Answer: Cilantro is Coriander, an annual herb that grows in full sunshine and average garden soil. As an annual, it it will develop flowers and set seed, and then die. You can prolong the life of the plant by regularly cutting or harvesting the leaves. What I've discovered with cilantro is no matter what you do to prolong its life, it only survives for 6-8 weeks. In order to have a ready supply of the leaves, plant your seeds at 2-week intervals. This way you will always have fresh cilantro.
Tarragon requires full sun to partial shade and rich, sandy, well drained soil. The plant often fails due to soil that is too wet or acidic. You might try growing it in a container filled with cactus mix or sandy soil. I think you'll have better luck with it.
Good luck with your garden.
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