Ultracompost is the most potent version of supercompost and compost and is used in conjunction with the Farming skill. It is created by filling a compost bin with 15 buckets of dragon manure, then collecting it with empty buckets.
A plant that has been treated with ultracompost has a 7% chance of dying, half that of supercompost, which has a 14% chance.
For herb and allotment patches, using ultracompost will increase the number of harvest lives by three (from a starting number of three lives). Every harvesting action will decrease the number of lives by one unless it is saved, with the patch becoming empty when it runs out of lives. This chance is dependent on Farming level and other boosts (magic secateurs, greenfingers aura, juju farming potion, master farmer outfit, etc).