Hi all, Back in February I bought 2 lemon trees and 2 orange trees, to live in my sunny conservatory (South Wales, UK). I repotted them using John Innes n.2 with some added grit and perlite for drainage. I also added a 10cm layer of clay pebbles at the bottom of the pots. I have been feeding them once a week with specific citrus feed, and watering them once a week (occasionally twice a week, when weather was very hot). Despite my efforts, the leaf colour doesn't look right. They are very pale, with visible dark veins. Also, in the last week lots of apparently healthy leaves have been falling. It looks as if someone has cut them off very neatly. Every morning I find 3-4 leaves on the floor. However, all the trees except for one have been producing new leaves and buds. One of them had dozens of oranges at some point, but they all fell off for no apparent reason when they were the size of an olive. Currently, all trees are again full of flowers, but I'm really worried the fruits are going to fall off again. Last week we had exceptionally hot weather, with temperatures reaching 37 degrees C inside the conservatory. Is it possible the extreme heat traumatized the plants (hence the leaf falling)? This would still not explain the pale colour of the leaves... Any suggestions is welcome! Thanks in advance
New leaves look like that at some point as they develop. The veins and the surrounding area become increasingly darker as nutrients are taken up by the tree. Make sure the fertilizer that you are using contains micronutrients. However once a week feedings may be excessive unless the solution is diluted appropriately. A fertilizer with a higher nitrogen component should be used as citrus trees are heavy feeders. One with a 5-1-3 NPK ratio is often recommended. Edit: After further consideration it occurred to me this may a case of iron deficiency. If so, the use of a fertilizer containing micronutrients should solve the problem. As for the fallen leaves, some leaf loss is normal as the tree sheds its older leaves. Do they have a yellowish appearance and are they from nearer the bottom? The leaf in the photo still has the petiole still attached which is normal. In case of stress the petiole is separated and remains on the stem or branch. Having said that it's not normal to have heavy leaf loss. What is the level of humidity in the conservatory? I wonder if the temperature/humidity combination is not to their liking. I would try lowering the temperature while maintaining humidity. A degree of fruit drop is also normal. A tree will develop many fruitlets but many will be shed before they ever mature. A tree will keep only those it can support. The layer of pebbles should be removed the next time you repot. It does not improve drainage: The Myth of Drainage Material in Container Plantings. (PDF)
Thanks a lot for your message, very useful. I attached a picture of the citrus feed I am using - do you think I should switch to something else? The petioles are actually mainly on the stem (see picture), so I am starting to think it is to do with the temperature/humidity. The humidity usually goes from 45% in the evening to 25% during the day. Is this too low? Any suggestions on how to raise it?
The fertilizer is a balanced formulation (1-1-1 ratio) that contains micronutrients. It's good but it would be better to have a higher level of nitrogen. The trees should not experience any deficiencies with this. However to have proper nutrient uptake the pH of the soil and water should be neutral to acidic. I noticed the label does recommend a weekly application. The humidity seems reasonable to me. I was going to suggest you spray the ground with water during the day but I noticed the room has a finished floor. You might try filling a couple of wide, flat saucers with water and placing them in the room to allow the moisture to evaporate during day. And if you don't want empty trays you could grow some carnivorous plants in them. I grow sundews in mine and they help to control the few fungus gnats that appear. Is the leaf loss continuing, even with more moderate temperatures? You'll need to ventilate on hot days if excessive heat is suspected to be the problem. In any case photosynthesis is reduced with temperatures above 35C. How did the pale leaves come about? Are these new leaves that started out completely pale then developed darker veins? How long have they been like this? I'm not familiar with John Innes mix but I imagine it's a typical houseplant mix containing mostly peat with some sand, and perlite added. It was good that extra components were added to increase the medium's porosity. Small sized bark chips could also have been included. It's important for citrus to have a porous, quick-to-drain medium.
