It depends on which sweet pea you mean. The fragrant annual is not invasive. But the perennial sweet pea spreads fast. It can earn the label invasive sweet pea in parts of North America. So the same common name covers two very different plants. One is a polite garden flower. The other is a tough roadside spreader.
You have likely seen the spreader already. It sprawls along roadsides, ditches, and old fences. The flowers form big drifts of pink to magenta color in summer. It pops up in spots where no one planted it. The vine climbs over whatever it can reach. That sight alone tells you how well this plant gets around.
That spreader is the perennial type. Its proper name is Lathyrus latifolius. You never need to replant it. The roots survive the winter underground. Each spring the vine pushes back up on its own. It can do this for years from the same crown. A patch you ignore one season can double in size by the next. So you have to stay on top of it if you want it contained.
The annual is a different plant with the same nickname. Lathyrus odoratus is the sweet-smelling sweet pea most gardeners grow on a trellis. It lives for one season only. It sets seed and then dies with the frost. You replant it each spring from a packet. So it stays exactly where you put it. There is no creeping root and no surprise comeback the next year.
The trouble you face with the perennial comes from two habits. First, it returns from a deep, woody root each year. Cutting the top back does very little to stop it. Second, it self-seeds with ease. The pods dry, split open, and fling seed into new spots. Both traits let it naturalize across open ground. Over a few seasons it can crowd out the smaller plants in your beds. You may pull it for years before your soil runs out of buried seed.
This spread is why some places treat it as a real problem. A few regions in North America keep an eye on the perennial. They watch it because it escapes gardens with ease. From there it settles into wild and open areas. This is where the invasive sweet pea label comes from. In certain spots it is managed as a noxious weed. That status can limit where you are allowed to plant or sell it. You may even need a permit, or you may be told to remove it. The annual never lands on these lists. It simply cannot come back on its own.
Here is how to stay on the safe side. Check your local invasive-species or noxious-weed list first. Do this before you plant the perennial sweet pea anywhere. The rules change from one state or county to the next. A plant that is fine in one area can be banned a few hours away. So a quick search now saves you trouble later on.
Want the climbing look without the risk? Grow the annual instead. Plant Lathyrus odoratus for scent and color you control. You get the vine and the blooms on your trellis. But it stays in its bed and dies back each fall. You can swap the variety every year for new colors too. Skip the perennial near wild land or open fields. That way it cannot jump the fence and take over the field next door. You keep the cottage-garden charm and lose all the worry.
Read the full article: Sweet Pea Vine: Complete Grow Guide
