Fast-draining soil and steady watering produces flavor
Tarragon is not particular about temperature and can be grown from Zone 2 to Zone 9. It will benefit from some winter protection in Zone 2, so lay down a 2- or 3-inch layer of straw or dead leaves.
Tarragon’s roots must have fast-draining soil, or they may rot. Keep an eye on plants during the winter or during rainy spells. When in doubt, plant tarragon in a raised bed where good drainage is ensured.
Young plants need to be watered every other day during dry weather. Mature plants should be watered every three days to encourage a continual supply of fresh leaves. Mature plants can survive for long periods without water, but under these conditions they will not grow new leaves.
Although average to good garden soil is adequate for tarragon, we top-dress our beds with compost every winter. This ensures that plants growing for six or seven years do not lose their flavor. If your soil is acidic, tarragon benefits from an application of dolomite for alkalinity and magnesium.
In the Pacific Northwest, tarragon does best in full sun. It will grow well in half-shade in our region, but may not have maximum flavor. In southern California, on the other hand, some shade is beneficial during high summer.
French tarragon is harder to grow in areas of high humidity where the dormant season is short. French tarragon appears to need a two-month dormancy period when the temperature drops close to freezing. Plants kept inside need to be cooled and rested to remain productive. In places without the necessary chill, Mexican tarragon is a good substitute.
Container growing is easy and works well for one season (top photo, p. 23), but the roots soon take up the space of all but the largest container, and the leaves lose flavor. We have had no problems from pests and diseases and theorize that the anise flavor works as a repellent.