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I have 3 Sun Parasol Mini-Crimson Mandevillas (they are the shrub-type). Today when I went out to water them, tons of leaves on them had turned yellow and left only little green dots of the foliage color. I've had leaves turn yellow before, but not so many at a time.
My other Mandevillas (larger cultivars) don't seem to have that problem. Any ideas what gives? Any ideas how to handle it?
Can you post a picture? My first suspect with yellowing leaves is always a watering issue (could be either too much or too little) but it might be something else too. I would definitely do the "finger test" in the pots to check the moisture level. (if you already watered them today, wait until whenever you would have been planning to water them next, then do the finger test before you water them to see how wet/dry they actually are)
ecrane: I knew you'd come through. I have a feeling it's TOO much water. It has been raining here and even though they are on the porch, when the wind is up, water comes onto the plants. Then, I watered them. That may be what I did wrong. They've been so beautiful and I was upset when I saw so many of the leaves turn yellow. I don't water the larger ones quite as much, so maybe, as you said, overwatering is the problem. I doubt that it's underwatering, because I water them almost every day because it's so hot here and dries my plants out in one day. I'm such a klutz about stuff still. I'll learn as time goes by.
ecrane: I am also a klutz at photos. I took a photo of the plant with my nice, new digital camera and put it on my Corel photo thingy. However, I haven't the vaguest idea of how to attach the photo to this mail. I'll try to find out and post it. I had already taken a whole bunch of yellow leaves off when I took the picture.
If you've had all that rain lately and then you watered them too then it could be too much water, although it really depends on how much rain got on them. Since they were somewhat sheltered and just getting a little rain that was blown in by the wind though I'm not positive it's that. The other thing to realize is that even if you're watering every day, if you're not watering thoroughly that could still be too little. When potting mix dries out it often becomes pretty hard to re-wet it, so if you just run the hose over them quickly you often won't fully rewet the potting mix, the water will find a couple of channels and run straight down and out the bottom. To really get it wet again, one way is to set it in a bucket of water for a little while and let it soak up what it needs, or if that's not feasible what I usually do is fill the pot with water several times and let it run through, each time you do that more of the soil will actually get wet. If you water thoroughly like this, you will also find that you probably don't need to water quite as often. I've found that if I have plants that have been chronically underwatered because I wasn't watering them thoroughly and then they do get watered right (like the rain might have done for you), sometimes the leaves on some of my plants will turn yellow and eventually drop off, but if you get in the habit of doing thorough waterings in the future then that'll stop and the plant will look healthier and happier overall.
If you want to upload a pic, right underneath the box where you're typing your post you'll see a place to choose a picture to upload. The only trick is it needs to be in a certain file format in order to post it, but my guess is your photo software probably saves things as a jpg by default and that's one of the formats that's allowed. (if you don't know what format it's in, try to upload it anyway, if it's the wrong format you'll get an error message telling you that)
ecrane: I tried doing the photo attachment thing. It looks as if it worked. It's not a very good photo, but maybe you'll see what I'm talking about. Also, it seems that all of my hanging baskets are in need of a good soaking as you suggested. The water almost runs right through them. I do have a lot of them, about 20. I hope this photo works and you can see what I'm talking about, even though I had taken a lot of the yellow leaves off before I took this photo.
Thanks for the instructions - now if I can only remember them next time. Maybe I'll learn how to take a macro photo and that would work better.
Are the spots on the leaves blackish/brownish? If so there might be some fungal leaf spots going on, otherwise I think it's just a watering thing (but over and under-watering often have very similar symptoms so I can't tell which one it might be). If it's blackish leaf spots then that's something that often happens when the leaves stay wet for too long and some fungus starts to grow--having lots of rain/humidity will contribute, or if you're watering in the evening instead of the morning that can make things worse too.
You'll also be surprised how much happier your plants will be when you start giving them a good soaking instead of just a pinch of water--I noticed a big difference with my plants once I figured that out. You do need to be more careful to avoid overwatering though when you're doing it that way, so I definitely recommend doing the finger test on a regular basis. Or I can usually tell by the weight of the pot/basket whether it needs to be watered also, especially with hanging baskets that's easier than pulling them down to stick your finger in them.
ecrane3: I did the bucket thing with my bouguies. They are the ones in the hanging baskets. You must have been right about not getting enough water (even though I know not to overwater bougies) because when I sat the basket in the bucket, the whole plant floated to the top, completely out of the basket. It must have been so dry! I could see that the soil was extremely compacted. Unbelievable! I'm going to soak the rest of them, then see if I have to water them less.
I plan to wait a little while on the Mandevillas. They have quit having yellowing leaves now that I have stopped watering them for a few days.
I know this isn't a bougie thread, but I wanted to let you know that, as usual, you were right. Don't know where you got all of your good knowledge, but you've been a lifesaver for a newbie.
Glad I could help! I spend too much time on here, that's where I learn most of it! LOL Also gardening books and magazines and of course my own experiences (I've killed many, many plants, but always learn something from each one!)
ecrane3: Oops. Today my Mandevillas leaves are still turning yellow. I found one that was just starting to turn yellow and the spots are little blackish/brownish pin sized spots, then the whole leaf slowly turns yellow.
If this is, indeed, a fungus, what do you suggest I use. I sure don't want to lose my Mandevillas, because they bloom all summer long profusely. I haven't watered them in 2 days, and the soil still seems moist.
I'd give it a little more time before you worry much--there's sometimes a bit of a delayed reaction where leaves will continue to develop symptoms, especially if the soil's still wet. I'd just pull off the leaves that have the spots, and hopefully soon the plant will dry out enough that you should stop seeing new ones do that. If the soil is still really wet it might be good to repot in some drier soil, but if it's drying out well then I wouldn't put that additional stress on the plant.