Hi, I live in Rome and I have a potted kumquat plant on a balcony that is exposed to the sun and protected by winds. For a few months I have noticed that the tops of the leaves, even the youngest ones, have burn marks. This situation is spreading rapidly, I state that the pint nn receives direct sun and is watered, in this spring period, about every 10 g. always on almost dry ground. Can you help me to understand how to take care of my sapling? Thanks Gio '
not seeing a photo of the spots is difficult to make a diagnosis; the foliage of a plant usually maculates due to fungi or other parasites present in the soil; or because of excessive watering (but it doesn't seem to me absolutely your case); or due to excesses or deficiencies of mineral salts in the soil.
If the plant is affected by rust or other fungal diseases, you can try to dissolve a systemic fungicide in the water of the watering, which will eradicate the parasite from inside the tissues of your sapling; being your kumquat in pot seems to me the best solution.
If the amount of water is not excessive, perhaps it may be too low; try to water your kumquat with more water, so as to wet all the ground bread well, then always wait for it to dry before watering again.
Don't talk about fertilizing, so the problem could be this too, even if the leaves usually turn brown when the mineral salts contained in the soil are excessive, not when they are scarce; kumquat is a citrus fruit native to Asia, where it is grown in areas where tea is also grown, therefore it loves soils similar to those used for these beautiful shrubs.
So let's grow the kumquat in a light and cool, slightly acidic soil, and try to water the plant with scarcely calcareous water; if the water in the aqueduct is too hard, remember to repot the kumquat every 2-3 years, using citrus soil, mixed with an equal amount of soil for acidophilic plants, in order to obtain a slightly acid mixture.
For citrus fruits a particular fertilizer is traditionally used, consisting of shredded dry lupins, these in addition to providing mineral salts, also improve the soil mix; then every two months spread a handful of shredded lupins on the surface of the pot, burying them slightly; every month you supply instead of fertilizer for citrus fruits, or for fruit plants, or for flowering plants, from March until September. Avoid supplying fertilizer during the winter months, because kumquat, unlike many other citrus fruits, has a period of vegetative rest with lowering temperatures.