>> Do you have your mango in a window or under artificial light while it is in the garage?
Yes, I do have a cheap LED shop light over it in the garage(The kind they have at Costco. Probably cost me $10-15)
Another thing I wanted to mention is to try a root pruning pot. I originally bought my tree in a 3 gal container. I up-potted it into a 5gal Rootmaker Injection Molded container. It put on a lot of growth in this container! Tripled in size in one season. Now I am looking for a 10gal root pruning container but have not found one I like. The largest Rootmaker makes is 5gal. They supposedly make a 15gal but have not seen it anywhere for sale.
Root pruning pot?!? This is the very first I've ever heard of such a thing!
My mango was not ever root bound that I could tell in the post-mortem. Usually you can tell because there will be a cylinder of roots with few to none extending outside the cylinder.
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OK, went to the Rootmaker website, but I'm not sure how this system would apply to me. I'm not planting a seed, I'm buying a plant that's already been grown and grafted in a nursery.
When I received my grafted Pickering Mango, I can't remember if it was bare root or not. Either way, I put it in a 3 gallon (nominal), tall black plastic nursery pot. I don't remember how long it stayed there, but it was long enough for the decline to start in the nursery pot. Usually that's my signal to pot a plant up into its permanent container. Allowing significantly more room for roots usually fixes the problem. My mango went exactly the opposite way--the decline accelerated.
My typical practice is to put a small piece of 1/2 inch hardware "cloth" in the bottom of the 3 gallon pot. This prevents the weed-prevent cloth from forming a seal over any of the drainage holes. When re-potting, I pull off these things. This usually loosens the roots at the bottom. If any roots are root bound along the sides of the container, I pull them away from the soil and make sure they extend into the new soil as I fill up the new pot.
I definitely did not wash all the soil off the roots. Some of the original potting mix was still clinging to the roots when I yanked it up.
I guess I could use a 3 or 5 gallon Rootmaker pot as the intermediate container...?