Lay a 4-inch layer of compost over the planting area, then apply a low-nitrogen, high-phosphorus fertilizer at the label-recommended rate. Till the compost and fertilizer into the top 12 inches of soil to add both nutrients and to aid drainage.
Fill a bowl with warm tap water. Soak the sweet pea seeds in the water overnight the evening before planting. Soaking breaks dormancy, so only plant the seeds that have visibly swelled after soaking as the other seeds are not viable.
Plant each sweet pea seed 1 inch deep and space them 3 inches apart in either rows or clusters. Plant vine-type sweet pea seeds within 2 inches of their support so they can easily find and begin climbing it after germination.
Water the bed just enough so that it is evenly moist to a 6-inch depth. Continue to water the bed as needed to maintain this moisture level, usually once a week during the cooler months.
Build up a 1-inch ridge of diatomaceous earth, available at garden centers, around the sweet pea bed to discourage snails from attacking the seedlings once they emerge. Alternately, use slug bait following the instructions on the package.