Some tips for harvesting oregano are to wait until the oregano plant is about 4 to 5 inches tall and to begin harvesting oregano leaves as they grow in, looking for the leaves that appear just before the flowers bloom. While any oregano leaves can be used, these are the ones with the most flavor.
While the oregano plant is still healthy, remove all the leaves, and freeze them for the winter. Do so before the bitter cold hits and destroys the plant. It is also possible to dry oregano leaves and keep them in a container to be used year-round. Even if you are not using the leaves right away, oregano plants need to be trimmed when they reach about 4 inches. This allows the plant to continue growing.
Oregano plants do need to be watered, but they do not need to be watered as much as many other herbs. When the soil around the plant feels dry, water it. Give it sufficient water when it needs it, but not frequently. When you plant oregano, make sure it gets plenty of sun, planting later in the season if necessary. Oregano can be planted from cuttings or seeds. Thin out the plant every few years in the spring.