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The Nutrient Film Technique

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Rows of ripe and ripening tomatoes grown the nutrient film technique way.
2 / 6
A lattice bed for lettuce.
3 / 6
Young tomato plants in plastic-lined gutters.
4 / 6
A bumper crop of buttercrunch.
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The cascade arrangement is an efficient use of space.
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Diagram shows the parts and configuration of a basic Nutrient Film System setup.

Hydroponic gardening is nothing new to most of MOTHER EARTH NEWS’
readers because the traditional methods of growing
plants without soil were all discussed in “Hydroponics Mini-Manual.”

Hand watering, wick growing, and periodic flooding with
nutrients (using a pump and timer)–all methods which have
their advantages and disadvantages–were described in that
story. But now there’s a new way to grow plants in liquid
culture that offers some significant improvements upon the
traditional procedures: It’s the Nutrient Film
Technique, or NFT (Sometimes also referred to as nutrient flow technique).

Based on research begun by England’s Dr. A. J. Cooper in
1972, NFT is a system that uses a “film” of nutrient
solution which flows continuously over the bottom of
the channel containing the plants. The fertile fluid is
constantly recirculated, and can be used (with periodic
enrichment) for several weeks.

American researchers at the Long Island Horticultural
Research Laboratory of Cornell University have been working
with NFT since 1975, and they claim the technique’s
versatility is enormous! For example, unlike other forms of
hydroponics, NFT can be used with or without a growing
medium (the latter method eliminates the otherwise
necessary beds of heavy–and hard to sterilize–gravel),
it can be set up with either horizontal or vertical growing
beds, it’s practical both indoors and out, and
it’s economical to use and basic in design.

An NFT system is a snap to assemble, too. All that’s needed
are [1] a growing bed of some sort; [2] two containers
(Plastic wastebaskets or dishpans are perfect for this job. Avoid unlined metal containers. The first supplies the nutrient–by gravity feed–to the growing bed, and
the second acts as a receiving basin to collect the fluid
after it has trickled past the roots); and [3] a pump,
connecting pipes or tubing, and some screw clips to be used
as control valves.

The fertilizer solution is contained in the elevated
nutrient tank, from which it travels by way of a plastic or
rubber hose to the growing bed. The rate of nutrient flow
is easily controlled by a screw clip on the tubing. The
liquid passes through the growing bed (which is at a
minimum 2 or 3% tilt) and then drains into the receiving
(or catchment) tank, picking up oxygen as it spills
into the receptacle. The fluid completes the cycle when a
pump in the lower tank–cued by the tripping of a float
switch in the upper container–kicks in and sends the
nutrient on its way upward.

In addition, a third tank–which holds water to replace
liquid losses caused by transpiration and evaporation–can
be added to automate even more of the process. The
replacement liquid is introduced into the lower tank when a
float valve trips. And that’s all there is to it!
Basically, the Nutrient Film Technique system is a closed
loop that uses gravity to supply the fertilizer to the
growing bed and a pump to raise the liquid back to its
starting point.

Lattice Your Lettuce

The NFT approach allows a great deal of flexibility in the
layout of the growing beds. Tomatoes and cucumbers started
in Kys Kubes or Jiffy-7’s (available in most garden supply
stores) can, for instance, be grown in sections of plastic
roof gutter without any growing medium. Or, if you fill the
gutters with several inches of perlite, you can raise
cauliflower or other heavy-heading produce. A lattice grid
of 2 X 4’s–with a sheet of plastic forming channels between
the boards–will support a huge crop of butterhead lettuce
in a sparse two inches of perlite, while a slightly sloping
bed of plywood–with 1″ X 6″ sides and a polyethylene
liner–can be constructed to almost any dimension and used
for just about any vegetable from radishes to beets.

Vertical Vegetables

Tall plants, such as tomatoes or cucumbers, are common in
hydroponic culture, but NFT allows normally “horizontal”
crops–such as lettuce, spinach, or even houseplants–to be
grown in spacesaving, sun-seeking vertical gardens.
Two-inch-diameter PVC pipes–pierced with holes that
accommodate preplanted Jiffy-7’s–become lush green columns
(the nutrient gravity-feeds in at the top, moistens
the roots as it flows down inside the pipe, and is
collected at the bottom to be cycled back again). A similar
space saver is the “cascade” arrangement, in which slightly
sloping (alternately right and left) PVC-pipe beds are
positioned one above another. The nutrient solution flows
in at the high end of the top pipe, passes from the low end
of that tube to the high end of the next one, and zig-zags
its way to the bottom, feeding the roots all the way
down.

It’s even possible to make a “radish A-frame” from plywood
sheets covered first with plastic and then with capillary
matting (sold by greenhouse specialty stores). Simply sew
felt weatherstripping onto the matting and tuck your
radish seeds into the flaps. A plastic feed pipe on top of
the structure delivers a constant stream of nutrient
solution, which flows down the matting to catchment gutters
at the bottom. Then, of course, the liquid is
pumped back up to the top.

Soup It Up!

Since hydroponically grown plants are solely dependent upon
the “feed” that you give them for nourishment, careful
attention to nutrient formulas and handling techniques will
be vital to your water garden’s success. There are three
factors to consider: the ingredients, pH, and potency of
the nutrient solution.

Everyone connected with hydroponics seems to have his or
her favorite fertilizer formula. I’ve had good results with
Hydro-Sol–a product of the Robert B. Peters Co., and
available from many garden centers–with the addition of
an ounce of calcium nitrate for each ounce of the commercial
product. Two ounces of this mixture will yield 15 gallons
of nutrient, and will supply all the nitrogen,
phosphorus, potassium, magnesium, and calcium (as well as
the trace elements iron, boron, copper, zinc, manganese,
and molybdenum) that most plants need. Other good
commercial mixtures are available from garden centers under
the names Hyponex, Dr. Chatelier, and Ra-Pid-Gro. Many mail-order suppliers offer their own blends.

Organic gardeners have often expressed concern about the
use of chemical plant foods in hydroponics. I must admit
that I find the explanation given by MOTHER EARTH NEWS contributor James B.
DeKorne convincing. Jim says that while organic
fertilizers are clearly superior in soil culture, where
bacteria in the growing medium can break down the nutrients
to their ultimate (and usable) form, in hydroponics we feed
the plant, not the “soil.” Therefore the nutrients must be
in an already broken-down form for the roots to absorb
them. Those who aren’t swayed by DeKorne’s argument should
look at “A Simple Solution” for some all-natural plant
food recipes. Pyramid Hydroponics also
offers an organic fertilizer.

However he or she may feel about the question of natural
vs. manufactured fertilizer, though, there are still two
other items that demand the novice hydroponic gardener’s
attention: maintaining the proper pH in the solution, and
assuring the potency of the nutrients. It’s easy to monitor
the acid/alkaline balance (or pH) with nitrazine paper
(available from most any drugstore) or by using test kits
sold by hydroponics suppliers.

Plants generally do best with a slightly acid nutrient, so a pH of 6 to 6.5 (pH 7 is neutral) is desirable. As
the roots remove chemicals from the fertilizer, the pH of
the liquid tends to drift toward the alkaline, which
causes some nutrients (especially iron) to precipitate out
and thus become unavailable to the plants. A small quantity
of distilled white vinegar–remember that a teaspoon of the
acidic liquid per gallon of nutrient will drop the pH by
two points!–will restore the proper “sourness” to the
solution. You can make the fluid more alkaline
(less often a problem) by adding a small amount–monitored
by nitrazine paper tests–of lime or bicarbonate of soda.

Strong Waters

Most plant food manufacturers have adopted a “baby with the
bath water” approach to maintaining nutrient potency. Since
the chemical analysis of hydroponic fertilizer is an
exacting (and expensive) process, the advice usually
offered is to chuck the soup out after a week or two,
preferably under a favorite fruit tree where it might do
some good! However, Hydroponic Growing Systems–a supplier
that specializes in the NFT method–does offer a kit that
permits a simple test of chemical strength. That
can help you avoid tossing out a jug of nutrient before its
time.

On Location

The Nutrient Film Technique is enormously versatile, but
certain sites are more appropriate to its use than are
others. Given the amount of plumbing involved in
hydroponics, for instance, living rooms are probably not
the ideal place to set up an NFT system. And–unless you’re
planning to grow houseplants (which can flourish under
fluorescent lights)–the dark corner of your basement
is out of the question. A greenhouse, of course, is an
ideal location for an NFT installation. Enormous
quantities of vegetables can be raised in even a small,
sunny spare room. In addition, don’t forget that (given a
receiving tank big enough to hold any overflow caused by
rainfall) all sorts of crops can be grown outside in
the country, suburbs, or inner city! Apartment roofs,
narrow urban back yards, small waste places . . . all can
be turned into gardens of plenty with NFT!

EDITOR’S NOTE:Here are some other
mail-order sources for fertilizers and equipment.

Charley’s Greenhouse Supply

Eco Enterprises

Hydro Gardens  

Published on Nov 1, 1979