When growing in soil, all the microbes (as well as the soil itself) help to make nutrients available to the plant. But when you take out the soil by growing hydroponically, all that unseen hard work by nature is now controlled by the grower. This can prove tricky, but when mastered can be extremely rewarding.
To explain pH, I’ll need to go fairly deep into the maths, but stick with it and all will become clear. pH is a measure of how acid or alkaline a solution is, which is controlled by the activity of Hydrogen cations, [H]. More specifically, pH is the decimal logarithm of the reciprocal of hydrogen ion activity (this sounds more complicated than it is!). It is by looking at the detail and understanding this equation a bit more that we realise why controlling the pH in your hydroponic system is so important.
pH = log10 (1/αH+)
(αH+ is the activity of the Hydrogen cation)
Let’s break things down into simple stages. First thing is the log10 part of the equation. This means that each time you go up or down by one whole pH point (e.g. 5 → 4) the change in the acidity (the hydrogen activity) is changing by a factor of 10! So pH 4 is ten times more acidic than pH 5, and a hundred times more acidic than pH 6! This explains why precise control down to 0.1 on the pH scale is necessary. The second part of the pH is the 1/αH+ bit. Basically this means that pH is the inverse of the hydrogen activity. So as the activity of the Hydrogen increases, the pH decreases. This is why all acids have a Hydrogen in them they can release into the solution to increase activity and lower pH (e.g. HCl = Hydrochloric Acid)
The pH scale runs from 0 – 14, with 0 being very acidic and 14 being very alkaline. Hopefully when growing you won’t see those extremes, with usual values between 5 and 7 and the ideal range between 5.8 and 6.2.
As you can see in the blog on foliar feeding, the pH of the soil, or hydroponic solution controls the availability of the nutrients to the plant. The elements themselves are still there, what changes is the form they are in. Plants need the nutrients to be in a form that is water-soluble so they can be taken into the plants ‘bloodstream’ (the sap) and transported to the area required. A change in the pH can change the form and therefore reduce or increase the availability. What makes things complicated is different nutrients are available at different pH ranges. In hydroponics the ideal pH range is between 5.8 and 6.2, with soil the target is slightly higher nearer 6.5 . This range provides the the plant with the maximum avilability of the most nutrients. pH testing kits and pens can be picked up for less than £10 and provide growers with a very useful tool to help maintain healthy plant growth.
EC stands for Electrical Conductivity. It is a measure of how well a material (in the case of hydroponics, a solution) conducts electricity. This is a function of the amount of electrolytes (charge carrying particles) in the solution. The more electrolytes the higher the conductivity. and the higher the charge carried by each particle, the higher the conductivity. There are other factors as well involving particle shape, temperature, solvent type etc… But for our purposes, EC is a good measure of how much salt is in your hydroponic reservoir. The salts are the mineral salts that are used in fertilisers to provide plants with all the elements they need, from Boron (B+) to Zinc (Zn2+). In a soil-based medium, the amount of salt is controlled by the humate levels (and their cation exchange capacity), the amount of water present (and it's contact with the roots) and the amount and type of microbes as well as a whole host of other mechanism. All these things provide a larger degree of control, reducing (but not removing) the chance of over-fertilisation compared with hydroponics. As such monitoring EC doesn't play the same role when feeding plants in soil, and so following manufacturer guidelines is always recommended.
While it has its uses and will give you basic information, EC will not however tell you what salts are in your solution. This is why some growers use water that has been filtered by Reverse Osmosis to remove everything (even things smaller than salts such as bacteria and viruses!) so they can start from a blank slate. That way they know exactly what is in their water, as they can look at the Guaranteed Analysis on their nutrient bottle to find out what it contains (this why it’s advisable to avoid nutrients with no guaranteed analysis!)
At Plant Magic we analysed water samples from around the UK to understand how to make fertilisers that balance with the water supply countrywide. To this end we produce our base feeds in both hard and soft water variants to help our customer’s better balance their pH and EC. The idea is to reduce the amount of pH adjustment needed that can upset the balance of NPK, which impedes the nutrient performance and costs growers more in both time and money. Where extreme soft water is causing deficiencies, we have Magne-Cal +, a magnesium-calcium supplement that can be used with any growing medium and any nutrient range to help keep your plants healthy.
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