Nutrients are just soluble powders or solutions containing .NITROGEN,
PHOSPHORUS, POTASSIUM, CALCIUM, plus soluble trace elements and
minerals. These all basically exchange electrons and ions to re-arrange
themselves in the chlorophyll and proteins of the plant. They
are the nuts and bolts that allow the factory in the leaves to
make the sugars that the plant uses for energy.
The many pre-mixed nutrient formulas on the market are all good
for general use. All the experts believe that their mix is the
best, and for them, it truly is so. The truth is, the plant does
not care what the marketing executives say about the mix, as long
as it contains what the plant can use. However, some of the more
expensive liquid formulas are truly superior for supercharged
growing because the most soluble elements and the best chelating
agents are more expensive than the regular products.
The most important thing about using plant nutrients is to make
sure the NPK (nitrogen, phosphorous, potassium, and calcium) and
the trace element ratios are correct. Nutrient mixes can have
a wide variation of these ingredients.
Experiment with different mixes until you find one that is good
for your garden. As long as you keep the general ratios of ingredients
the same, your plants will be able to get what they need. In short,
just give the plants a good menu and let them "read the menu
and order what they need." Only if you are going for high
production do you need to fine-tune the mix. By then, you will
be able to evaluate what is best for your plants when you are
ready to tailor your own nutrient formula.
It is very important for a gardener to keep the nutrient proportions
accurate. The labels on fertilizer containers recommend tablespoons
per gallon or grams per litre (gm/L). These quantities are generally
good, but with nutrients for supercharged production, just a little
more care should be taken. Always bear in mind that a mighty electrical
battle is constantly taking place between the water, the nutrients,
the trace elements, the medium, and the roots.
Because a plant takes whatever it needs from a nutrient solution
and leaves the rest, these unused salts start to build up in the
solution. Toxic build-up will then result if make-up nutrients
are continually added without knowing which have been left behind.
Some nutrients are buffered for this reason.
The nutrient also gets toxic build-up if the water content is
not kept reasonably constant. If the plants transpire 50% of the
water out of the nutrient tank, the PPM will be dangerously high.
The nutrient should be changed about every two weeks unless you
are doing constant monitoring.
CAUTION: Do not add any organic-based nutrients or additives
to water culture nutrient solutions.
Parts Per Million
Parts per million - PPM - is a way of measuring how much nutrient
is in the plant water. For example, 1,000 PPM means that 1,000
units of nutrients are present for every million units of water.
The PPM number is only a final reading of the total salts (nutrients)
in a nutrient solution; it does not tell how much of each salt
or what trace elements are in the nutrient mix, or how good the
Anyone who has eaten salty food knows how thirsty one gets afterwards.
Salts in water create a very high osmotic pressure, and the only
way this internal pressure can relieve itself is to grab more
water to dilute itself. This is why one can drink so much water
after eating salty food.
Since all nutrients are salts, the more nutrients that are in
the plant water, the more these salts will try to steal water
away from the roots. 1,500 PPM is a salty solution. After about
2,000 PPM, the osmotic pressure starts to get so high that the
roots struggle to get enough water (see graph on the next page).
As a result, the nutrient balance available to the plant changes
as the salinity rises.
There are still those who try to jam their plants with nutrients.
As the general level of the nutrient salts gets higher and higher
in a nutrient mix, the different chemicals start to fight each
other for water and this causes the roots to work harder to get
water. The more energy the roots must use to extract water, the
less they have for growth. This forces the plant to soon show
nutrient deficiencies and shortages, and the more salts are added
to fix these apparent shortages, the worse the problem gets. It
is far better to give the plant the correct amount of nutrients
for as long as it needs it.
For reasons mentioned before, all re-circulating water culture
systems should have one day a week on straight water. The nutrient
should be completely changed on this day. This is the only way
to avoid a cumulative error, which can occur if make-up nutrients
are continually added.
On a scale of high to low for water culture nutrient concentration:
over 2,000 PPM is high.
1,500 PPM is definitely saline.
1,000 PPM is an average.
500 PPM is workable, but on the low side.
The PPM Meter
The PPM meter is actually an EC (electrical conductivity) meter.
Electrical resistance is measured in ohms. The reverse of electrical
resistance is conductivity, measured in mhos (reverse the ohm
to mho). In the
metric system, the mho is called a siemen (the New Zealand Quick
Dip nutrient meter on its left scale shows the symbol S). However,
one is only dealing with minute conductivities, so units less
than a mho are used. Some meters will read either in :
1/1,OOOth of a mho (a milli-mho or mMho), or 1/1,OOOth of a siemen
(a milli-siemen or mS) .
The PPM / EC meter works by measuring how fast electrons can
work their way from one side of the probe to the other side. In
distilled water, because it is totally clean, the electrons can
find no salts as stepping stones to get to the other side, and
so the meter reads: EC = 0 mMho or mS.
As impurities - especially nutrient salts - are added, the electrons
find more and more stepping stones between the probes. This causes
the electrons to travel faster, and the EC increases. Like all
things chemical, the warmer the solution, the more active the
electrons become, and so the EC changes with temperature change.
Relationship of Parts Per Million (PPM) to Electrical
Conductivity (EC) of an Average Hydroponic Nutrient Mix at 77°F
700 PPM 1 ,400 PPM 2,100 PPM
1 mMho (mS) 2 mMho (mS) 3 mMho (mS)
Salt levels above 4.0 mMhos (mS) are usually toxic and slow down
Tomatoes and related plants like from 2.3 to 3.5 mMhos (mS).
Cucumbers need a lot less - only 1.8 to 2.2 mMhos (mS).
The PPM is a conversion from an electrical reading. With each
type of nutrient you add to the mix, you change the electrical
characteristics of the nutrient. The above conversion of 700 PPM
for each mMho or mS is a rough guess because the people who manufactured
the meter do not know what you are going to put in your mix. The
calibration mixes that you buy are not your blend, so the guess
can be far off. Most calibration mixes are not for nutrient mixtures
and can be 30% off what you want.
A generic reference solution that says 1,000 PPM on the label
was tested at 1,346 PPM (1.9 mS) on a nutrient meter. For nutrient
purposes, if a reference solution does not give you an EC value
in mS or give the conversion ratio that was used, it is not of
If the pH level is correct and there is a regular nutrient change,
supercharged plants do very well on 1,000 -1,500 PPM hydroponically;
use less when growing in pots with a medium. As well, a nutrient
aerator works quite well in a supercharged system.
Nutrient uptake and utilization by plants decreases with age,
so nutrient strengths should be decreased as plants mature. The
most efficient nutrient use by a plant is with high light and
nutrient solution PPM below where osmotic pressure starts to limit
water uptake. EC 5.0 is about the max.
Plants, when flowering and fruiting, need more phosphorous and
less Nitrogen relative to each other, but still less than the
starting quantities in the nutrient mix. The harder the plants
are driven to flower or fruit, the
I more quickly they use up their phosphorus. If you see purple
I leaf spots, leaf edges browning, or leaves curling down like
think phosphorus and correct the pH, or replace with an adjusted
nutrient. Do not just add phosphorus - you may make the problem
MOST NUTRIENT PROBLEMS ARE PH PROBLEMS
With nutrients, "more is not better" because a plant's
uptake of nutrients drops off after the first month. Nitrogen
has the biggest drop off. By the end of a plant's flowering and
fruiting life, the drop off will be about 30% on the nitrogen
and 20% on the others.
The nutrients in re-circulating tanks should be completely changed
once or twice a month to avoid a cumulative error of increasing
salts at the very time that the plant needs less of them.
On an average indoor garden with lighting around 1,500-2,000
lumens on the plants, a two or three weekly nutrient change with
a once a week nutrient addition to get the PPM up is good. With
only one or two nutrient make-up additions, the range of normal
nutrient usage in a regular indoor system is not likely to get
outside the plants' comfort zone.
Indoor gardens running on over 3,000 lumens on the plants need
weekly nutrient changes. Because they are being driven so hard,
these plants can develop shortages quickly within a week, especially
when they are transpiring lots of water, which multiplies the
problem each time the water gets low.