Any topics that are relevant to the member, I suppose.
If I can ever convince Shoe to appear (and I keep working on him!) then I'll want to talk about veggies, growing for market, chickens, and practical gardening tips.
KentPfeiffer would be excellent to geek out a bit on botanical things, perhaps talk about native midwest plants, and perhaps irises.
eclayne would be fun to talk about our plant database with, along with general gardening stuff (Favorite plants, etc)
Newyorkrita and vegetables.
and so on.