I am trying to say
What seeds are you planting in your garden?
I thought this was correct but, I feel like something is missing...
Kia semoj ke vi plantas en via ĝardeno?
Correct is: "Kiajn semojn vi plantas en via ĝardeno?"
"kiajn semojn" (= "what kind of seeds") is the object of the verb "plantas" (= "planting"), so it has to have an accusative ending. The word "ke" (= "that") is only used to introduce a subphrase.