I have a large gardenia in pot for about 5 years; for some months, however, I have noticed a progressive yellowing of the leaves, followed by a dark brown that starts from the apex to complete the entire leaf, provided that it does not fall first. Thus, the plant is almost completely undressing, but it is strange how all the apicals of the branches (even the youngest) carry gems. I tried with iron sulfate in watering, with systemic anti-fungal, but I still haven't found the solution to the problem. Help!
gardenias are plants originating from areas with tropical climate; in particular gardenia jasminoides tends to be resistant also to the conditions present in our gardens, resisting both the summer heat and the winter cold, but only if placed in a place slightly protected from frost. The main difficulties encountered when cultivating gardenias are related to the water needs of the plant: in fact gardenias love regular watering, and a fairly cool and moist soil, but at the same time they fear water stagnation, which even if it occurs for short periods of time, it can cause a rapid decay of the foliage. Therefore, watering must be provided only when the soil tends to dry out, avoiding leaving the shrub perennially immersed in water. In addition to this, it often happens that shrubs grown in pots for long periods of time, without being repotted, tend to get sick and deteriorate, due to the insects that nest between the roots; in fact, there are various species of insects that lay their eggs in the ground; these eggs then become larvae, or commonly we would call caterpillars or worms, and feed on the roots of plants, ruining them even quickly. For both problems, the best thing you can do is repot the plant; if you suffer from some fungal disease, simply providing a fungicide may not solve the problem, as the fungus is located between the roots and is leading to rot. Then lift the plant from the pot, and check the roots; cut, with a well sharpened and clean scissor, all the roots that appear dark and soft, and remove any insects present in the soil. Then repot your gardenia, using all new soil, of excellent quality, specific for acidophilic plants, and possibly lightened with pumice stone or washed river sand.