Sweet-pea flowers, known botanically as lathyrus odoratus, are sweetly fragrant annuals that bloom in abundance in the spring and summer. Sweet peas have a vine-growth habit and use fine tendrils to climb up any nearby structure. The seeds can be planted in late fall or winter or in early spring, depending on your climate, and typically germinate within one month's time.
Select a planting time for your seeds that coincides with your climate. In most regions of the United States, plant sweet peas in the very early spring while the ground is still frosty but can be dug into if not easily worked. In the Western and Southern regions of the country, plant your seeds in the fall or winter so that they are in the ground by the end of January.
Prepare a well-tilled and nutrient-rich soil planting bed for your sweet-pea seeds. Make sure the soil is moist and can hold some moisture, but is also well drained enough so that it is not consistently soaking wet. Amend the soil with a few pounds of aged manure and/or compost and till into the soil to at least a foot deep.
Scarify the sweet-pea seeds to speed up the absorption of water and, therefore, germination. You can do this by rubbing the seeds between two sheets of coarse sandpaper or by gouging a small spot on each seed with a nail clipper.
Bury the sweet-pea seeds 2 inches deep in the prepared soil, placing up to four seeds every 6 inches. Cover over the seeds with soil and water deeply.
Mulch over a well-marked seed bed with a thick blanket of straw or leaf mold to hold moisture and insulate the seeds from the cold or displacement by wind or rains.