From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-1888-284587
Question: I have tried year after year to grow herbs, usually basil
and oregano. The plants thrive and it seems after I harvest them they
are never quite the same. I usually pinch them with my fingers.
Help!!
Answer: I wonder if you're accidentally bruising the stems when you
harvest your herbs? Sometimes it's best to snip the stems with a pair
of scissors. A clean cut will heal quickly, and the act of snipping
the growing tips promotes new stem and leaf growth on the remaining
portion of the stem.
It might also be that you're not harvesting often enough. With both
the basil and oregano, try harvesting frequently rather than waiting
until late in the season. You can snip sprigs from spring through
summer. In fact, oregano sprigs can be harvested when the plant is
only 6" high, and you can continue snipping the leaves and stems
throughout the summer months.