Salad rocket or Arugula is by far the easiest and most satisfactory herb to grow in your garden. You do not need green fingers to grow these plants to yield an abundant supply of fresh leaves that are wonderful I. Salads, sprinkled on top of pizza or made into pesto. Have a look at the post I wrote on how to grow it successfully here.
Here is how to harvest Rocket Seeds.
All you need to do is store the seeds and sprinkle them onto the ground when you are ready.