When grass thins or does not grow, weeds can sprout up in its place. Weeds thrive on grass-thinning areas of a lawn and spread to more healthy patches. Lawns full of weeds usually have unhealthy grass or lawn with little grass. When a lawn is overcome with weeds, it you must treat it with a few different substances and landscaping tools. With a bit of care and some persistence, you can restore your lawn.

Step 1

Mow the lawn, setting the blade at high setting. A weed's worst natural enemy is thick, tall grass. Dense, healthy grass will largely keep weeds from growing. Weeds that do manage to sprout will have to compete with the grass system.

Step 2

Apply weed killer directly to the weeds in the lawn using a sprayer. Even weed herbicides that are labeled or designed as safe for grass may damage it. To preserve what healthy grass your lawn has, only spray the weeds, following the manufacturer's dosing instructions.

Step 3

Aerate the lawn with a grass or turf aerator. Work from one end of the lawn to the other in a horizontal direction, and then go across the lawn diagonally starting in one corner and finishing on the opposite corner. This helps air reach the grass roots.

Step 4

Put down grass seed and pre-emergent weed herbicide, following the manufacturer's application instructions. Mist the entire lawn with a garden hose. Do not saturate the lawn or the herbicide and grass send will run off the soil.

Step 5

Spread weed-killing lawn fertilizer over all the grass after the lawn has dried. Water on a regular schedule twice a week early in the morning to enhance the dew. This gives your grass much needed water and stop weeds from reinfesting the lawn.