"Overseeding" refers to a maintenance process on golf courses in which grass seed is spread on top of the existing grass to promote new growth or to swap out seasonal turfs, replacing one type of grass with another.

Overseeding is most commonly done by courses that use bermudagrass, which goes dormant during winter months.

In the autumn, a bermudagrass golf course overseeds with, for example, ryegrass seed on top of the bermudagrass, timed so that as the bermudagrass goes dormant the ryegrass grows in.

In spring, the process would be reversed: Bermudagrass seed is put down on top of the ryegrass, switching the course's turf back to bermuda.

(Bermuda and rye are used as examples because the overseeding of those turfgrasses in partnership is fairly common.

Various types of grasses might be involved in overseeding, but the process is most commonly used to switch a golf course over from a warm-season grass to a cool-season grass, and back again.)

Overseeding often involves putting the seed down along with a thin layer of sand, then allowing the new grass to grow in for many days without being cut.

So overseeding (which is sometimes done in conjuntion with aeration) can, for a period of a week or 10 days or so, result in very "hairy" greens, fairways and tee boxes.

Because greens with uncut grass can be difficult to putt on, some (but not all) golf courses offer green fee discounts during periods of overseeding.

Some courses also use "temporary greens" during the overseeding process to keep golfers from walking on the fresh and newly growing putting green grass.