Some products control with one application per season while others work best by splitting the herbicide rate in half and applying it in two separate applications. The first application is done in March then the second applied 6 - 6 weeks later, read label directions well before purchasing. If you use any of these products now you should not seed your lawn until fall, the herbicide will not allow the seed to grow. I always advise people to control weeds in the spring and summer and wait until fall to seed lawns because autumn is the best time. Broadleaf type weeds like dandelion, are controlled later in spring using a liquid herbicide applied directly to the weed instead of spraying the entire lawn.
Lime is required if the pH of the soil is too low for a healthy lawn.
Most turfgrass species used for home lawns do well with a pH between 6.5 - 7.0. A soil test is the best way to know for sure what the pH and nutrient level is in your existing lawn. Soil test kits are available free at my office. If you have had a problem with moles or grubs it is a good idea to apply a grub control. The newest insecticide available for this purpose is called Merit.