#It's also interesting to deduce or formulate his relationship with other deities because of this

[my-name-is-apollo]

If Apollo is connected with spring's fertility, does that make him an agricultural god? Did he have such cults? Why does Apollo have so many functions?

Apollo is not connected to the fertility of the soil or plants during the spring, that is Demeter's domain. But yes, he is an agricultural deity in his own way (which I'll discuss below), and his cults concerning that were present in Sparta, Athens, Cyrene and many other cities. Many of the festivals dedicated to Apollo were agricultural, including Thargelia which celebrated Apollo's birthday. But unlike Demeter, Persephone and other agricultural gods, he isn't concerned with fertility of the soil and crops. He is the protector of crops, the one who prevents plant diseases and pests. Look at some of his epithets

Erythibius - preventer of fungal diseases (blight/rust/mildew)

Sitalcas - protector of corn

Smintheus - lord of mice (in this context, he is the one who prevents mice infestation)

Parnopius - Lord of grasshoppers (again, he controlled the locusts that infected the crops)

Pasparius - god of meal, because he protects the harvested crops

Those are his major agricultural roles. He might also have functioned to some extent as a patron of the reapers, since his epithet Erithius means "god of reapers", though this might again be because he safeguarded their harvest. So, Demeter causes the production of crops, and Apollo protects them. He is indirectly connected to spring's fertility in his role as the leader of Seasons (Horomedon) and a light bringing deity, and some epithets concerning that -

Hersos - sending fertilising dew

Pandothales - he who makes everything bloom

Apollo had so many functions because he was an extremely popular deity and his cults were wide spread and appealing. It's nearly impossible to not be popular with arts and healing on your side XD Plus, his oracles were also a HUGE reason why he was all over the place in ancient greece. He has a large number of primary domains and functions, and almost equal number of secondary domains. One can wonder how one god was in charge of so many things, but well, ancient greeks believed it was nothing their great Apollo couldn't handle.

And to clarify Regarding his secondary domains - he doesn't control the the domain itself, but rather plays the role of a protector. Sea and agriculture are his main among the others. He didn't control waters like Poseidon, instead he helped sailors, and you can find many myths where Apollo helps sailors in many ways, and they pray to him and thank him for safe sea voyage. When it came to home, while Hestia was concerned with family & hearth, Apollo was invoked to protect doors and gates. When concerned with death too, he is the overseer of funeral rites and the protector of tombs. (he gets really angry when people don't do proper burial for the dead). In animal husbandry too (which is actually his primary area) Hermes, Pan and Apollo are seen as gods who can bring fertility, but Apollo alone appears as the protector of flocks and herds from wild animals. Yes, that's a ridiculous amount of secondary jobs for a single deity, but this will be seem natural once you learn that Apollo was generally called upon as the "averter of evil" in every aspect, throughout the ancient Greece.