Page 12 - GM Fall 2025 flipbook

Figure 3: Time series graphs monitor OM at each depth across multiple years, revealing patterns of accumulation or dilution over time.
The 2-4 cm and 4-6 cm depths
usually have a narrower range across
greens because OM accumulates at
the surface. This can be helpful to see
if a course has a few brand-new
greens with very low OM at depth or
a push up green with perhaps higher
OM than average at depth.
2. Time Series Graphs (see Figure 3)
Time series graphs track OM at each
depth over several years, providing a
clear picture of accumulation or
dilution trends. An accumulation or
dilution in OM is usually reflected in
the sand topdressing program
assuming no other major changes
(tree removal). For example, if OM
increases from 6% to 9% over three
years and then drops to 7% in the
fourth, the change likely reflects an
increase in topdressing or aeration.
Both tools help turf managers
identify trends, compare greens, and
set targets based on surface
performance. For example, a
manager may decide that 7% OM at
0–2 cm offers the best firmness,
while values above 9% are too soft.
Visualization makes it easier to plan
accordingly.
Ultimately, interpreting OM246
is not about reacting to one number
— it is about reading the pattern over
time and making decisions based on
how OM is changing at each depth.
REAL-WORLD APPLICATION & INSIGHTS
It may be tempting to aim for a universal OM range, for instance, 3–7% at the
0–2 cm depth, whereas real-world applications shows that optimal OM levels
vary by golf course. A green with 3% OM will play and respond very differently
than one with 7%. In my experience, a green with 3% OM requires significantly
more hand watering and is more likely to wear or thin out during the heat of
summer.
Determining your course’s desired OM level requires evaluating the
conditions and performance metrics that matter most to your property. The
evaluation process includes:
1. Factors Influencing OM Accumulation
Several elements drive how OM builds up.
•  Traffic: Courses with more rounds typically need higher OM to handle wear.
High traffic often reduces OM over time.
•  Green Size: Larger greens accumulate more OM because they distribute
traffic better. Small greens accumulate less and are more prone to wear.
•  Environment: Sun-exposed greens usually grow faster and accumulate
more OM. Shaded greens grow slower and accumulate less.
•  Turf Species: Bentgrass tends to build more OM than poa annua due to its
growth habit.
Many of these variables are hard to change — tree removal, returfing, or
expanding greens are not always options. However, understanding these
variables helps to explain why OM values differ across greens and provides
context for what optimal OM level might be for each one. I have found that
full sun large greens are consistently a superintendent’s favourite and usually
have the highest OM values. Lower OM is not necessarily better.
2. Assessing Surface Performance (looking at 0-2 cm depth)
Performance metrics help determine whether OM levels are appropriate.
•  Firmness: Measured by using tools like the Clegg Hammer, TruFirm, GS3
Ball. Softer readings may point to high OM and excessive moisture retention.
From experience, firmness can be achieved with OM values 8-9% or lower.
Anything higher than that will hold on to excessive water after rainfall.
Firmness is not just directed by OM, physical properties like sand particle
size also contribute to firmness.
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• CGSA • GreenMaster