Are Sweet Pea Plants Perennial? | The Two-Plant Truth

The answer depends entirely on which plant you have: true Sweet Peas (Lathyrus odoratus) are annuals that die each year, while Perennial Sweet Peas (Lathyrus latifolius) are herbaceous perennials that return season after season.

One wrong purchase at the garden center and you might spend an entire season waiting for flowers that never come back. The confusion is baked into the name itself — “Sweet Pea” actually describes two different species within the same genus, and only one of them acts like a perennial. The other finishes its life cycle in a single growing season, no matter how well you treat it. Here is the exact difference, which one you actually have, and how to make each one thrive.

Which Sweet Pea Is Perennial and Which Is Annual?

The short answer is a botanical split. True Sweet Pea (Lathyrus odoratus) is an annual that germinates, blooms, sets seed, and dies within one year. Perennial Sweet Pea (Lathyrus latifolius), also called Everlasting Pea or Perennial Pea, is a herbaceous climbing vine that dies back to the ground in winter and sprouts again from its root system each spring.

Both belong to the same Lathyrus genus within the bean family (Fabaceae), but their life cycles are fundamentally different. The annual variety produces the famously fragrant flowers that gardeners prize for cutting. The perennial version offers a longer bloom window into fall — but gives up fragrance entirely to do it.

Key Differences At a Glance

Before you buy seeds or plants, run through this comparison table. It answers the two questions most gardeners get wrong: will it come back, and will it smell like anything?

If fragrance is why you grow sweet peas, stick with the annual L. odoratus — the perennial version offers zero scent, a fact that surprises many gardeners who expected the same perfume from a plant that comes back.

How To Grow Perennial Sweet Pea (The One That Returns)

Perennial Sweet Pea is a low-maintenance vine once established, but the first season takes patience. Here is the step sequence that works reliably.

Seed Preparation

Nick the seed coat with a nail clipper or soak the seeds in water for up to 24 hours before sowing. This breaks the hard outer shell and speeds germination by days. The optimal soil temperature is 55–65°F — anything hotter slows sprouting significantly.

Sowing

Direct sowing is preferred because L. latifolius develops a taproot that resents transplanting. In cold climates (USDA zone 6 and colder), sow seeds 4–6 weeks before the average last frost date. In mild climates, sow in late summer to early fall for winter bloom. Plant seeds 2 inches deep in rich, well-draining soil, spacing transplants 4–6 inches apart.

If starting indoors, sow 6–8 weeks before your planned outdoor transplant date and maintain a soil temperature of 65–75°F until the seedlings emerge — which can take 3–4 weeks for this species.

Ongoing Care

Keep the soil evenly moist but avoid overhead watering, which promotes powdery mildew on the foliage. Use a balanced or tomato-specific fertilizer through the growing season. Pick blooms daily in the morning to prevent seed formation — this single habit extends the flowering period by weeks. In fall, once the vine goes dormant, cut the top growth back to 4–6 inches above ground. The roots survive winter and send up new shoots the following spring.

Perennial Sweet Pea is notably deer-resistant and drought-tolerant once established, making it a strong candidate for dry banks, roadside fences, or areas where you want vertical coverage without daily watering. NC State’s plant profile confirms its hardiness across most of the United States.

How To Grow Annual Sweet Pea (The Fragrant One)

If you want the iconic scent, you replant annual sweet peas every year. The process is similar but faster — germination takes only 7–14 days. Treat it like a cool-season annual: plant in early spring as soon as the soil is workable, or in autumn in regions with mild winters. It fades when summer heat arrives, so early planting gives you the longest bloom window.

Common Mistakes To Avoid

Three mix-ups account for almost every frustrated sweet pea gardener:

• Assuming any sweet pea comes back. If you bought a packet labeled simply “Sweet Pea,” check the botanical name. Lathyrus odoratus means annual; Lathyrus latifolius means perennial.
• Expecting fragrance from the perennial variety. Perennial Sweet Pea flowers are not fragrant at all — they provide color and cut stems, not scent.
• Thinking either plant is edible. All parts of both species are poisonous. Despite historical records of cooked L. latifolius seeds being consumed, they are generally considered unsafe. Neither plant belongs in the kitchen.

Perennial vs. Annual: Which Should You Plant?

This second table helps you decide based on your actual garden priorities.

Your Planting Decision Made Simple

One species smells, one returns. Buy annual Lathyrus odoratus seeds if fragrance is the point and you are willing to replant each spring. Buy perennial Lathyrus latifolius if you want permanent trellis coverage, even though the blooms carry no scent. Buy a mix of both if you want fragrance and a vine that outlasts the growing season — just plant them separately so you know which is which when pruning time comes.