Hello I have two lemon trees, over the summer they got a lot of new leaves. As winter came to our region, the current temperature is 15 ° C during the day and -1 ° C at night. With one of the lemons, the new green leaves started to turn black, so I removed them so that today I could see how its few leaves had fallen off, literally a small contact with the leaf and it was falling off. I don't know what is the problem , the other lemon is quite ok. I fertilize them every 2 to 2.5 weeks with citrus fertilizer. The last two weeks there has been little sun in our region, can the cause of the falling leaves be weak sunlight? If I put them by the window they will be close to the radiator. The window is tilted during the day, we are at home around 5 pm. Is it possible that the apartment is too cold for them? I post a picture before, during the appearance of blackness on the leaves and the current situation Any help welcome.
Welcome to the forums. The temperatures you stated are a bit cold for a lemon so I think that has something to do with your problem. Citrus roots reduce their activity when cold and go dormant once it reaches 13C. While in that condition, the tree is unable to provide moisture to the leaves for photosynthetic activity. If the tree is exposed to light in that condition it will drop its leaves. You do have some choice in how to over-winter the trees but it depends on the conditions available. It would help to know whether these trees are being grown indoors or outdoors.
It is hard to understand, were these citruses exposed to some night frosts or not. If they were, then that may explain blackening and dropping of leaves. I suggest you to stop fertilizing for winter. Also reduce watering. They don't need so much water, if they are in a cool place. I kept my citruses outdoors until ca 2 weeks ago, when couple of -5°C night frosts were predicted. Brought them in just before that. Now (there is usually +3...+10°C outdoors) they stay in a cool room (+10...+12°C) with as much natural light as it is available at our nordic latitude and currently just 9 hours of daylight. I haven't watered my citruses since I brought them indoors (for two weeks already, before that they got some rain, I watered them more than 1 month ago), and it seems, that they don't need watering for at least another week. I never fertilize my citruses between up pottings. When up potting, I mix some manure, compost and slow mineral fertilizers into the potting mix (mineral soil with sandy loam). So far there has been no negative effect of that kind of practice. Too much fertilizers during hot season may cause concentration of salts into the soil, messing up water intake by citrus roots.
