Weeds on the lawn can be a major challenge for homeowners. One of the best and least expensive ways of controlling them is to improve and stimulate the growing conditions for desirable turf grasses in order to crowd and shade weeds to the point they cannot thrive. Hopefully your lawn has, or can have, millions more desirable grass plants making up the turf than weeds, but you may still have to consider using either natural or chemical herbicides to gain and maintain control over an aggressive weed problem.
Feed the lawn, weeds and all, regularly using a calibrated spreader set to the recommended application rate. Fertilisers are the least expensive of lawn chemicals and can actually do the most to help control weeds because they will stimulate growth of desirable lawn grasses that will eventually crowd out most weeds.
Water the lawn in the early morning, less frequently, and for longer period of time. This will encourage desirable turf grasses to root more deeply, reduce water evaporation due to heat and wind and increase turf resistance to drought, insects, and diseases. Never water later in the day than the turf has time to thoroughly dry out.
Aerate and dethatch the lawn on a regular basis to help nutrients reach the plants and expand root systems of desired turf grasses.
Mow the lawn higher. Although dichondra and bent grasses, bermudas and other creeping forms of lawns need to be mowed at short heights, the most common blade-type turf grasses, such as fescue, bluegrass and perennial rye, will benefit from being cut to 2 inches tall. At this height, they will also shade out sun-loving broadleaved weeds and stifle their growth.
Mow more often and before weeds like dandelions and clover have a chance to "go to seed," leaving the seeds to get blown elsewhere in the lawn. Although mulching healthy lawn clippings is generally a good idea, until you get your weed problem under control it is a good idea to bag your lawn clippings, if your mower has this capability.
Identify what kind of lawn grasses you have and what types and species of weeds are growing in your lawn. Take samples to your local nursery or agricultural extension office, if you are not sure.
Select an herbicide product that is safe for your type of turf grass and appropriate for killing the types of weeds you have. Some have to be applied at certain times in the growing cycle of weeds to be effective, so check the labels or with your nursery. There are products for broadleaved weeds and different ones for creeping types, like crab grasses. Herbicides fall into three general categories: Post-emergents kill existing weeds; pre-emergents keep weed seeds from sprouting; and non-selectives kill anything they come in contact with, including healthy turf. Post- and pre-emergent herbicides are sometimes packaged together, and there are combination "weed and feed" products. Herbicides are packaged in granular forms or as liquids to be sprayed on with either tank, hand pump, or hose-end sprayers.
Use a calibrated spreader or sprayer to apply the appropriate herbicide according to the directions. With either method, wait for a calm day to minimise drift and ensure even distribution. Check to see if the product needs to be applied to moist or dry surfaces and whether it needs to be applied when no rain is expected for a period of time.
Clean equipment used for applying herbicides carefully and dispose of containers and excess product appropriately. It is a good idea to mark spray equipment used for herbicides for use with them only.
Digging weeds out completely still works if you have the patience and your lawn is not extensive. Never exceed the suggested application rates for herbicides, as it will do no good and could create an environmental hazard.
Always wear a mask or aspirator when applying herbicides or any garden chemicals. You probably will not be able to purchase any packaged herbicide with EPA or other restrictions, but also be aware that some Internet home weed killer formulas are dangerous. Borax is natural and can control stubborn weeds like Creeping Charlie but it is outlawed in many U.S. states because its inappropriate use and run-off renders soil sterile for many years. Some herbicides, especially many non-selective ones, are restricted from use by the homeowner and you will need to hire a professional with a license to apply them. Doing so can save lots of money wasted on ineffective products.