Adding flavors with the proper technique will produce your favorite variety of smells and taste like whatever you want. Do not pour syrup or similar sugar based flavorings on the harvested herb because sugar will make a harsh taste. The best flavor enhancing starts while the plant is still growing. There are two main approaches, inside out and outside in. You can apply flavors inside the plant while it's still growing and you can try to add flavors after it's been harvested from the outside. Select a flavoring that is very concentrated. Take orange for an example. You could use orange juice but it contains natural sugars. You will find some concentrated flavor extracts in the grocery store. Vanilla extract is cheap and readily available, so is lemon extract (cooking variety). Other extracts can be found in stores that specialize in baking supplies. Vanilla is our favorite taste. A coffee filter works well for filtering fruits but it'll take a while to filter it all. You may have to change filters a few times. Concentrated extracts are the best to use. Use extracts shortly before harvest. Most extracts have sugar in them. Sugar will ferment and decay rapidly, even more so in a hydro unit. With hydro put the flavoring in the water between 1 and 3 hours before harvest. Anything longer will produce harmful bacteria. Plants draw up solution fairly quickly, one hour should be enough for some of the flavoring to reach the top. Three hours should not be enough time for bacteria to grow. Dump out the solution right afterwards and clean out your unit. Use plain water for a few days before harvesting your hydro crop so all that will be in the water will be the flavoring. Soil growing is easier. Let the plant dry out a little before applying the solution. Do it in the watering just before harvest. Give your plants plain water for the last two weeks and near the end do this process. When the plant is somewhat dry and craving water, give the plant the water with the flavor when it's a little bit thirsty and it will draw it right up. One hour is more than enough time.

5. Don't treat your whole crop this way while experimenting. Dirt growers will find this easy because they could use something different in each pot. Hydro people may want to isolate a plant or two with the solution. This wouldn't be very hard because you wouldn't need circulation for the short period of time it would be soaking in it. Try guava, pineapple, grapefruit, cherry, mint or even pina colada. Stronger and more concentrated flavorings will have a more pronounced effect than more dilute products. You need gallons of orange juice to get what you want but a half ounce of concentrated strawberry essence might do the job nicely. In short, experiment and see what works for you.
(from:http://www.seedbankupdate.com/cure.htm)