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Mixing nutrients for hydroponic systems



Bob Taylor, chief chemist of Flairform (www.flairform.com) explains mixing nutrients...


Multi-part nutrient guidelines


1. Do not combine concentrated nutrients in too little water.

Think about it for a second. Two and three-part nutrients come in separate "parts" for a reason! If they come into contact with each other when still concentrated (or in too little water) you will see a white precipitate form and, depending on the formulation, this can happen well within a minute or so. Try this for yourself - mix an equal volume of each part in a glass, undiluted. You'll quickly see precipitate start to form. The majority of the precipitate is typically calcium sulfate. Now, add more water and see if it will dissolve. The longer you delay dilution, the more difficult (or impossible) dissolution becomes. Your plants can only use nutrients that are fully dissolved in the water. So all that precipitate represents food that your plants can no longer access. Along with poor pH control, this is a cause of the white precipitate within the body of the nutrient. Therefore to prevent this, always add the majority of water before combining nutrients. Additionally, always stir well before each subsequent part is added. Note that the source of white precipitate above the water line, on the surface of media and equipment (e.g. clay pebbles) is salt deposition from evaporation. Notably, the amount of precipitation from this source is greater at higher (EC) nutrient concentration.


2. Which comes first: A or B?

My advice is that you should always add the part containing the phosphate first. This is because the addition sequence of each nutrient 'part' can affect nutrient stability, particularly if your water has high alkalinity. "Alkalinity" (bicarbonate & carbonate) is the component of natural waters that causes high pH. Adding the nutrient dose to high alkalinity water can decrease the stability of several nutrient species (including calcium, sulfate, iron, copper, manganese, zinc). Therefore, rather than trying to pre-adjust the pH of the water (often a very difficult task - pH adjustment is better done after all nutrients and additives have been added) it is preferable to first add that part of the nutrient that lowers pH the most. This is usually the part that contains the phosphate. In two-part nutrients this is usually part "B". So there you have it. "B" comes before "A" after all! However, make sure you check with your particular brand. Note that the "part" without any phosphate will normally have relatively little impact on pH. Secondly, it usually contains the iron which is highly unstable at pH levels much above ~6.5. Note, in three-part nutrients the phosphate is sometimes dispersed across two bottles. Therefore, if you really want to be accurate, determine which contains the highest concentration of phosphate, and add that first.


3. Add equal amounts of each part.

Avoid "roughly measuring" out the nutrient dose. An excess of one nutrient species does not compensate for deficiencies in another. In the case of a two-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 excluding iron). This problem is compounded with two and three-parts because the dose volumes for each part will be roughly one-half to one-third (respectively) of what it would otherwise be if using a one-part. Therefore, without appropriate measuring equipment, when small tank volumes are being used the dosing error can be significant.


To some growers, the additional complexity of two and three-part formulations is an interesting challenge. To others, who want to make their lives a little simpler, the idea of dosing using multiple parts isn't so appealing. Certainly, using a high quality one-part formula readily ensures an optimal balance of nutrients and, as a result, one-part nutrient products are increasing in appeal among growers.


4. Thoroughly stir the nutrient.

Whatever type of nutrient you prefer, you should always follow the following dosing guidelines and always stir immediately after the addition of nutrient, additives or top-up water. Doing so will eliminate high zonal concentrations of the less soluble nutrient species. Further, it removes zones of extreme pH (either high or low), thereby preventing the destabilization of nutrients that are unstable outside of the optimum pH window of 5.0-6.5.


5. Be diligent with pH.

This is probably the most crucial area of nutrient management. Be cautious when using additives with a high pH. I don't mean to be alarmist here as it's important to note that essentially all additives will affect nutrient pH at least slightly. The best technique to adopt with those that elevate 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. Another less preferred but common alternative is to pre dilute the additive in a separate volume of raw water prior to adding to the nutrient solution, then quickly lower the pH to below 6.5 once this solution is added. Note, a white cloudy precipitate (calcium sulfate) may form when 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.


How much PPM to mix for different plant types

Below is a table with recommendations for mixing PPM for different plant types in hydroponic systems. Don't be afraid to adjust your feed program. Some plants might do better with more or less nutrients.


Plant EC PPM x 500 CF PPM x 700
Asparagus 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Basil 1.0 – 1.4 500- 700 10 – 14 700 – 980
Beans 1.8 – 2.5 900 – 1250 18 – 25 1260 – 1750
Beets 1.4 – 2.2 700- 1100 14 – 22 980 – 1540
Blueberry 1.8 – 2.0 900 – 1000 18 – 20 1260 – 1400
Broccoli 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Cabbage 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Carrot 1.4 – 2.2 700 – 1100 14 – 22 980 – 1540
Cauliflower 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Celery 1.5 – 2.4 750 – 1200 15 – 24 1050 – 1680
Chives 1.2 – 2.2 600 – 1100 12 – 22 840 – 1540
Corn (Sweet) 1.6 – 2.4 800 – 1200 16 – 24 1120 – 1680
Cress 1.2 – 2.4 600 – 1200 12 – 24 840 – 1680
Cucumber 1.6 – 2.4 800 – 1200 16 – 24 1120 – 1680
Eggplant 1.8 – 2.2 900 – 1100 18 – 22 1260 – 1540
Endive 0.8 – 1.5 400 – 750 8 – 15 560 – 1050
Garlic 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Lettuce – Loose Leaf 0.3 – 0.8 150 – 400 3 – 8 210 – 560
Lettuce – Iceberg 0.6 – 1.4 300 – 700 6 – 14 420 – 980
Melons 1.0 – 2.2 500 – 1100 10 – 22 700 – 1540
Mint 1.0 – 1.4 500 – 700 10 – 14 700 – 980
Mustard 1.2 – 2.4 600 – 1200 12 – 24 840 – 1680
Okra 2.0 – 2.4 100 – 1200 20 – 24 1400 – 1680
Onion 1.8 – 2.2 900 – 1100 18 – 22 1260 – 1540
Parsley 0.8 – 1.8 400 – 900 8 – 18 560 – 1260
Parsnips 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Peas 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Peppers 1.8 – 2.8 900 – 1400 22 – 28 1260 – 1960
Pumpkin 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Radish 1.2 – 2.2 600 – 1100 12 – 22 840 – 1540
Sage 1.0 – 1.6 500 – 800 10 – 16 700 – 1120
Spinach 1.8 – 3.5 900 – 1750 18 – 35 1260 – 2450
Squash 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Strawberry 1.8 – 2.5 900 – 1250 18 – 25 1260 – 1750
Thyme 1.2 – 1.6 600 – 800 12 – 16 840 – 1120
Tomato 1.8 – 2.8 900 – 1400 22 – 28 1260 – 1960
Turnip 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Watercress 0.4 – 1.8 200 – 900 4 – 18 280 – 1260


Learn how to mix nutrients for a hydroponic system.