Can I Harvest My Own St. Johnswort?

I am currently taking St. Johnswort for clinical depression, with the approval of my medical doctor. I have tried at least a dozen different anti-depressants over the years, without success, due to intense side-effects. St. Johnswort works well for me.
My question is: can I just pick the flowers and leaves growing wild on my property, grind them up and stuff them into gel caps? Will I get the right dosage this way? My purchased caps are 300mg, but the bottles talk about levels or amounts of hypericin.
I like the idea of using the whole plant rather than some chemists extracts. I also love the plants you sell: they give better yield than the wild ones around here.

First, we need to clear up a common misconception: hypericin is not the active constituent responsible for the anti-depressant property of St. Johnswort. Hypericin has some antiviral properties, but otherwise it really has no role in the medicinal effect of St. Johnswort in the treatment of depression. It serves merely as a "marker" compound, which means that it is merely an indication that the product inside the bottle may be the true St. Johnswort and not some other plant. That is *all* that this talk about hypericin means. Getting more hypericin definitely does not mean more anti-depressant effect!
In fact, there is no consensus yet on what component or components of St. Johnswort has anti-depressant action. Some have suggested that another compound, hyperforin, may be the anti-depressant compound but that is by no means clear yet.
In the meantime, the best strategy is to take remedies made from the whole tops of the plant. And if you make your own from plants you harvest yourself, you don't care what the hypericin content is because you already know that you have the right plant from seeing it in bloom or from growing it yourself.
According to John Lust, author of "The Herb Book" (available from Richters), you make an infusion from the dried herb as follows: steep 1 teaspoon of herb in 1/2 cup water for 5 minutes while covered. Take warm, 1/2 cup before breakfast and 1/2 cup before bed.