my avocado lost most of the leaves
Lost most of the leaves, which have yellow veins. What do I do?
Yellowing of leaves is called chlorosis, and it is usually caused by a deficiency of nitrogen and/or some other nutrient(s). Often, the fix is not simply adding more fertilizer, because if the pH is wrong, the plant can't absorb the minerals even if they're present in the soil. Avocados need a pH of 6 - 6.5, but anywhere between 5 and 7 should work. First thing then is to do a simple pH test (an inexpensive home test should work) then adjust pH if needed, then add a bunch of compost and some fertilizer, and make sure your plant has plenty of water. Here are a couple of articles with more information: https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm