Me and my brown thumb finally managed to grow an avocado tree. I'd like to grow it for a while and then plant it in the garden in a few years. I read that avocados shouldn't be left outside during the winter but some sites state that older plants tend to be more robust. Wikipedia says these trees will grow to heights of 20 metres so I figured at some point, it should be able to survive a few days below zero. Is this assumption correct?