Homemade remedies for ridding a lawn of crabgrass include scalding the weed with boiling water and applying solutions of salt, vinegar or bleach. All these methods kill regular grass and other plants as well as the crabgrass. To destroy weeds exclusively requires store-bought chemical herbicides or treated fertilizers.
To kill crabgrass by scalding, boil a pot of water, then pour the water over the weeds, taking precautions to avoid burns. Pour slowly to saturate the roots. Several applications may be necessary. This method kills all exposed plants but leaves no residues in the soil.
To kill with salt, either pour a solution of two parts warm water to one part salt over the crabgrass, or dump the salt directly on the weed. Salt in the soil can prevent other plants from growing for a year or more afterwards and can be spread by rain, so only use it on crabgrass growing in pavement cracks on sidewalks or driveways.
White vinegar or a weak solution of water and household bleach kills crabgrass when sprayed on the weed's leaves by altering the plant's pH balance. Lay down newspaper to avoid spraying other plants. Bleach breaks down in sunlight, and vinegar breaks down in the ground within a few weeks, so neither permanently damages soil when appropriately diffused.