But what for are you growing the tree? It won't make fruits 15 years for now, and this in the best growing conditions!

So, for foliage, I would cut the taller branch at the same level as the tip of the lower two ones. It will produce fast (in 2-3weeks) at least 2-3 new branches.

Your grapefruit tree will need to get to 15-20 feet tall before it has any chance to flower.

You can carefully break the top over and it won't die and continue to provide food for the tree and a bud lower down will take over as the dominant tree. This was done to force a grafted bud to grow. I have done this to seed grown trees to move the point of growth downward while leaving food producing leaves intact.

I use this to reflect all the light back on the tree until it is all used up. I get from 3 to 5 times as much light on my tree than your setup provides for your tree. You can mimic what I am doing by shining a CFL spot light down on your tree so that much more of the light hits your tree's leaves. My goal is to get maximum growth through the winter to put a nice size tree into the ground in spring.Tree is about 11 months old since bud break shown in the first picture above.

As your tree gets bigger you can shine spot lights from each side to aim at the lower to mid levels of your tree. Trees grow where the light is. My bucket light setup is not the answer for you and your tree. I grow my citrus trees outside when they don't fit in my bucket lights.

6b Steve

Thanks for the pruning and lighting advice. I'll try creating more reflected light with my setup. As for trimming, just to be clear, are you suggesting I cut the tree 2/3 down so the top reaches where the lower branches are currently reaching? It seems like a lot of tree to cut. But then again, I'm the plant "new-bie" here. :)

I'm currently using Foliage Pro 9-3-6 every other week (a few drops) while watering weekly. Is this enough for now? Thanks a million!

I would not cut any part of your tree at all

Got it. What did you mean when you suggested I "can carefully break the top over"? Thanks!

As eSilviu says, it's really, really unlikely you will ever see fruit on your grapefruit tree, given your growing conditions. So then you are simply growing it as an interesting foliage plant. If it were my plant, I would remove the top two thirds and let it get bushier. But that's me.

You can also split the difference between Dave and my self and tie the top of the tree to the pot to make a horse shoe and the tree will send out shoots from lower than center. You will have the top half of the tree still producing food while the tree grows from below.

6b Steve

I concur. It's going to be an interesting foliage plant given the indoor Wisconsin environment. Would cutting it 2/3 down kill the plant? And would bending l it like a horseshoe cause the central leader to snap?

Anyway, your suggestions are great! This is my first time interacting in this community, and I'm pleasantly surprised by the gentleness and expertise. Thanks.

eSilviu Beautiful tree That is what I am looking for. multiple trunks branching out at window sill level to fill the whole window. My pear tree does that and it sends growth out of to bent limes to reach out for an other bend making 2 or 3 arches. bend your tree over where you wnt thenew sprouts to grow. You can also prune the new growth before it spends all that energy making it permanent. I like weeping willows (citrus).

Cutting the 2/3 of the main branch will lead to something like this:

(Amoa8 clementine grafted on grapefruit seedling. Grafting point is 30 cm lower than the part in the picture.)