Does one say shehecheyanu on a new, seasonal haadama fruit? People have told me not to but is there a source for this?
Gemara Eiruvin 40B: Rav Yehuda would say shehecheyanu on a new gourd.
A gourd would have the brachah of borei pri ha'adamah.
Shulchan Aruch Orach Chaim 225:6 says that it should be a fruit that is new once (or twice - Rema) a year. Otherwise, the fruit's blessing is not a criteria.
In fact, the Rema there allows a shehecheyanu blessing on a new vegetable as long as it was not standing the whole year in the ground.
So, I am not seeing why you would have heard that the brachah of Ha'adamah by itself would stop one from making a shehecheyanu.