How Grass Seed Starts
All grass seed contains the embryo of a grass plant and food to get it through a dormant period (winter for cool-season grasses or summers for warm-season grasses). When soil reaches the right temperature (60 to 65 degrees F) and it has an adequate supply of moisture, most grass seeds germinate and establish "crowns", tangles of roots that send up a few blades and send roots down as they shoot off horizontal roots called rhizomes to establish new plants. The first work of grass seed is to protect the embryonic grass plant and release it at the right time. The value of a grass seed is determined in part by how many seeds will produce plants---its "germination rate."
All Seeds Are Not Alike
Because of the popularity of lawn grasses as a ground cover, grass seed is widely planted--even in areas where the climate does not cooperate with traditional germination processes. To solve the problem, varieties of grass seed are cross-fertilized using native grasses that thrive in an area until a hybrid grass seed produces a plant that will be successful. The type of grass seed that will be successful depends on the climate of the area in which it is grown; many cool-season grasses grown in New York would never thrive in areas like Florida and Southern California where warm-season grasses thrive. Some, like Kentucky bluegrass, do well in several areas, New York and Virginia among them. Root and crown structure and growth patterns vary among grass types. The second job of grass seed is to carry specific genetic material and accurately reproduce the parent grass.
Seed Shape, Size and Seeding Rate
Each type of grass seed is a bit different in size and shape. In order to produce a lawn, grass seed must be planted densely enough to crowd out other plants. The "seeding rate" is an abstract number that differs for each type of seed; it provides the threshold at which seeds can produce a lawn that will compete successfully with common weeds like crabgrass, clover and plantain. The U.S. Golf Association recommends a seeding rate of 1.2 to 2 million seeds per 1,000 square feet for good cover. Since seed size varies, this number requires different weights of grass seed depending on the variety or mixture. For grass seed's toughest jobs, like golf greens, the rate of seeding is often double that of a residence. A lawn grass' popularity depends on its seed's reliability. In the end, the job of grass seed, whatever its variety and germination rate, is to respond to the right conditions in a predictable way each time it is planted.