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Get a dandelion-specific herbicide from a local gardening or lawncare store. Read the label and follow the manufacturer’s instructions to ensure that you apply the herbicide to the dandelions correctly. Every herbicide’s instructions are different, but in general, they will take a few days to begin killing the unwanted plants. Selective herbicides are designed to kill a single species of weed or plant while non-selective herbicides are designed to kill every major type of weed. A selective herbicide is usually less effective than a non-selective herbicide. But if you’re trying to grow any other plants in your yard, the non-selective herbicide can be a risky proposition. If you want to target other weeds in addition to the dandelions, opt for a non-selective herbicide. Follow the manufacturer’s instructions to apply the herbicide to your lawn. Typically, it only takes non-selective herbicide 2-3 applications to completely kill weeds. Non-selective herbicide may damage other plants or flowers in your lawn. Pre-emergent weed killer prevents the germination of seeds that are already under the topsoil. Using a pre-emergent treatment will prevent any dandelion roots or seeds from growing or developing into mature plants. Get a pre-emergent treatment from a lawn care store and spay it over your lawn in the spring or after removing dandelion plants to keep them from coming back.

Summary:
Use a selective herbicide to target dandelions specifically. Choose a non-selective herbicide to kill dandelions and other weeds. Use a pre-emergent weed killer after removing plants or in the spring.