EHUF 490B Native Plant Propagation –
Spring 2003
Group 3 ~ Caren Crandell, Crystal Elliott,
Kevin Kline,
Christer Lundstrom & Rodney Pond
IF YOU CAN’T LEAD A
PLANT TO WATER, HOW CAN YOU MAKE IT DRINK?
CAPILLARY AND WET BEDS:
ESSENTIAL TOOLS FOR
RESTORATION PROPAGATION
What are they?
Capillary beds and wet beds serve similar functions in a
restoration propagation operation. They both supply a constant and steady
supply of moisture to the root zones of plants from the bottom up. This is in
contrast to top-down watering such as drip or sprinkler irrigation where water
must percolate through the growing medium down to the root zone.
Capillary beds are low walled enclosures lined
with waterproof material and filled with a fine grained medium such as sand,
mulch, pumice etc. Water is supplied through drip irrigation, soaker hose or
some other water delivery system laid at the bottom of the bed beneath the
medium. Plants are placed in pots with bottom holes into the medium and the
water travels via capillary action up through the medium and into the potted
plants via the bottom holes. Bare root plants can also be placed directly into
the media. The primary use for capillary beds in restoration operations is to
support plants needing constant moisture (but not saturation) whether they are recently
salvaged or greenhouse grown. Capillary beds are especially useful for reducing
water stress associated with salvaged plants that have lost a goodly portion of
their root systems.
Wet beds are also low walled enclosures
lined with water proof material. In general they are not filled with media but
rather with a constant level of water and therefore are used almost exclusively
to hold and propagate wetland plants, especially obligate wetland plants. The
plants may be held in containers with media in the wet bed or a limited amount
of rooting media may be placed in the bed for larger scale propagation.
Floating aquatic plants can merely be allowed to cover the surface of a bed
without a container.
What are the advantages of capillary and wet
beds?
Certainly the clear advantage for both of these systems is
the passive, low-tech, low cost approach to supplying an efficient, constant source
of moisture to plants as they need it. A variety of recycled (and recyclable) materials
can be used to construct these beds and they can be made to be moved as needed
fairly simply.
What are the disadvantages of capillary and wet
beds?
For many plants they are too consistently wet. Capillary and
especially wet beds really do their best for plants preferring moist soils.
Plants requiring complete drainage between waterings would not do well in
either system. In capillary beds, plants not adapted to constant moisture may
benefit immediately after salvaging as a water stress reducing technique or for
temporary holding of harvested bare root material immediately prior to
installation. However any plant prone to root rot should not be held in a
capillary or wet bed for extended periods of time. It had been noted that mulch
as a capillary medium may promote root rot more so than other media.
Cost? Operation? Flexibility? Low-tech?
|
Capillary bed |
Low, can be easily made from mostly recycled materials |
Easy, simple design and maintenance |
Limited, moisture tolerant plants only |
Yes, few basic
parts, electricity optional |
|
Wet bed |
Low, can be easily made from mostly recycled materials |
Easy, simple design and maintenance |
Limited, wetland emergents and aquatic plants only |
Yes, few basic parts, electricity optional |
|
Top-down irrigation |
High, requires almost all new materials |
More complex design and many parts to maintain |
Broad, serves a variety of plant moisture regimes with
more precision |
Often not, many complex parts, reliance on electrical power |
The why and
how of capillary beds
Capillary beds are an efficient water
delivery technique for containerized plants, and a good alternative to overhead
watering. The philosophy behind the
design of these beds is that water will by way of capillary action move through
the pores between the particles of a medium such as sand, mulch or sawdust.
Water is added to the bed at a regulated level, and is subsequently drawn-up
and distributed to drier areas of the bed, promoting uniform water availability
and allowing containerized plants in all areas of the bed to be watered
evenly. Both the frame and the medium in
the bed should be level in order to ensure the uniform distribution of water.
The capillary bed design we developed
consists of a re-bar reinforced treated-wood frame lined with a triple-layer of
6 mil plastic sheeting over a thin cushioning layer of sand. The bed is then
filled with 6” of sand (or another medium), along with a self-regulating water
distribution system such as a drip line irrigation with a timer valve. A
latching hinged section at one end of the bed allows for easy removal of the
medium and cleaning of the bed liner. At the opposite end is a drain pipe with
a valve to allow for winter drainage and for cleaning. With careful
construction, this design will require minimum maintenance after set-up.
Advantages to capillary beds as opposed to
overhead watering are many. Capillary beds exhibit much higher water use
efficiency, reducing usage by 50-70%.
Also, since capillary beds are closed systems for the most part, there
is no run-off, meaning that fertilizers won’t be washed away and be lost to the
plants as well as polluting water bodies.
Since plants are being watered from the bottom up, the surface soil does
not have high water content, thus reducing the occurrence of opportunistic
weeds. Also, eliminating overhead water
spray reduces occurrence of disease-causing fungi that thrive under moist
conditions, such as molds and mildews.
And finally, as mentioned before, they require little maintenance when
set-up properly.
Although capillary beds have many positive
characteristics, there are some limitations to this watering technique. These include a large initial financial
investment that can be offset by the use of recycled materials, even though the
long term costs are lower than overhead watering. Also, capillary beds can not support plants
in containers greater than two gallons because the strength of the capillary
rise is not sufficient to deliver adequate water. In addition, salts can build up on the
surface of the soil in containers during the hot part of the year (especially
if the water source is high in salts), and must be rinsed and dissolved using
overhead watering.
How much does a typical low-tech capillary bed
cost?
As seen from the cost estimates below, the construction of a
new capillary bed with drip line irrigation as specified in the design
schematic above prices out at just over $300 for new materials. Substituting
recycled materials for any of the components below would bring the cost down
considerably. Just replacing the new lumber with recycled would drop the costs
by $60. Simpler water supply systems such as soaker hose or a sump at one end
of the bed with a float valve could bring the cost down another $100.
|
Capillary
Bed (30' x 4' x 8") |
|
|||
|
|
|
Price |
Quantity |
Total |
|
Wood
frame |
2" x
8" x 8' pressure treated lumber #2 fir |
$6.46 |
2 |
$12.92 |
|
|
2" x
8" x 10' pressure treated lumber #2 fir |
$8.15 |
6 |
$48.90 |
|
Hinges |
Galvanized
3” x 4” |
$4.98 |
2 |
$9.96 |
|
Slide
latches |
Galvanized |
$3.98 |
2 |
$7.96 |
|
Brackets |
Simpson
L70 reinforcing angle |
$1.26 |
4 |
$5.04 |
|
|
Simpson
TP-37 Tie Plate |
$0.57 |
4 |
$2.28 |
|
Wood
screws |
#14 galvanized,
50/box |
$2.29/box |
1 |
$2.29 |
|
Re-bar |
0.5"
x 2' |
$0.56 |
26 |
$14.56 |
|
Liner
clips |
Heavy duty
2” binder clips 12/box |
$2.98/box |
3 |
$8.94 |
|
Drain
pipe |
½” 1’
length |
$2.98 |
1 |
$2.98 |
|
Pipe
valve |
Brass ½” |
$8.98 |
1 |
$8.98 |
|
Nails |
#8,
hot-dipped galvanized nails |
$1.59/lb |
1 lb |
$1.59 |
|
|
#16,
hot-dipped galvanized nails |
$1.59/lb |
1 lb |
$1.59 |
|
plastic
sheeting |
6 mil
black 6’ x 100’ roll |
$15.49 |
1 |
$15.49 |
|
Sand |
screened
sand |
$13.00/ton |
3 |
$39.00 |
|
Total Cost |
|
|
|
$182.48 |
Capillary irrigation
system
|
Quantity |
Description |
Unit
Price |
Total |
|
|
digital battery timer valve |
39.95 |
39.95 |
|
|
2.05 |
2.05 |
|
|
|
3.60 |
3.60 |
|
|
|
2.45 |
2.45 |
|
|
|
1.30 |
2.60 |
|
|
|
28.00 |
56.00 |
|
|
|
12.50 |
12.50 |
|
|
|
9.00 |
9.00 |
|
|
|
50’ -
¾” mainline tubing |
15.00 |
15.00 |
|
Sub-Total |
$143.15 |
||
The how and why of wet beds
Wet beds most typically are used to
propagate and hold wetland emergents and aquatic plants. The design of wet beds
can of course vary with the demands of the situation. Most wet beds are simpler
versions of capillary beds; a wood frame lined with plastic and filled with
water. The basic operating principle of wet beds is to maintain a certain water
depth that promotes good plant growth. Plants can either be in containers with
media and submerged, free-floating in the case of aquatic plants or the entire
bed can have a layer of growing media and planted. The King County, Washington
Conservation district incorporates the following design features and concerns:
Wet beds built with recycled wood (Trex®) and plastic sheeting over a
bed of gravel.
Half of each bed dedicated to a different species, the watering conditions for which
can be varied.
Beds lined with 3 layers of 6 mil plastic.
Thicker liners are commercially available but would be more costly to
repair and/or replace. Liners can last
from
Irrigation for each bed regulated with a manually operated valve. In the summer months, beds must be filled
every other day.
Plant grown in pots, which can be elevated if necessary with upside down flats
or trays. Pressure on the liner is also
thereby reduced.
Seedlings started in
multi-sectioned trays that are positioned flush with the surface of the
water.
Food-grade barrels
cut in half serve as small wet beds.
This wet bed design is essentially the
capillary bed design sans capillary medium. It also consists of a re-bar reinforced
treated-wood frame lined with a triple-layer of 6 mil plastic sheeting over a
thin cushioning layer of sand. The bed is then filled with 6” water with a
self-regulating water supply system in the form of a simple toilet float valve.
As the water level drops below a 
certain
level the float valve opens refilling the bed back to the original volume.
Another added improvement is the use of a large fish tank type aerator to
oxygenate the water sufficiently for good root growth and to keep algal growth
down. A latching hinged section at one end of the bed allows for easy cleaning
of the bed liner. At the opposite end is a drain pipe with a valve to allow for
winter drainage and for cleaning. With careful construction, this design will
also require minimum maintenance after set-up.
How much does a typical low-tech wet bed cost?
Since the wet bed in this example is really
just a pared down version of the capillary bed (minus sand and drip line
irrigation), it is far less expensive, just under $200. Again using recycled
components could make this standard wet bed much, much cheaper, potentially for
$100 or less.
|
Wet
Bed (30' x 4' x 8") |
|
|||
|
|
|
Price |
Quantity |
Total |
|
Wood
frame |
2" x
8" x 8' pressure treated lumber #2 fir |
$6.46 |
2 |
$12.92 |
|
|
2" x
8" x 10' pressure treated lumber #2 fir |
$8.15 |
6 |
$48.90 |
|
Hinges |
Galvanized
3” x 4” |
$4.98 |
2 |
$9.96 |
|
Slide
latches |
Galvanized |
$3.98 |
2 |
$7.96 |
|
Brackets |
Simpson
L70 reinforcing angle |
$1.26 |
4 |
$5.04 |
|
|
Simpson
TP-37 Tie Plate |
$0.57 |
4 |
$2.28 |
|
Wood
screws |
#14 galvanized,
50/box |
$2.29/box |
1 |
$2.29 |
|
Re-bar |
0.5"
x 2' |
$0.56 |
26 |
$14.56 |
|
Liner
clips |
Heavy
duty 2” binder clips 12/box |
$2.98/box |
3 |
$8.94 |
|
Drain
pipe |
½” 1’
length |
$2.98 |
1 |
$2.98 |
|
Pipe
valve |
Brass ½” |
$8.98 |
1 |
$8.98 |
|
Float
valve assembly |
Valve
& float |
$10.00 |
1 |
$10.00 |
|
Nails |
#8,
hot-dipped galvanized nails |
$1.59/lb |
1 lb |
$1.59 |
|
|
#16,
hot-dipped galvanized nails |
$1.59/lb |
1 lb |
$1.59 |
|
plastic
sheeting |
6 mil
black 6’ x 100’ roll |
$15.49 |
1 |
$15.49 |
|
aerator |
Aquarium
air pump |
$30.00 |
1 |
$30.00 |
|
Sand |
screened
sand |
$13.00/ton |
1 |
$13.00 |
|
Total Cost |
|
|
|
$196.48 |
Restoration applications for capillary and wet
beds
Both capillary and wet beds are important native plant propagation
tools. Both systems can be used to germinate seed in flats, root cuttings and
hold potted-up plants from the green house. Both systems also have the capacity
to function as temporary holding areas for recently harvested bare root and
salvaged plants to avoid water loss stress associated with root loss and
damage. And finally both systems have
the flexibility to accommodate all these functions simultaneously, if
necessary.
Often temporary on-site holding or even propagation facilities are
needed, especially with large restoration projects and in harsh climates. The
simplicity of the wet and capillary bed design translates easily to a smaller
scale and often recycled containers such as 55 gallon food grade plastic drums
cut length-wise (see photo below) or ‘kiddie’ wading pools can be modified to
suit on-site needs.
How do I keep critters from eating my plants?
Herbivory is a major concern for all plant propagators. In
the 
culprits that wreck propagation operations. Crows, either out of sheer
malice or in search of worms or other invertebrates, are notorious for
uprooting plants and flinging pots.
How much does it cost for your basic herbivore
exclusion structure?
A basic PVC pipe structure to support protective netting or
even shade cloth costs just under $65 and would be well worth the investment
given the potential losses from herbivory.
|
Herbivore
Deterrent Cage (30' x 3' x 4') |
|
|||
|
|
|
Price |
Quantity |
Total |
|
PVC pipe |
1" x
10' plain end PVC SCH-40 pipe by Silverline |
$2.19 |
12 |
$26.28 |
|
PVC
fittings |
3 way L-1
inch Fittings |
$2.15 |
4 |
$8.60 |
|
|
4 way
LT-1 inch Fittings |
$2.31 |
4 |
$9.24 |
|
Netting |
protective
mesh covering, black, 14' x 45' |
$19.96 |
1 |
$19.96 |
|
|
|
|
Total |
$64.08 |
References
Agri-Supply agricultural & horticultural suppliers: http://www.agri-supply.com
Dripworks Irrigation: http://www.dripworks.com
Home Depot: http://www,homedepot.com
King County Native Plant Salvage: http://dnr.metrokc.gov/wlr
Marine & Reef aquarium supply: http://www.marineandreef.com
David Kerr ~ Ornamental Crops Adviser: David.Kerr@dardni.gov.uk