The bag was black, so I think it was the 51 or 52:
https://www.hummert.com/product-deta...-growing-media
A guy not too far from me owns a flower-growing greenhouse. He is listed as a dealer for Fafard. He has the components of the mix delivered by semi-trucks, and mixes it himself. He has the conveyor apparatus that feeds mix into bags. It's all quite impressive. He sold me a few bags the first year I had my greenhouse, which he was doing just to be nice.
Hummert will deliver that mix to me by the pallet for like $12-14 a bag I think (the prices listed on their web site are not the real prices). I can get a pallet delivered for only a $35 shipping fee if I wait for the bi-monthly truck delivery. But I never have the money to buy a season's worth of mix all at once, and end up using the peat mix from Menard's.