Late summer and early fall (mid-August to mid-September) is the best time of the year to overseed lawns and establish new lawns by seed. There are several advantages to seeding your yard in late summer and early fall opposed to the spring. First, there is less competition from weeds. Most weed seeds do not germinate in the fall; therefore, there will be fewer weeds present for you grass seedlings to compete with. Second, the soil temperatures are warmer than they are in the spring. This will lead to grass seeds germinating much more quickly. Third, the warm days and cool night temperatures of the fall are ideal conditions for rapid growth and development of cool season turf. Finally, by seeding yards in the late summer/early fall, it gives the seedlings enough time to develop good root systems before the heat of the following summer.
When choosing what type of grass to plant in your lawn, there are several factors you need to take into consideration. What is the desired quality of your lawn? Is there going to be a lot of foot traffic on your lawn? How much time do you want to put into maintaining your lawn? What are the site conditions (soil conditions, light availability)? It is best to use mixes (combination of two or more grass species) and blends (a combination of two or more cultivars of the same species) of turfgrass. By doing this, you will have better tolerance of different environmental conditions and pests.
When seeding in full sun, choose a Kentucky bluegrass blend or a mixture of Kentucky bluegrass (at least 80%) with perennial ryegrass, and/or tall fescue blend. For shaded areas use a blend of shade-tolerant Kentucky bluegrass (30-50%) and fine-leaf fescues blend or tall fescue blend (50-70%).
When purchasing seed make sure to purchase high quality seed and read the seed label. The label will include important information such as what species and cultivars are present, the seed purity, seed germination percentage, weed seed content and when the last testing date. You want to choose seed that has been tested within the last 9 months, and that has high purity and germination rates. Also choose seed that is low in weed seed content and inert materials. Avoid purchasing seed that is not labeled, this seed tends not to be as high quality. High quality seed will cost more than lower quality seed, but you end up with a higher quality lawn in the long run.