First thing- Crabgrass or another crappy looking grass?

Annual Grassy weeds like Crabgrass can cause problems in many Lawns and can be treated through Integrated pest management (a combination of chemical and non-chemical practices). encouraging a dense stand of vigorously growing ornamental grasses is the best way to prevent weeds including crabgrass from invading. Mowing height has a big impact because Lawns mowed 2½ inches or higher tend to have less problems with annual grasses like crabgrass. Close-mowed lawns are more open to the sun with more direct sunlight warming the soil, even shining down the cracks in the soil allowing more crabgrass seed to germinate and proliferate. Studies confirm crabgrass seed can germinate over a hundred years later, so yes the sun shining down cracks in the lawn finding seed already in your soil just waiting for favorable conditions or maybe it found its way in on the mulch or even the wind.  The first frost kills the plants, but the seeds remain dormant through the winter. When the ground temperature warms up, the seeds begin to grow. Open bare soil is ideal for crabgrass whether preventive chemicals were applied or not. To keep crabgrass out of a lawn it must first have a lawn grass covering the soil in partnership with a pre-emergent treatment that can keep bare soil weed-free. Light, frequent watering favors crabgrass, the opposite of proper watering practices (Heavy infrequent watering). Crabgrass often invades areas seeded in late spring because of bare soil, frequent watering, and the onset of hot weather - all ideal for its growth. Weed Control treatments (weed Killer/Herbicides) are available to manage annual weeds and in combination with proper mowing height, good control is usually achieved. Pre-emergent herbicides prevent annual grassy weeds like crabgrass from emerging and completing its germination cycle and growing. Some products can treat preventively and post emergently so some products can be applied right up to and through the very germination and the first few growing leaf blades (tillers). Applying pre-emergent herbicides are ideally applied before crabgrass starts germinating/growing. Crabgrass will germinate when soil temperatures are above 55 to 60F° for 7-10 consecutive days and will continue germinating as the soil gets warmer also many other annual grasses germinate at 60 degrees and higher. In Northern Illinois, Pre-emergent crabgrass herbicide should be applied by early to mid-May and if the spring is colder, such in a late spring, this treatment can be put down through May. The best way to avoid crabgrass is to improve the lawn through better cultural practices along with a foundational Lawn care program with pre-emergent applied in the spring.  Until the conditions that promote crabgrass are corrected, crabgrass and other weeds in the lawn will continue to thrive. Using cultural practices like improving growing conditions with better soil with organic fertilizer/top dressing, core aeration to reduce compaction and work the soil, over-seeding to increase grass density, proper watering/irrigation, and mowing at the proper height,  will reduce problems crabgrass as well as other weed problems in a lawn.