I have a dwarf banana plant growing indoors by my living room window. It is about 3 feet high. The most recent leaf has an unusual appearance. About 6 inches at the tip looks like it didn't develop properly. The central vein is there but the rest of tip of the leaf blade is deformed. It is somewhat reminiscent of an oak leaf shape or a leaf that has been chewed by something (although on close inspection it doesn't actually seem chewed). The rest of the leaf seems normal so far (it hasn't fully emerged yet). None of the other leaves have looked like this. I'm just wondering if anyone knows what might have caused this and if it is something that I should be dealing with before it gets worse.

The most recent leaf has unusual appearance, and the leaf blade is deformed, as if it had been chewed by something, but if we look closely we find that nothing has chewed it. If the climatic conditions are appropriate, like good temperature and RH, then this is the symptoms of zinc deficiency, usually zinc and any micro-element deficiency appears in sandy soils. If the temperature was not appropriate during the formation of the leaf (before opening, or emergence) then this would be to the low in temperature stress. But I think it is zinc def. try to add micro-element fertilizer. Bye, I hope this will solve the problem.

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bob

The next week you will have the emergence of the next leaf, (if the mean temp is equal to 22 degrees Celsius), I think the next page will not show these symptoms. I am thinking of the banana seedling you have planted is off type, like it is an abnormal plant, these off type usually occur in tissue culture banana plants at a rate of 4 percent.

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bob

Thanks, I will try some micronutrient fertilizer the next time I water. I wasn't aware of what zinc deficiency looks like in a banana. I'm not using a sandy soil - I'm using a mix that contains quite a bit of organic matter. I've also moved the plant a bit further from the window, just in case the temperature right near the window is too cool. I can just see the very tip of the next leaf coming up inside the petiole of the deformed one - I should know in a day or two whether it has the same shape.
Edited by spectrum on Feb 21, 2005 at 04:36 AM

Banana likes fertilizers too much, not only micro elements but also macro elements are necessary. A banana plant (producing 40 kg bunch), needs about 700 g to 100 g of pure potassium, 400 g of Nitrogen, and 80 grams of pure phosphorus, and 80 grams of Ca, and 80 g of Mg, these are the macro-elements. The micro elements are also very important but they are needed in very little amounts. if you have ornamental bananas (tall varieties) then these amounts should be cut into half.

bye

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bob

The fertilizer that I use contains all the macros and a wide variety of the micros. My banana is not an ornamental - it is supposed to produce edible fruit and is a dwarf variety. I'm not sure exactly which one. Here is a photo of the leaf in question:


Edited by spectrum on Feb 21, 2005 at 02:56 PM

Ok I saw the picture, this could be:
1. Zinc deficiency.
2. Stress. Cold temperature.
If the new leaf grows normal, then it was caused by stress, if not, and after adding micro nutrients, then it is a kind of mutation (can not absorb Zinc) or an off type plant. But I think the next leaf will be fine, because the picture shows good green color, but the base of the plant it seems that it is very thin, I think your plant needs more fertilization. Do not worry about the purple brown patches, they will turn green by time, this is linked to chlorophyll formation in the leaf.

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bob

Thanks. I'm not worried about the dark patches as I have read that reddish spots are normal for some dwarf banana varieties (they look more red than brown in real life) The base of the plant is a lot wider than just that leaf - the petiole is still emerging and hasn't fully opened up so it looks thin in the photograph. The base of the plant where it meets the soil is roughly 2 or 3 inches in diameter.

BTW, roughly what is the temperature threshold at which a banana will start to exhibit symptoms of cold stress?

Below 13 degrees Celsius, it will show chilling injury on the fruit pulp. And the plant will stop to grow, the first symptoms of chilling injure on the leaves will be like burned leaf. The last leaf to be effected is the central leaf or the leader; this is kind of a surviving mechanism

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bob

So is 13 C also for the leaves or just for the fruit? Winter temperatures in my house generally range from 20C to 25C but I'll have to put a thermometer in the window to see how cold it gets there.

The best temperatures for banana to grow, is between 28 and 33 degrees Celsius. And relative humidity is between 85 to 95 %.
The burning of the leaves will not appear at 13 degrees Celsius usually when we talk about chilling injury and symptoms we have to take in consideration both the temperature and the duration of this temp. for example 7 degrees for 24 hours is not like 7 degrees for 48 hours. Mainly speaking we have to avoid the temp to drop below 13 for the bananas.

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bob

In the summer my plant may get its 28-33C, but it's probably not going to get a high relative humidity at the same time. Right now it is getting 20-25C and a fairly low relative humidity as I don't have a mini greenhouse built around it. Indoor air is usually quite dry here in the winter. Of course, it is possible that it sometimes gets a bit warmer even now as the window does produce a greenhouse effect on sunny days.

The leaf after the deformed one is now unfurling and it looks normal

Yes, no need to be afraid. It happens a lot in subtropical area, and in calcareous soils, or irrigating with water of high pH.

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bob