When a cultivator loses his blood, although it won't harm him, it would affect his daily cultivation. So, the Spirit Farmers who already have low cultivation, don't use their own blood.
Also, at the same time, they won't buy the blood of Spirit Beasts because it won't be cost-effective for them to nurture a Rank 2 Spirit Plant. Instead, they buy animal blood, which is cheap.
Even if there were animals in the Mystic Soil Domain, Ethan would have still used his own blood to nurture the Blood Spirit Grass because a Cultivator's Blood…especially a Level 3 Foundation Establishment Cultivator's Blood would greatly enhance the quality.
'Unlike other cultivators, I don't cultivate at all, and losing some blood won't affect my cultivation at all.'
Once Ethan had enough Life Points, he could directly buy the cultivation from the [Interface of the Killer's Stats].
