I read somewhere that regular bagged sugar is fine, that you don't need special sugar of any kind. I'm not sure about beet sugar... honestly I use the store brand sugar regular granulated sugar and the hummingbirds (and bees) don't seem to mind . I wish the bees minded actually =)

I recently did some research on this topic. Here are my findings:

Droll Yankees recommends using Domino Pure Cane Sugar (not beet sugar) which ensures there are no preservatives or additives.
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In an email to Cornell Lab of Ornithology

I asked: "What about beet sugar vs cane sugar?"

Anne Hobbs, Public Information Specialist replied: Great question! And I don't know. They're both more than 99 percent sucrose, but have trace amounts of different other chemicals.
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For me, I'm sticking to my Pure Cane Sugar.