Lawn grass is not as difficult to take care of as advertising might have you believe. Grass, like you, wants food. If left to its own devices and given the food it wants, it will generally take care of itself. That includes policing its own weeds. Herbicides do a lot of damage to microbial, plant and animal life--including humans. If possible, they should be avoided. If you care for your lawn grass well, you should not ever need to use these dangerous chemicals. The best part is, the best lawn care requires very little work at all.
Call your local county extension service. Inquire about whether they do soil pH testing. In most cases, the answer will be yes. Your county extension office's phone number should easily be found in the phone book. You can also ask if they know of specific types of weeds that are prevalent in your area, so you have a better idea of what you are dealing with.
Submit soil samples from your lawn to your local county extension service, along with any fees required. Paul Wheaton of Rich Soil advises against using soil pH test kits that can be found in garden supply and hardware stores, because their results are not always accurate.
Amend your soil as the county extension service's pH test directs. Your county extension service will be able to give you specific directions as to how much sulfur or lime to apply.
Apply compost to your lawn at least once a year. If you compost your kitchen waste, this should be relatively easy and inexpensive. Compost helps to neutralize your soil's pH, no matter what that pH is. It is also excellent food for the earthworms and beneficial microbes that a healthy lawn has living in it. Encouraging worms in your lawn, like encouraging them in your garden, leads to a healthy and vibrant landscape.
Use your sprinkler to water your lawn, but do not do so on a regular basis. Instead, Wheaton recommends watering it deeply once or twice a month. Watering it regularly encourages weeds. Grass has very deep roots, usually much deeper than most weeds. By not watering so often, you encourage those roots to go deeper for moisture, and weeds will not be able to keep up.
Mow your lawn, but mow it high. Mowing it short forces the grass to go into panic mode, using all its reserved nutrition to grow its blades longer so that it can get more sun. This leaves the root system weaker, which makes for sickly grass that is easily choked by weeds. Additionally, taller grass creates shade. Weeds do not like to grow in shade, so it is a natural deterrent. Your healthy grass will procreate and make a dense grass carpet that will choke out weeds.