From level 3+ you can access this Short-Time quest in the Farmers Society building:

There will be 2 new crops:

____
Lucky Clover___&___Dentallaria

You will receive 10 of each crop at the beginning of the Event.
You will NOT be able to buy any more at the Market or the Seed Shop. If you have donated ALL your seeds to the Event, you'll need to wait for the automatic replenishment of 5 new seeds roughly every 6 hours
These seeds can be planted on all your farmlands, including the island (all from level 3+).
During the Event here are the new crop stats:

No, not for this event

Reminder: ALL items donated to a quest, even partially, can NOT be refunded. If you're not sure to be able to finish a Job, then do NOT start it

Prize Items

Event Sticker

Once you've completed the job that gives the sticker,
you'll find it in the Sticker Album (in the Post Office building).
You might need to move some of the other stickers around to see this new one.

base item:
warning: once upgraded, these items can NOT be un-merged!!!
Miss Moo's Table

size: 1x2
Gives: 65 EP
Time: 11 hours

Miss Moo's Table + 1 upgrade = Table with waiter

Gives: 125 EP
Time: 12 hours

Table with waiter + 1 upgrade = Festively decorated table

Gives: 185 EP
Time: 13 hours

Festively decorated table + 1 upgrade = Miss Moo takes a seat

Gives: 245 EP
Time: 14 hours

Miss Moo takes a seat + 1 upgrade = Cheerio Miss Moo

Gives 350 EP
Time: 15 hours

As usual, this option is possible by clicking on the gold chest on the right of the quest window.
Even if you have partially donated items, the amount will be adapted to show how many BBs you still need to pay to complete that particular Job.

Yes & No.
Dentallaria/Plumbago will remain in the Game.
It will become a level 88 crop.
If you don't yet have that level at the end of the event, your seeds will remain hidden in your barn inventory until you do get there.

Lucky Clover, however will disappear after the event, it will be exchanged for 5 EP each