From our perspective, the answer to whether we, sweet peas (Lathyrus odoratus), can be grown as perennials is rooted in our fundamental genetic design. We are, by our very nature, annuals. This means our entire lifecycle—from a dormant seed awakening in the soil to producing our own seeds for the next generation—is programmed to be completed within a single growing season. Our biological imperative is to germinate, grow, flower, set seed, and then die. This is not a choice but the core instruction written into our DNA. Attempting to overwinter us is a fight against this intrinsic programming, and it is a fight we are destined to lose in most climates.
Our physical structure is simply not built for long-term survival, especially in cold conditions. We are tender plants with soft, herbaceous stems and foliage. We lack the woody tissue, protective bark, or deep, hardy root systems that true perennials develop to withstand freezing temperatures and winter dormancy. When frost arrives, the water within our cells freezes, causing irreparable damage to our cell walls. This leads to our complete collapse and death. Even if the cold doesn't kill us, our energy is entirely depleted after the massive effort of flowering and seeding. We have no reserves left to draw upon to resprout.
It is crucial to distinguish us, Lathyrus odoratus, from our very close relative, the everlasting pea, Lathyrus latifolius. This cousin is a true perennial. From a plant's viewpoint, the difference is significant. Lathyrus latifolius develops a robust, spreading root system that allows it to store energy and lie dormant underground through winter, ready to send up new shoots the following spring. Its stems are hardier. However, it lacks our most cherished trait: our powerful, sweet fragrance. This is the trade-off. So, while a gardener might see a similar-looking vine and call it a "perennial sweet pea," we are two distinct species with different survival strategies.
While we cannot live as individual perennial plants, our species has a clever tactic to create a perennial-like presence in your garden: self-seeding. If you allow our finished blooms to develop into seed pods and do not deadhead them religiously, we will drop our seeds onto the soil below. These seeds possess a hard coat and can lie dormant through winter, protected in the earth. When conditions become favorable again in spring, these seeds will germinate, and a new generation of sweet peas will emerge in the same spot. To a gardener, it may appear that we have returned as perennials, but in reality, it is our children taking our place, carrying on our legacy season after season.
