Looks severely drought-stressed. With avocados, that's typically from damaged roots (too much, or too little, water) or root rot.

The thing is its winter here in Canada, so its well below freezing outside the greenhouse and very little sunlight. Its warm in the greenhouse but only around 50F at night and 60F during the day. the tree is well mulched with leaves and compost, and a moisture meter is reading 2.8. Just not sure drought stress under these conditions would be likely. It was full of leaves in the summer, I remember it did this last winter too. I've heard Hass avocado trees lose most of their leaves before they flower in the spring? It appears that have many small flower clusters forming at the moment. How would I tell if the roots are rotting or not have enough water?

Did it died?

Hass will drop its old leaves and flush new leaves during bloom in the spring. Some leaf tip burn and ragged looking leaves at that time is normal. The attached photo shows the current state of my Hass tree 3/16/21. The tree in your picture looks pretty bare and beyond normal. Possibly not the right amount of water, fertilizer, poor draining soil or a combination of those.

I would really like to know more about your greenhouse design. I am also in a cold climate (zone 4) and really want to nail down the cost/return on the designs I am considering (I have looked at a lot). Can you email me: adamsmith.rv@gmail......