Seeds go towards basic crops; plants go toward fruit plants which are a size between between regular crops and trees (bananas, pears, jackfruit, anything that comes as a seedling in the white bags).
#seed upgrade vs plant upgrade
elder marsh
solar relic
Seeds go towards basic crops; plants go toward fruit plants which are a size bet...
i see, but then why the fruit sapling option to upgrade 
elder marsh
Saplings go towards proper fruit trees - apples, durians, peaches, anything in a brown bag/pot. :p
There are three sizes of things to plant, if that helps. Small crop seeds, Medium plant seedlings, and Large tree saplings.