1. Seeds from greens and herbs are found in the flower heads.
2. They will produce flowers at the end of the season. At a certain point, you may need to stop picking the food to allow the plant to flower.
3. Once the plant has flowered, it will start to brown. It looks like it is dying back, but it is producing seeds.
4. Wait until the seeds are fully mature. Pay close attention. You may need to put a paper bag around flower pods, or collect regularly as they ripen to prevent them from dropping or blowing away.

Here are some photos of various leafy greens going to seed:

 This is some lettuce seed in the stage after it has flowered (above)

When collecting leafy green seeds, pay attention to the plants. They will begin to “bolt”, grow upwards & create flowers (they will no longer taste very good at this stage), let those flowers bloom & die back, and then seed pods will form. Let them brown & then collect! Dry further indoors, pop open pods, and there is the seed!

 Romaine Lettuce bolting, it is about to send out it’s flower stalk

 Romaine sending out flowers

 Leafy green flower stalks against a beautiful august evening sky

 Red Romaine just about to flower

After the flowers have bloomed, you will have to wait another few weeks for the pods to form and start to dry out . . .watch carefully, when they are ready, they may burst open & you will loose the seed. Take them inside to dry before that stage . . .