I have a lemon tree, planted from seed from a store bought lemon approximately 5 or 6 years ago. It's in a pretty big terra cotta container now. The size of the container is aprox 19 inches across at the top, a little more that 2 feet tall I guess.

It has been "potted up" maybe three times. All in standard commercial potting mixes. It is immature. Lots of thorns. Never fruited or flowered. Gets full sun on my deck. Very healthy and vigorous. Occasional catepillars on new growth. The trunk at its widest point is probabaly two inches or so across. The container planting is extremely heavy so it lives on a custom plant dolly I built.

I've kept in a tree form the past several years. It's tendency is very shrub like. I pruned it pretty extensively early this spring and fertilized it over the course of a month with two or three applications of very diluted micronutrient fertilizer.

It's gone crazy with new growth. From the top of the tree to the bottom of the container is about 7 1/2 feet. This fall I want to do the first root prune, remove 100% of the exisiting potting media, and repot in the same container in a more exotic container mix (turface, coir, crushed granite and pine bark), I will substantially reduce the size of the tree.

I know some of you hate pruning to reduce the size of a tree. But this is and will always be a container specimen. Planting in the landscape here probably wouldn't work becuase it is not quite cold hardy enough. That being said I want to maintain a small size and nice shape. Not a traditional bonsai form, but same principal. If it fruits some day that would be great. But Im not necessarily in a hurry.

My questions are:

(1) how drastically can I prune the tree without killing it? If I whaked it in half and left a few small branches and leaves would it survive? I've read you can prune up to two thirds of the foliage without killing a tree. I'd like to do a that or more.

(2) Should this be done at the same time as the repot and root prune? Does the time of year matter? I've been told fall is good, but since I'm really going to severely stress the plant, should it have some growing season left to recover?

(3) any other advice?