Great post! I look forward to reading those links later. I've wondered the same thing about deep watering and root die off in the summer. I've always felt that my KBG here in NJ didn't do well with infrequent during the summer heat. I was going to water during the summer 1x/week no matter what to see what would happen, but maybe you links will suggest something different. I hate to say it, but many of my neighbors water all the time in the summer. Their lawns look nice and I can't recall ever seeing a fungal outbreak of any of them (except mine, lol). I think some stress is expected with the infrequent method, but at least it should come with the benefit of fewer diseases, right?

Too bad morpheus doesn't post here anymore because he usually has an informed opinion on these things.

I noticed once the lawn had a few years of dedicated moderate to heavy fall fertilization accumulated the lawn handles summertime drought and high temperatures a whole lot better.

I want a healthy lawn year all season, but don't have a dedicated irrigation system. As a practical matter it's almost impossible to lay down enough water in hot weather, unless you don't mind moving hoses around all the time and watering for hours and hours. There's also an expense involved, water is cheap where I live, but that's certainly not the case everywhere!

A dormant KBG lawn, so long as heavy foot traffic is kept off, is fairly resilient and will bounce back quickly once the cool fall temperatures and rains return. I happen to like the reduced mowing requirement in the high heat too. Set the mower high and let it grow long, to shade the roots.

Light waterings will keep the lawn green, but encourages shallow root development. What we want is deep roots in the soil.

Kind of have to make up your mind, If you decide to water, always water deeply, and keep up on it. Otherwise the lawn may roast to a crisp, bringing it out of and back into dormancy back and forth is not good practice.

It's worth mentioning first of all, though it's fairly obvious, that summer in NC/VA/TN is not the same as summer in PA/NJ/IA etc. The statements I'm about to make are based on transition zone summer conditions.

It's been my experience that heat in of itself is not an issue. What I mean by that is, the grass will not die of heat stress alone. I have had fescue take many days of 95 degrees like a champ. The grass is stressed, it stops growing, roots die back, it thins out, but it will survive and stay green as long as there's water in the soil. Root growth stops about when soil temps hit 75, so root development is a non-issue. Summer is about survival, and survival means providing the grass with sufficient water.

My watering regimen is shaped by 2 big constraints: my cost of water is very high and I don't have an irrigation system. Thus my goal is to use the least amount of water, and irrigate as infrequently as possible since it's manual. I water 1" of water whenever I see drought stress. Sometimes it's every 4 days, sometimes it's once a week, sometimes I can go two weeks if it's not as hot or it rains. If the two constraints were eliminated, I would water 0.5" every 4 days through summer.

I can confirm temperature at the canopy level is 15-20 degrees higher than air temp. I measured 110 canopy temp when air temp was 95. I can also confirm syringing lowers the canopy temp by about 10-15 degrees for about 10 minutes. It provides a brief reprieve from brutal heat and I think it's worthwhile doing if your run into some days in the mid 90s.

As far as increasing drought tolerance, PGR makes a significant difference. I skipped spraying last year to let the grass grow out of a fungal infestation and immediately saw a decrease in the length of time I could go between watering. I estimate a 30% increase in drought tolerance with PGR, but you have to start about April and keep it going.

This year, in addition to the PGR, I will be using Lesco Moisture Manager with Hydretain monthly to try and further increase drought tolerance. My expectations are low, but at a minimum it's 50% NIS so it should improve water penetration.

Bottom line: it's all about water. Deep an infrequent the rest of the year helps a lot. PGR helps a lot. Last summer we experienced a record setting 63 days over 90 here in NC - my fescue made it through under the regimen described above. Summer is about survival - all other considerations can wait until September.

I agree that taking a lawn in and out of dormancy is harmful. But tttf does not seem to go into dormancy; it just dies. If it does go dormant, it's only for a very short while and then it dies. I suspect the fact that KBG has rhizomes and tttf does not plays a part in this. Tttf, on the other hand, once it's well established, has much longer roots than KBG and can weather a drought better before closing up shop (dormancy for KBG, death for tttf). The trick is to get it through a few summers so it develops those longer roots.

The mycorrhizae fungi (my new favorite topic) play a part. If you have a good colony, they greatly increase water absorption and help the grass survive. Slight drought stress causes them to increase their network. So waiting to water until the grass shows signs of thirst is beneficial to make the mycorrhizae more active.

Some people have sandy soil and need to water more often. Some people have shade and need to water less often than if they had full sun. I suspect most everyone has areas of their property that need water more often than other parts. The one inch a week all at once is a good starting point, but needs to be adjusted for everyone's situation. I am wondering if the fact that cool season root systems shrink in the summer is a reason to adjust the watering accordingly then. Putting more water down there past the roots (which have shrunk up over the summer) doesn't make them grow if the plant itself isn't growing. In the summer, because the roots have shrunk, they will need water more often. They don't have the deeper reserves that they had in the spring and will have in the fall.

Cool season grass has a harder time in the summer than warm season grass because of the way it does its photosynthesis. Cool season grass is a c3 p!ant and warm season grass is a c4 plant (crabgrass, by the way, is a c4). Cool season roots are always going to shrink up in the summer.

J4c11, any thoughts on the best time of day? Early morning lets the grass blades dry off early in the day. But an afternoon watering might help bring the soil temperature down. There would also be more evaporation losses.

Morning is the recommended time, because the grass has time to dry out. Watering late in the day is a no-no since it will stay wet all night.

Morning water > afternoon water > evening water > no water.

I have been watering in the evening for the last 3 years but this last season I had an outbreak of I think summer patch. I hadn't been watering for awhile because it was raining enough (and hot) but I still had an outbreak. I saw enough people talking about watering in the evening and not having problems so I did it as well. This year I am going to water in the morning only just in case.

@Joe BigBlue

Such an important point. If you see the grass curling up and turning grey, WATER IMMEDIATELY regardless of schedules, weather etc.

i never found hydretain to make a noticeable difference. i also found primo maxx to be useful only when trying to keep the lawn looking good for the entire summer. however in doing so I saw a noticeable uptick in poa triv and poa annua. so i now let my kbg go dormant and water both my tttf and kbg areas just enough for survival from July 4th until mid August. the tttf gets overseeded with spread it and forget it method every fall for inevitable losses. works for me.

I may try to let the bluegrass go dormant next year. I'm a little nervous to do it this year since it's the first year of establishment. That was one of the major considerations going to bluegrass, the ability to let it go dormant if need be and have it recover in the fall. Fescue has failed to ever recover for me, if it's brown it's dead.

https://u.osu.edu/athleticfieldmanagement/2016/07/20/managing-sports-fields-during-summer-heat-drought-stress/

Nice information, very interesting. I can't say that drought pre-conditioning is much use for most of us above the Mason-Dixon.

But drought preconditioning is the same thing as "deep and infrequent." It's letting the grass get to a mild stress condition and then replenishing throughout the root level (one inch of water wetting down to around 6 inches). Surely you're not saying that deep and infrequent is not the preferred practice up north? Since the roots shrink up dramatically in July and August, wouldn't watering to 3 inches instead of 6 work to replenish the root zone then? If growth is pretty much non-existent then, roots aren't going to be growing either. The mycorrhizae can help but without getting carbohydrates from the plant, they probably shut down too. So I'm thinking we need as much deep and infrequent in the spring (and the previous fall too) as possible to build up the roots and mycorrhizal colonies prior to the summer, then try to keep the grass alive in the summer with water as needed (the grass tells us when) matching what we judge the root level to be. Maybe there isn't as much root loss up north as down here, but there is some. What kind of watering do you do? Do you think it's worth using up my compost pile for mulch to protect from the heat or that it won't make much difference? I wouldn't have enough for the whole yard but I could put it in the full sun parts.

What I'm saying is that in much of the upper mid-west and N.E., we don't very often get drought conditions until long after soil temperatures are well above those conducive to root growth. So any advantage to conditioning would likely be limited solely to K app. uptake (for cell turgor/osmosis regulation) which I'm not sure would occur that late into the season due to reduced ET.

I can see conditioning being implemented as an option in a region where cool temps are present and Spring/early Summer rains are limited and water application could be controlled.

Is the theory that conditioning can be made after true drought conditions and our high temperatures (July and Aug) have started?

Read this article. Just found it and it seems in agreement with my musings. The preconditioning needs to be done before the summer. Do you not do "deep and infrequent" watering when you water? That's the only mantra on watering repeated over and over. I would think up north you could do it all year long as your practice for watering. But here in the transition zone, irrigation practice probably should change for the hottest summer months.

I don't even water September through June. It may happen once or twice if we get a spell of hot weather in April/May, otherwise Mother Nature takes care of it. I would think in the NE you would be able to get away with very little irrigation even through summer.

My underground irrigation system has helped but applying a fungicide this time of year helps as well. I like in KY where it is very humid.

Weather is of course, variable and inconsistent from year to year, however here are my most recent monthly daily temp averages and monthly precipitation amounts. They are pretty indicative of what is normal and in March, April, May and the first 3 weeks of june, pretty evenly distributed from week to week:

March 2017: 48F, 4.76"

April 2017: 57F, 5.8"

May 2017: 61.F, 5.18"

June 2016: 71F, 3.56" (majority prior to the last week of June)

July 2016 77F, 2.47" (This is When daily temps are commonly in mid to high 80s and we start getting 90s and 100. Also rainfall is from sporadic storms that can drop 2" an hour that results in run-off.)

August 2016: 75F, 3.12" (Once again, temps will vary from high 80s to 100. Rainfall is solely due to sporadic storms dropping high per hour rates with run-off. Like in July, it is not unusual to go two to three weeks w/o rainfall.)

September 2016: 68F, 6.98"

Per the study, preconditioning was conducted by withholding water for two 2 week periods while air temperatures were held at no higher than 65F (prime for root growth soil temps of 50-65F). This was followed by a three week period where temps were raised to 91F - drought conditions similar to our pattern for July and August. My inquiry is, with soil temperatures already above prime for root growth (65F) by the end of June, when regular rain patterns switch from regular to infrequent and drought conditions start in July, when or how would you implement drought preconditioning? It appears to be interesting data, but near impossible to implement. How would we in the North withhold water during the Spring months when soil temps are <65F when we get regular rainfall during that period? or am I missing something?

We can't control when it rains. But usually rain in the spring and fall comes in a day of rain followed by a stretch of dry days. The front or whatever goes through, producing rain, and then we dry out until the next one comes. It's only occasionally that we get day after day of rain or weeks without rain. So I consider that usual pattern of just one day with rain followed by a number of dry ones as falling into the "deep and infrequent" category (deep if the rain was sufficient). If I were irrigating every couple of days to supplement, that would be shallow and frequent. That would upset the drought preconditioning that nature is doing. I'm thinking that we should not irrigate in the spring and early summer unless the rain does not provide a deep enough watering or if the dry interval is unusually long. That would be the drought preconditioning, otherwise known as deep and infrequent watering, which nature usually provides without us having to do it in the spring. I am just talking about east coast weather. Out west it's different. The question I'm exploring is whether "deep and infrequent" is the best practice for the hot part of summer. "Deep and infrequent" is what we preach. Perhaps we need a more nuanced recommendation.

Oh, issue is watering frequency, NOT drought preconditioning. NM.

If you have an in-ground system and can afford the water, then hands-down watering daily in the morning will result in a great looking lawn. If not, learn to do deep and infrequent. The lawn wont look primo in most cases but it should survive the period of drought for the most part.

Glad we are not talking past each other because of terminology. "Drought preconditioning" is just the term used in the research. But the concept is the same as what we refer to as infrequent watering. In the article it's defined as "infrequent or deficit irrigation." I think Daniel and I were talking past each other in another thread (it was a strange exchange about mowing weeds) and I start wondering about why I can't communicate.

For anyone reading who didn't pull up that article I referred to today, I am going to copy in a few sentences:

"Improved heat tolerance of cool season grasses by drought preconditioning suggests that infrequent or deficit irrigation that induces mild drought stress during spring can be used to encourage root growth and enhance physiological hardiness to heat stress during summer. During summer, when evapotranspirational demand is high and rooting depth is reduced, frequent, light irrigation should be applied as needed. However, it is very important to avoid over-irrigation, especially on poorly drained soils. Excessive irrigation under high temperature can cause more damage to turf than high temperature alone, because wet soils retain heat for long periods and are associated with lack of oxygen."

I'm starting to realize what a science it is.

I understand the concepts, but to implement them correctly takes not only the know-how, but some intuition as well.

More to the point:

"Frequent, light irrigation" without over watering should be defined as?

I don't know but I would guess enough to rehydrate the grass and then wait until it shows more signs of thirst. It would depend on how hot it is, the soil temperature, how deep your roots are (maybe dig up a grass plant somewhere to see?), what kind of soil you have, the duration of sun exposure, the angle of the sun, how old your grass is. I think you just need to be alert. Mind you, I am throwing this out here as an idea for consideration and it would be applicable just to cool season grass in the hottest part of summer. How much to rehydrate? Experiment and see. Frequent, light irrigation is not something that anyone generally recommends so I doubt there are general guidelines. There might be information on overwatering out there. If you find some, please share.

I had another thought today. When I clone hydrangeas from cuttings I cut 1/2 to 3/4 of the leaf off, to reduce evapotranspiration(ET) and thus water loss. But what about grass? We always recommend cutting as high as possible in the summer, but is a 4.5" grass blade losing water at 50% higher rate than a 3" grass blade?

Transpiration cools the leaf. In the hot summer the leaves need all the cooling they can get.

I agree with that, but an 800 sq ft apartment is going to take a lot less energy to cool than a 3200 sq ft house. Less leaf surface, less surface to cool, less water loss. In theory.

Looks like it's one of the mechanisms that gives grass under PGR enhanced drought tolerance:

http://www.syngentacropprotection.com/assets/assetlibrary/primo_maxx_prestress_pres.pdf

Dr. Bingru Huang - Rutgers University - 2006
“Of the water absorbed by turfgrass, about 90% is transpired and only about
3% is used for photosynthesis”

“If transpirational loss can be reduced then it may be possible to maintain
turf growth with much less water use”

So then, does maintaining a shorter height of cut reduce water usage by the grass? The answer seems to be yes. Obviously you wouldn't want to do that all year because it impacts root development, but during summer when water usage becomes #1 concern and root growth stops anyway?

The concern is, is water loss via direct evaporation from the soil going to exceed water savings from reduced evapotranspiration of the shorter grass. Long grass would "shade" the soil underneath better and keep it cooler. Maybe there's a happy medium somewhere.

Here's Dr. Haung's take: "Mowing at the highest acceptable height in midsummer will maintain the needed balance between food production and consumption and, thus, promote healthy, vigorous turf."

Here is Van Xu and Bingru Huang's study on Responses of Creeping Bentgrass to Trinexapac-ethyl and Biostimulants under Summer Stress. "This study suggests that proper application of TE and selected biostimulants could be effective to improve summer performance of creeping bentgrass."

Excessive irrigation under high temperature can cause more damage to
turf than high temperature alone, because wet soils retain heat for long
periods and are associated with lack of oxygen."

Makes no sense. Moist soil maintain a more consistent temperature (high or low) because water holds heat better than minerals. As the moisture evaporates it cools the soil.

So then, does maintaining a shorter height of cut reduce water usage by the grass? The answer seems to be yes.

As many of you will remember, back from 2011 through 2014 I lived in an odd part of Texas influenced by the humidity of the Gulf breezes but on the edge of the desert. While we got the humid breezes we rarely got enough rain to grow anything but mesquite and live oak trees. While I lived there I allowed my St Augustine (Floratam) lawn to grow without mowing. The idea was to see if taller grass used less water than shorter grass. The lawn started out low, and I stopped mowing. The grass in the most shade grew up the fastest and reached 32 inches tall within six months. We had been in a drought, so I watered all the grass regularly on my deep and infrequent schedule. We got in inch or so of rain that fall and I no longer needed to water that tall spot. From October 2011 through Feb 2015 when the house sold, I never watered that spot. The weather went from drought to rainy and back to drought. As the grass in the rest of the yard grew up I reduced the frequency of watering accordingly. At the end almost all the yard had grown up to the full 32 inches. I completely stopped watering the normal part of the lawn. It did not need it. Nor did it need fertilizer, herbicide, or insecticide. I never got snakes (in rattlesnake and coral snake country), mosquitoes, rats, or any of the pests people told me I should have. I still had scorpions and tarantulas, but not apparently in the grass. I focused all the watering on areas where the St Augustine was spreading out from under trees into the hotter parts of the soil. Here's a reminder image for those of you who were here with us in 2014.

When I sold the house the new owner immediately mowed from 32 inches to 2 inches. I told them to use a string trimmer and bring it down gradually, but no. They had to do it their way. They broke a commercial riding mower in the process. It took awhile for the lawn to recover from the drastic mowing, but it seemed okay the following summer. Now, according to Google Earth aerial imagery, it is dead. I presume they could not afford to water an acre and just let it go. I'm going by that town this weekend. I'll do a drive by and see what it looks like. It should be green with the rain they've had.

So my point is that rather than adjusting the deep and infrequent watering approach, my first thought would be to completely stop mowing when the summer heat hits. Allow the grass to get as tall as is practical for you in your situation (spouse, children, pets, HOA, and/or neighbors). Then when the temps cool down or you get more frequent rain, bring the height down with a string trimmer at little at a time. The trimmer goes very fast because you can swing swath of 6 feet or more with each pass. Holding the cutting height is not that hard once you get into a rhythm. In fact I'm string trimming now on the weedy part of my current lawn instead of mowing. I want the grass to grow taller but don't want the weedy bluestem seed heads sticking up. The seed heads seem to be scientifically designed to not mow off with a blade. So I am mowing the St Augustine and weed eating the weeds.

You know, with the grass that tall, the soil was bound to be a lot cooler than it would have been otherwise. Heat stress is a problem only with the C3 plants, which include the cool season grasses. Warm season grasses, like your St. Augustine, are C4 plants. Their photosynthesis process is much more efficient than that for C3 plants in the summer. Their roots GROW during the summer. For warm season grasses, deep and infrequent watering is the only way to go. Mild drought stress stimulates the mycorrhizae. Roots grow deeper. But cool season grasses are in a different situation. The shoots stop growing and send less food down to the roots. Roots use up their stored resources and start dying back. Fewer roots provide less nutrients to the shoots. There is less photosynthesis, resulting in less food to the roots, etc. The water use gets imbalanced too. When summer stress gets bad, KBG can go dormant. TTTF has longer roots if it's old enough but just dies instead of going dormant. Grasses in lawns less than a year old don't have mature roots and are especially vulnerable to summer stress. It makes sense to me that we ought to match the irrigation to the roots. Cool season roots are not going to grow in the summer so it's wasteful to put water deeper than the roots. But because they are smaller, they will need water more often. For mature grass, it may be that roots are developed enough that even with the dieback they have enough resources to keep supporting the shoots. The grass would tell us by either showing drought stress or not showing it. I think we should take our cues from the grass. Once the summer stress is over, deep and infrequent watering will help the roots grow. So I think we should promote deep and infrequent watering, but also give some caveats, for cool season grass only, for when it would be appropriate to change during summer stress. We should also tell people when it would be appropriate to let grass go dormant and when it would not be. Watering for dormancy is different than deep and infrequent.

You and Dr. Huang are saying the same thing: wet soil in the heat retains the heat longer. Yes, the soil will cool as water evaporates. But the heat in the soil is retained for a longer period of time than it would be than if it were dry. She was talking about excessive irrigation. Giving the grass enough water to get down to the root zone is not excessive.

Letting the grass grow without mowing in July and August is pretty much how it works out, because the grass doesn't grow.

I found a description of light and frequent in this U of Tennessee article

"Another irrigation philosophy, based, in part, on

research conducted at Michigan State University,

is to irrigate lightly and often (e.g., 1/10 to 2/10

inch of water every other day) during the summer.

A goal is to meet the daily water requirement

of shallowly rooted turfgrasses while conserving

water by preventing runoff and the percolation of

water below the turfgrass root zone. Damage from

certain diseases and insects may be reduced when

water is applied by light, frequent rather than

deep, infrequent irrigation."

Here is Michigan State U article that says about the same thing.

Has anyone read this?

http://heartlandturffarms.com/tips-and-guides/lawn-maintenance/kentucky-bluegrass/

Temps in NNJ are going to be in the 90's the next few days.

I plan on watering about 45 minutes a day.

This is early June, not the height of summer. I would think you should still be drought preconditioning (deep and infrequent watering). If course, if you see drought stress (footprints don't spring up, color change, leaves roll up, cannot stick screwdriver into ground), water. A few days of temperatures in the 90s is no big deal. When it gets up to 95-100 for days on end with no prospects of relief, then you might think about changing to deal with summer stress. For now you should be making your grass work for its water, encourage those roots to seek it out.

Why do they call KBG a warm-season turf grass? It is not. Mow KBG between 1 and 3 inches? Really?

Well they are speaking about the St. Louis area specifically, KBG more generally.

I don't see any problems with this:

Once established, turfgrass should receive approximately 1 inch of water per week, by either rain or irrigation. Mature lawns should receive deep, infrequent waterings, approximately every 5 to 7 days, to promote a healthy, extensive root system. Watering too frequently will result in shallow roots and weaker turf. Ideally, water in the early morning to minimize evaporation. Avoid evening watering in hot, humid weather, as this can contribute to disease.

Or this:

Water requirements may vary from lawn to lawn due to soil conditions, terrain, etc. In order to practice responsible water use, you should learn to recognize signs of dry turfgrass. Grass in need of water will have a grey-blue cast, rather than its normal green color. The grass blades may also shrivel and have a pine-needle appearance. Turfgrass in this condition should be watered immediately. Inspecting your lawn frequently will help to detect water requirements for your lawn and to avoid over- or under-watering. Consult our watering guide for greater detail.

I DO agree mowing at 1-3 inches is not a good idea and prefer the "lawnmower at the highest setting" routine.

@Joe: agreed in general. I think they may just have a typo. KBG is not a warm season grass no matter where you try to grow it. Trying to grow bermuda in Maine does not make it a cool season grass.