I've got my potted Oleander in my overflow greenhouse for the winter and I noticed the other day that the leaves now have a reddish color to them (see photos). Any ideas on what might be causing this? The greenhouse is currently unheated.

Could the reddish tint possibly be weather related from cooler temp's? My first thought was maybe a type of fungal infection; a sometimes common malady for Nerium oleander is the fungal disease Xylella fastidiosa http://www.bing.com/images/sea... but when I enlarged your photos that doesn't appear to be the case; at least it doesn't look the same to me.

At our old house I had four large Oleander trees in the yard but the only problem we had on occasion was the oleander caterpillar: http://entnemdept.ufl.edu/crea... which defoliates the trees if you don't get them in the early stages. Hopefully someone more knowledgeable with Oleanders (Nerium oleander) will be able to offer advice on your plants.

I wonder if it might be a magnesium deficiency? My orchids' leaves get a reddish tint like that if I don't add extra Epsom Salts to the spray fertilizer that I use.

You can get Epsom Salts at the drugstore or grocery store for a couple of bucks. Try dissolving a teaspoon or so in a quart of water and watering it with that a couple of times. It absolutely won't hurt, and if the red is Mg deficiency, it will improve dramatically within a week or two!

Also if it works, I'd keep on adding some to your fert at least through the winter. Plants can't photosynthesize without Mg and it is a highly soluble mineral. Most fertilizers have a tiny bit (listed as a "trace mineral" on the label) but in winter when the sun is not so strong, a lot of tropicals need extra.

Thanks Lin, it might be since it's in the unheated greenhouse.

I didn't think of that Elaine, I found a 4lb box of Epson Salts in the bathroom closet after I read your post. I'll wade through the jungle after while, pull it out and give that a try. Wondering also if on nice days when the temperature is decent and there's full sun if it would benefit from sitting outside for the day. I guess it wouldn't hurt.

Did it get nipped by cold weather before you brought it in?

Does not look like any insect related problem. Could be fungal related. You might try one of the triple cides that take care of insects, mites and fungus. It won't hurt. I use GardenSafe Fungicide 3.

Were you/are you watering it adequately? My Oleander sucks up water fast.

And yeah - the Epson Salts might help - cannot hurt. During the regular growing season, I give most everything a shot of Epsom Salts periodically. (Rose love it and my Brugmansia certainly appears to respond well.)

Not before but the day we finally got the new greenhouse finished there was a cold snap that night. Unfortunately I haven't gotten a propane heater for this one yet but it's beginning to look like I'd better soon. I've got some Bayer 3-in-1, I'll give it a shot of that.

It was getting watered almost daily during the summer and into the fall along with my Angel Trumpets.

I have a potted oleander that spends summer outside and winter inside. It discolours similarly some years during fall when I leave it out as long as possible, even through frosts, until it gets so consisently cold I have to bring it into the basement. The winters are so long here that once it's indoors it won't get outside again until probably May, hence I delay its coming in as long as possible - it can take some cold but does protest at too much.

Thanks Sue, I'll give it a shot of the Bayer today anyway and get my heater up and going. I really hate these cold snaps we get here in the fall/winter. They say 31 tonight, 34 Friday night then upper 40s and 50s for lows until the 28th.

Hey Chris...

Was this plant a cutting that you started this year? Or a new plant for you that you purchased this year?

Chris, I'd recommend you try one thing at a time, or you won't know what the problem was.

i.e. If the plant recovers and you gave it both fungicide and magnesium at the same time you won't know which remedy worked so you can prevent it next time.

As far as heat for the greenhouse goes, a large tub (like a plastic storage tub) full of water in the middle of the greenhouse can make a great heat sink. It warms up during the day when the greenhouse is in the sun, and releases its heat slowly through the night. Also helps keep the humidity up. I had a friend in Salt Lake City who heated his greenhouse with just tubs of water and waterbed heating mats to keep the water warm on the coldest nights. Easy, cheap and safe, too!

DavidLMO said:Hey Chris...

Was this plant a cutting that you started this year? Or a new plant for you that you purchased this year?

Actually neither David, I found it growing in my front yard this past spring next to my Lantanna. I dug it up and potted it.

Good idea Elaine, for now I'll just go with the Epson Salts and sun to see what happens. How often do you think I should apply the Epson Salts? I've tried that before in the first one and it didn't work as well as I thought it should. I bought another small propane heater today for the new greenhouse. I closed up all the openings in both greenhouses yesterday with Mylar insulation. It's not real pretty but it keeps the north wind out.

In general that is sometimes good advice - sometimes not. Some things take time to work - some faster than others. If it was a matter of the leaves getting zapped a bit by weather their recovery - if they do recover - could be weeks or months. Just saying. And many things do not work overnight - fungicide or Epsom salts.

I'd water the plant with the Epsom salts added to the regular water you give it for a week or so. (about a tsp. to a quart of water) You should see improvement in the color of the leaves in 2 weeks or less, if the plant is still growing.

My orchids responded in about a week, but our weather is warmer than yours so they may have been metabolizing faster. But magnesium is very quick to be absorbed and used by most plants.

It was thought for years that reddening of foliage was a response to cold weather, but (at least in orchids, anyway) it's now widely accepted as a symptom of magnesium deficiency. As the weather cools, and light levels decrease, people slow down or stop fertilizing, so the little bit of magnesium most plants were getting is reduced or stopped altogether. The plants develop reddish tints to the leaves as they run out of magnesium, make less chlorophyll and can photosynthesize less and less.

It's best to continue with a little bit of magnesium in all your water through the winter when you're growing tropicals that (in nature) don't go dormant. You can let them slow down by reducing fertilizer, but keep them healthy with enough of stuff they are still using.

Thanks Elaine, I'll do that. Regarding orchids, I use this brand name orchid food that comes in a resealable pouch, I can't remember the name right now but you probably know what I mean. Since most all of my orchids in the greenhouse are putting out flower spikes should I add a little bit of Epson Salts to my regular feeding also? I'll assume that Epson Salts wouldn't hurt my Angel Trumpets, Datura or Hibiscus either?

In most plants the first sign of magnesium deficiency is chlorosis (yellowing) between the veins (veins stay green) on the older (bottom) leaves. It starts there because magnesium is one of the minerals that is mobile within the plant, so in a short supply situation the plant moves the magnesium from the older leaves to the newer ones that need it more, causing the older leaves to lose theirs and show symptoms. As the deficiency continues it can spread throughout the whole plant from bottom to top. It typically looks like iron chlorosis but that latter starts on the newer leaves not the older like Mg deficiency, which is how one can usually differentiate.

Certainly don't disagree with Elaine that orchids (and some other plants) can turn reddish but FWIW when my oleander did the above it was actually, for the first time in its life, getting Epsom salts (because it was next to a potted tomato plant and got what was left in the watering can).

Magnesium is often left out of soluble fertilizers altogether because it can react with the other minerals therein (ditto for calcium). If you look at the analysis of Miracle Gro soluble "all purpose" for example, you will see it contains neither calcium nor magnesium. Magnesium is a secondary major nutrient (macrontrient) so plants do need a fair bit of it, so I'm not trying to discourage you from trying it, especially if you're using a fertilizer with none in it, but wasn't the problem with my oleander at least.

@sooby My conclusion as well Sue. Did you ever figure out what the problem was with your Oleander?

@chris1948 I regularly give many of my plants Epsom Salts, including my Brugmansia, Datura and Oleander. The Brugs seem to love it. I have grown Orchids for many years and never seen this problem with them and have never given them Epsom Salts - maybe I will give them a bit.

Like Sue - I leave ALL my Tropicals out til the last possible minute - sometimes beyond the last minute I do usually cover from 10 - 30 plants with frost blankets for several nights before I finally toss in the towel and bring things in. This year that was the day after it got down to 28 here. Many, many leaves get zapped a bit. My Oleander did not exhibit the reddish color you indicate above, but clearly they were impacted - and not happily.

Thanks everyone for all the helpful suggestions. Here's what I've done.

Wednesday after reading Elaine's post about Epson Salts I mixed some up in a small watering can and watered it with that. Yesterday and today I've set it out in the sun as soon as the temperature rose into the 40s I also watered it really well this morning. At night of course it will go back into the greenhouse with the heater. I noticed that not all the leaves have the reddish tint just some of the larger ones at the top of the plant.

DavidLMO said:@sooby My conclusion as well Sue. Did you ever figure out what the problem was with your Oleander?
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I just put it down to cold and didn't really give it much thought until the topic came up here. It was outside past my low temperature threshold for bringing it in because the forecast was wrong and it got way colder that night than it was supposed to. Supposedly oleander can take down to 20F (-7C), albeit with possible damage, or thereabouts so I usually bring it in to at least the enclosed unheated porch when it is forecast to be -5C or worse. Poor thing had the same happen another night and that time the leaves were so badly damaged that I've pruned it back, otherwise I'd be able to post a picture.

According to an article back in 2002, anthocyanin pigments can accumulate in leaves for various reasons, such as UV exposure, injury, pathogens, high light, cold, pollution, osmotic stress and nutrient deficiency:

The functional role of anthocyanins in leaves:
https://researchspace.auckland...

The delay in bringing things in is stupid on my part. ** But after that one night down to 28 we went right back up and it never got below 40 at night for several weeks.

** Perhaps I think that if I leave thinhs out it will warm up. As it turned out, I WAS right this year.

I hate ... nay .... detest bringing stuff in. I have a lot.