French tarragon cannot be grown from seed. The only way to grow this herb is to purchase the plant, to take divisions of an established plant in the spring, or to take cuttings from new growth in the summer or fall.
French tarragon is a perennial plant that grows from 12 to 24 inches tall. This plant grows slowly and spreads by underground rhizomes. Any seed that may come on the French tarragon plant will be sterile and it rarely flowers.
French Tarragon From Cuttings
If you have an established French tarragon plant, or you have a friend with a French tarragon plant, you can start a new plant with cuttings.
Fill a pot with moist sand or well-drained potting soil, then go out and take 6 to 8 inch cuttings from the French tarragon plant. When you take your cuttings, make the cut right below the node. The node is where the leaves connect onto the stem.
Remove the leaves growing at the bottom third of the stem. Dip the bottom end of the stem into a glass of water. Shake off the excess water and then dip the wet end into some rooting hormone.
Stick the end with the rooting hormone into the moist sand or you can use well-draining potting soil. You need to keep the sand moist so the cutting will root. Place the pot in a bag and close the bag. This helps keep the humidity and moisture content higher.
Check the sand daily to make sure it is still moist. If you see any mold growing on the sand or tarragon cuttings, leave the bag open for a while, otherwise the cuttings may rot. The cuttings should have formed roots after four weeks. To know if your cutting has formed roots, look at the stem. When you see new growth on the stem, roots are forming in the soil.
Remove the plastic bag from your pot. Keep growing the French tarragon plant in the pot for another month, then, you can plant the tarragon outdoors, or keep it in a pot. Grow French tarragon in a pot that is 12 inches in diameter and 12 inches deep. Place the pot in a warm location, out of direct sunlight.
Planting French Tarragon Outdoors
Work up the soil where you are going to plant your tarragon, if you are going to plant it outdoors. For people living in colder climates or any areas that have a frost, you can plant the tarragon in the soil, but you will need to dig it back up and transplant it in a pot to take indoors. As you dig or till up the soil, add plenty of compost. This helps to lighten the soil and also adds nutrients to the soil. If your growing site has a lot of clay in it, add some sand or perlite to help improve the soil for drainage.
Dig a hole for your French tarragon plant. Do not dig it any deeper than the rootball of your plant, because you need to keep the top of the rootball and the soil the same. Space each plant 24 inches apart.
Water the French tarragon thoroughly after planting. Place a layer of mulch over the soil around the French tarragon plant. The mulch helps retain moisture which is important because the roots of the French tarragon plant are shallow.
When fall comes, and depending on the area you are living, you will need to prepare the tarragon plants. For places that only have a mild freeze, you need to trim back the tops of your French tarragon plant back after the first frost. Cover the plants with a thick layer of mulch to protect them. For areas that have colder winters, trim the plants back and then dig them up and transplant them into pots. Keep as much of the rootball in tack as possible, so your tarragon plant doesn't suffer from shock.
Place the pots in your home, choosing a sunny window. For tarragon plants to grow well, they need 6 hours of sunlight a day. French Tarragon is relatively pest free, but it is susceptible to powdery mildew, downy mildew, and root rot.
To use French tarragon, wrap leaves in a paper towel and place in a plastic bag. French tarragon keeps in the refrigerator for two to three weeks. You can also dry French tarragon or freeze it for later use.