What’s going on with my avocado tree?
I am currently growing an indoor avocado tree. I have had this avocado for quite some time...Almost six months if I remember correctly. I grew it from a seed from a Florida avocado. I keep the plant out of direct sunlight, give it a light misting from time to time, and have it planted in soil that's made for avocado and citrus trees. I usually try to water my plant once a week or whenever it needs it. Recently, my tree started developing these weird brown spots that start out forming between the leaves of the tree. As these dark spots get larger, the leaves will curl up, but the veins will continue to remain green. This has been going on for a little over a couple of weeks. I have no earthly idea what is going on or where to start. This actually came out of the blue. I thought that it was a vitamin or mineral issue, but then thought about how when I repotted my tree, the formula of soil that I used provides nutrients of that sort for over the course of time. I used a soil that was fast draining and provides away for plenty of air to circulate so that the plant shouldn't get water logged. I just don't understand what is going on.
I appears to be primarily a possible Calcium deficiency, and probably along with other nutrient deficiency. Out of direct sunlight means deficient photosynthesis for metabolism of nutrients and sugars for plant tissue nourishmen. Nutrients are used up by the plant and they leach from the soil profile with watering.
No soil provides mineral nutrients indefinitely. And fast draining soil is fast leaching soil.
Your photos don't show the entire plant or the container, but from the glimpse in one pic it appears to be very small for a large growing tree like avocado. A small container means small soil volume to hold minerals, and a small absorbing root system.
First recognize that avocado is a large growing tree, and will have a very limited life span indoors in a pot, especially a small pot.
To keep it going for awhile, if mine I would re-pot into a larger container. I don't know what potting soil you used, it sounds like it has some of the important qualities for avocado, maybe it's fine. But as an example, I like this one or something similar:
No matter how good the potting soil, fertilization is important. This complete organic fertilizer has full range of vital nutrients. See the "guaranteed analysis":
As you seem to be aware, water management is important, not too much or too little. I like a soil moisture meter to take out the guess work:
Hope that helps, Don