Life is full of little and big things that are simply out of our control. No matter how diligent you are at looking out for and weeding dandelion sprouts, you can't ensure that no seeds will ever set foot there again. Because just next door, or across the street, the lighter-as-air dandelion seeds in your neighbors' yards are just waiting for the right gust of wind to bring them over to yours. And surreptitiously weeding the neighbor's yards at night is, after all, trespassing. Short of sending out a neighborhood wide request, the best way to control your neighbors' dandelion seeds is to make your lawn a difficult place for dandelions to take root.
Crowd out dandelion seeds. In a healthy lawn, the grass grows so thickly that there are few places for dandelion seeds to take root. Overseed your lawn to fill out any thin or bare spots. And when you mow in the future, leave the clippings on the ground. They will help to crowd out weed seeds and act as a healthy mulch.
Protect bare areas. Dandelion seeds can easily take root in a hidden patch of your garden, or in the grassless area around the trees on your property. Spread a 3-inch layer of organic mulch around these areas to prevent dandelion seeds from reaching the soil.
Sprinkle corn gluten meal over any sprouting dandelion plants. Corn gluten is a natural herbicide that can kill young dandelion plants by drying out there roots. After you sprinkle the corn gluten over the dandelion, water it well to help the corn gluten reach its roots.
Hand weed any adult dandelion plants that establish themselves in your lawn. Be sure to dig out each plant's root system, including its long tap root. Or else, the dandelion will simply sprout again.