I have a lemon plant I started from seed about a year ago. It’s been slowly growing straight up, however about a week ago it started a bunch of new sprouts all around the top that seem great, but then all the leaves started turning yellowish and a few have now fallen off. It’s an indoor plant in a south facing window, and has good drainage. I usually water about once a week. Is the leaves falling off normal with all the new growth? Or is this odd?
You may have an infestation of spider mites. The leaves in the first two photos appear to be speckled and have signs of webbing. Also, do you fertilize the tree regularly?
Yellowing leaves could be a sign of iron deficiency. Have you tried supplementing your lemon plant with iron? Spider Mites usually occur under very dry conditions. They're difficult to get rid of once you have them. To prevent them, prevent the plant from drying out too much. Container plants often fall victim to Spider Mites due to becoming overly dry. I'll admit I don't know that much specifically about lemon plants, but these generally are causes of yellowing and/or webbing.
Spider mites can be treated with a number of soap-based insecticides available, including insecticidal soap. Some choose to make their own soapy solutions. Whichever one you use, spray the plant thoroughly by covering all plant surfaces. Repeat every 7-10 days until they're gone. Applications must be repeated at least once since the spray is ineffective against the eggs.
Nutritional deficiencies are usually not an issue if the plant is fed regularly using a fertilizer that contains micronutrients. Check the label on your fertilizer to make sure they're present.
