Hello everyone! I've got an Improved Meyers Lemon tree that I purchased last spring which has really been struggling and I would love some advice to try and help it out.

I live in Edmonton, Alberta, Canada in Zone 3A. Definitely not a good place for a citrus tree to live outside for 8 months of the year. I had put the tree in a very large planter pot when I first got it, and more or less left it alone outside on a southern exposure of our deck where it received full sun from dawn to dusk. We watered it more or less weekly with the other potted plants on our deck unless it had rained that week. The planter pot had normal black soil in it, and I did not fertilize the tree at all. It flourished all summer and nearly doubled in size during that time before it flowered in the fall. Just as the flowers were beginning to fall off and little lemons were starting to appear, I brought the tree inside for the winter before the outside temperatures dropped to 10C (50F) outside.

Inside I placed it on a table near a South East facing window to give it the most sunlight I could. I watered it weekly with my other indoor house plants and misted the leaves with water every couple of days. Our house is kept at 23-24 (72-75F) year round, day and night and is humidity controlled at 30%. It was fine for a month or so, then suddenly it dropped all of it's fruit literally over-night. It happened so fast, I thought that the dog had eaten all the fruit off it. Then it started to form yellow spots on all of the leaves and look a little bit wilted. I thought it was maybe needing fertilizer, so I bought some 5.1 : 2.5 : 3.7 NPK citrus specific feed and started fertilizing it about once a month since it was out of growing season. The tree continued to decline, and on closer inspection I discovered that it was infested with spider mites. I tried to fight them off with neem oil and spraying them off the leaves and branches with the water bottle on spray mode, then tried attacking them with a spider miticide but wasn't able to get rid of them. I finally resorted to taking the entire plant, pot, soil and all and submerged it all in a garbage can full of room temperature water with a brick in the pot to sink it to the bottom for 10hrs. This wiped the mites clean out and I haven't seen any evidence of them at all since.

With the spider mites being in that room now, I opted to move the plant to another room so it wouldn't be re-infested. I set it up in our kitchen and added a 40W LED grow lamp which is on from 7:30am-7:30pm to replace the lost sun-light. The tree started shedding leaves like crazy (5-6 per day) and the rest of the leaves were starting to form yellow splotches on top with dark brown splotches on the bottom. The tree also suddenly went through a major growth spurt where it sent 3 shoots up with leaves that were significantly bigger than the rest.

I did some reading and figured that the roots must be dying. I took the tree out of the pot and discovered that the roots looked fairly healthy, but that it was root bound in that gigantic pot it was planted in. I pruned the roots back some and broke them all up. I then re-planted in a smaller pot with Miracle Gro Cactus / Citrus soil and pruned off the three big shoots. The pot does not sit in standing water, and I make sure that it gets enough water with each watering that it flushes out the bottom of the pot to prevent salt buildup. I use tap water, which is on the city supply and it isn't run through a softener.

The plant looked okay for about three weeks, but it has started to form brown tips on the leaves within the past couple days and the leaves are starting to drop again.

Can anyone give me any suggestions about what I might be doing wrong, or how I can help bring this poor little tree back from the brink? I fear it won't make it to spring when I can put it back outside again.