Here is a reply regarding this question in the FAQ: Snow White forum thread:
It depends on what kind of food you use, whether you use two snowdrops or not, whether you get all of the Dwarves you need on one plate. Generally using superfood, people were able to complete it with 12 - 14 or so seeds but you might get away with even fewer than that with the new 20 feed superfood.
Here is the link to the thread in case you need it and it is located in the Most Useful Topics section of the forum:
https://www.fairylandgame.com/fbfairy/forums.php?tid=76672 The answer I pasted here is located at the top of page 80 from Tracey.
