Drop rate is not bad. Can't remember for sure, might even be 100% - kill this type of enemy, drop this type of seed. Difficulty is spawn rate, those are elites or mini-bosses, quite rare. Some only appear at night, some only when raining (so you talk to the cows for weather forecast - yes cows, don't ask - then rest in camp till it rains), and only in specific areas, so you have to really go hunt for them. And you have to equip certain items to increase luck or something to have better spawn rate. Then kill them. Remember, this is turn-based rpg, so it's time consuming (a couple of them I could rubble band my controller to farm).
The bigger problem is that by the end of the game, you are still very far from having some of your 9 attributes maxed at level 999. Some I am short by 400, even 800 (each seed gives 1 point increase). And there are like 8 characters in your party. So it is quite impossible, and honestly totally pointless apart from OCD reason. You are not supposed to max them out (not even your char levels, certainly not each individual attribute), the game can be completed way earlier before you max anything. To be honest, I only wanted to max certain attributes for certain chars, it's ridiculous to attempt more than that, but I gave up anyway (did max all char levels iirc).
