The gather rate of rare resources can be increased in various ways, as described in the main article.
Healing effect Edit
With a Citrus, ships at sea are repaired at a rate of 1 hit point per 1.33 seconds and a flashing green 'glow' appears under the ship each time a hit point is restored. At this rate, most ships would take 3–4 minutes to get all their hit points restored.
The healing rate from Citrus is slower than the repair rate of the Dock. The repair rate at the Dock can also be improved by researching Herbal Lore, Medicine, and Pharmaceuticals at the Granary. Ships garrisoned inside a Dock can be repaired in less time (with all three upgrades five times faster). So especially in the late game, it might be more effective to pull damaged ships back to a dock for repairs.
Also note, that transport vessels like the Transport Barge do not profit from this resource (and also cannot be repaired at a dock).
The healing effect of Citrus stacks with the natural healing of Aircraft Carriers.
Sometimes, citrus appears on land maps where there are no oceans thus reducing its effectiveness.
- The effect of ships healing at sea when supplied with Citrus is due to the fact that citrus prevents scurvy, a disease especially common on ships from the 15th to the early 19th century. Moreover, the fruit and bark of citrus trees can explain the resource's contribution in Food and Timber.