Why isn't it "In spring, we work in a garden"? I don't see anything indicating "the".
I have the same question. Why cannot be "in spring we work in a garden" with article "a"?
"In THE garden" sounds more natural to my (US English) ear, but there's nothing grammatically incorrect about "in A garden." Try reporting it, if you get this one again. DL may decide it's an acceptable translation.
What kind of case of spring in this sentence? And can someone explain why does we use that case?
"Jaře" is the locative singluar form of "jaro." As I am learning too, I can't tell you exactly WHY the locative case is required, other than to suggest that "na" (in) hints at location -- we are saying "IN the spring."
Two of the seasons use "na" for "in" (spring and fall) and the other two (summer and winter) use "v" instead.
na jaře -- v létě -- na podzim -- v zimě