Pick individual leaves or wait and harvest full heads.
For ongoing harvest, you can begin harvesting once the leaves reach about 4 inches tall.
Harvest the outer leaves of the head and let the inner leaves continue to grow and mature. Just snip either single outer leaves or grab a bunch of them and cut them with scissors one inch above the base of the plant.
Be careful; if you cut into or below the base, the plant may die, so leave the small leaves in the middle to regrow easily.
Do not cut more than a third of the plant in you want it to keep growing.
For the Dressing
For the Salad
Make the Dressing: Whisk lemon juice and zest, lime juice and zest, honey, and dijon in a small bowl. Slowly drizzle in the oil, whisking constantly, to emulsify the dressing. Season, to taste, with salt and pepper. Set aside.
Make the Salad: Cut the root end off the lettuces and gently wash and dry the leaves. I like to rinse leaves separately, under the tap, and spin them dry in my salad spinner. Tear the larger leaves into smaller pieces. Pile leaves into a large bowl. Sprinkle in the tarragon and toss it gently with the lettuce. Just before serving, toss the salad with just enough dressing to coat. Serve immediately.