February 2019 - 23

RESEARCH
When applied at the maximum label rate, wetting
agents (WA) can increase the effective capacity
to 90 percent of the potential capacity after a
single watering. Wetting agents cost from about
$1 (liquid) to $3 (granular) per cubic yard, but
this is a small cost if it allows for easy and full
rewetting when using a higher fraction of wood in
the media.
WATER MOVEMENT
The ability of water to move vertically and
horizontally in a container is important to
maintain uniform water in the root-zone. The
wicking of water to the surface of a container
is often reduced with higher fractions of wood.
This makes it appear that the plants need to be
watered when only the surface is dry (Figure 3).
The reduced movement of water is caused by
reduced ability of water to move from wet to dry
areas (called reduced hydraulic conductivity). If
water moves slowly to the surface it also moves
slowly from side to side. Hydraulic conductivity
can be improved by adding a wetting agent (WA).
Not only do substrates with a WA absorb water
more quickly and evenly at the first watering,
they rewet more quickly and uniformly in
subsequent waterings. Our studies suggest that
the addition of a WA is particularly beneficial
in substrates with more than 50 percent wood,
regardless of the wood's texture.
EFFECT ON PLANT GROWTH RATE
Fresh sawdust contains numerous compounds
that can inhibit plant growth. The Crop
Physiology Laboratory at Utah State University
has conducted eight comprehensive growth
studies with wood percentages up to 75 percent.
So far we have studied: petunias, pansies
and dianthus (from plugs); and cucumbers,
sunflowers and tomatoes (from seed). Somewhat
surprisingly, the effect of wood was similar for
each of these diverse species.
All studies included liquid feed with a 21-5-20
fertilizer; which was applied at both our standard
(120-ppm nitrogen) and at an elevated (240-ppm
nitrogen) fertilizer rate. The pH of all containers
was maintained at 6.2 ±0.4 with custom
additions of dolomitic lime to each mixture.
The buffering capacity of the wood products
was insignificant compared to peat, so the lime
addition rate depended on the percentage and
buffering capacity of the peat. These studies have
not yet included a wetting agent, but plants were
frequently watered to minimize water stress so
we could examine only the chemical effects of
the wood.
We expected that more aged sawdust would
result in better growth than less aged sawdust,
so we tested both one- and three-month-old
sawdust. The red line in the graphs is sawdust
stored moist for about one month after sawmill
cutting. The blue line represents sawdust stored
moist for about three months. No fertilizer was
added during storage.
The shredded wood (HydraFiber in these
studies) was not aged, but the high temperature
in the shredding process can cause the
equivalent of rapid aging. Plants were grown
TOP
GRADE,
SALE
MADE
Count on
Selecta One®
for poinsettias
that sell! Each
variety features a
V-shaped habit for less
breakage and better shipping.
selectanorthamerica.com
60
50
40
30
20
10
20
40
WOOD PERCENTAGE
CHRISTMAS MAGIC™ RED
Figure 2. The potential water holding capacity decreases as the percentage of wood increases.
Visit selectanorthamerica.com
for Current Terms & Conditions of Sale.
©2018 Ball Horticultural Company 19050-B
™ denotes a trademark of and
® denotes a registered trademark of
Selecta Klemm GmbH & Co. KG in the U.S., which may be registered
in other countries.
60
80
potential capacity
effective capacity
(without wetting agent)
PERCENT AVAILABLE WATER

http://www.selectanorthamerica.com http://www.selectanorthamerica.com

February 2019

Table of Contents for the Digital Edition of February 2019