Actually it's recommended not to fertilize when newly planted, at least in the 1st month, but I guess it depends on the roots systems. The root systems on the trees I planted last month was mostly poor except for the peach. I've barely given some miracle grow but I did that as much to help new leaves grow that were eaten by the deer. I wonder is there a 'root fertilizer'? Or do you have to have created compost already on hand to get roots on newly planted to grow best?

I would agree with the previous assessment. Young avocados cannot tolerate anything under 30 (or over 100)... but it sounds a lot like root rot which unfortunately is common in avocados, at least here in CA. Overwatering, or trying to grow them in clay or boggy soil, makes the plant susceptable to rot root (they need well-drained moist soil but never wet feet), which often shows up as branch dieback and general lack of vigor due to the damaged roots' inability to uptake nutrients and moisture. The symptoms are often misdiagnosed as lack of water, so most people make it worse by watering more. I would keep cutting it back and adjust the water. Avo trees are sensitive to salts, so water deeply in well-drained soil and let dry before watering again. We usually deep water twice a week on average. I've seen young trees come back after being cut off just a couple inches above the graft... so don't give up unless you can confirm root rot.

Maybe I can help. Let me start by saying if you cant get them in the ground and grow them outdoors in your zone, it's kind of a waste. At some point, its going to outgrow pots and what is reasonable for most people indoors. They require alot of care for the first 3 years. What size pot are yours in? I place mine in 5 gal buckets in a 60/40 blend of organic soil / perelite mixture. Mine are in a local soil blend with no ferts added. They dont tolerate high nitrogen so stay away from miracle grow organic. When was your last repot? Do you have access to quality organic soil? You want something without any fertilizers, chemical or organic. The only thing I add to mine are Dolomite lime and Azomite. The lime is to keep the PH at around 6.5 as well as add Magnesium and the Azomite is a mineral supplement. Many important minerals are mobile and will wash out with regular watering. More quickly if you overwater with lots of runoff. Every part of an Avocado above ground is photosynthetic including the stems and trunk. Mine have lost all of their leaves before and they come back. They dont like change and they are best grown in one spot outdoors with lots and lots of shade. As little direct sun as possible. Any direct sunlight will roast the leaves. A southwest corner along the fence works best as its easy to put a 2x4 across the corner and drape shade cloth. Do you know your tree's watering routine? I let mine go dry until I start to see the leaves droop a bit. They can go dry for weeks sometimes. They dont like wet feet and are susceptible to root rot. Make sure you let the water you use sit for at least a day so the chlorine can evaporate. Moving them when they become stressed can sometimes be a bad idea. It is probably reacting to changes in humidity which can be very low indoors. If you are getting big temperature and humidity changes, than can trigger it too. Do you know what kind of Avocado it is? I found the Mexican kind to be the easiest and most hardy. They are fairly frost tolerant as well. Dont give up on them. Especially the young ones. I watched seedlings regenerate an entire trunk after severe frost damage. I have two in my garden area that are absolute survivors that I had written off. There is alot of energy stored in that massive seed. Hopefully yours will pull through and adjust. Dont overthink it or mess with it too much.

@socks: Yes, the trees looked healthy when we bought them. They are planted in our backyard. The backyard soil has a lot of stones/rocks since we purchased the property, and it looks like a construction site. I was told by the nursery that native soil is sufficient for planting avocado, as they have sensitive root system and don't like compost and manure. I told the nursery the soil in my backyard has a lot of stone and the quality is poor, but they told me it's fine, and not to water the trees often. When we were planting the trees, we filtered away the rocks/stones, so the soil was like thin powder form. Since I haven't been watering the young trees much, the leaves started to fall off. The nursery told me that it's lacking of water, so I started to irrigate more often. Then, the new leaves, buds, and branches are starting to die back. I contacted them again today, and they said the tree has root rot now, and the most I can do at this point is to reduce the irrigation amount and keep my finger crossed. I did research online, and i'm not sure if it's really root rot or not. If it is, I doubt the trees can survive without taking any treatment.