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Advanced Nutrient Management
By: Larry Brooks
Owner: General Hydroponics
To the skilled hydroponic grower, nutrient management
represents an opportunity to enhance plant growth. To the
novice, it represents a challenge to be dealt with. The
difference is in knowledge, understanding and equipment.
Consider the following questions to test your nutrient IQ:
What temperature is your nutrient solution, what is the range
during a day and during a season?
What is the "dissolved solids" content of the water you use to
mix your nutrient and does this content vary greatly from
season to season? Does your water supplier provide you with
good water from one reservoir at one time of the year and bad
water from a different reservoir at another?
Are there any components in your water that could affect the
availability of nurtrients to your crop?
What is the "EC" or strength of your nutrient?Do you mix
special nutrient blends for different kinds of plants and for
each stage of the crop's life-cycle?
Does the pH of your nutrient stay within a reasonable range?
Are there any pathogens in your nutrient from a contaminated
water supply or from sick plants that may spread disease to
the rest of your crop?
Do you change your nutrient often enough to prevent excesses
from salt accumulation or deficiencies from nutrient
exhaustion?
Did you know that an important reason to change your nutrient
solution is to eliminate the wastes your plants discard into
the nutrient? Did you know that as plants transpire, moisture
and nutrient levels drop in your reservoir and the EC or
strength of the nutrient can rise to dangerous levels?
These are only a few basic question that may help you better
realize what you already know, and what you may need to learn
to achieve outstanding crops every time. This discussion is
especially for the advanced grower who wants to achieve the
highest yields and is seriously interested in being at the
leading edge of plant growing technology. Hobby growers
generally don't have to worry about all of these questions,
but don't stop reading just yet. When problems arise and a
crop isn't growing as well as it should. the problem can often
be traced to nutrient management. Once you know what can go
wrong, it's easier to recognize a problem when it happens.
The root environment is what separates hydroponics from soil
cultivation. In soil, plants await rainfall or irrigation, and
their roots search out essential nutrients. With good, fertile
soil and abundant water plants thrive.
In hydroponics, the plant roots we constantly provided with
water, oxygen and nutrients--no searching for available
nutrients or waiting for the next rain. The challenge for the
grower is to keep up with the plants' needs and to avoid
damaging plants with excesses or deficiencies of minerals,
extremes in pH and temperature, or a lack of oxygen. A few
simple tools and techniques can make the difference between
success and failure.
What's In Your Water?
The first question to consider is water quality. With good,
soft water it's easy to succeed. Just add the right
combinations of nutrients to the water and you're off and
growing. If you have very hard water, or water contaminated
with sodium, sulfide, or any number of heavy metals, you may
have to filter your water using "reverse osmosis."
So, what's in your water anyway? The most complete answer
comes from having an analysis of your water done by a lab. If
you're on a municipal water system, call your water district
and request a copy of their most recent analysis.
Another approach - highly recommended - is to check your water
regularly with a dissolved solids meter, also called an
electrical conductivity (EQ) or parts per million (PPM) meter.
These instruments are one of the most important tools for a
-grower to have and use regularly.
All of these instruments work in essentially the same way.
They measure the electrical conductivity of the water. It is
the dissolved salts in most water that allows it to conduct
electricity. Pure water is a poor conductor since there are
none of the conductive salts found in impure water. Purified
water will show no, or very low, salt content (conductivity)
when tested with a dissolved solids meter.
It is not uncommon to find high levels of salts in well water
or municipal water supplies. Calcium and Magnesium carbonates
are among the most common ingredients in tap water and in well
water. In fact, water "hardness" is defined as a measure of
the water's content of calcium and magnesium carbonates, or
sulfates.
Since calcium and magnesium are important plant nutrients.
water with reasonable levels of these elements can be just
fine for hydroponic cultivation. However, even a good thing
can become a problem if the levels are too high.
Generally, a calcium content of more than 200 PPM, or 75 PPM
for magnesium, are on the verge of excessive for most
hydroponic applications. An excess can cause other important
elements in the nutrient solution to "lock-out" and become
unavailable. For example. excess calcium can bond with
phosphorous to make calcium phosphate, which is not very
soluble and therefore not available to the crop. The key is to
start with decent water and add the right combination of
nutrients.
Too Hot, Too Cold
Water temperature is another important factor. If your
solution is too cold, seeds won't germinate, cuttings will not
root and plants will grow slowly - or stop growing and die. If
it's too hot, the same seeds won't germinate, cuttings won't
root and plants will die from oxygen deficiency or simply from
temperature stress. Most plants prefer a root zone temperature
range of between 65 degrees (18 C) and 80 degrees (27 C),
cooler for winter crops, warmer for tropical crops. When
adding water to your reservoir, it is a good idea to allow it
to come to the same temperature as the water in the reservoir.
Remember, plant roots have evolved in a soil environment,
where temperature changes occur slowly, tempered by the
thermal mass of the earth.
Plants do not like rapid temperature changes, especially in
the root zone!
Water pH
A subject that is often discussed but rarely understood by
many growers is nutrient pH. Generally, we worry about pH and
its affect on nutrient availability. For example, if pH is too
high, iron may become unavailable. Eventhough your nutrient
solution may have an ideal iron content, your plants may not
be able to absorb it, resulting in an iron deficiency: the
plant's leaves will yellow and weaken.
On the other hand, advanced hydroponic plant foods contain
special "chelates" that are designed to assure iron
availability at higher pH ranges. The result is that your crop
will grow reasonably well. even at higher pH levels.
Nonetheless, high pH can damage plants in other ways, The
cause of a high solution pH can be fairly complex. Most city
water supplies contain calcium carbonate to raise the pH of
the water and prevent pipes from corroding. As a consequence
you are starting with water that has an abnormal pH, typically
8.0 for city water.
The beg way to deal with this is to mix fresh nutrient with
your water, let stand for a while to stabilize, then test and
adjust the pH. With city water supplies you will often have to
add a bit of pH down (usually phosphoric acid) to lower the pH
to the range for most plants, between 5.8 and 6.2.
As the plants grow. it is a good idea to occasionally test the
pH and adjust it if needed. You can safely allow pH to drift
between 5.5 and 7.0 without adjustment. in fact, constantly
dumping chemicals into your system to maintain a perfect pH of
5.8 to 6.0 can do a lot of damage. It is common for pH to
drift up for a while, then down, and up again. This change is
an indication that your plants are absorbing nutrient
properly. Adjust pH only if it wanders too far.
A pH below 5.5 or above 7.0 can mean trouble. but don't
overreact. An apparently sudden and dramatic shift in pH can
be the result of a malfunctioning pH meter. If in doubt,
double check with a reagent (color match) pH kit before
adjusting your solution. Also remember that all pH measuring
methods are temperature dependent. Read and follow all of the
instructions that came with your meter or test kit.
Media Culpa
Another cause of unstable pH is poor quality growing media.
Industrial grade rockwool and gravel are notorious for having
very high pH levels that cause your nutrient pH to rise, often
to constantly rise, often to dangerous levels.
A simple way to test a new growing medium is to put some of
the medium - rockwool, gravel, soil - into a clean cup, then
immerse (soak) the sample. in distilled or "deionized"
(chemically pure) water. Let this sit for a little while and
then test the pH of the water, note the pH and continue to let
the sample sit. Test the pH occasionally for about a week
until it has stabilized. Has the pH risen to 8.0, perhaps 9.0?
Construction grade gravel can go as high as 10.0 - torture to
roots. death to plants!
Never underestimate growing media as sources of pH problems.
This is one of the primary reasons that "waterculture"
hydroponic methods are gaining popularity over "media-based"
hydroponics. The less medium you use, the fewer problems you
will encounter with pH instability and salt accumulation.
Plus, the water-culture systems require less water and
nutrient than media-based methods, due to higher efficiency
and reduced evaporation.
Time for a change?
How often should you change your nutrient solution? That's one
of the most common questions asked, and one of the most
difficult to answer. Many people have tried to come up with a
simple, easy-to-follow rule - once a week, every two weeks -
but they're all wrong! They're wrong because there is no
simple answer. It all depends on the species, the number and
size of your plants. the capacity of the reservoir, the kind
and quality of nutrient you use, water quality, environmental
conditions such as temperature and humidity, and the type of
hydroponic system used. Instead of a simple answer, what we
need is a procedure that takes many of these variables into
account and is responsive to changing conditions.
It sounds complicated, but it's actually quite simple. All it
takes is a little monitoring and some basic record keeping.
Start with a fresh reservoir of nutrient and make note of the
date, pH, and EC or PPM of the solution. As you run the
system, the level will drop in the reservoir. Note the EC/PPM
level, then top-up the reservoir with fresh water. Test again
for nutrient concentration. If the nutrient strength has
dropped significantly, add a bit of nutrient to bring it back
up to specs.
Be sure to record how much water you added to top-up the
reservoir. Repeat the procedure every time you top up the
system, carefully recording the amount of water added. When
the total amount of water added equals the capacity of your
reservoir. it is time to drain and replace all of the nutrient
solution.
For example, imagine a hydroponic system in a cool, spring
greenhouse with 24 strawberry plants and a nutrient capacity
of 20 gallons. Typically, such a system would require about 5
gallons of added water each week, After four weeks the plants
will have transpired 20 gallons - the capacity of the
reservoir. You need to completely drain and replace the
nutrient every four weeks in this example.
Nutrient Pathogens
The problem of pathogens or disease in the nutrient solution
can be a serious one. It is not uncommon for this to be a
regional and seasonal problem. For example, in Holland during
the winter, fungi thrive in the cool and damp environment: the
air is full of spores. All kinds of soil-borne diseases become
endemic in the Dutch winter and growers have to work hard to
avoid infestations. One of the reasons Dutch growers adopted
hydroponics so readily was to avoid soilborne diseases.
Keep your growing area clean. Never allow soil to get into the
nutrient stream. If soil is accidentally kicked into the
reservoir, the entire crop can be at risk. Some growers will
place a sponge-mat soaked with disinfectant at the doorway of
the greenhouse. Everyone who enters must clean their shoes on
this mat before entering. This is an effective and practical
way to prevent disease organisms from entering the greenhouse
and endangering the crop.
If an infected plant is introduced into a hydroponic system,
the disease can race through the entire crop. By the time a
problem is noticed it may be way out of control. Plant
diseases are beyond the scope of this article, but the best
advice is to avoid problems by working clean, planting only
healthy disease free plants, and closely monitoring the crop.
If you see evidence of disease in a single plant, remove and
destroy it quickly before the disease spreads. Watch the crop
closely and destroy any other plants that show signs of
disease. It is better to lose a few sick plants than to risk
an entire crop.
If you do encounter disease problem, it in a good idea to
completely drain and renew your nutrient after removing the
sick plants. If it is possible there is nothing better than to
flush the system by running fresh water without nutrient for a
day. Then drain and refill with fresh nutrient. Flushing
between every three or four nutrient changes can help maintain
cleanliness in the root zone and in the hydroponic system.
Periodic flushing is especially helpful for gravel systems to
remove salt accumulation in the medium.
To the Limit
To some hobby growers,especially those who come to hydroponics
from the " U-plant-em-and-pray" school of outdoor gardening,
the techniques described above might seem too difficult and
time-consurning. Remember, hydroponics offers great control
over the health and quality of plants todays grower with the
interest and the skill to exercise that control. That's what
this article is all about - pushing it to the limits.
Remember, too, that it is possible to produce a hydroponic
garden that will out-perform any soil garden by simply
following the manufacture's instructions on system operation
and nutrient changes, and paying attention to the condition of
your plants. But even the most casual grower can benefit from
an understanding of a few basic concepts.
Quality water is a great advantage, poor water is a challenge.
Use only the highest quality plant food, designed specifically
for hydroponics. Low grade plant foods and common fertilizers
offer your plants poor and incomplete nutrition, cause pH
drift, and sometimes contain impurities that can become toxic
to hydroponic plants, Only high-quality plant food can grow
superior plants. Healthy plants grow faster, generate higher
yields and are resistant to disease and insect infestation.
When you mix fresh nutrient always measure carefully.
Keep notes an your observations of EC drift, pH drift, total
water usage, temperature range, and comments on crop health
and progress. Keep an eye on pH, and an especially close
watch on nutrient strengh (PPM.
EC, dissolved solids). Look out for diseases and remove and
destroy sick plants immediately.
Control your nutrient temperature - use high quality aquarium
heaters to warm nutrient in the winter, look for "chillers" to
cool your
nutrient in the summer if high nutrient temperature becomes a
problem. The aquaculture or fish farming people have developed
excellent chillers. Fish don't like water that's too hot or
too cold either.
Don't be overwhelmed or intimidated. Plants can tolerate quite
a lot of stress and still produce well. On the other hand, the
grower who knows the questions. and how to find answers, is
the one who will have consistently good crops. It is far
easier to avoid problems through knowledge and proper
technique than to fix them after they arise.
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