I have a few mango and avocado trees. They are between 5 and 6 months old. They appear to have stopped growing. Should I fertilize them, or is it too early? If it is too early for fertilization, what can I use to feed them in the mean time? When I seeded them, I added them to the soil with no other ingredients.
I'd suggest that since both trees are suffering, then you've used the wrong material for potting these trees, and their roots are suffering. So, pull them out to have a look to see if they're rotting or something else is wrong. It's highly unlikely they've exhausted the nutrients in their pots.
And be careful. My avocados came with a warning not to remove by holding the stem when removing from their pots. So it will probably be a two person job to remove them to examine the roots.
You don't say where you are geographically but, most of us are having winter right now. In such case they should be at rest. If you are in the southern U S I would wait until late March before doing anything. Just stick with moderate watering for now. They may have had a bit of cold damage. If you are experiencing freezes I would bring them inside during the freeze return them to there places when it passes. Hold of fertilizing until growth resumes.
Well, given where you are, its whatever passes for winter in your part of the world. Do not fertilize at this time of year, even in warmer regions, growth will slow or stop winter.
Although you've said the pots are 14 inches deep, I can see that they are not all full to the top with potting medium, which reduces the amount of root room available, so I'm not sure that isn't causing a problem. I note you say you used Nature's Care Organic Soil - is that what you actually mean, because that particular formulation isn't meant for potting plants? They also sell Nature's Care Organic Potting Soil, so if you used that, it should be fine. However, if you actually used the non potting version of this product, it likely isn't the ideal potting medium.