Have had such great success in the past, but last few seem to have an abundance of fruit when very small, and present one has lost all its leaves with 4 oranges remaining. Finally cut off oranges, and have used plant light (as sun is very rare in Toronto this year). I mist it and branches seem to be turning brown. Anything I can do at all?????? Condo dweller, so can handle only smallish plants. Any help would be “so appreciated”. It was so lovely on the balcony all summer.
Thank you for writing with your orange tree question; how nice to have been gifted with small plants as souvenirs of Florida. In addition to their beauty and wonderful aroma, citrus are, however, known to be susceptible to a wide range of problems, from nutritional deficiencies, to environmental stressors, to pests and diseases. Any one of these can result in rather sudden, and startling, leaf drop.
The fact that your current plant bore plenty of fruit and leaves indicates that the root system had been healthy, enjoying the correct amounts of nutrients and water, and the leaves received light, air and moisture to their liking for successful photosynthesis. However, leaves have dropped since migrating indoors from your balcony, and this could be due to one, or several, issues.
Nutrients: assuming the root system is in the original soil and pot, the first question is: have you been fertilizing your plant. All citrus, including lemons, limes, oranges, love a generous and consistent source of nitrogen, so fertilize every 3 months or so with a 20-10-15 fertilizer: consult with a nursery to purchase the right product (for a citrus in a pot, not in the ground), and carefully follow the directions.
Next: water deeply, but infrequently. Leaf drop (did the leaves drop while still green?) can be caused by water that stagnates in the tray: citrus roots will rot. The soil should dry out slightly between watering. Water when the soil is dry a couple of inches down into the pot.
Regarding pests: as a rule of thumb, plants that are relocated indoors, even from a balcony, should be carefully inspected for any outdoor hitchhikers, including insects, spiders or fungus. In the case of citrus plants, keep a vigilant watch for mealybugs, spider mites and scale. Nutrients will be sucked out of the plant’s fluid system, causing leaves to fail to survive. So get out your magnifying glass, and search the stems for mealybugs, for brown domes of scale, and for whitefly. (Did the leaves curl or deform before dropping?) If you discover evidence of one, or more, of these pests, the good news is that you can work at eradicating the problem: your plant sounds to be small enough that you could spray off and any of these pests with insecticidal soap (follow directions on label), available at your local garden center. This treatment will have to be repeated every 7-10 days until all the generations of mealy bugs/ white fly/scale have been destroyed.
And finally, light/temperature/humidity: citrus need eight hours of direct sun per day, maybe six during the winter off-season. Be aware that too-much, too-hot, direct sunlight can scorch leaves, so, again, it’s a bit of a balancing act. Regarding using a plant light, your plant will need to generate new leaves before photosynthesis can begin again. Likewise, your indoor air temp and humidity, and soil temp, should be moderate.
You have your detective work set out for you, and here’s hoping for a good outcome, and that you can revive your orange plant to it’s once-vibrant condition, Below are a few links of interest to help you with further research.