French type only grows from roots, the other types are seeds and don't have the traditional taste of true tarragon. My plants were reducec down to one out of three, and its planted right next to my greenhouse in a 6 inch wide strip of poor gravely soil. Nearby, I also have some thyme and thats on its thrid year now, and was grown from seeds. I guess both do well, because they don't get much direct sun after about 2PM. I just cut many of the stems of the tarragon and dried it. Richters offers decent plants and actually credited me for the two that died. It may be that your soil is too acidic, or is laching something necessary for their good growth. Because i had such good luck, I planted a couple of oregano plants in between the other two, and that was also started from seeds. The thyme smells very powerful when I walk by it.

Tarragon requires a cold period each year, so when dividing the root crowns, refrigerate them for about 2-3 months or freeze them for about a week or longer before planting. It requires a sunny position (partial shade in hot climates) in light, well-drained soil, pH 6.7. Water well in dry weather, though it is fairly drought-resistant and fertilise often. Over-watering will cause root rot. Usually becomes dormant during winter and may be difficult to grow in warmer climates. In cold climates, cut the plants to the ground after frost has killed the top growth and mulch well with straw. Foliage dies back in winter. Roots should be lifted and divided every 2 years. The plant is susceptible to mildew and root rot.