The more you know, the easier it is to grow!
Carbon Dioxide
During photosynthesis, plants use carbon dioxide (CO2), light, and hydrogen (usually water) to produce
carbohydrates, which is a source of food. Oxygen is given off in this process as a by-product. Light is a
key variable in photosynthesis.
Conductivity
Measuring nutrient solution strength is a relatively simple process. However, the electronic
devices manufactured to achieve this task are quite sophisticated and use the latest microprocessor
technology. To understand how these devices work, you have to know that pure water doesn’t
conduct electricity. But as salts are dissolved into the pure water, electricity begins to be
conducted. An electrical current will begin to flow when live electrodes are placed into the
solution. The more salts that are dissolved, the stronger the salt solution and, correspondingly, the
more electrical current that will flow. This current flow is connected to special electronic circuitry
that allows the grower to determine the resultant strength of the nutrient solution.
The scale used to measure nutrient strength is electrical conductivity (EC) or conductivity factor
(CF). The CF scale is most commonly used in hydroponics. It spans from 0 to more than 100 CF
units. The part of the scale generally used by home hydroponic gardeners spans 0-100 CF units.
The part of the scale generally used by commercial or large-scale hydroponic growers is from 2 to
4 CF. (strength for growing watercress and some fancy lettuce) to as high as approximately 35 CF
for fruits, berries, and ornamental trees. Higher CF values are used by experienced commercial
growers to obtain special plant responses and for many of the modern hybrid crops, such as
tomatoes and some peppers. Most other plant types fall between these two figures and the
majority is grown at 13-25 CF.
--Rob Smith
Germination
When a seed first begins to grow, it is germinating. Seeds are germinated in a growing medium, such as
perlite. Several factors are involved in this process. First, the seed must be active--and alive--and not in
dormancy. Most seeds have a specific temperature range that must be achieved. Moisture and oxygen
must be present. And, for some seeds, specified levels of light or darkness must be met. Check the
specifications of seeds to see their germination requirements.
The first two leaves that sprout from a seed are called the seed leaves, or cotyledons. These are not the
true leaves of a plant. The seed develops these first leaves to serve as a starting food source for the
young, developing plant.
Growing Medium
Soil is never used in hydroponic growing. Some systems have the ability to support the growing plants,
allowing the bare roots to have maximum exposure to the nutrient solution. In other systems, the roots
are supported by a growing medium. Some types of media also aid in moisture and nutrient retention.
Different media are better suited to specific plants and systems. It is best to research all of your options
and to get some recommendations for systems and media before making investing in or building an
operation. Popular growing media include:
- Coco Coir. Natural coconut husks in different textures that provide an organic, natural, reusable medium and is eco friendly.
- Composted bark. It is usually organic and can be used for seed germination.
- Expanded clay. Pellets are baked in a very hot oven, which causes them to expand, creating a
porous end product.
- Gravel. Any type can be used. However, gravel can add minerals to nutrient. Always make sure it
is clean.
- Oasis. This artificial, foam-based material is commonly known from its use as an arrangement
base in the floral industry.
- Peat moss. This medium is carbonized and compressed vegetable matter that has been partially
decomposed.
- Perlite. Volcanic glass is mined from lava flows and heated in furnaces to a high temperature,
causing the small amount of moisture inside to expand. This converts the hard glass into small,
sponge-like kernels.
- Pumice. This is a glassy material that is formed by volcanic activity. Pumice is lightweight due to
its large number of cavities produced by the expulsion of water vapor at a high temperature as
lava surfaces.
- Rockwool. This is created by melting rock at a high temperature and then spinning it into fibers.
- Sand. This medium varies in composition and is usually used in conjunction with another
medium.
- Vermiculite. Similar to perlite except that it has a relatively high cation exchange capacity--
meaning it can hold nutrients for later use.
Hydroponic Systems
The apparatuses used in hydroponic growing are many and varied. There are two basic divisions between
systems: media-based and water culture. Also, systems can be either active or passive. Active systems
use pumps and usually timers and other electronic gadgets to run and monitor the operation. Passive
systems may also incorporate any number of gadgets. However, they to not use pumps and may rely on
the use of a wicking agent to draw nutrient to the roots.
Media-based systems--as their name implies--use some form of growing medium. Some popular mediabased
systems include ebb-and-flow (also called flood-and-drain), run-to-waste, drip-feed (or top-feed),
and bottom-feed.
Water culture systems do not use media. Some popular water culture systems are raft (also called floating
and raceway), nutrient film technique (NFT), and aeroponics.
Light
Think of a plant as a well-run factory that takes delivery of raw materials and manufactures the most
wondrous products. Just as a factory requires a reliable energy source to turn the wheels of its machinery,
plants need an energy source in order to grow.
Artificial Light
Usually, natural sunlight is used for this important job. However, during the shorter and darker
days of winter, many growers use artificial lights to increase the intensity of light (for
photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum
(wavelength or color of light) suitable for plant life, different types of artificial lighting are
selected for specific plant varieties and optimum plant growth characteristics. Different groups of
plants respond in physically different ways to various wavelengths of radiation. Light plays an
extremely important role in the production of plant material. The lack of light is the main
inhibiting factor in plant growth. If you reduce the light by 10 percent, you also reduce crop
performance by 10 percent.
Light transmission should be your major consideration when purchasing a growing structure for a
protected crop. Glass is still the preferred material for covering greenhouses because, unlike
plastic films and sheeting, its light transmission ability is indefinitely maintained.
No gardener can achieve good results without adequate light. If you intend to grow indoors, avail
yourself of some of the reading material that has been published on this subject. If you are having
trouble growing good plants, then light is the first factor to question.
--Rob Smith
Natural Light
A large part of the success in growing hydroponically is planning where to place the plants. Grow
plants that have similar growing requirements in the same system. Placing your system 1-2 feet
away from a sunny window will give the best results for most herbs and vegetables. Even your
regular house lights help the plants to grow. Make sure that all of the lights are out in your
growing area during the night. Plants need to rest a minimum of 4 hours every night. If your
plants start to get leggy (too tall and not very full), move the system to a spot that has more sun.
Once you find a good growing area, stick to it. Plants get used to their home location. It may take
some time to get used to a new place.
--Charles E. Musgrove
Macronutrients
Plants need around 16 mineral nutrients for optimal growth. However, not all these nutrients are
equally important for the plant. Three major minerals--nitrogen (N), phosphorus (P), and
potassium (K)--are used by plants in large amounts. These three minerals are usually displayed as
hyphenated numbers, like "15-30-15," on commercial fertilizers. These numbers correspond to the
relative percentage by weight of each of the major nutrients--known as macronutrients--N, P, and
K. Macronutrients are present in large concentrations in plants. All nutrients combine in numerous
ways to help produce healthy plants. Usually, sulfur (S), calcium (Ca), and magnesium (Mg) are
also considered macronutrients.
These nutrients play many different roles in plants. Here are some of their dominant functions:
- Nitrogen (N)--promotes development of new leaves
- Phosphorus (P)--aids in root growth and blooming
- Potassium (K)--important for disease resistance and aids growth in extreme temperatures
- Sulfur (S)--contributes to healthy, dark green color in leaves
- Calcium (Ca)--promotes new root and shoot growth
- Magnesium (Mg)--chlorophyll, the pigment that gives plants their green color and absorbs
sunlight to make food, contains a Mg ion
--Jessica Hankinson
Micronutrients
Boron (B), copper (Cu), cobalt (Co), iron (Fe) manganese (Mn), molybdenum (Mo), and zinc (Zn)
are only present in minute quantities in plants and are known as micronutrients. Plants can usually
acquire adequate amounts of these elements from the soil, so most commercial fertilizers don't
contain all of the micronutrients. Hydroponic growers, however, don't have any soil to provide
nutrients for their plants. Therefore, nutrient solution that is marketed for hydroponic gardening contain all the micronutrients.
--Jessica Hankinson
Nutrient Solution
In hydroponics, nutrient solution--sometimes just referred to as "nutrient"--is used to feed plants instead
of plain water. This is due to the fact that the plants aren't grown in soil. Traditionally, plants acquire
most of their nutrition from the soil. When growing hydroponically, you need to add all of the nutrients a
plant needs to water. Distilled water works best for making nutrient. Hydroponic supply stores have a
variety of nutrient mixes for specific crops and growth cycles. Always store solutions out of direct
sunlight to prevent any algae growth. See also conductivity, macronutrients, and micronutrients.
Disposal Unlike regular water, you need to be careful where you dispose of nutrient. Even organic
nutrients and fertilizers can cause serious imbalances in aquatic ecosystems. If you do not live near a
stream, river, lake or other water source, it is fine to use old nutrient on outdoor plants and lawn. Another
possibility is to use it on houseplants. However, if you live within 1,000 feet of a viable water source, do
not use your spent nutrient in the ground.
Osmosis
The ends of a plant’s roots aren’t open-ended like a drinking straw and they definitely doesn’t
suck up a drink of water or nutrients. Science is still seeking a complete understanding of
osmosis, so to attempt a full and satisfactory description of all that’s involved in this process
would be impossible. However, we can understand the basic osmotic principle as it relates to
plants.
First, consider a piece of ordinary blotting paper, such as the commonly used filter for home
coffee machines. The paper might appear to be solid. However, if you apply water to one side of
it, you’ll soon see signs of the water appearin on the opposite side. The walls of a feeding root
act in much the same way. If you pour water onto the top of the filter paper, gravity allows the
water to eventually drip through to the bottom side. Add the process of osmosis and water that’s
applied to the bottom side drips through to the top.
With plants, this action allows water and nutrients to pass through the root walls from the top,
sides, and bottom. Osmosis is the natural energy force that moves elemental ions through what
appears to be solid material. A simplistic explanation for how osmosis works, although not 100
percent accurate, is that the stronger ion attracts the weaker through a semipermeable material. So,
the elements within the cells that make up plant roots attract water and nutrients through the root
walls when these compounds are stronger than the water and nutrients applied to the outside of
the roots.
It then follows that if you apply a strong nutrient to the plant roots--one that’s stronger than the compounds inside of the root--that the reverse action is likely to occur! This process is called
reverse osmosis. Many gardeners have at some time committed the sin of killing their plants by
applying too strong a fertilizer to their plants, which causes reverse osmosis. Instead of feeding
the plant, they have actually been dragging the life force out of it.
Understanding how osmosis works, the successful grower can wisely use this knowledge to
promote maximum uptake of nutrients into the plants without causing plant stress--or worse, plant
death--from over fertilizing. All plants have a different osmotic requirement or an optimum
nutrient strength.
--Rob Smith
Oxygen
As a result of the process of photosynthesis, oxygen (O) is given off by plants. Then, at night, when light
isn't available for photosynthesis, this process is reversed. At night, plants take in oxygen and consume
the energy they have stored during the day.
Pests and Diseases
Even though hydroponic gardeners dodge a large number of plant problems by eschewing soil (which is
a home to any number of plant enemies), pests and diseases still manage to wreak havoc from time to
time. Botrytis, Cladosporium, Fusarium, and Verticillium cover most of the genera of bacteria that can
threaten your plants. The insects that can prove annoying include aphids, caterpillars, cutworms, fungus
gnats, leaf miners, nematodes, spider mites, thrips, and whiteflies.
A few good ways to prevent infestation and infection are to:
- Always maintain a sanitary growing environment
- Grow naturally selected disease- and pest-resistant plant varieties
- Keep your growing area properly ventilated and at the correct temperatures for your plants
- Keep a close eye on your plants so if a problem does occur, you can act quickly
With insects, sometimes you can pick off and crush any large ones. Or you can try to wash the infected
plants with water or a mild soap solution (such as Safer Soap).
If a problem gets out of control, it may be necessary to apply a biological control in the form of a spray.
Research which product will work best in your situation. Always follow the instructions on pesticides
very closely.
Alternatively, there are a number of control products on the market today that feature a botanical
compound or an ingredient that has been synthesized from a plant material.
On botanical compounds as controlling agents:
Over the last few years, researchers from all around the world have started to take a much closer
look at any compounds present in the plant kingdom that might hold the answer to our pest and
disease control problems. Many companies have even switched from producing synthetic
pesticides to copying nature by synthesizing naturally occurring compounds in a laboratory
setting. Extracts of willow, cinnamon, grapefruit, garlic, neem, bittersweet, lemon grass, derris,
eucalyptus, and tomato have been helpful in controlling diseases and pests.
--Dr. Lynette Morgan
pH
The pH of a nutrient solution is a measurement of its relative concentration of positive hydrogen
ions. Negative hydroxyl ions are produced by the way systems filter and mix air into the nutrient
solution feeding plants. Plants feed by an exchange of ions. As ions are removed from the nutrient
solution, pH rises. Therefore, the more ions that are taken up by the plants, the greater the growth.
A solution with a pH value of 7.0 contains relatively equal concentrations of hydrogen ions and
hydroxyl ions. When the pH is below 7.0, there are more hydrogen ions than hydroxyl ion. Such a
solution "acidic." When the pH is above 7.0, there are fewer hydrogen ions than hydroxyl ions.
This means that the solution is "alkaline."
Test the pH level of your nutrient with a kit consisting of vials and liquid reagents. These kits are
available at local chemistry, hydroponic, nursery, garden supplier, or swimming pool supply
stores. It is also a good idea to test the pH level of your water before adding any nutrients. If your
solution is too alkaline add some acid. Although such conditions rarely occur, sometimes you may
have to reduce the level of acidity by making the solution more alkaline. This can be achieved by
adding potassium hydroxide (or potash) to the solution in small amounts until it is balanced once
again.
--Charles E. Musgrove
Photosynthesis
Plants need to absorb many necessary nutrients from the nutrient solution or--in the case of traditional
agriculture--the soil. However, plants can create some of their own food. Plants use the process of
photosynthesis to create food for energy. Carbohydrates are produced from carbon dioxide (CO2) and a
source of hydrogen (H)--such as water--in chlorophyll-containing plant cells when they are exposed to
light. This process results in the production of oxygen (O).
Plant Problems
Every now and again, you are sure to run into a problem with your plants. This is just a simple fact of
any type of gardening. The key is to act quickly, armed with quality knowledge.
Mineral Deficiency Symptoms
Nitrogen deficiency will cause yellowing of the leaves, especially in the older leaves. The growth
of new roots and shoots is stunted. In tomatoes, the stems may take on a purple hue.
A phosphorous deficiency is usually associated with dark green foliage and stunted growth. As in
nitrogen deficiency, the stems may appear purple. But since the leaves don't yellow as they do in
nitrogen deficiency, the whole plant can take on a purplish green color.
Iron deficiency results in yellowing between the leaf veins. In contrast to nitrogen deficiency, the
yellowing first appears in the younger leaves. After a prolonged absence of iron, the leaves can
turn completely white.
--Jessica Hankinson
Wilting
This condition can be caused by environmental factors or disease (usually caused by Fusarium). Nutrient
and media temperature can be adjusted to remedy wilt. However, if Fusarium have taken hold, the
chances that your plants will survive are slim.
If wilting is due to environmental causes:
Try to spray the plants and roots with cool, clean water to rejuvenate them. If this hasn’t helped
them by the next day, try it again. If the plants respond, top-off the nutrient solution and check the
pH. If the plants don’t respond to the misting, empty the tank, move it to a shadier spot, and refill
with cool, fresh nutrient solution. Don’t reuse the old solution--start with fresh water and
nutrients.
--Charles E. Musgrove
If wilting is due to a system blockage of nutrient:
I have seen tomato plants that have been so dehydrated due to a nutrient supply blockage that they
were lying flat and for all the world looked stone-cold dead. When the nutrient flow resumed and
the plants were given the less stressful environment of nighttime, they rebounded so well that I
wondered if I had dreamed the previous day’s "disaster." The moral of this story is to always give
plants a chance to revive, even when the situation looks hopeless.
--Rob Smith
Propagation
Plants can be propagated by a number of methods. Growers can let a plant go to seed, collect the seeds,
and then start the cycle over again (see germination). Another method is to take stem cuttings, which is
also known as cloning (because you are creating an exact copy of the parent plant).
Although this process won't work with all plants, it is a highly effective technique. Simply cut off a side
shoot or the top of the main shoot just below a growth node. Make sure that there are at least two growth
nodes above the cut. Remove any of the lower leaves near the base of the new plant. This cutting can
then be rooted by placing it in water or in a propagation medium (perlite works well) that is kept moist.
The use of some rooting hormone can help your chances of success.
Pruning
Remove any discolored, insect-eaten, or otherwise sick-looking leaves from plants. Picking off some
outer leaves or cutting the top off a plant can help it grow fuller. Use sharp scissors to prune your plants.
Sometimes you will want to prune a plant to focus its energy on the remaining shoots. Pruning is an art
and should be performed with care. Damaged or dying roots may also need to be pruned from time to
time.
Soil
Never use soil during any aspect of hydroponics. If you ever move a plant from a soil-based
situation to hydroponics, remove all traces of soil or potting mix from the roots. Soil holds lots of
microbes and other organisms and materials that love to grow in and contaminate your
hydroponic system. Some of these will actually parasitize your plant and slow its growth. This is
another advantage of hydroponic growing: The plant can get on with growing without having to
support a myriad of other organisms as happens in conventional soil growing.
--Rob Smith
Temperature
Different plants have different germination and growing temperatures. Always make sure that you check
each plant’s growing requirements--especially minimum and maximum temperature levels. Keep in mind
that specific varieties of plants may have different requirements.
Water
Because the water supply is the source of life for your plants, quality is important. All plants rely
on their ability to uptake water freely. Between 80 and 98 percent of this uptake is required for
transpiration (loosely compared to perspiration in animals), which allows the plant to produce and
somewhat control its immediate microclimate. Plants also need clean, uncontaminated water to produce their own healthy food supply.
--Rob Smith
The water you use in your hydroponic system needs to be pure. It is always a good idea to test your water
source before adding nutrients so you aren't adding an element that is already present. In small systems, it
would be wise to use distilled water.
If you are starting a larger hydroponic operation, it would be a good idea to have a water analysis
completed. Factors such as sodium chloride (NaCl, or salt) content and hardness will be of great use to
growers. Also, groundwater can have elements normally not present in conditioned water. A key piece of
advice: Get to know your water!
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