Nutrient performance is far
more complex than simply using a quality brand. This article addresses the
key issues that can hinder a nutrient’s effectiveness.
Nutrient performance is reduced by not
following specific dosing procedures:
Step 1.
Volume of nutrient solution: As a guide, allocate at least 10 litres
(2.5 gal) of nutrient solution per large plant (e.g. tomato), or around 2
litres (½ Gal) for smaller plants (e.g. lettuce).
This is especially important for
‘re-circulating’ systems because larger nutrient volumes will undergo
smaller changes in concentration (EC) and “pH”. In hot weather, insufficient
nutrient volume could result in EC soaring to toxic levels which could
seriously damage your plants. Larger nutrient volumes will also reduce how
frequently top-up water is needed.
Step 2.
Dosage rates: The dose rate depends upon your growing medium (e.g. soil,
expanded clay, etc) and the phase of growth - seedling, vegetative or
flowering. See
Dosage
Chart.
Step 3.
Add the majority of water before adding nutrients and additives:
Never mix nutrients and additives together in small amounts of water.
With 2 and 3-part nutrients, the “parts” are
kept separate for good reason. When these parts are mixed together in
concentrated form (or in too little water), a white precipitate will form -
as often seen in nutrient reservoirs (Fig 3.6b).
Step 4.
Thoroughly stir the nutrient: Always stir immediately after adding each
nutrient and additive (or even top-up water). This eliminates regions where
less soluble nutrient species are concentrated. It also removes regions of
extreme pH (either high or low), thereby preventing the destabilization of
nutrients that are unstable outside of the pH window of 5.0-6.5.
Step 5.
pH control: Do not leave pH unchecked for a long period of time.
Quickly add all nutrients and additives then, after thorough mixing,
immediately check pH and adjust if necessary. Allowing pH to rise above 6.5
is a common cause of white precipitate in nutrient reservoirs. See
section on pH.
Step 6.
Maintaining nutrient concentration: (Does not apply to
‘run-to-waste’ systems) As plants grow they simultaneously remove both
water and nutrients from the nutrient solution. This may cause the nutrient
strength to either increase or decrease – depending on which is being
consumed at the faster rate. Typically the nutrient concentration tends to
increase, especially in hot weather because water loss can be excessive due
to both plant uptake and evaporation. Therefore ensure the water level is
kept relatively constant. When this is done, the concentration (or
conductivity, EC) will be
relatively predictable i.e. Concentration will slowly decrease as the plants
consume nutrients^. Check the EC about every second or third day and if
necessary add sufficient nutrient to stay within the target range.
^ NOTE: High salinity (salty) make-up water
may cause EC to increase.
Step 7.
Further notes:
+
Beware of high pH additives: The best dosing technique to adopt with
additives that increase pH significantly (e.g. silica, PK additives) is to
add them to the water and adjust the pH down to ~6 prior to adding the
nutrient.
The less preferred but simplest alternative is
to pre dilute the additive in a separate volume of raw water. Then once this
solution is added to the nutrient solution, quickly lower the pH to below
6.5. Note, a white cloudy precipitate (calcium sulphate) may form where the
pre diluted additive initially merges with the nutrient solution. However,
because the initial particle size of the precipitate is small, it will
usually re-dissolve if the pH is immediately re-adjusted (Fig 3.6a).
+
2 & 3-part nutrients: Avoid “roughly measuring” out the nutrient dose -
always add the correct amount of each part. In the case of a 2-part, 'under'
dosing part 'B' for example, could cause a deficiency in over half the
nutrients required (i.e. P, K, S and all of the trace elements - except
iron).
