Production rate is more determined by the employees assigned to the factory (you can level up employees to increase their productivity). Levelling up facility to 3 allows you to assign one more employee, which makes production rate higher. Seeds need to be planted in correct season and have at least one employee with more than 0 stamina to maintain it.
Yeah, there is Sweet Lovers 2 book but I forgot which mission rewarded it... (No access to laptop now :x)