5 Feet and Climbing

We have been trying to grow rhubarb for three years now and finally can claim some success.  Two plants from last year have made it through the hot hot hot DC summer and then the blistering cold, long winter (though with very little snow fall, that is true).

The one plant in the Victory Garden seems to be outdoing itself. Not only are some of the leaves about 3 feet long and 2 1/2 feet wide, but the center stalk is literally 5 feet tall, and full of white seeds-- you can see them in the photograph here. 

We aren't sure what to do with this central stalk.  Are we to cut it down? Shake the seeds off it? Just let it be? If we let it be, will the plant take over that part of the garden, which is fine, but take over to the point that it crowds out the blackberry and golden raspberry bushes, which is not fine.

We have a bunch of gardening books, but non e deal with rhubarb. Apparently we aren't zoned for rhubarb.  Um, those garden experts haven't seen how happy this guy is.  If anyone has an advice (Gardner Harry, we are looking at you), we would be much obliged!