Planting dwarf weed seeds are very profitable, so therefore players are advised to make sure that the herb does not die. Supercompost (or Fertile Soil spell) is strongly recommended, as this is the best way of preventing your herbs from getting disease. Or better yet, if you have completed My Arm's Big Adventure, plant it in the disease-free herb patch on top of the Troll Stronghold, to ensure that your dwarf weed doesn't die. Even if you plant it there however, you should still use supercompost to increase your yield and profit.
The following table shows the profit yield, assuming all the herbs and seeds are purchased/sold at the Grand Exchange, for the guide price. If the herb dies, you will lose -8,465 coins.