Anonymous

“Can inanimate, conceptual nouns "possess?"”

Yes, however, there are different ways in which we express possessive of inanimate nouns.

Sometimes the noun is used in the sense of an adjective:

The summer months

The summer holiday

The church tower

The car door

Sometimes the apostrophe is used.

The computer's hard drive failed suddenly.

All the houses' roofs were blown away by the storm.

And "of the" is used:

The door of the house was painted green.

The hood of the car was dented by the hail.

The spires of the cathedral were designed in the gothic style.

Your example does not make sense to me. I would say the following:

Summer is 90 days long.

The 90 days of summer were rain-free this year.