The pH of Your Organic Aerophonic Garden

Keeping pH within the correct range means your plants will have access to the full menu of essential nutrients for optimal growth and productivity. As an Organic Aerophonic grower, you need to get perfect pH level as much as possible in your reservoir.

The first sign that pH has drifted out of range is a slight paling or yellowing of the younger foliage as the plants struggle to take up certain essential nutrients.

Many inexperienced growers tend to misunderstand this, so a quick check of pH is always worthwhile when troubleshooting growth problems.

What is pH?

In simplest terms, pH is a measure of the acidity or alkalinity of a solution. The pH scale is logarithmic, which means a pH of 4 is 10 times more acidic than a pH of 5 and 100 times more acidic than a pH of 6. With a pH of 7 being neutral, such as with pure water, values below 7 are acidic and those above are alkaline (or basic).

Plants grown in organic aerophonics have a different optimal pH level than those grown in soil, so soilless gardeners need to be careful not to apply the pH recommendations for soil-grown crops to those they produce in aerophonics.

For most commonly grown organic aerophonic crops, an optimal pH range is between 5.5 and 6.5. Commercial growers often use a narrower range of 5.8 to 6 for most crops when they are using automatic controllers that regulating recirculation systems to maintain this precise level.

The optimal acidic pH range for organic aeroponic crops is important as it affects the solubility, availability and uptake of several essential plant nutrients.

If the pH drifts too high (past 7), plant uptake of some nutrients becomes less efficient. For example, plants can become iron deficient, even if sufficient iron is present in the nutrient solution.

Calcium is also affected by high pH, forming insoluble salts that precipitate out of the nutrient solution to form whitish deposits on reservoir walls, channels and equipments can be seen.

This type of nutrient lockout will typically show up as iron deficiency on new foliage (yellow, interveinal chlorosis on the foliage) and as tipburn and leaf cupping, which are symptoms of a reduction in calcium availability and uptake.

Inexperienced growers may misinterpret these nutrient deficiency symptoms as a problem with the nutrient formulation or product itself, rather than an issue with pH rising above optimal levels for iron and calcium uptake.

What Causes pH Fluctuations in a Garden?

In a healthy, well-run organic aeroponic system, pH fluctuations are normal and in some instances, such as recirculating nutrient film technique with a large crop of mature plants and small nutrient volume, pH changes can be quite rapid and require frequent adjustments to stay within a narrow range for optimal nutrient uptake.

As plants remove nutrient ions from the solution, the solution’s pH drifts up or down. If left uncontrolled, the pH will often drift downwards for several days after planting a new crop, after which the pH will steadily increase.

This is due to the differential uptake of ions from the solution, with the release of hydrogen (H+) or hydroxyl (OH-) ions from the root system.

As positive ions such as cations Ca2+, K+, Mg2+ are removed from the solution, hydrogen ions (H+) are released from the root system to equalize the ratio of anions to cations in the root zone and this lowers the pH of the solution.

When the crop begins an active growth phase, anions such as NO3 are taken up, which increases the pH through the release of hydroxyl ions (OH-) into solution.

Once plants are well established, most hydroponic systems tend to see a gradual and continual increase in pH over time, which is countered with doses of diluted acid.

With our organic nutrient recommendations, the pH variations could not be a major problem if your water pH is around 7.

Water Supply and Water Treatment for pH

The best water for organic aerophonic is rain water.

The alkalinity of a water supply describes the strength of a high pH so a water supply with a high starting pH and a high alkalinity takes a far greater volume of acid to bring it down to optimal levels than a water supply with a low alkalinity and of the same pH.

High alkalinity is considered greater than 300 mg/L of calcium carbonate and low alkalinity is less than 100 mg/L. When high-alkaline water is first added to the nutrient reservoir, it can take large volumes of acid (pH down solution) added over a number of days to finally bring down and stabilize the pH in the 5.8 to 6 range.

However, adding large amounts of acid is not only time consuming in terms of monitoring, adjusting and readjusting, but it can also create imbalances in the nutrient ratio as acids also add in nutrient ions.

Nitric, phosphoric and sulphuric acid all add N, P or S to the carefully balanced nutrient solution, so accumulation can occur. Growers with a water supply of high alkalinity can prevent this issue by pre-acidifying the source water down to a pH of 6 before using it to make up nutrient solutions or adding as top-up water to a nutrient reservoir.

Once the water supply has been stabilized at a pH of 6 and the alkalinity countered to the point, it remains at that pH for 24 hours and can be used in the aerophonic system. Much less acid will then be required for pH control.

Organic Aerophonic Nutrient Formulation and pH

With our Organic nutrient formulations, initial pH is remain around 5.5 to 7, which is ideal for the growth of aerophonic crops. This will depend only on pH of original water source of the Gardner.

Many of the nutrient products in the market, designed for hard or alkaline water sources. And use certain percentage of ammonium nitrate to help counter pH increase. So, don’t use substitutes and destroy total crops in the garden.

Testing and Adjustment pH Levels

Best recommendation is to use our organic fertilizer balancing techniques with our professional’s advices.

What is pH Up?

What is pH Down?

Commercial growers usually make up their own pH adjustment solutions of 10% nitric or phosphoric acid or potassium hydroxide for increasing pH.

By using a ratio of 50% nitric and 50% phosphoric acid, the solution can be kept in better balance as both N and P are added, but when a lot of acid is being used, the nutrient formation should be adjusted for these additional N and P sources, as they are macronutrients.

There are organic acids such as citric acid and white vinegar (acetic acid) that are sometimes used in small systems to bring pH down, but these are weak acids and only give a short-term pH reduction.

Organic acids also add carbon to the nutrient solution, which microbes (both good and bad) love to feed on, encouraging an unwanted reduction in dissolved oxygen in the solution.

There is a wide range of pH testing equipments available, from inexpensive liquid test kits and strips sold by aquarium/swimming pool suppliers to high-tech, electronic meters. Test kits and strips should only be used for the lower pH range—many of these measure pH 5 to 7.

Commercial growers with electronic meters should also invest a few dollars in a cheap liquid pH test kit or strips just to double check the accuracy of their electronic meter from time to time. Meter probes tend to drift over time and need to be calibrated on a weekly basis, cleaned and replaced annually.

Keeping a garden’s pH within the correct range means your plants will have access to the full menu of essential nutrient ions for optimal growth and productivity.