How do I kill mint in my flower bed? Help please, it's out of control?

any people have had luck using boiling water to kill mint. Others swear by using a homemade mixture of salt, dish soap and white vinegar (2 cups salt, 1 teaspoon soap, 1 gallon vinegar). Both methods will require frequent applications onto the mint over some time in order to kill it. Be aware that these methods will kill any vegetation that it comes in contact with.

Read more at Gardening Know How: Invasive Mint – How To Kill Mint Plants https://www.gardeningknowhow.com/edible/herbs/mint/invasive-mint-how-to-kill-mint-plants.htm

Best solution is to DIG it out.

Mint should always be planted in a pot. It runs rapid in the garden.

Sad to say, but, you will have to keep digging it until you get it all...mint is extremely invasive. I made the mistake of planting it once; took me all summer to get rid of it.

I agree that unless you want to kill the rest of your plants in the affected area, the only solution is to dig, dig, dig. Make sure you dig deep, as the mint can go down deep and spread side to side. Good luck! This is why I didn't plant mint in this garden, or any other herb. If I want to grow any herb it will be in a pot.

Dig it out after it rains because the ground is softer, you'll have to keep after this plant, it is highly invasive as you have discovered.