I have an accidental avocado tree growing outside (not in a pot) that has so far survived 4 winters in zone 6 and is now 7 feet high. I don't expect it to fruit, and I am very surprised every year when it leafs out. It is in a protected area right next to my house on the west, and just past it is an old fashioned well structure of the wishing well type but it is a real well with real water in the bottom. This house is of stone, built in 1925 and the walls at the bottom are close to 2 feet thick. The ground to the south falls away steeply, so cold air does not pool in this area. All of that probably has a lot to do with the survival of the tree. It has gotten down to zero F in the last couple of winters but that hasn't happened often or lasted more than one night. I have not done anything to protect this tree such as wrapping it. One of these winters the temperature will go down far enough that the tree won't make it. But, at this point it's an interesting anomaly. This is in the most southwest corner of Pennsylvania.

How fast they grow depends upon the fertility, the amount of moisture and the environment in general. I have seen them grow 6-8" inches per year. They may be slow, but they are worth the wait. I cannot say enough good things about the new hybrids like green mountain and green velvet. I even have an older Varder Valley that is supposed to be dwarf but is probably 6-8' across and about 5 feet tall.

Mike, I had two 50 ft. lengths of drip hoses wound in, out and around the plants with mulch covering them - all throughout the garden in the veggie garden. The mulch was piled on 8 inches thick or thicker under and around them. I put covers over the tomatoes in late July through August. I have good well water, so no chlorine that can damage plants. Notwithstanding all that I did, when temps reached 110-120, everything just turned brown, and then blister beetles ate what was left. I had tall, dark green, beautiful corn plants with 2-3 huge ears on each plant, but upon checking them, they had few developed kernels. Total loss. I planted more than one hundred tomatoes (seven varieties), corn, beans, cantaloupe, watermelon, bell peppers, three types of hot peppers, Red bells, zucchini, and onions. Normally I get enough to can, freeze, eat fresh and sell at the Farmer's Market & Health Food stores and still have enough to donate to the Food Bank. Not last year. The only tomatoes I got were a handful from the plants I grew in large pots, but only a few. They were sure good though. Cherokee Purples were especially yummy and the Lemon Boys. I think I got about 20 tomatoes altogether. I got more than everyone else around here. Their plants kicked it in June and July. I did get some okra from the plants in the smaller, lower garden and a few pitifully small Early Girl tomatoes, and a pretty good harvest of Jalapenos in September when it cooled down a bit, but that was all. I put so much work into it and expense. But it was just too hot. It was like standing inside a furnace ever day. I lost several small trees, one large weeping willow and several Eponymous shrubs. And what the heat didn't kill, the voles did, chewing the roots off several of my roses. What a horrible year! Sorry to go on about it...

BTW, here is another interesting Latin naming issue, although there appears to be an explanation for it (?) Anyway, according to the ACS database: 1. Pinus sylvestris 'Glauca Nana' http://conifersociety.org/conifers/conifer/pinus/sylvestris/glauca-nana/ is a different plant from (note that the two words in the cultivar name are transposed) 2. Pinus sylvestris 'Nana Glauca' http://conifersociety.org/conifers/conifer/pinus/sylvestris/nana-glauca/ Although, in this case, the naming of plant 2 appears to have been necessitated to differentiate it from yet another different plant 3. Pinus sylvestris 'Nana' http://conifersociety.org/conifers/conifer/pinus/sylvestris/nana/ When plant hunting, make sure whether it is plant 1 or plant 2 that you are bringing home. Plant 1 is hardy to USDA zone 3, whereas plant 2 is hardy to USDA zone 5. It is all according to the ACS database, I am innocent :-)