I suppose you could somehow collect nectar from the plants you'd like and feed it to them, but I know of no one who does that. The foraging area for a single hive maxes out at about 78 square miles (circle with radius 5 miles), so you would need that much area to make them forage for a specific thing. Actually not too difficult for some honey such as clover, orange blossom, and (not anymore) alfalfa.
So with the alfalfa thing, places that grew alfalfa (good hay/forage stock for livestock) would let the alfalfa bloom before the first cutting of the year. This made alfalfa fields sources of some of the best nectar flows in the world. Then years ago, a bunch of agricultural scientists (like myself) figured out that the protein content of alfalfa is at its absolute peak just before the plant flowers. This led to farmers cutting their alfalfa just before they bloomed, cutting out the nectar flow entirely. This switch utterly destroyed entire states worth of honey bee businesses especially in the Mid Atlantic region. Whoopsies.
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