Horticulturists know crown vetch as Securigera varia or Coronilla varia. You may have introduced the plant as a means of erosion control on sloping areas of your property. Since crown vetch spreads extensively---one plant may account for coverage of 70 to 100 square feet areas in just four short years--and grows a very strong root system, it is an excellent choice for this function. Unfortunately, these very properties also make the plant hard to get ride of. If you are thinking of introducing other plants to soil currently inhabited by crown vetch, you have to first learn how to kill this plant, since it is notorious for its domination of garden space.
Mow your crown vetch when it shows flower buds. Even though this will not prevent the spread of already present seeds in the soil, it will greatly diminish the plants' strength and ability to spread above ground. This is a good option if you choose to selectively kill crown vetch rather than eradicating the entire patch. Clean out your mower and discard all remnants of the plants, especially seeds.
Spray Clopyralid on reappearing growth. Clopyralid receives mixed reviews. On the one hand, it is very specific in targeting the broadleaf crown vetch, which cuts down on the eradication of desired plants in the same flowerbed. On the other hand, this substance remains in the soil without breaking down for more than a year, potentially damaging future vegetable crops you might plant in the flower bed. If you use this herbicide, consider growing flowers instead of vegetables.
Scrutinize your flowerbeds consistently and remove new shoots as soon as you locate them. Seeds may sprout years after you killed off your initial crown vetch patches. If you allow the young plants to sprout and grow extensive rhizome systems, you will have to once again remove the invasive plants with a broad application of herbicide.
Mark the extent of your crown vetch patch with craft sticks. This makes it easier to keep track of your progress and lessens the odds of any missed underground rhizomes.
Mow the patch. Kill off the above ground crown vetch by mowing down the plants. Empty your mower's bag into the garbage bags and tie them securely. Rake up any broken plants---pay particularly close attention to seeds---and discard them into garbage bags as well.
Dig up rhizomes with your spade or pull them up by hand. These rhizomes can measure up to 10 feet in length, so it is crucial that you remove all of the underground plant structures. Place rhizomes into the trash bags and tie them securely.