I have a single citrus plant (a donor plant, but he did not know what kind of citrus it was). It is full of blossoms. Do I need to do anything for this plant to form fruit? It is in my greenhouse. It is only a single plant and there are no other citrus trees anywhere around me as far as I know.

You don't need to do anything but let it grow Ken. As long as it gets plenty of sunlight and is kept above freezing, it will produce.

It will likely drop most of its flowers and young fruit, but almost every group of flowers will surely hold on to from 1-3 fruits. You will have something...

Congratulations on your tree.

I need to go out and finish picking mine now that you remind me. We have so many Citrus trees around here in DeLand its easy to take them for granted...

for the info, David Paul. Since it is in my "Everything Else" greenhouse with several hundred other plants, it will stay nice and toasty. I keep it well-watered and since I mist my other plants every-other-day, it gets the same treatment. I have no real shading on my greenhouses during the winter months, only the translucent solar blanket material. So there's plenty of light.

I am excited to see just what sort of citrus tree this is. When/if it sets fruit (is that the right term?), it will bring as much enjoyment as when I have a first-time orchid bloomer. (I excite sort of easily )

Hi Ken -- I replied to this on another forum; where your question also appears. In case you haven't wandered back there yet; here's my response:
It would help if you knew what kind and how old it is. Apparently, the day of citrus growing for the backyard gardener won't be for many more years as Florida now has that fatal disease "greening". Citrus greening is one of the most serious citrus plant diseases in the world. It is also known as Huanglongbing (HLB) or yellow dragon disease. Once a tree is infected, there is no cure. Unlike the canker that hit our citrus some years ago; this makes the fruit unpalatable and also kills the tree.
I have one citrus tree growing in the ground; a Meyer lemon. Those lemons are huge and juicy. However all the fruit is growing on the lower limbs of the tree - nothing on the top branches. I don't know why and neither do my gardening friends. Very odd.
I have a Key Lime tree in a huge pot, and it's loaded with blossoms at the moment (for the second year); also a Persian lime (also in a huge pot) which produced quite a bit of fruit. I actually made a few key lime pies this past year - something I'd never done before; just wonderful. I had some English friends staying with me last weekend and served it for dessert -- they raved about the pie.
Back to your citrus tree; it would be good if you could identify it -- I'm pretty sure you don't need another citrus tree to encourage blooming and fruiting (as you would with Papaya). Just get a good citrus fertilizer and apply at the right time for your area. I'm sure you won't have to worry about greening for a few years yet.

Elfie, this was a donor seedling and the guy had no clue what it was. I don't think he had ever even seen his plant bloom. He sent me the plant two years ago. I don't know whether the seedling was actually grown from seed or from a cutting, but in any case, I would say my tree is now two years old. It would be 6-7' tall and 3-4' wide if I had not trimmed it back in the fall, knowing it would go into my "Everything Else" greenhouse. It is now a 5'x3' tree and is putting on new growth on those cut branches.

Since there are scant few citrus plants anywhere within a hundred miles of me, I wouldn't think I even have to concern myself with the greening problem. It sure sounds like that's a big thing down where you are though. That's too bad considering all the thousands of acres planted in citrus in Florida.