Keep it well watered, but don't drown it, especially during the dog days of summer.
Prune the plant on a regular basis to prevent it from bolting , try to keep the height to around 2 feet , as it sometimes becomes top heavy and falls over. In late Autumn, if you intend to keep the tarragon outdoors, it should be mulched prior to the first winter frost so that it overwinters successfully.
How to Propagate French Tarragon
If you'd like to grow French Tarragon from seed , I wish you a lot of luck. It's a difficult herb to get started , germination rates are generally abysmal, and it's simply not worth the effort when it is readily and inexpensively available as a seedling.
You can also start Tarragon from cuttings in the spring or fall. Older plants sometimes become root bound, even those growing in the garden, so it is advantageous to start new plants every 2 - 3 years. Dig up an established plant and separating it, is one method that doesn't always work. Cuttings are the best option
Tarragon is susceptible to rusts and fungal disease as well as Downy mildew and Powdery mildew. Spots on underside of foliage, orange or yellow blisters on the undersides of leaves, yellow leaves, stunted growth are all signs of plant Fungus. These diseases are spread by insects , some are air or soil born. They are promoted by poor air circulation around the plants.
Remove any plant debris and or infected leaves. Try to avoid overhead irrigation if feasible, drip systems are best. If drip systems are not available try to water in the morning in order to allow plant foliage to dry off during the day, and are not overly moist overnight. Ensure plants are properly spaced to ensure adequate air circulation.
You can harvest a few tarragon leaves at any time from younger plants when they reach about 8 inches in height. From older established plants you'll to wait till mid summer. Tarragon loses a lot of its flavor when its dried, fresh is always better. You can also freeze your harvest, trim plants back a few inches in the Autumn and store them in freezer safe bags.
Growing Tarragon Indoors
Tarragon needs a period of dormancy in late fall or early winter to be grown successfully indoors. The acclimation process used on other herbs differs for Tarragon. If you are not purchasing from a nursery, pot a mature plant from outdoors and leave it there until the leaves brown and die off. Bring it to the coolest indoor location you have for about a week, then place it in a south-facing window for as much sun as possible to prompt the plant out of its dormancy. Learn more about Indoor Herb Gardens