In the time plants have evolved on Earth, they have adapted to utilise five major resources in order to grow. These are
Light, Water, Oxygen, Carbon Dioxide, and mineral elements. From these, plants can synthesise a wide range of
organic molecules required for life. Of these five factors, it is the mineral element requirements of plants which we aim
to provide through the use of hydroponic or soilless culture, and under optimum conditions of light and temperature the
productivity of crops is largely dictated by the mineral composition in the root zone.
As hydroponic growers and suppliers, it is therefore worth taking a look at what elements are actually required for
plant growth, what their purpose is inside the plant, and what levels and ratios are most appropriate for optimising
plant growth in a range of conditions.
Hydroponic Elements – Why we need them …
The elements required for plant growth include the following.
Nitrogen is a component of all amino acids in proteins and enzymes used in plant tissue, as well as flavour
compounds and lignin, and as a result the entire plant metabolism depends on nitrogen supply.
Example of Amino Acid containing NITROGEN :HOOC-(CH)n-NH2
Without nitrogen, plant growth ceases, and deficiency symptoms rapidly appear. Most obvious deficiency symptoms
are yellowing or purple colouration of the older leaves, thin stems, and low vegetative vigour. Nitrogen is readily
mobilised within the plant, so deficiencies first appear as symptoms on the older foliage. Excess nitrogen, or specifi-cally
a high nitrogen to carbon ratio within the plant, predisposes the plant to lush soft growth, usually undesirable for
commercial crops and can retard fruitset, promote flower abscission, and induce calcium deficiency disorders as fruit
Nitrogen is supplied as nitrate in the hydroponic nutrient solution, usually from sources calcium nitrate, and potassium
nitrate (Saltpetre). Occasionally, for example under low light conditions, a small amount of nitrogen is supplied in the
ammonium form from compounds such as ammonium nitrate or ammonium phosphate, but this should be limited to
less than 10% of the total nitrogen content of the nutrient solution to maintain balanced vegetative growth and avoid
physiological disorders relating to ammonia toxicity. Urea should never be used in hydroponics.
Potassium is a key activator of many enzymes, especially those involved with carbohydrate metabolism. Potassium is
also responsible for the control of ion movement through membranes and water status of stomatal apertures.
Potassium therefore has a role in controlling plant transpiration and turgor. It is generally associated with plant ‘quality’
and is necessary for successful initiation of flower buds and fruit set. As a result the levels of potassium in nutrient
solutions are increased as plants enter a ‘reproductive’ phase, and as crops grow into lower light levels, in order to
maintain nutrient balance in solution. Symptoms of potassium deficiency are typically, scorched spots towards the
margins of older leaves, along with generally low vigour and susceptibility to fungal disease. Crops such as tomatoes
can almost double their uptake of potassium during fruiting. An ideal source of potassium for hydroponics is
monopotassium phosphate, along with potassium nitrate. Potassium sulphate can be used as an additive to boost
potassium levels without affecting nitrogen or phosphorous. Potassium chloride should be used sparingly if at all, to
avoid excessive chloride levels in solution.
The energy utilisation process within plants relies on bonds between phosphate molecules – energy is stored and
released by the compound adenosine triphosphate (ATP).
ATP ———> ADP + Pi + energy
Phosphorous is an integral part of the sugar-phosphate molecules used in respiration and photosynthesis, and is a
major component of all cell membranes formed using phospholipids.
NUTRON2000 TM is a registered Trademark of Casper Publications Pty Ltd and Suntec (NZ) Ltd.
The phospholipid Lechitin, a component of every living cell.
Phosphorus is involved in the bonding structure of nucleic acids DNA and RNA. Deficiency of phosphate appears as a
dull green colouration of the older leaves followed by purple and brown colours as the foliage dies. Root development
becomes restricted as phosphorous deficiency occurs, due to sugar production and translocation being impeded. The
main source of phosphate in hydroponics is monopotassium phosphate, although limited amounts of ammonium
phosphate can sometimes be added. Compounds such as calcium superphosphate should be avoided. Small amounts
of phosphorous are also supplied by the use of phosphoric acid for pH control.
Magnesium is the central ion of the chlorophyll molecule, and therefore has a primary role in the light collecting
mechanism of the plant and the production of plant sugars through photosynthesis. Magnesium is also a co-factor in
the energy utilisation process of respiration in the plant.
Magnesium deficiency first appears as yellowing of the leaves between veins on the older parts of the plant, although
under worse deficiency the symptoms can spread towards the newer growth. Magnesium deficiency can also occur
during periods of low light intensity or heavy crop loading and when excessive levels of potassium are provided in the
nutrient solution. The main, probably universal source of magnesium for hydroponics is magnesium sulphate (Epsom
salts). Although limited use is sometimes made of magnesium nitrate it is rarely an economical option. Soil fertiliser
salts magnesium phosphate or magnesium ammonium phosphate are not suitable.
Calcium is deposited in plant cell walls during their formation. It is also required for the stability and functioning of cell
membranes. Calcium deficiency is common in hydroponic crops, and is apparent as tipburn in lettuce, and blossom
end rot in tomatoes. Calcium is almost totally immobile in the plant, as once deposited in cell walls it can not be
moved. Therefore the deficiency occurs in the newest growth. Calcium transport is dependent on active transpiration,
and so calcium deficiency occurs most often under conditions where transpiration is restricted, ie warm overcast or
humid conditions are often referred to as “calcium stress” periods. Increasing calcium content in solution is unlikely to
improve uptake, and in fact, reducing CF is one way to improve calcium uptake in most species by enhancing the
uptake of water. Calcium is supplied by default in most formulations through the use of Calcium nitrate. Extra calcium
can be provided by calcium chloride.
Sulfur is used mainly in sulfur-containing proteins using the amino acids cysteine and methionine. The vitamins
thiamine and biotin, as well as the cofactor Coenzyme A, all use sulfur, and so this element also plays a key role in
plant metabolism. Sulfur deficiency in hydroponics is rare, usually because sulfur is present in adequate quantities
through the use of sulfate salts of the other major elements particularly magnesium and potassium, and plant require-ments
for the element are reasonably flexible within quite a wide range. Where it occurs, sulfur deficiency shows up as
a general yellowing of the entire foliage, especially on the new growth.
Iron is a component of proteins contained in plant chloroplasts, as well as electron transfer proteins in the photosyn-thetic
and respiration chains. Deficiency occurs on the newest leaves, and appears first as a yellowing of the leaves
between veins, and eventually the whole leaf becomes pale yellow, even white, ultimately with necrotic (dead) spots
and distorted leaf margins. Iron must be supplied as chelated Iron EDTA, EDDHA or EPTA in hydroponics, rather than
sulphate. Iron is the element most susceptible to precipitation at high (>7) pH, so pH control to below pH6.5 is
necessary to maintain Iron in solution in hydroponics.
Manganese catalyses the splitting of water molecules in photosynthesis, with the release of oxygen. It is a co-factor in
the formation of chlorophyll and the respiration and photosynthetic systems. Manganese deficiency appears as a dull
grey appearance followed by yellowing of the newest leaves between the veins which usually remain green. Spots of
dead tissue become apparent on affected leaves. Manganese is supplied by manganese sulfate, or manganese EDTA
in hydroponics. The content of manganese in these fertilisers can vary widely between different sources, due to such
factors as different ‘water of crystallisation’ (MnSO4.nH2O), and different chelating agents and raw ingredients as well
as manufacturing processes. Manganese, like iron, is less available to plants at high pH.
Zinc contributes to the formation of chlorophyll, and the production of the plant hormone auxin. It is an integral part of
many plant enzymes. Zinc deficiency appears as distortion and interveinal chlorosis of older leaves of the crop, and
retarded stem development. Zinc is provided by zinc sulfate, or zinc EDTA in hydroponics.
Boron is required mostly for cell division in plants, and deficiencies appear similar to calcium deficiencies, with stem
cracking and death of the shoot apex being the most significant symptoms. Boron is supplied as either borax (sodium
borate) or boric acid in hydroponic production.
Copper is required in small amounts as a component in several important enzymes . Toxicity is more common than
deficiency of copper in hydroponics. Copper sulfate is most often used, although copper EDTA can also be used in
Recently silicates have been reported to improve the growth and development of some crops. When readily available,
silica is incorporated into the root system, and appears to enhance nutrient uptake, improving the potential of crops to
produce higher yields. Silicates have also been implicated in enhancing pollination, as well as providing increased
structural strength of stems and some resistance to foliar diseases.
It should be noted, that among the 110 or so known elements, many more are likely to be implicated in plant growth.
Nickel, cobalt, chromium, titanium, iodine, selenium, lithium and numerous others have been reported to have some
function in some species of plants.
Hydroponic Nutrient Basics
There are several important factors to decide when purchasing salts for hydroponic nutrient formulae:
1. The salt must be completely soluble in water, that is the salt must not contain additives or insoluble fillers, or
components (such as insoluble sulphates and phosphates) which while useful for soil fertiliser are unacceptable in
2. Contents of sodium, chloride, ammonium and organic nitrogen, or elements not required for plant growth should be
minimised under normal use. These elements if not used by plants tend to accumulate in recirculating hydroponic
nutrients to the extent that the measured CF includes a high proportion of unusable salts.
3. The salt must not react with other components in the same mix to produce insoluble salts, and it should not radically
alter the pH of the nutrient solution.
4. For commercial use, the fertiliser source must be economical. There is no point using expensive fertiliser salts when
a cheaper source is perfectly adequate.
What Salts to Use
Calcium Nitrate (15.5% N): Commercial calcium nitrate also forms 1% Ammonium-N in solution, and supplies 20%
Potassium Nitrate (13% N): Also supplies 36.5% Potassium
Ammonium Nitrate (33% N): Nitrogen form is split between ammonium-N and Nitrate-N, the total ammonium-N % of a
formula should be kept below 15% in most conditions.
Ammonium Phosphate (10%N): Supplies N and is soluble, but all N is in the ammonium form, which limits its appli-cation
Ammonium Sulfate (21%N): As above, redundant if using conventional salts. Urea (46%N): Can cause problems with
ammonia toxicity, and has no CF charge so difficult to measure.
Nitric Acid: Used often for pH control, but should not be considered a nitrogen source, especially not mixed with salts
in stock solutions.
MonoPotassium Phosphate (21% P): Also provides 25% Potassium.
Ammonium Phosphate (22% P): Not used as the main phosphate source as too much ammonium would be produced.
Phosphoric Acid: As for Nitric acid above. Older formulations used it as a P source in ‘Topping-up” mixtures but this
approach is no longer valid.
Calcium Superphosphate (10% P): Phosphate is highly soluble (as phosphoric acid), but produces an insoluble
calcium sulfate / calcium phosphate residue in hydroponics.
Potassium Nitrate (37% K)
MonoPotassium Phosphate (25% K)
Potassium Sulfate (40% K): Also adds sulfur (17%). Useful as an additive to existing formulae to boost potassium
Potassium Chloride (49% K): Can be added in small amounts, although preferably omitted due to its chloride content.
Magnesium Sulfate (10% Mg): Also adds sulfur. Is highly soluble and universal Mg source
Magnesium Nitrate Expensive, and unnecessary
Dolomite (Magnesium carbonate) Insoluble residues
Fertiliser sources of magnesium used in agriculture (Dolomite, Causmag etc) are generally very insoluble, and can not
be used for hydroponics.
Calcium Nitrate (20% Ca): Calcium is supplied almost entirely by this salt in most nutrient formulations
Calcium Chloride (36% Ca): Useful to add extra calcium without altering other elements. Limited use due to its
chloride content, so only used as an ‘additive’
Calcium chelates: Expensive and unnecessary
Calcium Ammonium Nitrate: Not recommended due to ammonia content
Calcium cyanamide: Release amine – N into solution which produces free ammonia.
Calcium carbonate: Insoluble, and inherent pH problems
Calcium Sulfate: Highly insoluble.
Magnesium sulfate (13% S): Potassium sulfate (18% S)
Iron EDTA (6 – 14% Fe): Readily soluble, and stable form of Iron for nutrient solutions. Ensure the element (Fe)
content of the chelate is known before making formulations.
Iron EPTA: Using different chelating agents the iron can be protected in solution at higher pH levels.
Iron EDDHA ” ” ”
Iron Sulfate (20% Fe): No longer widely used in hydroponics due to its instability in solution. In nutrient solutions iron
sulfate tends to form iron hydroxides which are insoluble.
Iron Chloride: As above
Manganese Sulfate (24%): Different sources may vary in Mn% due to being hydrated or anhydrous. In solution with
Iron EDTA, the manganese becomes partly chelated.
Manganese Chelate (*%): As for Fe EDTA * the content of Mn can vary between sources.
Boric Acid (18% B), Sodium borate (Borax) 11 – 14% B
Zinc Sulfate (23% Zn), Zinc EDTA (*%)
Copper Sulfate (25% Cu), Copper EDTA (*%)
Ammonium molybdate (48% Mo), Sodium Molybdate (39% Mo)
Ratios and Content of Elements in Nutrient Solutions
Once we have the source of elements (fertiliser salts) for a nutrient formula, the next stage is to combine these into
ratios which give the acceptable element contents in solution. Plants will take up nutrient elements roughly according
to their needs, this is especially true for the major elements, so adding elements to solution when they are not required
results in the formula becoming unbalanced for plant growth. Adding excessive quantities of some of the trace
elements can in fact lead to toxicities, while adding insufficient amounts of any element will eventually lead to
deficiency and poor crop growth. As hydroponic growers it is essential to have an understanding of acceptable ratios
for all the elements used in hydroponic formulations to ensure the nutrient solution is supplying the plant’s needs and
is neither toxic or deficient. Generally the range of acceptable element concentrations is wider for the major nutrients,
than for the trace elements as can be seen from the table below.
Element Range in PPM for Nutrient Solution
N 100 – 450
P 10 – 100
K 100 – 650
Mg 10 – 95
Ca 70 – 300
S 20 – 250
Fe 0.5 – 6
Mn 0.3 – 4
B 0.1 – 0.8
Zn 0.1 – 0.5
Cu 0.05 – 0.1
Mo 0.02 – 0.07
Even within these ranges, nutrient elements can become very unbalanced if the ratios are incorrect. Leaf analysis of
crops is a good indicator for acceptable ratios for a formulation within the above range. The ratios for a hydroponic
nutrient for any new crop can be estimated from leaf analysis of a well grown plant, as if a plant appears to be thriving
and producing well, then we can assume its nutrient mineral content is optimum, hence tissue analysis will give the
nutrient ratios optimum for the root zone solution. This basic formula can then be fine tuned during different crop
growth stages and seasons. Some indications for acceptable ratios of major nutrient elements are given below.
Element Ratio Ratio
N: P 3 – 8
N:K 0.25 – 1.5
Ca:N 0.8 – 1.2
Mg:N 0.1 – 0.4
P:S 0.6 – 1
CF and EC PPM.
‘CF’ or ‘EC’ is a commonly used measure to determine the strength of a hydroponic nutrient solution. As salts disso-ciate
into ions in solution, they carry a positive or negative charge (eg KNO3 –> K+ + NO3-,) which can transmit
electricity. Pure water will not transmit electricity, but as soon as salts are added, the ability of the solution to conduct
electricity increases. This conductance increases with increasing solution strength. CF (Conductivity Factor) and EC
(Electrical Conductivity) are a measure of this characteristic of nutrient salt solutions.
While CF seems to be a very convenient measure, there are problems associated with relying only on CF to control
hydroponic nutrient formulae.
I) The CF will be roughly the same regardless of the element content of the solution. A nutrient solution with CF 20 can
not be distinguished from a sodium chloride solution with CF 20.
ii) Different nutrient salts show different capacities to conduct electricity when in solution, so that depending on the nutrient
ratios and the individual salts used, the CF may give a very different indication of the true ionic strength of the solution. A
solution of potassium nitrate at CF20 will be approximately half the strength (in ppm) of a solution of magnesium sulfate at
CF20. This is because potassium nitrate conducts nearly twice as much electricity at the same ionic strength.
iii) Even if the nutrient element content of the formula was known accurately at the start, once the solution has been
recirculating through a growing crop for a few weeks, the element content changes – the CF may well stay the same.
Conductivity of Some Common Hydroponic Nutrients at 2000 PPM
SALT mg/l CF EC
Calcium Nitrate 2000 20 2
Potassium Nitrate 2000 25 2.5
Magnesium Sulfate 2000 12 1.2
The CF of a nutrient formulation is a combination of the CF contributed by all the dissociated nutrient salts from the A
and B stock solutions as well as impurities from the water supply, and is not really any indication of the quality of the
formula, just an estimate of its strength. In hydroponics the only way to determine the nutrient makeup of a formula is
either to have a complete mineral analysis done, use a range of specific ion meters or to calculate the nutrients in
advance and use these in drain to waste systems. Any solution in recirculating hydroponics will change over time.
Outside of hydroponics CF may not even be a measure of the strength of a formula, as a range of nutrients (eg Urea)
and compounds (eg fungicides) are added to water in fertigation or spraying which do not conduct electricity.
The other common indicator for hydroponic nutrient strength is PPM, or parts per million. 1 part per million is equivalent
to 1 mg per litre, or 1 g per m
In theory, this is a measure of the actual strength of the nutrient elements in
solution, and would seem to be an ideal measurement for hydroponics. However, measuring this in practice is very
difficult for a grower in hydroponics.
Why Not TDS Meters?
An alternative to solve the problems with CF as a measurement may seem to be to use ‘TDS’ or total dissolved solids
as a measure of nutrient solution strength, and if ‘TDS Meters’ in fact did this, it would solve the problems. However a
‘TDS’ meter is simply a ‘CF’ meter with different calibration and display – it still only measures electrical conductivity,
and in fact is less accurate because of the assumptions made regarding the salt makeup of the solution – many
assume sodium chloride and have a fixed conversion factor (eg 70ppm per CF unit) which can not be adjusted for
different solution formulations. TDS meters which can be calibrated for different formulations are a better alternative,
but still are only measuring CF in reality.
CF Effects on Plant Growth
If we assume that in hydroponics, the CF is a measure of the strength of a nutrient solution, this has a significant
affect on the growth of plants, regardless of the mineral content of the solution.
Osmosis describes the behaviour of ions in solution when separated by a semi-permeable membrane, as for example
at the interface of root cells and nutrient solution. The concentration of ions on either side of the membrane deter-mines
the net flow of ions through the membrane, as if ions are more concentrated in solution than in root cells and
the membrane permits the transmission of ions, then ions will tend to flow into the roots. This process is known as
‘passive’ transport or diffusion, and is assisted by the flow of water in the transpiration stream of the plant. In fact, root
cells tend to maintain quite high ‘osmotic potentials’ but low concentrations of ions which attract water and ions into the
roots. Some ions, Ca
and K+, NO
, for example, are able to be transported into root cells, even against a concen-tration
gradient by the energy requiring process of active transport. Once water and ions are inside the roots they
diffuse through into the xylem vessels and flow with the transpiration stream up into the stem. A natural reaction of
some plants to increasing solution strength, is to accumulate assimilates in the leaves and fruit to equalise the osmotic
potential with the root zone.
This explanation may seem complicated, but it is the basis for the effects noticed by increasing or decreasing CF in
hydroponics. CF influences the ‘osmotic potential’ of the solution in the root zone, which influences the plant’s rate of
water and nutrient uptake, and the adjustments made to osmotic potential inside the plant. Increasing CF will reduce
water uptake by the crop, and cause many crops to concentrate organic compounds in fruit and foliage. Increasing CF
tends to slow vegetative growth, and ‘harden’ plants. Conversely, lowering CF will increase water uptake, and produce
lush soft growth. Consequently, the CF of solutions is normally increased during winter and for fruiting crops, while
summer growing and leafy crops are normally run at a low CF to maintain optimum quality.
CF can be maintained at higher levels in solution culture than in media or drain to waste systems. In solution
culture there is a constant supply of water and the CF does not fluctuate in the root zone, whereas in media
systems evaporation from the surface of the media and plant water uptake can result in the CF becoming much
higher in the rootzone than in the ‘feed’ solution. The ratio of CF in the feed to rootzone and leachate solutions
needs to be well regulated in drain-to waste systems, and CF ‘in’ (feed) and CF ‘out’ (drainage) are standard
The pH of a nutrient formula is the measure of acidity below pH 7 or alkaline above pH 7. It is defined as the “inverse
log of the hydrogen ion concentration”. The practical implication of this definition is that each pH reduction of 1 unit
actually means the formula becomes 10 X more acidic, a solution with a pH of 4 is 10 x more acidic than pH 5, and
100 x more acidic than pH 6.
pH and Formulations
The strength (CF) of the formula does not affect the pH, but it does affect the ‘buffering capacity’ at any pH. This is
demonstrated by the amount of acid/alkali needed to change pH by 1 unit at different CF – as CF increases, more pH
adjuster is needed to alter pH by the same amount.
Different formulations will have different starting pH values, because different salts become more or less acidic when
dissolved into water. Salts such as monopotassium phosphate lower the pH more than salts such as calcium nitrate.
Most formulations will result in an initial pH of around 5.5 – 6.0, which is ideal for the growth of most crops. This pH
results from only the commonly used salts being dissolved into stock solutions, and so addition of acid or alkali to
stock solutions is usually unnecessary. However, these pH levels assume neutral water supplies, if the water supply
has a high pH, along with high ‘alkalinity’ then the pH of the stock solutions when diluted into water will be quite
different. ‘Alkalinity’ refers to the strength of the high pH, as a water supply with high alkalinity will require more,
stronger acid, to reduce the pH by the same amount as a water supply with low alkalinity. This inherent buffering ability
will carry on into the nutrient formulation. It is best to correct the pH of unsuitable water before making up the stock
In hydroponics, some salts can be used to influence the pH control of the nutrient solution, reducing the requirement
for acids during growth development phases of the crop. Ammonium nitrate is one salt used for this purpose, and the
optimum amount seems to be that which provides 15% of the total nitrogen of the formula in the ammonium form.
Ammonium in nutrient solution tends to be acidifying, as firstly unlike nitrate it is a positive ion, and when taken up by
plants is replaced by hydrogen ions reducing pH in the root zone, and secondly ammonium forms ammonium
hydroxide and hydrogen ions which produces a mild acidifying effect when in solution.
pH and Hydroponic Crop Growth
Consideration of pH is important for hydroponic growers, because the pH of the solution affects the solubility of
elements, and their availability to plants. Most problems occur where pH becomes too high, above 7, resulting in
firstly iron then manganese and calcium forming insoluble salts which precipitate out of solution. As the pH
increases above 7, plant uptake of some ions becomes less efficient, so plants become deficient even if the ion
is present in solution.
As plants remove some ions from solution, the solution pH drifts, upwards or downwards. If left uncontrolled,
typically the pH will drift downwards (to approx 4.5) for several days after planting a new crop, after which the pH
will steadily increase (to approx 7 or above). This feature is due to the differential uptake of ions from solution,
with the release of hydrogen (H+) or hydroxyl (OH-) ions from the root system. As positive ions, cations (Ca
etc) are removed from solution, hydrogen ions are released from the plant root system to equalise the ratio
of anions to cations in the root zone. This lowers the pH of the solution. As the crop commences active growth
anions (NO 3 etc) are taken up which increases pH through the release of hydroxyl ions into solution.
Hydroponic Nutrient Formulation Basics
The range of hydroponic nutrient formulations available seems very diverse, and yet if we look closely at their content
there are several underlying principles involved in formulating hydroponic nutrient solutions. The following are some
standard features of hydroponic formulations:
Reason for ‘2-Part’ ‘A’ and ‘B’ mix.
In order to combine all the elements commonly needed for plant growth into a concentrated form, the salts need
to be mixed into 2 separate solutions. The reason for this is that, while in dilute solution all ions become soluble,
in concentrated solution certain ions react together to form insoluble salts. If an ion is in an insoluble salt, it is no
longer available for plant growth. Once ‘precipitated’ it can only very slowly dissolve back into solution when
diluted again. Precipitation is simply the result of two ions combining in solution to form a salt which is insoluble,
eg when calcium nitrate and magnesium sulfate are added to water in strong solutions the salts dissociate
producing magnesium nitrate along with calcium and sulfate ions which then combine to form calcium sulfate or
gypsum which ‘precipitates’. This occurs because compounds such as calcium sulfate have very low ‘saturation’
values (see later)and can not exist as concentrated solutions. Generally it is necessary to keep the calcium
separate from the sulfate and phosphate salts. Therefore the calcium nitrate and calcium chloride is kept
separate from the magnesium sulfate, potassium sulfate, sulfates of trace elements, and monopotassium
phosphate, all other salts can be mixed in either A or B. There are certain brands of nutrient which seem to
combine all elements into a single mix, but the manufacture of these products is beyond the reach of most
g r o w e r s .
Grow vs Bloom, Summer vs Winter, Drain-to-Waste vs NFT
Plants in nutrient solution culture will remove different ions faster from solution at different stages of growth or
development, as well as during different light and temperature conditions, and if left unchecked this quickly
results in formulations being unbalanced. Note that unbalanced does not necessarily mean ‘precipitated’, or
‘ t o x i c ‘ .
While there are for example, ‘Grow’ and ‘Bloom’ formulae available, it is important to note that using eg a
“Bloom” formula will not suddenly force vegetative plants to commence flowering and fruiting, any more than
using a “Summer” formula produces fine weather. The differences between the formulae is simply to allow the
nutrient solution to remain balanced for longer periods, while estimating the likely rate of removal of certain ions
from solution under different conditions.
In general, as plants grow from being vegetative to flowering and fruiting, the uptake of potassium and phosphorus
increases in proportion to nitrogen. Therefore a ‘Bloom’ formula will typically have more potassium or a higher K:N
ratio than the equivalent ‘Grow’ formula. Other changes can result from the increased K:N ratio, the pH of the formu-lation
can become slightly lower, the working CF may become higher, and the amount of magnesium supplied can
also increase to avoid potassium induced magnesium deficiency, common for example on tomatoes with heavy fruit
loads. Conversely a ‘Grow’ formula will provide a higher N:K ratio, slightly lower CF at the same dilution, and less
extreme variation between the ratios.
Plants growing under low light conditions and cold temperatures usually take up extra potassium, and tolerate a higher
CF. Therefore a ‘Winter’ formula may be similar to a ‘Bloom’ and summer formula can be similar to ‘grow’. The CF for
warm, high light conditions is usually lower to allow for increased transpiration and water uptake.
The differences between the two sets of formulae becomes more extreme the further the grower is from the equator,
and obviously depends on the crop being grown. For example a Norwegian tomato grower is likely to make bigger
changes to their nutrient solution during the year, than a lettuce grower in Singapore.
The difference between growing in media and drain to waste, compared to recirculating solution as in NFT, is mainly
due to the CF and the fact that nutrients do not become unbalanced in media systems to the extent that they can in
NFT. Generally solutions used for media and drain to waste are run at lower CF than if the same solution was running
in a recirculating solution culture system. For example a capsicum grower using rockwool may apply nutrient solution
at a CF 16, whereas in NFT the same solution would be used at CF 25. This difference is due to the solution applied
being at a different CF to the ‘root zone’, and the drainage solution in media systems. Some media are reported to
influence the retention or chemical nature of the applied nutrient solution especially the pH, but this is often only a
minor problem when using new material, and in the case of pH alteration is easily managed. In reality, there should be
no difference between nutrient solutions used for different growing systems other than the working CF, and the
frequency of replacement.
Strength and Dilution
There is a physical and chemical limit to the amount of salts which can be dissolved into nutrient stock solution. This
limit, the saturation value, is different for each salt, and restricts most formulations to a maximum dilution rate of 500 -1000
times. This value varies depending on how the formula is split between A and B, and the predominant salts used,
for example, much more calcium nitrate can be dissolved into 1 litre of water than potassium nitrate. Above the
saturation value for a particular salt, the salt remains in crystal form and does not dissociate in solution. A useful
practice to overcome this limitation is to split the potassium nitrate requirement of the formula equally between the A
and B solutions – as potassium nitrate has the lowest saturation value of the major salts, this increases the potential
concentration of the formula above what could be achieved if all the potassium nitrate was in part A or B.
Under certain conditions, for example if alternating between ‘A’ and ‘B’ stock solutions in drain to waste, it is useful if
both stock solutions each have the same CF when diluted for use. In this situation the ratio of potassium nitrate in A to
B is adjusted until the CF are the same. Normally, this is not important, and the CF of ‘B’ is usually about 1.5 or 2
times the CF of ‘A’ if potassium nitrate is not divided between A and B. When both are diluted equally the correct CF
Buying Pre-Made or Make Your Own
It was commonly suggested by nutrient manufacturers that it was false economy if not disastrous for mere growers to
attempt to make their own nutrient formulations. Often these suggestions were prompted by commercial interests, and
the few failures that occurred in growers making their own nutrients were capitalised on and used as examples of why
growers should only trust ‘reputable’ nutrient manufacturers.
However, there are significant cost benefits to making your own nutrient formulations, there is great flexibility, and if
done correctly growers are likely to end up with a better formula.
There are of course advantages and disadvantages to both situations.
Buy Pre-Made If . . .
You can not obtain all the correct nutrient salts at an economical price or acceptable quality.
You do not have weighing equipment capable of weighing down to about 5g (small amounts for trace elements are
weighed out in large amounts and the stock solutions diluted into A or B)
You do not have the time to weigh out salts and dissolve them.
Good brands are available which you have used successfully, and the price difference to change isn’t warranted.
You do not see the need to change your formula during growth.
You don’t have the information or understand the calculations involved in making your own nutrient formula.
You don’t trust your own ability to make a correct decision.
You like to have someone else to blame if things go wrong.
Make Your Own If . . .
You can spare the time.
You want to save money, where salts are available and cheap with good quality.
You want to optimise your nutrient solution so you are not dumping so frequently – save money again.
You have the equipment to weigh and measure salts.
You would like to customise your solution to crop growth and environment to get better results.
You can handle the calculations and you have the correct information.
You want to maintain flexibility.
You get nutrient analysis done every so often and you are confident you know what to do.