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Copyright 2005, Board of Trustees, University
GULF COAST RESEARCH & EDUCATION CENTER
L IFAS, University of Florida
LI -Lt *' 5007-60th Street East
Bradenton, FL 34203
Bradenton GCREC Research Report BRA1984-12 October 1984
CAPILLARY MAT IRRIGATION FOR BEDDING PLANTS
B. K. Harbaugh, R. W. Henley and C. D. Stanley
Bedding plant producers now produce many of their crops in 3, 4, or 5-inch pots
as well as in trays or cell-packs. With this change to larger pots also comes
the potential to use capillary mat irrigation. Capillary mat irrigation is a
versatile irrigation system that is ideal for the 3-6 inch pot sizes. Advantages
of this system include:
1) Conservation of water and reduction of pumping costs.
2) Several crop species or crops in different size pots can be grown on
the same bench or irrigation system.
3) Eliminates the "tangle syndrome" common to spaghetti tube systems used
with close pot spacings or small pot production.
4) The system is easily automated and provides uniform water distribution.
5) Plant foliage is kept dry, reducing disease potential and the need for
frequent reapplication of pesticide.
6) Can be used with controlled release fertilizer to reduce fertilization
costs and the need to inject fertilizer.
All irrigation systems have disadvantages and capillary mat irrigation is no
exception. However, for many production situations, these factors are not limiting
and may be equal to or less than problems with overhead or spaghetti tube systems.
Disadvantages of capillary mat systems include:
1) High initial investment costs compared to overhead systems.
2) Excessively succulent growth of some species.
3) Problems with design, water quality and engineering may be increased.
4) Frost protection and capability to root cuttings is lost, compared to
5) Plants must be watered overhead once or twice to establish capillarity
requiring two irrigation systems or a temporary overhead or hand-water
6) Algae or weed growth on the mats reduces mat life if algacides or mat
overlay films are not used.
7) Lack of flexibility to adjust fertilization within a crop cycle since
controlled release fertilization is used; i.e., mat fertilization
(injecting soluble fertilizer into the capillary mat irrigation
system) is not recommended since it increases algae problems and
stimulates roots to grow into the capillary mat.
One of the most troublesome problems we had with capillary mat irrigation was
the growth of algae and weeds on the mat, especially with production in a saran
house (shade cloth structure). We prevented this problem by covering the mat
with opaque polyethylene, cutting holes the size of the bottom of the pot, and
placing the pots on the mat in the holes left by removing the cut polyethylene
pieces. Although this procedure worked well, eliminated the algae and weed
problem, and extended the life of the mat, it was very time and labor consuming,
especially for pots less than 6 inches diameter. Recently, Capillary Sheet
was introduced which is a commercially prepared polyethylene film with tiny
perforated holes (pin sized). We evaluated this material and found no reduc-
tion in growth of several species produced in 4 inch pots compared to capillary mat
or hand watering (Table 1). This material eliminated algae and weed problems, as
well as root growth into the mat. To date, only two potential problems have been
observed with this material. Small pots (3-3 inch) with light-weight mixes do
not appear to establish capillarity readily or uniformly. There does not appear
to be enough weight to push the pot against the polyethylene, therefore, not
allowing a water film to develop that is necessary for capillary movement of water
into the pots. Without the polyethylene covering, the pots "settle" into the mat
fibers so that good moisture contact is made. Secondly, after several crops, salt
and dirt appear to plug the small perforations making periodic removal or scrubbing
of the covering necessary.
Although the capillary mat system has been discussed as an independent system, a
combination capillary mat and overhead system may be better than either one alone.
The use of overhead systems for plant establishment, rooting, injection of fertili-
zer, and frost protection are valuable assets but are only needed occasionally.
During the bulk of the production time, the capillary mat system would be used with
all the advantages listed previously and many of the disadvantages eliminated by
the occasional use of the overhead system.
Successful use of capillary mats depend on several factors. The following are
guidelines which are important to implement if one is to be successful with
capillary mat irrigation:
1) The bench must be constructed so that water does not stand in depressions
or have high spots that dry out. A crowned bench or one sloping 1-2
inches across the bed can alleviate these problems.
2) An overhead system should be installed for use with the mat system.
3) An opaque polyethylene film with performations should be used over the
4) The mat should be kept moist at all times, but pots should not stand in
water. Thus, set the clocks to turn on the water 3-5 times a day and
punch holes in the 2 mil polyethylene used under the mats where water
5) Automate the irrigation system and fertilization by using controlled
release fertilizer in conjunction with capillary mat irrigation.
Plants can be "toned" at the end of the production cycle if the
controlled release fertilizer does not last by injecting fertilizer
once or twice thru the overhead system, but this is usually not
necessary in Florida with bedding plant production. In more arid
parts of the U. S. with low humidity or with long-term crops, salts
may build up on the soil surface and leaching the soil with overhead
irrigation may be required every 6-8 weeks.
6) Turn the irrigation system off on rainy days with production in
saran houses. Even though the irrigation system is automated, the
producer still has to manage the overall production regime!
7) Do not use media with large pore spaces, or extremely light media.
Remember, the pots must be heavy enough to push into the mat so that
water can move into and through the media by capillary action. Large
air spaces under pots caused by footed plastic pots or large air
spaces in the media (undecomposed bark usually not used in bedding
plants) will prevent use of this system.
8) Buy pots with flat bottoms and clean cut drainage holes in the bottom.
9) Establish capillarity by watering overhead one or twice thoroughly
(water should come out of the bottom of the pot). If pots are moved
or soil becomes dry due to irrigation failures, irrigate overhead
Table 1. Evaluation of Capillary Sheet, a perforated plastic overlay for
capillary mats, for production of Begonia semperflorens 'Vodka', Exacum affine
'Blue Charm', Euphorbia pulcherrima 'Diva', and Caladium hortulanum 'Heart-throb'
in 4 inch diameter pots in a greenhouse.
Height Width Quality Rating
Irrigation Methodz (inches) (inches) (1-5, 1=Best)
Begonia semperflorens 'Vodka'
Hand Water 5.5 9.4 2.8
Capillary Mat (Vattex) 6.2 10.6 2.8
Capillary Sheet (Over Vattex) 6.2 9.0 2.2
Exacum affine 'Blue Charm'
Hand Water 9.8 13.4 2.5
Capillary Mat (Vattex) 10.2 14.2 2.5
Capillary Sheet (Over Vattex) 10.6 15.0 2.5
Euphorbia pulcherrima 'Diva'
Hand Water 8.7 11.0 1.5
Capillary Mat (Vattex) 9.4 12.6 2.0
Capillary Sheet (Over Vattex) 9.4 12.6 1.2
Caladium hortulanum 'Heart-throb'
Hand Water 5.1 9.1 2.0
Capillary Mat (Vattex) 5.9 9.4 1.5
Capillary Sheet (Over Vattex) 5.5 9.8 2.0
ZNo significnat differences among irrigation systems within each plant species
at the 5% confidence level.