Papaver somniferum. The very largest poppy flowers appear in early summer, followed by the very largest seed heads. The seed head of Giganthemum poppy is the size of a baseball, and chock full of edible poppy seeds for baking. This is an easy plant to grow, but you'll want to give it some room in full sun, in soil that is well drained and not too fertile. Direct sow the tiny seeds on the surface of the soil, and keep the area moist until germination. They need light to germinate. The massive flower stems grow 90-120cm (36-48") tall, topped by flowers around 10cm (4") across. Bees love the dark blue pollen.
These annual and perennial flowering plants have striking similarities, but a surprising range of colours and growth habits. It is easy to grow poppies from seeds. In the right setting, they grow and then self-sow with abandon, without becoming weedy. They will thrive for years at a time in surprising spots, like a crack in the driveway.
Papaver nudicaule (perennial), P. rhoeas & P. somniferum (both annual)
Season & Zone
Exposure: Full sun to partial shade
Zone: P. nudicaule is hardy to Zone 3
Start perennial poppies outdoors in early spring, when some chance of frost is still a possibility. Start annual varieties outdoors at the same time in Zones 3-7. In Zones 8-10, the best bet is to direct sow in the fall.
Poppies are famously difficult to transplant, so starting them indoors is not recommended. If absolutely necessary, use peat or coir pots, and maintain a soil temperature of 12°C (55°F). Seeds will sprout in 20-30 days.
Sow on the surface of the soil, or barely cover seeds. Thin to a minimum of 15cm (6″) apart.
Poppies are easy to grow and the self-sow with abandon, without becoming weedy. Simply pull up unwanted plants (an easy task) before they bloom, or better yet, let them tell you where they want to grow. They will thrive for years at a time in surprising spots, like a crack in the driveway. Other times, they simply won’t take, no matter how much you try. Keep them moderately well watered in hot, dry weather, and do not fertilize.
For the largest heads on Papaver somniferum, sow seeds in the fall or early winter. Thin plants to allow them some space, and keep the area weeded as plants grow larger. Grow this variety in full sun in well-drained, but ordinary garden soil. If spring and summer are cool and damp, or plants are over-crowded, expect smaller seed heads.