Valerian seeds can be planted in a farming patch to grow grimy valerian. This requires a Farming level of 18, and harvesting grants 18.1 experience per herb. Seeds can only be farmed in dungeons with complexity level 5+.
The seeds can either be obtained from monster drops or bought from the Smuggler.
As with all seeds in Daemonheim, the upgraded Ring of kinship's Gatherer effect has a chance to produce extra herbs when farming.