With flowers similar to the highly fragrant annual sweet pea, perennial sweet peas (Lathyrus latifolius) have no fragrance and grow on vines that are perennial in U.S. Department of Agriculture hardiness zone 6 or warmer. The flowers are pink, white or red. The vines rapidly grow about 6 to 12 feet high, grabbing onto their support structure with tendrils or twining around it.
Choose a spot in full sun with an existing support structure or install a decorative obelisk, trellis or arbor. Perennial sweet pea vine grows well in soil of average to low fertility, but requires good drainage.
Loosen the soil in the planting site to a depth of 6 to 8 inches by turning it over with a garden shovel. Do not add soil amendments or fertiliser to the planting hole. Rake the surface of the soil smooth with a garden rake.
Plant seeds about 1/2 inch deep and 4 to 6 inches apart. Thin them so that the remaining plants are about 8 inches apart when they germinate, which takes 14 to 21 days.
Cultivate around the base of the vines shallowly, to remove weeds while they are still small.
Mulch the soil when the seedlings are about 8 inches high. At the same time, give them a start on their support structure by tying them to the base of it.
Supply them with additional moisture when rainfall is less than 1 inch per week.
Prune perennial sweet pea vines in early spring only to remove dead or diseased branches and to maintain the overall shape and appearance of the vine.