So watching video's on the game, I saw people putting acorns in the seedling storage to grow saplings to plant. (for renewable trees)  But when I tried it, I get 15 seeds in the storage (has the initial 5 fertilizer) and then nothing.  I can't add more seeds or fertilizer and nothing appears to be growing.  I've likely encountered a user error.  

I've managed to grow trees by directly planting the acorns in holes in the ground.  And they grow pretty fast.   But am left wondering what to do with the Seedling storage?  

You need to put 15 seeds and 5 fertiliser into the seedling tray. Once you've done that they change into 15 seedlings.