Pictures are always good. If you want the best help you should post a few. Moss may mean the area is too shady to grow a proper lawn, for example, so photos help. Also, where you live is important. There are cool season grasses and warm season grasses for north and south locals, typically. If you can post more information you'll get better help.

Weed and feed products are generally discouraged because they don't work that well and they feed the lawn at the wrong time of year.

Take a very close up picture of the "crabgrass." Crabgrass is a full sun, summer annual plant that dies completely in the fall. If you have a weed right now, it is probably not crabgrass. Before recommending an herbicide, we really need to know what it is.

Also need to know where you live and what kind of grass you have/want. Seeding in the spring is not recommended unless you live in a very few special places.

Wait another month to fertilize, but now is the time to kill weeds. If you want to spot spray a herbicide now, again we would need to know what kind of grass.

dchall, I need some advice. I live in the city of Orange, California and I’m getting a sprinkler system put into my back yard. The dirt is clay and I have a big dog who pees on everything. I’m looking for a great looking grass for my dog and little son to play on. What do you recommend? My landscaper was mentioning Marathon I. What about St. Augustine?

@dchall_san_antonio

Germ Ram: Marathon is a fescue with poor recovery from damage (pets and kids). It requires reseeding to fill in holes and thin spots. St Augustine is self repairing and can fix itself within the growing season assuming the damaged area is avoided for a few weeks. If you have full sun then UC Verde would work, too. It is a hybrid buffalo grass that spreads easily and does not get flowers or seed stems.

Before you beat yourself up trying to work with clay, please get a soil test from Logan Labs and post the results here...in a different topic, with the subject of Soil Test Results, Orange County, or something like that. That will get the attention of people here who like to read soil tests. My thought is that you don't have clay. Instead you have a long history of someone over using Epsom salts to make the grass greener. The soil test will give the information on how to get the most out of your plantings. Get the $25 test from LL.

Also when they replace the soil on the sprinkler system trenches, make them mound up ALL the soil that came out of the trench back into the trench. If they do not, then when the trenched soil settles, it will settle lower than the surrounding soil leaving permanent trench lines in the ground.