Poppies are a beautiful addition to any flower garden. They are typically grown for their flowers and seeds, or as memorial flowers for veterans, but some plants have a high alkaloid content and are used for creating opium. While these are the same seeds, growing them in your garden for seeds and flowers is a legal use of these plants. Papaver somniferum is also known as a bread seed poppy, because the seeds are edible, and are typically used in baking. The seeds contain oil, and can be pressed to harvest the oil for cooking.
Poppies are easy to start in fall or spring. If your area experiences hard freezes, save your seeds for spring. Poppy plants can tolerate light frosts, but flowers do not. Choose an area with fertile soil in a sunny area. You should plant your seeds directly as they do not transplant well. Poppies only germinate in cool soil, so choose late fall or early spring to plant, as later spring sowings are often unsuccessful. You will “cast” or scatter your seed and press them into the soil but do NOT cover them. The seeds are very tiny and require light to germinate. Typically the seeds take only a week or two to germinate, and will quickly grow to 3” tall. You will need to thin your poppies as they grow, so that they eventually have 8-12” of space. Since poppies have very sensitive roots, just cut the plants you are removing at soil level. If you don’t thin the plants, you will not get as many flowers, as they are sharing nutrients.
Poppies are annuals (meaning they only last one season), but are prolific self-seeders. If you want poppies in the same area year after year, they can be left alone, but will need more thinning next season. You can cut off the seed capsules when they are brown to harvest seeds (or before then if you want to reduce the number of seeds in the area). There is a short time period once the seed pods have turned brown and are ripe before they split and spill seeds, so try to harvest them in this window. You can just shake the capsule into a bag and the seeds will fall out.