First, it was the U.S. Supreme Court that decided, not Congress.
Second, it was anything moving in commerce between the States or anything that had a substantial effect on Congress' interstate regulatory efforts.
"it involved a farmer who grew a small crop"
That farmer, and millions more like him, would have a substantial effect on the wheat that Congress was regulating if they were allowed to grow more than their allotted share.
Are you saying that he and the other farmers should be allowed to get the federally subsidized price for their wheat (which was 3X world market price) and still be allowed to grow all they wanted, thereby undermining the program?
Are you saying that he and the other farmers should be allowed to get the federally subsidized price for their wheat (which was 3X world market price) and still be allowed to grow all they wanted, thereby undermining the program?
The way Wickard has been interpreted as precedent, the federal subsidy issue is irrelevant. It may be that for the particular facts at hand, the decision was reasonable, but other courts since have regarded the decision as saying that anyone who grows any commodity which is involved in interstate commerce is subject to federal government control, even if they themselves never put their commodity into the general interstate market.