Temperature and light data from Fairbanks and Hilo for illustrative purposes

Temperature and light have a major influence on how ultradwarf bermudagrass will grow. I've shown the distribution of DLI at Tokyo and Watkinsville, and the DLI and temperature at Fukuoka, Tokyo, and Watkinsville.

Before going any further with calculations and combinations of light and temperature from transition zone locations, I thought it might be illustrative to show how these charts look for a couple non-transition zone locations -- Fairbanks, Alaska, and Hilo, Hawaii.

First, the temperatures. I've included Tokyo as a reference. Remember, Tokyo had an annual temperature, as represented by the cumulative sum of daily mean temperature in 2014, slightly more than Watkinsville, and slightly less than Fukuoka. All those cities, however, were pretty similar. Not so with Fairbanks and Hilo.

Temperature_3_disparateHilo has a tropical rainforest climate, and because the daily mean temperature is almost the same throughout the year, adding them together produces a straight line. Tokyo is the same as what was shown previously. And Fairbanks, where we won't be growing ultradwarf bermudagrass, has a cumulative daily mean temperature in 2014 that just barely stays above 0. The point of showing Hilo and Fairbanks is to point out what these charts would look like in a tropical situation, and in a subarctic one.

As an aside, one sometimes hears of ultradwarf bermudagrass being a big thatch producer, and requiring a lot of work for organic matter management. I would look at it differently, noting that any grass is going to grow at a different rate based first on the temperature and PAR at a location, and secondly based on the nitrogen and water supplied. Clearly, based on temperature alone, an ultradwarf bermudagrass would require no organic matter management in Fairbanks, because there would be no thatch production.

So Hilo is looking pretty good for ultradwarf bermudagrass, by temperature, and how does it look for light? Hilo is 19.7°N, Tokyo is 35.7°N, and Fairbanks is 64.8°N.

Hilo_disparate_dliInteresting. Fairbanks looks about like I would expect. That far north the DLI in winter is negligible. But how is it that Hilo just barely tops Tokyo for cumulative DLI? That's the effect of clouds, and it is why bermudagrass grows so poorly in Hilo. In fact, Watkinsville in 2014 had cumulative DLI of almost 12,000 -- more than the cumulative DLI in tropical Hilo.

I've mentioned previously the importance of light (DLI) when temperatures are close to an optimum for warm-season grass growth. The climate.asianturfgrass.com website has lots of charts and videos about that. 

In these recent posts, I've shown the temperature and the DLI separately. Coming up, I'll add one more transition zone location, and then see what happens when various combinations of DLI and temperature are made.

Combining temperature and light to compare location effect on turfgrass growth

The daily light integral (DLI) is the total amount of photosynthetically active radiation (PAR) at a location in one day. The DLI in an open (full sun) area changes with the latitude, time of the year, and cloud cover. There will be further reductions in DLI if there is shade from trees, structures, or mounds/mountains.

Nitrogen supply, plant water status, the DLI, and temperature all influence turfgrass growth, or even the ability of a particular species of grass to provide the desired surface conditions at a given location. With professionally-managed turf, the nitrogen and the water are controlled by the manager, so it is the DLI and the temperature left as the major factors, outside of the manager's control, that will influence the turfgrass growth.

I showed the distribution of DLI and how it differs from place to place. The implication of that, for ultradwarf bermudagrass, is that the place with higher DLI will be more suitable for the grass, and the place with lower DLI will require more actions to improve turf performance in shade, such as increasing the mowing height and reducing the N rate.

I was curious about the combined effect of temperature and DLI, so I looked up data for a few more locations. I'll make a series of posts about this, in each one describing what I've done. The previous distribution of DLI looked at Tokyo, and then Tokyo and Watkinsville, Georgia (near Athens), on the days in 2014 when the mean daily temperature was greater than or equal to 20°C (68°F). I pick that temperature because I expect ultradwarf bermudagrass can grow relatively well above that temperature, and will grow quite slowly below that temperature.

This chart shows Fukuoka, Tokyo, and Watkinsville, which had a similar number of days above that temperature in 2014 -- 150, 150, and 151 respectively. 3cityDensity

The distributions of DLI at each of these locations show that Fukuoka and Tokyo have more days with DLI less than 20, and Watkinsville has more days with DLI above 40. The median DLI at Watkinsville was 42.1, at Tokyo it was 35.8, and at Fukuoka it was 31.8.

What about the total DLI over the year? Rather than my arbitrary cutoff at 20°C, one can also add the DLI through the year. This chart shows the cumulative daily sum of DLI at these same 3 locations.


The cumulative sum of DLI was 9,139 at Fukuoka, 10,135 at Tokyo, and 11,736 at Watkinsville. Over the course of the year, there was more PAR at Watkinsville than at Tokyo, and more at Tokyo than at Fukuoka. This will have some impact on how ultradwarf bermudagrass would grow, and also on how the grass should be managed at each location.

What about temperature? I added together the temperature for each day at these same three locations, and the temperature doesn't vary as much between locations as the DLI did.


By adding together the temperature for each day, by the end of the year, Fukuoka has the highest total, then Tokyo, and then Watkinsville. The median annual temperature was 17.8 at Tokyo, 17.7 at Fukuoka, and 16.6 at Watkinsville.

With PAR, as represented by DLI, Watkinsville was highest, and Fukuoka was lowest. With temperature, as represented by the cumulative sum of daily mean temperatures, Fukuoka was highest, and Watkinsville was lowest. Can these be combined to get an index of growth, or an index of light and temperature affect on growth? I think so, and I will share some more calculations, and add in data for some other representative locations, in future posts on this topic.


Distribution of daily light integral (DLI) at Tokyo and Watkinsville in 2014

I discussed photosynthetically active radiation during a seminar this week in Tokyo.

This slide showed the distribution of the daily light integral (DLI) in Tokyo during 2014 on days with an average temperature greater than or equal to 20°C.

I mentioned that one could make an overlay of the distribution of DLI at other locations, and that a distinctive feature of the Tokyo-area climate is that there will be more days with a low DLI than at locations with a similar temperature in the southeastern USA.

In this plot, I show the density of DLI in 2014 for Tokyo and Watkinsville.


The temperatures in these locations were similar in 2014; the mean of the mean daily temperatures was 16°C in Watkinsville and 16.8°C in Tokyo. There were 151 days in 2014 with mean daily temperature >= 20°C in Watkinsville; Tokyo had 150 such days.

For the DLI on those days, however, there is quite a difference. The median DLI for those 150 days in Tokyo was 35.8, compared to 42.1 in Watkinsville.

Seminar on the fundamentals of turfgrass maintenance

Yesterday I gave a private seminar in Tokyo on the fundamentals of turfgrass maintenance.

I spoke about how I define greenkeeping, the four factors that influence growth, some specific challenges of turf maintenance related to the climate of Japan, and the fescue playing surfaces at the recent U.S. Open at Chambers Bay.

The slides for this seminar are available in Japanese or English.

Turfgrass ecology, part 1: abandoned turf in Japan

These photos from an abandoned golf course in the southern part of the Tohoku region of Japan are fascinating. They show clearly how three different species perform when they are not maintained for 18 months in that climate. From a consideration of the grass performance when abandoned, one can get a good idea of the maintenance requirements for the grass when it is being actively maintained.

These photos are provided courtesy of Mr. Norifumi Yawata, who kindly shared them with me along with some details about this site.

Formerly a creeping bentgrass green, now covered in weeds, but the korai around the green has very few weeds by comparison.

This site, formerly a golf course, has not been maintained for 18 months. One is essentially looking at what happens to 3 species of grass after 2 growing seasons (2013 and 2014) with no maintenance.

The greens were creeping bentgrass. The tees and the collar immediately around the greens were (and still are) korai. Korai is Zoysia matrella – the common name is manilagrass. Everywhere else, the fairways, the roughs, and so on, are noshiba. Noshiba is Zoysia japonica – the common name is japanese lawngrass.

Noshiba in foreground at the edge of the bunker. Korai border immediately surrounding the green. The green surface was formerly creeping bentgrass.

In these photos we see the characteristics of these grasses as they are adapted to this environment. Creeping bentgrass on the green surfaces has been overtaken by weeds. Clearly, creeping bentgrass in this environment seems to require mowing and supplemental irrigation and fertilizer and probably some pesticides in order to persist. It dies quickly without those inputs, or at least it becomes thin, with many voids in the turf that allow for invasion by other species.

The photo above shows a sand bunker in the foreground. Then comes some noshiba with the characteristic autumn symptoms of the wonderfully-named elephant's footprint disease caused by Rhizoctonia cerealis. At the edge of the green surface itself is a band of korai, finer-bladed than the noshiba. And then the green, now a weed patch.

View of an abandoned green complex from a high vantage point, showing the rapid colonisation of a creeping bentgrass putting green by weeds.

The korai and the noshiba both persist at this site for at least two years. It looks like some mowing of the korai and noshiba would get these surfaces back to acceptable condition by next summer. But the bentgrass is beyond saving. Because the korai and noshiba persist, it is evident that they survive without irrigation, and without fertilizer, and that the mowing, and perhaps some weed control, are all that are required to keep them at a minimal level of performance.

The dense korai turf is the most resistant to weed invasion when formerly maintained turf was abandoned for 18 months in the Tohoku region of Japan.

There are various implications of these observations on weed invasion of abandoned turf. This supports something I've written about before: for large areas of maintained turf, it makes sense to use a grass that won't die. Then one will be assured that with minimal maintenance, the quality will be acceptable. And with intensive maintenance, that grass that won't die will be able to tolerate every type of aggressive maintenance, allowing one to produce high performance turfgrass surfaces.

Korai forms a denser turf than noshiba and this is reflected in the relative amount of weed invasion in abandoned turf.

In this case, and at most golf courses in Japan, this good practice of grass selection is used. The creeping bentgrass area is small, less than 5% of the maintained turf area. So the grass that dies, the grass that requires intensive inputs, is planted only on a minimal area. The grasses that don't die, and that require relatively fewer inputs of irrigation, and fertilizer, and pesticides, and mowing – in this climate these are korai and noshiba – are used on more than 95% of the maintained turf area.

Zoysia on putting greens? Why?

Korai green on the 18th at Keya GC during the 2014 KBC Augusta tournament

Why would one deliberately use manilagrass (Zoysia matrella, or korai in Japan) on golf course putting greens? If one would grow bermuda (Cynodon) and korai side by side, and give them the same maintenance, the ball will roll better – smoother, and farther – on the bermuda than on the korai. One can manage korai to get an impressively smooth roll, as seen here, but overall one will see a smoother roll on bermuda than on korai.

So why, then, are there hundreds of golf courses in East and Southeast Asia with korai greens? It has to do with climate. The 2014 KBC Augusta tournament was held at Keya Golf Club in Fukuoka during the last week of August. Keya has noshiba (Zoysia japonica) rough and korai greens, tees, and fairways. Zoysia everywhere. And the conditions there make a good explanation of why one might prefer korai over bermuda.

Clouds above Keya GC on 24 August

There is considerably less sunshine in East and Southeast Asia compared to locations in the United States and Europe where warm-season grasses are grown. Even so, August 2014 had especially low sunshine in Fukuoka. The closest weather station to Keya GC with sunshine data is Maebaru

Mowing a practice green on a rainy morning at Keya GC

During August, there were 75.5 hours of sunshine at Maebaru. Sunshine duration is the time during which the direct solar irradiance is greater than 120 watts per square meter. That's an average of 2.4 hours of sunshine per day during August. And there were a full 8 days in August in which no sunshine was recorded. That is, the direct solar irradiance never exceeded 120 watts per square meter.

Trees around the 1st green at Keya GC

That relative lack of light for photosynthesis does not take into account the further shading caused by trees. As at most golf courses, many of the greens and other highly-maintained turf areas at Keya sit close to large trees.

Pumping water from a bunker on the 1st hole at Keya GC during the 2nd round of the KBC Augusta tournament

During the tournament week, there was some sunshine and plenty of clouds and rain. There were an average of 2.6 hours of sunshine per day during the tournament week itself, and rain fell on 4 of the 7 days during tournament week, for a total of 52.5 mm (at Maebaru).

The 13th green at Keya GC on 30 August

In these conditions, with such a low amount of sunshine, korai grows pretty much close to normal. Sure, it might be a little better if the sun were shining, but the relatively low light requirement of korai allows it to be maintained aggressively even during the cloudiest and rainiest of weather. 

To put this amount of sunshine – 2.4 hours per day on average at Maebaru during August 2014 – into perspective, that's less than London on average in February (2.5 hours) or my hometown of Portland, Oregon, during January (2.8 hours). Portland in January and London in February are not exactly bastions of sunshine. 

Atlanta and Fukuoka are at a similar latitude. On average, there are 8.3 hours of sunshine per day in Atlanta during August. There were zero days in August 2014 with that much sunshine at the Maebaru weather station in Fukuoka.

The reason for choosing korai instead of bermuda in East and Southeast Asia is that korai doesn't die. Imagine growing bermudagrass greens and trying to prepare them for a tournament when the amount of sunshine is less than London in February or Portland in January, or when not a single day for a month has as much sunshine as an average day in Atlanta.

For more about this, see:

More about the measurement of grass clippings

Pg (1)
2 liters of clippings from the putting green

One can measure the volume of clippings collected when mowing greens through the simple process of bringing along a bucket to empty the clippings into.

This technique is used at Keya GC in Fukuoka, the host club for this week's KBC Augusta tournament. The greensmowers bring along a bucket and take note of the volume of clippings collected from each green.

Mowing the practice putting greens at Keya GC

In a previous post, I mentioned some of the ways that this information can be put to use. Here at Keya, the target for tournament week was to be at less than 10 L per green. During the 2013 tournament, the clipping volume averaged 11.8 L per green during tournament week, and 5.3 L per green in the week immediately after tournament week. The course superintendent, Andrew McDaniel, thought that putting surfaces for the 2014 tournament would be best if the clipping volume were slightly less than in 2013.

The clipping volume is collected year round, and from most of the greens. I've taken a subset of the 2014 data and plotted it for the month of August, with the average clipping volume from greens 1, 2, and 4, just to show how the yield has been this month, through this morning, the 2nd round of the tournament.


It looks like the clipping yield is close to the target range. By tracking the amount of clippings, one can adjust nitrogen rate, growth regulator applications, and mowing height and amount of mowing in order to modify the amount of clippings.

The use (or not) of brushes, or groomers, or the effects of various other maintenance practices can be evaluated when the clipping volume data are available. The Shibaura G-EXE22 mowers used on the greens can be fitted with this brush.

Brush fitted between the front roller and the bedknife on the Shibaura G-EXE22

Andrew found that use of the brush increased the number of clippings by a factor of 2. During the tournament, the brushes are not being used, but in the lead up to the tournament, the brushes were used to increase the amount of clippings and help create the desired surfaces.

View from behind the 14th green at Keya GC

Now, during tournament week, the korai (Zoysia matrella) greens at Keya GC are growing at just the desired rate, and the mowers are removing the targeted amount of clippings. It doesn't take much extra time to collect this information, and having a time series of these clipping volume data can help a turf manager make decisions about the adjustments to make in green maintenance.

Korai green surface at Keya GC

Measuring and tracking grass clippings

Many golf courses in Japan track the volume of clippings mown off putting greens using this simple technique. A plastic bucket is brought along on the mowing runs, the clippings are placed in the bucket, the bucket is shaken to allow the clippings to settle, and the volume of the clippings is recorded.


This information can be useful to check, track, and improve the management of putting greens, For example, the data can be used to:

  • ensure that all mowers are set up the same way
  • measure the effect of fertilizer applications
  • measure the influence of growth regulators
  • evaluate the effect of weather and maintenance practices on growth
  • track clipping yield for special events


Andrew McDaniel is the golf course superintendent at Keya GC in Fukuoka, where the Japan Golf Tour Organization (JGTO) holds the KBC Augusta tournament. Leading up to the tournament, the clipping volume of the korai (Zoysia matrella) greens was generally more than 20 L per day per green with a single cut. Today, on the Wednesday of tournament week, a double cut of the greens is collecting about 5 L of clippings per green. The progression to the tournament target clipping volume has been monitored carefully.


He also used brushes on the mowers in the lead up to the tournament. When two mowers were used on the same green, each mowing the green once, the mower with the brush collected about twice as many clippings as the mower without the brush. 

For an even more detailed look at clipping production over time, and different ways I've seen it measured, see my report on clipping yield from putting greens.