In ancient times, grass was cut by hand with something like a scythe. Early lawn mowers, reel or cylinder mowers, used long blades that mimic the cutting motion of a scythe. Later mower designs made use of a more simple blade that relies on more rapid motion for grass cutting.
Straight Rotary Blades
A very common lawn mower blade is a straight steel blade with a bolt hole in the center. This type of blade is common in less expensive gas and electric mowers. As the blade spins, the cutting edge slices off the grass. The grass is then discharged via an opening in the side or the back of the mower. Straight blades are cheaper to manufacture and easier to sharpen than curved mulching blades. If you are gathering your grass clippings for composting, a straight blade is a good choice.
Mulching Rotary Blades
Mulching blades are curved. The curved shape of the blade tends to keep the grass in the cutting path longer. This results in multiple cuts per blade and smaller bits of grass that settle down below the level of the living grass to create a layer of mulch. Mulching your grass and leaving it in place has a couple of advantages. The first advantage is that the mulch helps maintain a higher soil moisture and results in lower water requirements for lawns. A second advantage is fertilization. As the mulch decomposes, it returns many of the nutrients used in grass growth to the soil for re-use by your lawn.
Cylinder Mower Blades
One of the earliest lawn mowers is the reel, or cylinder, mower. Although powered reel mowers are rare, manual versions are very popular for people with small lawns. Versions of the reel mower were made to be pulled with a tractor for cutting large expanses of lawn or field grass. The blade assembly of a reel mower contains a number of blades that spin either from back to front or from front to back, depending on the design of the mower. These blades spin on the vertical plane, as opposed to on the horizontal plane, as in most gasoline or electric mowers.