What Is It?

The perennial sweet pea (scientific name Lathryus latifolius) is a non-native, invasive perennial plant currently in low density but increasing in the Fitch Mountain area. In the spring and sometimes early summer, you may notice a strikingly beautiful pink-flowering vine sprawling in a few spots along the roadsides around the mountain.

Look closely and you’ll see its stems have distinctively flattened “wings.” The leaves are shaped like a pair of rabbit ears. Perennial sweet pea is not as sweet-smelling, if at all, as the annual “sweet pea” (Lathyrus odoratus) sold in nurseries, with which it can be confused.

Variously called everlasting pea, wild sweet pea, perennial peavine, and perennial pea, it originated in Europe and was brought over a long time ago as a garden plant. Its seeds have been used in seed mixes for erosion control, which helps explain its spread.

It spreads easily on its own, is pervasive, and in large infestations it is difficult and time consuming to remove. Because of this, it is often considered to be a weed, despite its attractive appearance. It now is found in several western states and is not new to California or even Sonoma County, especially in west Sonoma County, where large and spreading roadside infestations have cropped up in the past few years. Fortunately, it appears to be limited to a few manageable spots in the Fitch Mountain area, so far.

So Why Is It a Problem?

Perennial sweet pea can show up in your garden as what might seem to be a welcome guest for its gorgeous flowers, but later, as it climbs your other shrubs and starts seeding itself where you don’t want it, you’ll see why it is regarded as a bane of gardeners. Perennial sweet pea vines grow quickly as they emerge from perennial roots and are capable of climbing up and over other plants, completely covering them and shading them out. By the end of summer, its foliage becomes rather ragged and yellowish, but the growth cycle repeats itself the next spring. Perennial sweet pea can also encroach on natural areas, as evidenced by a small patch at the edge of the future Fitch Mountain Open Space. It is this ability to invade natural areas that especially concerns me. Invasive plant species often out-compete native wildflowers and other plants for space, light, or water. This can affect the area’s ability to support wildlife that depend on native plants, thereby resulting in an overall lower quality of native habitat. This is but one issue with invasive plants. (You’re probably well aware of the fire problem associated with nonnative French broom, which has long been established on Fitch Mountain.)

What Can We Do About It?

The most cost-effective way to thwart the spread of an invasive weedy species is to go after it early after detection, before the problem gets too large to tackle. So whether you are interested in keeping the top of Fitch Mountain as a beautiful native plant and animal community to enjoy for generations and preventing yet another invasive there, or just want to keep a pesky invader out of your garden, it makes sense to take steps now to prevent the spread of this pretty perennial.

Use the link at the top left of this page to see a step-by-step approach to removing perennial sweet pea. As with any invasive plant removal project, persistence and long-term commitment are key. Removing it only once, with no follow-up, will set you up for discouragement. Keep at it! Fortunately, it is a soft, herbaceous plant, easy to pull anytime of year. If you can’t get the roots, at least pull it enough times to prevent it from blooming and, most importantly, to keep it from going to seed, and don’t move seed pods around except directly into a garbage bag for proper disposal.

If you’re in the Fitch Mountain area and would like help in identifying perennial sweet pea and/or removing it as a courtesy of your FMA membership, contact me, Kate Symonds, kate@terraserve.net.

Kate Symonds is Secretary of the Fitch Mountain Association and a biologist whose day job involves working with others to restore native habitats