I mow at 4 inches all year, including the last mow of the year. I guess there is a greater chance for snow mold if you have long, heavy snow, but I haven't had a problem with that and I know morpheus, our resident KBG expert, doesn't care one way or the other. In my case, I have been bombarding my lawn with leaf mulch in the fall, so the longer grass is better because it can incorporate more mulch without getting drowned out. Leaving it long has also helped train the blades to become stronger and stand up straight at the longer length.

Snow mold prevention is one of the reasons that lower mowing height <2 1/2" is often recommended. Shorter turf is thought to reduce the the conditions likely to make turf susceptible to snow mold- i.e. matting of the blades and lack of air flow that allows for sustained wet conditions. Grey snow mold most often occurs during periods of long (40+ days) of snow cover. Turf will normally recover from grey snow mold. Pink snow mold is much more often deadly to affected turf. Pink snow mold can occur without snow cover and can develop during periods of cold wet conditions. Both are more prevalent where excessive thatch is present (or thatch like conditions are created by excessive fresh clippings- if you're going to drop from 4" to <2 1/2" on that last cut of the season when the micro biology has ceased being active--best to bag). The basis for the theory for low mowing is that shorter turf is less likely to mat and will allow more air movement between the blades reducing wet conditions. How effective short mowing is for preventing snow mold is debatable. Akin to the effect of lowering your cholesterol by 5 pts. would be in preventing a heart attack.

The most beneficial reason for lowering turf height by the last mow of the season is that it will improve warming of the soil the next Spring making for earlier Spring green-up and growth. promoting healthier turf next year.

@yard: I'd say "improved warming of the soil...and...healthier turf next year" are also probably marginal benefits, it they help at all. I have been winterizing here in NJ into late November and my lawn is green all the way through winter, even under the snow. When spring comes the lawn (4") doesn't seem to have any problems getting started up for the new season.

I don't know, for me it sounds like it isn't really necessary to mow low. You make a good argument against it. If you all of a sudden cut 2" off the blade in cold conditions, that dead grass might cause more problems than benefit. Of course that argument also may not hold up because I've been putting tons of mulched leaves into my lawn in the fall. By springtime much of the evidence of those leaves is gone.

@yard: I agree with much of what you are saying. I think the leaves mostly disappear probably through settling over the winter and certainly some micro activity before soil is too cold and then when it warms in the spring. I can't give you an exact % of volume reduction. My point is that the leaves don't seem to cause any problems that we are trying to avoid with grass clippings. Maybe I've just been lucky, but I know morpheus hasn't had problem with mulching, either.

I wonder if somebody has actually measured soil temps in the spring between 4" grass and 2.5" grass (I don't think it is recommended to take KBG shorter than that). I'm having a little trouble believing it makes much difference. Maybe under a particular set of specific conditions it might matter... just a guess.

@danielj: It's the N that causes problems. Clipping are relatively high in N content, especially in lawns that are lush from high maintenance N treatments.

I believe leaves are high carbon and low N. I'll have to look that up.

I wonder if somebody has actually measured soil temps in the spring
between 4" grass and 2.5" grass (I don't think it is recommended to take
KBG shorter than that).

I'm not aware of any reports of actual measurement, but it would be an operation of the same principles that justify recommending short cutting for overseeding- more sunlight/radiation gets to the soil surface

I wouldn't recommend maintaining any cool season grass below 3-4" (with the exception of the current topic of discussion), at least not without regular irrigation, a system to apply it, and the budget to support it. However, I believe if you check with any of the turf program sites, you will find that KBG can be maintained at heights as low as 1". I have read about a few northern golf links that have KBG fairways that are kept at 1". I'm not aware of any cool season grass that couldn't be maintained/trained to grow at very low heights with proper care. I just wouldn't be interested in supplying that amount of care.

it would be an operation of the same principles that justify recommending short cutting for overseeding- more sunlight/radiation gets to the soil surface.

To me, that's not a reason to scalp before overseeding. I scalp to reduce competition to seedlings from established grass - scalping stunts growth and prolongs the time until the first mowing. It also helps with seed to soil contact.

@yard yes thanks for the reminder about nitrogen. You are correct that leaves are very low in nitrogen.

To me, that's not a reason to scalp before overseeding. I scalp to
reduce competition to seedlings from established grass - scalping stunts
growth and prolongs the time until the first mowing. It also helps with
seed to soil contact.

If lowering the canopy doesn't open the soil surface up to sunlight (and consequently, seed finding its way to the soil as there is less canopy to block the seed during overseeding), what is the existing turf out-competing the seedlings for that you are reducing by "scalping"?

BTW, I am not talking "scalping". We are talking marginal, yet significant reduction of the canopy to open up access to the soil. If mowing down to 2-2 1/2 inches doesn't reveal access to the soil, then the lawn is already as thick as it is ever likely to be and neither overseeding nor promoting spreading are necessary, likely to be effect, or desirable.

If lowering the canopy doesn't open the soil surface up to sunlight (and consequently, seed finding its way to the soil as there is less canopy to block the seed during overseeding),what is the existing turf out-competing the seedlings for that you are reducing by "scalping"?

I guess I said that in the context of sunlight warming the soil via canopy thinning. I'm not sure that's one of the reasons for cutting low before overseeding. Giving the seedlings access to light is, you are correct.

I see the confusion. My bad. My point was that reducing canopy allows more sunlight to reach the dark medium of the soil. For my purposes, more sun=more heat=warmer soil. The flip-side is more canopy results in less sun reaching the soil=cooler soil=less evaporation=more soil moisture being retained than in warmer soils. One of the reasons to mow higher when Summer approaches.

I don't remember the science, something to do with photons exciting the electrons causing them to jump a shell and when they return to their previous shell, the energy release is in the form of heat?

Tough crowd today.

The wide spread in winter conditions seems to have brought various opinions to the winter grass height.

????

Yard sed: I don't remember the science, something to do with photons exciting the
electrons causing them to jump a shell and when they return to their
previous shell, the energy release is in the form of heat?

If we're talking about fluorescent lights or neon signs, then you'd be correct, except the energy release is in the form of light. However, this is not the way things warm up. It is motion that determines the temperature of a substance, be it solid, liquid or gas. Vibration in the molecular bonds between atoms, and the kinetic energy (aka translational energy, or motion) of the molecules themselves is mostly what determines how "warm" something is. You can upload that to Wikipedia. :)

@ gle2011: why don't you just leave it as is and see what happens in the spring, and see if you get any snow mold? It is mostly harmless anyway. When my seeded lawn was in its first season I got some mold, but the sodded part (also a year old) did not. In the two following winters I haven't had any issues with mold. It also seems like even though the lawn was cut at 4", somehow in January it looks shorter.

I just think that if I'm fertilizing in October and then winterizing, chopping off half the nice green blade while the processing of that nitrogen is going on just sits wrong with me.

I wouldn't worry about it too much.

I am confused.

Why bag last cutting if you are going to apply a winter fertilizer with a high nitrogen number?

In zone 5 southern coastal Maine; is the end of October to early to apply a winter fertilizer?

The 6 month community I have a small cottage in closes on October 31st,

thanks

@gle: The idea is to put the hi N fertilizer down after the top growth has stopped, or pretty much stopped, but before the ground freezes. I'm not sure at what point that happens in Maine, but I would guess you're not too far off with the end of October.