Q: Should we cut our grass anymore this fall? How short should it be for the winter?
A: Hopefully you haven't cleaned off the old lawnmower yet, as you should plan to mow into mid-October or so.
It basically boils down to one thing -- mow as long as your grass continues to grow. If your lawn grows fast and needs mowing frequently during the summer, you may still need to cut it once a week. If, like I, you have a lawn that doesn't seem to grow very fast (hurray!), you may only need to mow a couple more times.
If you can, try to determine what type of grass you have, as this will determine at what height you should mow it during the summer. Kentucky bluegrass, fine fescue and perennial ryegrass should be kept between 2 - 2 ½".
If we have a stressful summer (hot and dry, like this past July was), increase the height an inch or so. This will help shade the roots and lower the soil temperature, which reduces heat stress.
In any event, if you're not sure what type of grass you have, you're fairly safe mowing at about 2-3" for most grasses. Sometimes, even 4" is acceptable (at least that's what I've convinced my wife).
Keep in mind that mowing frequency is important -- never remove more than 1/3 of the leaf blade length at any one time. If you want to maintain your lawn's height at 3" and it's grown to be 6", only take off 2". Let the lawn "rest" for a while (a day or two should be enough), then finish the job.
By removing too much at one time you may create an open appearance, weaken the plant, and leave too much clipping debris on the surface. Excess clipping debris is not only not pretty, it can shade the grass, further reducing its health.
For winter, your last 1-2 mowings should be the closest, down to about 2". This will help keep the grass blades from bending over under the snow, which can lead to matting. It can also lead to such nasty things as snow mold (which comes in 2 pretty colors -- pink or gray, so take your pick), giving you something else to do in spring (trying to clear it up).
I normally reserve my last cut for late October or early November. I'm blessed with having large shrubs surrounding the back yard. I can start going up and down from the middle out, and blow not only the grass clippings but any leaves outward into the shrubs. By doing so, I provide nicely-shredded leaf mulch to my shrubs, and dispose of the small amount of clippings at the same time. They all mingle together and get lost in the ground cover, and are pretty much unnoticeable by spring, when the mowing season starts all over again!