steved at ncatark.uark.edu
Thu Jan 8 06:36:04 EST 1998
Educational Concerns for Health Organization (ECHO) in
Florida has a couple of small publications on Roof Top
Gardening. They have a web site, too. Anyways, they focus
on shallow bed gardening methods for rooftops.
Shallow bed gardening can be done many ways, but it
focuses on a shallow layer of growing mix to raise plants.
The roots go down and meet a barrier (plastic or geotextile
layed on top of a bench or floor), and then move laterally,
thus creating a matted root system similar to NFT hydroponics.
I seen this done in commercial-scale greenhouses that raise
sprouts (wheat grass, buckwheat, sunflowers) in California,
and for specialty lettuces in Arkansasa. Note: a compost-based
growing mix is rather important in my opinion for the biological
factor (soil microbes, enzymes, slow-release nutrients, humus, etc.)
rather than a completely soilless mix.
The Dynamic Root Floating Bed method in hydroponics
will also work for roof tops. University of Hawaii has
pubs and videos on this method.
Here are some excerpt from a publication on hydropic
vegetable production from Appropriate Technology
Transfer for Rural Areas (ATTRA):
Non circulating/Dynamic Root Floating Hydroponics
Non circulating hydroponics and the dynamic root floating technique
(DRF) are passive liquid systems with a similar mode of operation.
They were both developed at the Asian Vegetable Research Center in
Taiwan for low-tech hydroponics in tropical agriculture. Whereas most
hydroponic systems require circulation or aeration of nutrient
solutions and continual monitoring and adjustment of temperature, pH,
electrical conductivity, and nutrient levels, non-circulating
hydroponics and DRF can be done without electrical pumps or
The main feature of these two systems is the placement of plants on a
panel fitted onto a bed or box filled with a shallow layer of
hydroponic nutrient solution with a space between the panel and
solution. In DRF, crops are grown above a ridged culture bed
containing the solution, with the roots dangling freely into the
solution. In non-circulating hydroponics, crops are grown on a panel
fitted with tree planting tubes (or any similar container) filled with
a soilless medium, and the bottoms of the tubes are immersed in two
inches of solution.
In each system the bottom roots are immersed in the solution and the
top roots are exposed to humid air inside the chamber. Roots
suspended above the solution specialize in absorbing oxygen
(aeroroots), while the lower roots dangling in the solution specialize
in water and nutrient uptake (nutriroots). Vegetable yields obtained
are comparable to those produced by more conventional liquid systems such
Dr. Bernard Kratky, a horticulturist with the Beaumont
Agricultural Research Center,University of Hawaii, has
published several articles on non-circulating hydroponics, and
produced a 38-minute video on this method that is available for $50.00
(checks payable to University of Hawaii). Contact:
Dr. Bernard Kratky
Beaumont Agricultural Research Center
University of Hawaii
Hilo, HI 96720
The Dynamic Root Floating Hydroponic Technique: Year-Round Production
of Vegetables in ROC on Taiwan is Extension Bulletin No. 330 of the
ASPAC Food & Fertilizer Technology Center in Taiwan. This 18-page
bulletin can be obtained through Inter-Library Loan, or the Food &
Fertilizer Technology Center in the Republic of China (ROC) on Taiwan.
Food & Fertilizer Technology Center
P.O. Box 22-149
Taipei City, ROC on Taiwan
Shallow Bed Culture
Shallow bed culture, also known as thin layer culture, is the
production of sprouts or herbaceous herbs and vegetables in a thin
layer--1 to 2 inches in depth--of compost laid on top of plastic. At
least one commercial sprout grower in California uses this method in
the production of wheat grass, sunflower, and buckwheat sprouts.
Herbaceous crops adapted to shallow bed culture include specialty
lettuces, greens, cresses, and selected culinary herbs. In the
California operation, a commercial-scale greenhouse is devoted to this
method. Root-zone heating tubes are laid underneath the plastic to
provide bottom heat. In turn, they rest on top of polystyrene panels
laid directly over the greenhouse soil. Gas-fired water heaters are
used to heat the water, but such a system could easily be retrofitted
to solar collectors located outside the greenhouse. Narrow boards are
laid out every three feet to walk up and down between the beds to
seed, water, and harvest.
ECHO, a nonprofit organization that works in agriculture development,
is promoting the shallow bed method as a technique for rooftop
gardening in urban settings. The beds they describe are deeper--3 to
6 inches in depth--and are more typical of standard trough culture
using a soilless mix. They've achieved good success raising a variety
of vegetable crops using locally available materials such as leaf mold
ECHO has published several reports on shallow bed culture and low-tech
hydroponics. For more information, contact:
Educational Concerns for Hunger Organization (ECHO)
17430 Durrance Rd.
North Ft. Myers, FL 33917
Another pub you should know about is "More Food From
Your Garden: The World-Famed Mittleider Method of
Grow-Box Greenhouse Gardening". It uses soilless mixes
in framed raised beds. Very nice photos and stuctures and
ideas. May be available from Hydroponic Society of America.
Another method you should know about are Grow Bags.
Again, soilless potting mixes are placed inside layflat
polyethylene bags. Holes are punched into the bottoms
for drainage, and plants are planted through slits in the
top. Three tomato plants per 3 ft long by 1 foot wide bag.
Vertical bags, 2-3 gallon size, are very common in greenhouse
Also, vertical tubes filled with potting mix and suspended from
trellising, are used in greenhouse production, too.
Please share more details--design, production techniques--when
your project gets underway.
> Hello all:
> We at the City of Port Phillip (inner suburbs of Melbourne) recently
> received a government urban design grant to undertake a research project on
> the concept and practicalities of roof gardens in the inner urban context.
> The first stage of the project will involve environmental science,
> landscape, horticulture, engineering and architecture students from four
> universities, local conservation organisations, and we are looking to
> involve local industry and developers as well. The outcomes will include a
> lot of research data, a public exhibition of student work, pilot plots and
> practical "how to do it" guidelines. Stage 2 will involve fairly large scale
> implementation in a new Council-run housing development.
> A few research topics for the students which initially come to mind include:
> * Structural implications for roofs
> * Species selection in general, and with reference to particular conditions
> (coastal, drought resistant, shade tolerant where roofs are overshadowed etc.)
> * Retrofitting rooftop gardens to existing roofs
> * Hydrology - drainage and water balance
> * Growing media
> * Geotextiles, cells and membranes
> * Edible rooftop landscapes (vegetable plots etc.)
> * Weed control through appropriate initial species selection
> * Aesthetics, urban design and implications for historic buildings
> * Insulation properties of roof gardens - implications for energy efficiency
> * Quantification of improvements to air quality (interception of particulate
> air pollutants, production of oxygen)
> ..... etc.
> Anybody out there with comments, suggestions and best of all, first hand
> experience, we would be delighted to hear from you. Before we do anything
> else, we are scouring the Internet and other sources to find out what others
> have done, to avoid reinventing any wheels and help identify the "gaps"
> which will frame the tasks for the students. And, anything which we find out
> will be shared over the Net so that others can benefit from our (hopefully)
> successes and (inevitably) errors!
> Cheers, Paul Osmond
steved at ncatark.uark.edu
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