Floating Islands can have Dew Lilies planted on them.
Cost to plant might be something like:
°1 Dew Lily Plant
°1k Twilight Berries
°1k Kindle Berries
°1k Frost Berries
(I don't see that as too much considering its a one time cost and it will keep you from having to replenish plants by hand)
The combined ingredients would create a Floating Spring.
Floating Springs would have a dew capacity of 15 at level one and be upgradable to hold more dew by multiples of 3.
Dew Tears will have to be refilled into the spring.
Plants under a Floating Spring and within radius would get auto replenished provided enough dew is in the spring.
After a month the Dew Lily will wither away and ONLY a new Dew Lily will need to be replaced to continue the effects of the spring.
Upgrading would take Mourning Berries and Dew Tears?