Was, congrats on your new tree..Is this the only citrus you have?
You ask how often to repot...It depends on the roots..If you want to keep the plant small, transplanting to a larger pot will send out new growth.
Is your grapefruit listed as a drawf? As long as it's in a container, the plant won't grow like Jack and the Beanstalk, lol...How tall is too tall?
I see you're in z6, so the citrus will have to be sheltered in winter..which means either keeping in your hot house or indoors. But again, as long as the tree's container grown, and since you're in z6, the tree shouldn't exceed 7-9' tall.
What size is the grapefruit now? Toni

WASABISWORLD.. If you are in a dirt mix I would recommend Once a Year I prefer the early spring for mine..Although I perfer chc/peat I have read on the Fourm any time is good....grapefruit does like sun an heat..Myself I would not.. TOP it off,..If you are looking for fruit...Dale

As the tree is only two feet tall and already is producing flowers than it is a grafted tree. I would not top off the tree, however, you probably will not have to because it is growing in a container. Just being potted will considerably reduce the size of the tree. If your hothouse (greenhouse??) is heated during the winter I would surely keep the tree in the greenhouse rather than in your home in front of a window. If heat lamps are your sole source of heat I doubt heat lamps will keep a greenhouse warm enough during the winter months. Grapefruit likes heat, light and HUMIDITY, to produce fruit. Unless your tree is presently in a very small pot a two foot tree probably will not need to be repotted. Spring is the best time to transplant into a larger container, however, if done correctly and carefully you should be able to transplant most any time. I guess I have transplanted in just about every month of the year. If you do change to a larger container just increase the size 2 or 4 inches. Welcome to the citrus forum. Hope to see you around for a long time. Millet

Thank you all my garden buddies for your wonderful responses....
from wha you say, I have a healthy grafted tree, which seems to love it in the back yard for now...it has put on new leaves and blooms since I boughtit just a week ago....
I have taken pictures and though I cannot post in here with my lil ole webbie thing I will have them in a week or so on my yahoo photo site and can share with anyone who would like to correspond by email....
special thanks to hopeful....we have been chatting away for a week now, I think I have a garden sis...
OH heres a question....the new leaves on my plant are much lighter in color than the older ones...is this normal or do I need to feed it something? it is blooming again also...?

It is normal for the new leaves to be a lighter green. They will darken up to a nice healthy color over the next 3 - 5 weeks. Millet

Millet, I'm curious why you emphisize humidity? The Coachella Valley is a world renound Ruby growing region anywhere. Although TX may have us on it a bit because it is more humid, we still grow fantastic Rubys here. I can say that for sure because I just ate one off one of my trees today! We have a good domestic and international market for them too. :) Humidity is helpful, but we do well without it. Todays humidity here was 7%. And it was 116F here at my place. whew!
Arthur the Date Palm Guy

Arthur, everything you say is certainly correct. The Coachella valley can and does grow quality grapefruit. Heat is of course required to produce the sweetest grapefruits. The advantage that locations like Florida and Texas have over desert locations is high humidity. In areas that have high humidity the temperature does not fluctuate much between day temperatures and night temperatures, as it does in the areas with dry air. The humidity retains the heat during the night. It is this constant high heat that gives Florida the extra sweetness that their grapefruits are famous for. BTW I enjoy reading you posts. Take care. - Millet

Was, just wondering how your grapefruit is coming along..are the leaves growing and turning green? Toni

UPDATE on my ruby red....
I am really happy that I got this pretty little tree...it is such a pleasure watching it grow...
and it really seems to enjoy being hereLOL
I still have it in the container...and it has at least doubled in size since I purchased it....
it origanally put on about five small fruit....only one remains now..but it is the size of a small grape....and the tree itself is very small considering it is trying to grow a fruit....
the folaige( leaves) continue to come on and them mature to a darker color...
well I am just really pleased with this little thing....
I hope I can keep it alive a long long time.....and possibly plant it in ground in the future....far future...

please feel free to continue with suggestions.....I will happily take all and any....
this is such fun....

I went to Laredo, bought some ruby reds that were very tasty. I tossed a couple of seeds in a pot and one is growing like wild fire. Will it produce fruit? Someone told me it would not because it was not a grafted tree.

Thanks,

Oz

My relative did air layering from her ruby red. She gave me and my sister one tree for each. A creek separates her yard from mine. Her fruits are sweet and mines are sour. Teachers and friends: please tell me what minerals make the fruits sweet. I sure thank you very much in advance. Kim

Dear Oz; We planted ruby red by the seeds. It has been over 15 years now, we haven't had any fruit at all. Honey tangerine is faster: 3-4 years only. Kim

Here in southern Arizona many trees froze the last winter. My tree was about 10 feet with approx 80 grapefruit. I cut the tree back to approx 5 feet. The tree is now very bushy with dark green branches from the bottom up. How long should it take before it again bears fruit?