Flushing the Faux Flush

For the sake of discussion spanning geography, lets just assume that in most climates, at some point, push-up or all sand greens need to be flushed. Today I’m thinking about the word Flush and what it means to different people at different times. In the field, if I ask 10 supers how much water a flush means to them, I’ll get 10 answers ranging for 10 min to 10 hours. Seriously? The math is pretty easy in the simple form so lets do it together.

Lets say we have 5,000 square feet of a 12 inch rootzone at 45% total pore space. A typical sand based green. That means I have 2250 cubic feet of pore space (sq ft x ft depth x pore space). Water is 7.48 gallons per cubic foot. So to get to Field Capacity in this example we take 2250 x 7.48=16,830 gallons (cu. ft. of pore space x gal per cu. ft =gallons to field capacity). If I fill these pores, pretty soon the forces of gravity take over and much like grabbing the handle on the toilet, BAM, there’s a flush. A rush of air into the rootzone and the bad stuff either hits the drain tile or goes to the next perched water table.

Our 16,830 gallons has to be applied and in this particular example, we have 4 heads covering this green and all 4 do 28 gpm and they are part circle sprinklers. We would double the GPM (assuming that they are exactly half circles…they never are but, we have to have an example). So that’s 4 x 56 or 224 gpm. We need to put out 16,830 gallons so our run time here would be 75 min (gallons needed/gpm=run time).

So if you tell me that you usually run green 6-8 min and today you flushed with 12 min, I’m gonna teach you this math because you are a Faux Flusher…an Irrigation Drag Queen. And this is an on paper calculation, the truth is with things like part circles that are more than 50% arc, leaching fraction and the like, you are probably closer to 120 min in the real world of this example. In fact, I think that the Faux Flush is probably one of the most damaging things that you can do. It often only makes things wetter, never gets to a real flush where the air gets exchanged and the surface actually might become firmer.

Consistently, when I talk about a flush and we see the real numbers, I’ll hear something to the tune of, “If I turn on heads for

more than 4 min, the water just runs off”. I’m sure that’s true with the daily double cutting and rolling and the like today and ideas like venting being something that not everyone gets, infiltration rates are bound to be minimal in the upper rootzone. However, when hydraulics and gravity and adhesion/cohesion take over in the presence of more water being applied, there’s a pull that happens. Think about it from a rain event perspective. The greens always puddle at the start of the rain event, but after several hours of rain, they don’t do it as much. Oh, and does any of this inspire you all with sand amended push-ups to want to have drainage? Not a bad color of lipstick for you to try.

I thought I might stimulate your mind on a pretty important topic. Don’t be a Faux Flushing Drag Queen.

18 Responses to “Flushing the Faux Flush”

  • Totally agree with all points here.
    However, I know of only of a few of our XGD clients who performs the real flush of 120 minutes or so that you are speaking of. One client uses reclaimed water, and he flushes once a month to push salts a little deeper in to the profile.
    As Dave says the myriad of other harmful gases that will be pushed deeper in to the profile and out of the root zone would be highly beneficial to any turf manager.
    Most supers without internal drainage are terrified of doing so, as they fear it will only cause more disease issues for them if the complete flush isn’t accomplished, and that’s a legitimate concern.
    In the near future, the full flush will hopefully become a more widespread tool for turf managers.

  • Dave Wilber:

    Reclaimed may perhaps be more of a rule, rather than an exception. It’s part of my daily life. I’m thinking drainage will be more important than ever.

  • Richard Lavine:

    Dave,
    Great point about the water necessary for flushing. I had the same conversation with Ray Davies when I worked with him. As you mentioned about the run off, ours occured after four to five minutes. To compensate for this, we cycled the irrigation, 5 minutes on 5 minutes off for usually two hours, at least monthly. Our ec’s dropped dramitacally following the flush. Good info you put out. It should be required reading.

  • Dave Wilber:

    Thank you, Rich. Great example.

  • Chuck:

    Is the ‘check the exit pipe’ method a bad method? I typically see about a 1/2 pipe flow on a 4″ exit after ninety minutes or so. I guess at that point another 30 minutes of irrigation won’t hurt because we have the flow we’re looking for.

  • When I got to Anthem CC my first few years I was flushing the greens for anywhere between 1 1/2 to 2 hours, depending upon when I had good water in the exit pipes. As you know I learned this practice from you when I was at Troon. Two summers ago I demo’ed soil sensers from Toro on one of my greens by the shop and found out that even after a 20 minute cycle on the greens I had a flushing event (sodium level dropped). At the most we water the greens during the summer every other day but usually every 3rd night. I would like to stretch them out even longer but this practice still allows me to maintain good surfaces during the heat of the summer. I have since been flushing less often (once per month instead of 3-4 times). What do you think about the flushing event I was seeing on the sensors with only 20 minutes? The greens are much better/consistent now than they were when I flushed more often.

  • Wally Dowe:

    Great article Dave. I will forward this to my assistants. Hope all is well. A 1/4″ solid quad tine before flushing will greatly help the puddling in 5 minute scenario.

  • Randy Long:

    Thanks Dave. Thought provoking article but a few thoughts here.

    In your run time calculations, you are assuming the soil is 100% devoid of water when in actuality there will be a certain amount of water remaining in the smallest pore spaces. Therefore, you will be attempting to fill up something less than 45% of the media zone.

    Then, since part circle heads are outside the green “circle”, they generally have less than a 180 degree arc, not greater than 180 degree. So I would fudge downward and not upward in time estimate.

    Next, the term “field capacity” describes the water that is left in the soil after the gravitational water has drained out so in flushing, you don’t really irrigate to field capacity as you state. Irrigate toward saturation and it flushes out to field capacity.

    I agree that the faux flush is bad, but in your example, you could probably flush with half the time you describe, reaching your goal and wasting less water and nutrition.

  • Dave Wilber:

    @ Randy
    Strongly disagree, but thanks for the opinion.

  • Dave Wilber:

    @ troy
    I think you found the magic spot where it all happens and know to cycle.


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