© Janet Davis
If your cabbage patch is
10 storeys up on a rooftop in India, in the middle of the Sahara Dessert, or on
an oil rig in the north Sea, you’re probably already practicing hydroponics.
But if you‘re an ordinary Canadian gardener who grows vegetables the
traditional way all summer, hates the digging and weeding, but loves fresh
lettuce, tomatoes and basil in February, then you might be a 
candidate to join the growing ranks of soil-less
gardeners.
Commercially, hydroponic
gardening is responsible worldwide for a huge share of greenhouse vegetable
production as well as that of cut flowers, poinsettias, potted mums, started
seedlings and tropical house plants. There’s even a society devoted to the art
-- the Hydroponic Society of America.
But what, exactly, is
hydroponics? Generally, it’s the cultivation of plants by supporting their
roots in a non-soil medium, using a solution of water and dissolved nutrients.
Although ornamental plants can be very successfully grown using hydroponic
methods, it’s vegetables and herbs that interest the majority of the gardeners.
Some advantages of hydroponic gardening over traditional soil gardening are:
·
the elimination of
soil-borne insects and viruses
·
the absence of weeds
·
reduction of heavy
tasks such as digging and tilling
·
increased crop yields
·
faster growth
·
fresh produce
out-of-season, harvested from your own, soil-less, indoor garden.
Hydroponics is practiced
around the globe by millions of people for whom conventional soil-based
gardening is inconvenient, inefficient or physically impossible. It’s ideal for
those who live in apartments and enjoy balcony gardening but don’t like lugging
bags of soil up a dozen storeys. It works for gardeners who aren’t satisfied
with the size of their crops, or those living in an area with a short growing
season.
The word hydroponic was
coined in the 1930s by an American professor, Dr. William Gericke, who combined
two Greek words – hydro, meaning water, and ponos, meaning work –
to convey how water and nutrients could cultivate plant life. Gerickle’s
experiments at the University of California with outdoor soiless crop
cultivation involved suspending tomato plants on a wire mesh framework with the
roots submerged in a water/nutrient solution. The resulting plants, which grew
to 25 feet (eight meters) tall, had to be harvested with ladders. During World
War II, Gericke’s ideas were adopted by the U.S. military services to produce
vegetables for their personnel.
How to Grow Hydroponically
The essential requirements
of plant growth are simple: water; light; air; nutrients, also called mineral
salts; and root support (the growing medium). Notice that soil, loam, manure or
compost are not included. In conventional soil gardening, plants can’t directly
utilize organic components; these must weather or
break down into intrinsic mineral salts – nitrogen, phosphorus, potassium and
trace elements including calcium, magnesium, sulphur, iron, manganese, boron,
zinc, copper, chlorine and molybdenum. In hydroponic gardening, these elements
are provided by the gardener in a controlled nutrient mix. The nutrients are
available to the plant the instant they come in contact with the roots. Ratios
depend on an informed understanding of the need of specific plants and
suppliers can provide the beginner with an inexpensive combination mix that
works for most plants. Some serious hydroponic gardeners prefer to mix their
own. A slightly acidic level (pH 5.6 to
6.5) is generally acceptable. If a batch of nutrient mix is used for too long,
the solution that remains after minerals are absorbed by plant roots can become
dangerously alkaline, but a simple test can be done with litmus paper.
Aggregate mixes used as growing media should be flushed clean with fresh water
at least once every two weeks. Similarly, experienced hydroponic growers use an
EC (electrical conductivity) meter to check that the nutrient solution does not
develop toxic concentrations of salts.
Getting the nutrient mix
into the growth medium is accomplished several ways. A simple system involves
periodic hand watering of plants growing in waterproof containers fitted with
plugs, which are removed before watering to allow the old solution to drain
off. Frequency depends on the environment – indoors, it might be two or three
times a week; outdoors on a hot balcony in summer, it might be two or three
time a day. The growing medium, which could be water or an inert material such
as sand or vermiculite, should always appear moist, but not water-logged. A more complex and expensive system, but one
that drastically reduces labor, involves the ebb-and-flow method and uses an
automatically timed recirculating pump to force the nutrient solution up from a
reservoir to the plant container, where it floods the roots before returning
the solution to the reservoir. A timer regulates the number of floods and the
duration of each. Before you decide
which method is right for you (and let’s not forget the plants – balance and
timing of nutrients are critical) it’s important to do some advanced reading
with a good book on hydroponics.
Hydroponically-grown plants are raised in inert
media, all of which permit the roots to spread out in search of nutrients.
Although water, sand, gravel, vermiculite, peat moss and perlite are
acceptable, most commercial growers and a rapidly increasing number of
hobbyists use a growing medium called rockwool, which is molten rock spun into
threads. It’s much like fiberglass insulation and is sold compressed into small
plugs and larger cubes or slabs. Lettuce can be seeded into a plug until the
roots develop, then inserted into a larger cube to grow until harvest.
The right temperature,
light and humidity are essential, and requirements vary according to the plant.
To carry on photosynthesis, plants must have adequate warmth. This usually
means a daytime temperature of 68o to 72oF (20o
to 22oC) and a night temperature of 59o to 63oF
(15o to 17oC). Temperatures must be significantly lower
at night to allow plants to metabolize the energy produced during the warm
daylight hours.
For a windowsill planter,
a south-facing window might provide adequate light, as long as care is taken to
protect the foliage from burning. In summer, south- and southwest-facing
balconies are good for outdoor growing, as are sunny sites in the garden or a
deck. Greenhouses, naturally, are well suited.
Indoors, it’s possible to grow short crops (under 16 inches/40
centimeters) of herbs, salad greens and small tomato varieties such as ‘Tiny
Tim’ and ‘Red Robin’ under florescent lights turned on for 16 to 18 hours a
day. Although two cool white and two warm white tubes 48 inches (120
centimeters) long are satisfactory, a better choice would be four
broad-spectrum tubes.
Many homes hydroponicists
intent on maximizing indoors crops are installing the more expensive ($250 to
$500) H.I.D (high-intensity discharge) sodium or metal halide lamps. Because
they have a spectrum and foot candle power close to that of natural sunlight,
and a three to four foot (one to 1.3 meter) penetration area, a wider variety
of crops can be grown. But such lamps can produce 400 watts of heat,
necessitating venting and cooling. Air exchange fans cost about $100 each.
Plants need an average relative humidity of 60 per
cent for good growth, but hydroponic cultivation usually provides adequate
humidity. An inexpensive hygrometer is useful for measuring humidity.
Regular inspection of the
growing environment is also important, even if automatic timers are used to
control nutrient pumps and artificial lighting. You, after all, have taken over
nature’s role, providing all the food, light and the growing medium, and it’s
important to pay rigorous attention to the system to make sure it’s working
well.
The Important Details
Unless you happen to be an
apiarist you won’t have bees, but plants don’t bear fruit unless they’re
pollinated. Self-pollinating plants can be assisted by gentle vibration of the
stem. Others, like cucumber, must be carefully hand-pollinated by brushing the
pollen from the stamen of one flower to the stigma of another.
Air-borne insects can be a
problem. For aphids or whiteflies, spray with organic homemade insecticide: mix
in a blender or mash a whole garlic bulb, two hot peppers, two large onions,
and one tablespoon (15 mL) of Tabasco sauce. Add water to cover and leavefor 24
hours. Force through a sieve and place resulting puree in a coffee filter, set
over a one-gallon (four- litre) container and pour water through the filter
until the container is full. Store in a glass bottle. Spray plants twice, 10
days apart, and check in another 10 days to be sure insects are gone. If this
seems too much like work, try a name-brand insecticidal soap, following
instructions given on the container.
Protect plants growing on
a balcony or deck from the wind. If they’re not under a cover or roof of some
kind, make sure that containers are drained and nutrients adjusted after a
heavy rain.
Adapted from an article published originally in
Canadian Gardening magazine