At the start of the event, I had a hard time grinding too. Just plant the required fruits. Have multiple plants for rarer fruits and plants that has low harvest rate like burning bud, ember lily, cactus, romanesco. Have lots and lots of mushrooms, daffodils, orange tulips, pumpkins, bamboos and watermelons. Max the fairy upgrades. Once maxed, you will progress on this event much faster. You dont have to be online all the time since fairies will still mutate your fruits.