summer heat our plants had to suffer through, they are so happy for this cool spell they are blooming again! All three of my clematis have several blooms each, and my blackeyed Susans, Mexican petunia, Shasta daisies, butterfly weed and three rose bushes are all blooming again too. You'd almost think it's spring time around here.
If gardenias are happy, they'll bloom for much of the year. I've never seen them bloom in winter, but spring/summer/fall are all fair game. So it can bloom now and still bloom again for you next year.
The yellowing leaves could be a watering issue or an iron deficiency (probably other things too, but those are I think the two most likely). Are they solid yellow colored, or are they yellowish green except for around the veins and right around the veins is still green? If they're all yellow, then it's more likely a watering issue (too much or too little) but if the veins are green then it's iron deficiency. The trick is to check your soil pH before you add iron though--if your pH is too high then even if there's iron around the plant can't absorb it, so you'd need to adjust your pH first.
This gardenia is in the ground. It is about 5 feet tall.
I did some light pruning after the first bloom because there were some spindly branches, so maybe it is my fault it is blooming again. As far as the leaves...a few of the leaves are solid yellow. The soil is somewhat acidic...
it could be stress from our extreme hot/dry summer. (Although the leaves didn't turn yellow then.) Now that it is cooler and we have had some rain... is when it is blooming and leaves turning...
I have a correction to make: it was in Logee's catalog (little text-boxes for different plants), however it was black tea (diluted) about twice a month, not coffee. I gave my gardenia coffee once this month, and it did not get upset about it... I guess I just gave it what I like most, but black tea is alright with me as well...
With regard to the leaves, I would avoid fertilizing now, especially if you have cold weather coming. Fertilizing might give the plant a boost of new fragile growth, that might die in the cold weather. And it has flowered on you, so I would say it has resources still. Just take care of it during cold weather, and fertilize it in spring.
I also have some yellow leaves now. But I've just discovered that two of my plants (the gardenia and my mandevilla), out of the blue, got aphids, and it might be my cause. Same yellowing pattern. In both plants. So now I'm fighting it to the death, hope I win!
Check your plant carefully: gently browse your hand thru, and see if anything flies. Also, give a close inspection to the fresh growth and buds. If you see anything suspicious, take measures.
I wouldn't worry about underwatering, as long as you don't have a wilted plant. Gardenias don't like to be overwatered, they only need to be watered when the soil looks and feels dry atop.
Julie I pruned mine this year right after the spring bloom and the same thing happened for me. I did a severe pruning of one of them (to the ground) and it even popped back and bloomed this fall. I did not prune one of them and it did not rebloom so I think it has something to do with the pruning.
Once established, gardenias are carefree. I treat them brutally (being alergic, I don't really like them much) and they just come right back. The one I cut to the ground this year, I covered with a box and threw mulch over that (future beds) and guess what. Leaves started popping through the mulch a month later! I've since decided to let it live.
Edited to add: Don't worry about the yellowing of the leaves on an established gardenia, perfectly normal. At least for me it is. All of mine yellow every year. Now not all of it should be yellow but some of the leaves just turn yellow and die. Now if the whole thing would die... muahaha