I've been digging around to try and figure out if there is a good way to test this at home, but I haven't had much luck.
One method I saw used a known hop and your unknown homegrown hop and make tea. Then measure how much sugar (in 1/2 teaspoon increments) it takes to cut the bitter bite off the hops in both teas.
If it takes X teaspoons to counter-act the acid in the known hop, and Y teaspoons to counter-act the acid in the unknown hop, then the unkown AA is roughly:
Y/X * AA_of_the_known_hop
This same reference also says that homegrown hops are generally 50% stronger than the same type of hop purchased commercially due to the freshness.
Finally, this same refereces gives this fallback:
If this method seems too imprecise for you, send a one-ounce sample of hops to Jim Murphey at Murphey Analytical Laboratories Inc., (509) 577-8969. He will do an alpha-acid and beta-acid spectrographic analysis for about $28 and a hop oil profile analysis for $80. He also will perform an IBU analysis of your beer for $25. (Send two bottles - one for testing and one for qualitative analysis while doing the write-up - to 7 W. Mead Ave., Yakima, WA 98902.)
I've not seen anyone mention trying to use PH readings to do this, so either I'm the first to think of it (not likely) or it simply doesn't work.
-walker
oh, and here's the page I got this stuff from:
http://pw2.netcom.com/~dluzanp/backyard.htm