one frost it may survive,but after that you are pushing it!.bring it indoors now if you want to save it.
35-40 is fine,but remember this is a huge tree!dont know if you will have the room to keep doing this.
they will not fruit untill at least 10 feet.
MOVE TO CA OR FL!!ha!ha!
trust me i know its frustrating,i used to live in england.
i now live in los angeles
gary

Surprisingly it has already been through at least 3 light frosts and one night in the upper 20's! I did take it in this morning and will see what happens. I've had a couple big avocados that wintered over in the greenhouse but they never flowered. I lost them and a number of other plants when our heaters went out during an ice storm a while back. I didn't make it down to the greenhouse for a few days and by then it was too late : (

There are some smaller dooryard varieties of avocados that are grafted. They cant really take much freezing temp. This web site says that 25-26F will cause damage. They also have alot of varieties listed.

Here is a link that might be useful: avocado varieties and info.

I have seen "Winter Mexican" listed as hardy to 18 Deg. "Brogdon" which I have planted is good down to 22 Deg. I would imagine a young seedling would not be as hardy as it would as an adult. Maybe your seedling is of Mexican descent which is the hardiest of the 3 Avocado types. However, being in zone 7, the cold is probably going to get it sooner or later.

Nelson

I felt sorry for it and took it inside. We are now down in the 20's and I'm sure it would be quite dead if it was still outside. It's growing well and never dropped any leaves. It has to be a variety that was sold at the grocery store.