In the last 50 years, many hydroponic systems have been developed in order to make crop cultivation easier, cheaper, faster and denser. Amongst the systems that have been developed, one of the hydroponic systems which has caught the most attention and is used more frequently is the so called NFT (Nutrient Film Technique) system.

The system’s operation principles are quiet simple. A PVC (or or other polymer) rain gutter is placed on an aluminum frame with a certain inclination, plants are placed in small containers introduced inside the gutter and a nutrient solution is sprayed at the most elevated side of the gutter. The spraying forms a thin film on the gutter’s bottom and flows towards the other end due to the slope.

The fact that the NFT system allows most of the plant’s root system to remain outside the nutrient solution is the main reason for it’s success. Throughout a lot of research, it has been found that plants just need to be “barely” in contact with the nutrient solution. Plant’s seem to greatly benefit from their roots abosrbing oxygen from open air and taking just the little amount of necessary nutrients they need by a small contact with nutrient solutions.

The NFT system is great for crop cultivation and is one of the most efficient systems for the growing of crops such as basil, lettuce, spinach and cabbage. However it does have some disadvantages such as gutter length limitations due to nutrient and temperature changes (usually gutters are never more than 15 feet long), of course they also have the strong disadvantage of much higher costs (fue to the gutters being expensive) and lower planting densities (due to the spaces needed between gutters to allow personel). Nonetheless, many companies growing NFT systems have been able to make “foldable” gutters which allow automatic recollection of lettuce, transplanting and sterilization.

In conclusion, one could say that the NFT system is one of the best hydroponc growing systems that have been developed due to the fact that it allows greater oxygen and nutrient absortion. In fact, the hydroponic nutrient film technique is one of the most used systems for lettuce cultivation.
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As I talked about in a previous post, the disinfection problem in hydroponics is very important as many pathogenic microorganisms as well as algae develop through the course of any hydroponic gardening attempt. Hydrogen peroxide, as I said earlier, is a very good disinfectant with incredible properties but most of the time it is not used because of it’s high cost.

Amongst one of the most common disinfectants available we find sodium hypochlorite. This chemical substance with formula NaClO is a good disinfectant because it oxidizes organic matter producing Cl2 which then further oxidizes organic matter tu produce Cl(-). As you can see, the several steps available for oxidation as well as this compound’s innate reactivity make it one of the best and cheapest disinfectants available today. This is the reason why sodium hypochlorite solutions have been used for a long time and now have commercial names, such as Clorox.

In hydroponics, sodium hypochlorite solutions are commonly used to sterilize a hydroponic system prior to use or in between different crops. However, this does not achieve the purpose of maintaining the nutrient solution sterile throughout the whole gardening cycle.

In order to achieve this in a very simple way (for the home hyroponic and commercial gardeners) several peer reviewed papers have studied the effect of hypochlorite ions on different plants and at different levels of concentration. In general, it has been found that concentrations of hypochlorite of 5.5 ppm offer good protection agains microorganisms without affecting the crop qualities.

If you do not have any industrial grade hypochlorite you can still achieve this concentration by applying 0.1mL of Clorox (check that it is less than 6% hypochlorite, usually 5.25%) per liter of nutrient solution. This can be easily measured and applied for small systems with the aid of a 1mL syringe as the ones diabetes patiens use for insulin (these syringes can be easily purchased at any pharmacy). Remember to try this with a small batch of plants before applying it over your whole garden to ensure compatibility with your particular nutrient solution.
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In a previous post, I explained how concentrations are given in hydroponic gardening and what they actually mean. For example, I exemplified that 200 ppm of N equals a solution which contains 200 mg per liter of nitrogen although the form in which nitrogen is present is not described by the concentration data. In this post, I intend to explain how nutrient concentrations can be translated adequately to a mass weight of a certain salt that will be the actual source of the nutrient.

Let us start by supposing that you have a certain solution recipe given in concentration data, for example, the solution demands 200 ppm N and 700 ppm K (this is just an example as 700 ppm of K is too high for any hydroponic nutrient solution). This means that the solution requires 200 mg per liter of nitrogen and 700 mg per liter of potassium. Our mission now is to translate this concentration information into the actual amount of a given salt that needs to be weight and dissolved.

The first thing we need to do is find a suitable salt or salts that can give us the nutrients we want in the appropiate forms. In this case, we will use potassium nitrate (KNO3) as a source of both nitrogen and potassium. This salt gives the plant nitrogen as NO3(-) ions and potassium as K(+) ions.

Our next step is to figure out how much solution we want to prepare. In this case, let’s suppose we want to prepare 100L (around 32 gal) of nutrient solution.

Following this, we must calculate how much much K(+) and how much NO3(-) need to be added in order to achieve the concentrations we desire. Since K(+) contains a single K atom, we need 700 mg/L of K(+) in order to achieve 700 ppm of K, for the nitrate ion (NO3(-)), since it contains more atoms, we need to know how much of the nitrate ion is actually nitrogen. In order to do this we calculate what fraction of nitrogen resides in nitrate by relating their molar mases (you can google nitrate molar mass and nitrogen molar mass to get this values or calculate them using your periodic table) . The calculation would be 14/62 which equals 0.22. This means that 22% of each nitrate ion is nitrogen. If 22% of each nitrate ion is nitrogen then we need 200ppm x(100/22) of nitrate in order to get the concentration of nitrogen we want. The result is that we need 909 mg of nitrate per liter in order to achieve our required concentration of 200 ppm.

Since our salt is KNO3 and not K or NO3 by themselves we need to decide which nutrient we want to fit in an exact manner. For this example I will take NO3(-). Since we want to weight 909mg per liter of NO3(-) we see how much KNO3needs to be weight in order to achieve this amount for 100 liters. For this we use the relationship between the molar mases of nitrate and the salt, potassium nitrate. The equation is 62/101, which equals 0.61, meaning 61% of potassium nitrate is nitrate. Since we want to know how much is 100% knowing that 61% is 909mg per liter we calculate 909ppm x 100/61, which equals 1490mg per liter which needs to be multiplied by 100 in order to find the amount needed for 100 liters of solution. The final result is that 149 g of potassium nitrate are needed in order to achieve a concentration of 200 ppm of N in 100 liters of solution.

Now what happened to the potassium ? Since we added potassium nitrate, we also added potassium with the salt. We now need to calculate the concentration of potassium which we get when we arrive at a concentration of 909 ppm for ntirate. Since we know nitrate is 61%, then potassium must be 39% of the concentration so 1490 ppm x 0.39 equals 581 ppm.

As you can see, we matched our nitrogen requirement perfectly but ofset our potassium requirement by an important amount. This problem is due to the fact that each salt gives two nutrients to a soltuion. Meaning that a good salt combination needs to be used in order for our errors to be reduced when preparing the hydroponic nutrient solutions. This problem can be solved by using the hydroponic nutrient solution calculator I described in an earlier post, however, it is important to know how the calculator works in order to understand its possible errors.

As you can see, preparing nutrient solutions and turning concentrations into weights can be a little bit daunting at first but with practice and the aid of calculator tools, the preparation of custom hydroponic solutions becomes very easy and paves the way towards major improvements for any commercial or hobbyst hydroponic gardener.

Most amateur growers, both hobby and commercial, who do not have a chemical knowledge background are most of the time stunned by the amount of chemistry involved in hydroponic cultivation. One of the things that proves to be the most difficult for this new comers is the understanding and description of nutrient concentrations.

Concentration, to start, is just a way of expressing the amount of something inside something else. In hydroponics, we are interested in expressing the amount of nutrients per amount of nutrient solution. To do this, we use several tools available in chemistry.

In general, concentrations in hydroponics are either expressed as moles of nutrient per liter of solution or as milligrams of nutrient per liter of solutions. The first unit is called molarity while the second unit is generally referred to as ppm (parts per million). This means that a solution containing 12 ppm of Nitrogen contains 12mg of nitrogen per liter of solution and a solution containing nitrogen in a 0.001M concentrations contains 0.001 moles of nitrogen per liter of solution. The first form of concentration (ppm) is often used in hydroponics while the second (M) is used in hydroponics only in research papers and such.

In practice, the use of concentrations in ppm makes preparation a little bit easier as the leap from concentration to mass becomes easier if the unit of measurement inside the unit belongs to mass. Since the ppm unit can be translated as (mg/L) going to the mass of salt required is easier than with molarity (although not by much).

Another advantage that we come across when using ppm as a main unit of concentration measurement in hydroponics is that the numbers are likable. We, humans, tend to like numbers between 0 and 1000, so concentrations of 120 ppm, 250 ppm and such, seem much easier to grasp than their equivalents in molarity which would be 0.0012 M, 0.00023 M or the like.

In an article to be written soon, I intend to describe how to do the leap from this concentration measurements onto the mass of salt that is needed to weight in order to achieve the desired concentration inside a hydroponic solution. So stay tuned to know a little bit more about the science of hydroponic nutrient solution making !
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It is a common mistake in hydroponic gardening to assume that the chemical forms of nitrogen that can be used in hydroponics are the same that can be used in regular soil gardening. Don’t get me wrong, plants in soil and plants in hydroponic media use the exact same chemical forms of nitrogen as nutrients, what changes dramatically from hydroponics to soil gardening is the environment in which the plant is.

Let us talk about the available forms of nitrogen first. Plants absorb nitrogen either as NO3(-) (nitrate) or NH4(+)(ammonium) ions. Both of these ions supply nitrogen to the plant but they have dramatic differences inside the plant’s metabolic pathways. Nitrate is absorbed by the plant slowly and provides the materials needed for the synthesis of amino acids and other structures while ammonia is absorbed rapidly and causes immediate plant toxicity if present in highly enough concentrations.

This is the main difference between soil and hydroponic gardening. In hydroponics, most of the nitrogen must be supplied as NO3(-) because the hydroponic media allows ammonium ions to become toxic exceedingly fast. For example, hydroponic plants can withstand concentrations of nitrogen (as nitrate) up to about 250 ppm while concentrations of nitrogen as ammonium are only withstood up until about 30 ppm. This is the reason why urea cannot be used as a nutrient salt in hydroponic gardening to supply all the nitrogen needed by the plants.

So if plants in soil and hydroponic media assimilate the same nutrients, why can plants in soil be fed nitrogen as ammonium but hydroponic plants cannot ? The answer is quiet simple. Bacteria present within the soil are able to efficiently convert ammonium ions into nitrate ions, effectively reducing the amount of ammonium the plant “sees”. In fact, plants in soil also absorb nitrate, the only difference is that there are bacteria that can convert ammonium to nitrate, reason why nitrogen can be supplied as ammonium to plants present in soil.

So next time you are searching for a nitrogen nutrient for your hydroponic plants, remember to search for nitrate salts as more than 90% of your total nitrogen source. The most important salts for providing nitrogen as nitrate in hydroponic gardening are potassium nitrate and calcium nitrate. This is important to remember, as using ammonium salts to provide your plant’s nitrogen will ultimately kill them in hydroponic media ! (below, an image showing the effects of ammonium fertilizer in hydroponic plants)
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When gardening, it is sometimes most convenient not to start a plant from seed but to start it from a cutting from another plant. Most of the time, the science of starting cuttings involves the use of root growth hormones and other chemicals which can prove hard to get in some regions of the world and sometimes are not desirable because of their conflicts with some organic food regulations.

Luckily, there are ways to root and get cuttings up to a good start without the use of any root hormones. In order for us to do this, we should first understand the problem and how to solve it.

When a part of a plant is cut, and this part has no root system, the ability of the cutting to get nutrients from it’s surroundings becomes minimal. The idea is to maintain the plant’s food requirements as low as possible until it develops a healthy root system that can take up nutrients and grow a healthy new plant.

The first step is to place the cutting inside some growing media (remember to cover the cut wound with candle wax in order to prevent possible fungal infections) (either potting soil in soil gardening or perlite, rice husk/ sand in hydroponic gardening) and to place it somewhere where light is scarce. When diminishing the amount of light that reaches the cutting, we slow down photosynthetic processes and therefore the nutrient needs of the plant. The media should be watered daily so that the new root system can be developed.

In order to supply nutrients for the plant, a suitable foliar spray should be applied. A 1/10 strength Hoagland’s solution can be used effectively or a suitable organic foliar spray can be used if the desire to achieve organic food certifications is present. Plants are able to feed throw their leaves in some way so the application of nutrients on the leaves or “foliar feeding” is a good tecnique when starting cuttings whose root systems have not developed.

After 3 or 4 days of this process, the plant should be ready for it’s reintroduction into normal growing conditions. If you are a hydroponic gardener, start applying a one third strength hydroponic solution on the plant’s growing media. In any case, the plant should be brought into light in increasing intervals, first day one hour, second day 2 hours, third day 4 hours, fourth day 8 hours and fifth day left outside.

This whole process should provide an adequate environment and growth for the new cutting’s root system with the final gradual adaptation providing enough time for the leaves to readjust to normal lighting conditions. I hope this guide proves useful and all of you enjoy new cutting in your organic or hydroponic gardens.
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Few people have been able to experience the joy of gardening without encountering the nasty problem of insects. Every year, many gardens suffer from the amazing attacks of these small creatures that turn beautiful plant spaces into infested focuses of insect populations.

Up until now, most chemical solutions have acted on insects quiet effectively. In fact, some insecticides are good at removing more than 99.99% of insect populations with a few applications. Chemical insecticides are most of the time harmful for humans but sometimes they can even be safe for us. The main problem with synthetic insecticides is that they affect beneficial insect populations much more dramatically than they do harmful insect populations. The main problem with this is that is effectively diminishes the amount of insects that can predate bad insects and pollinate plants.

Organic (in the sense of natural) insecticides are sometimes good but they are never as effective as available synthetic solutions. In the few studies done about this issue, (mainly dealing with cabbage) all of them have found synthetic solutions much better at controlling insect pests. However, garlic based insecticides have proven effective at controlling insects if not completely removing them from the garden (they also prove almost non fatal to beneficial insect populations).

In order to control your insect populations easily, you can manufacture an insecticide with garlic, vegetable oil and water. Cut 3 cloves of garlic into small pieces and place them in a jar with 200 mL (about a cup) of vegetable oil for two nights (this ensures that the organic non polar molecules present inside garlic are extracted efficiently). Next, mix this with 2/3 of a gallon of water . Agitate strongly before each use. Then your insecticide is ready to be spread on your garden.

Hopefully, if spread adequately over every inch of the plant (including the underside of leaves), the insecticide should prove efficient against most types of bad insects. It also proves effective in being resistant to rain so your plants should remain protected for a prolonged amount of time. Bear in mind that soap or detergents should not be added to improve surface tension properties because this increases the capacity of rain to remove the insecticide effectively.
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Even though there has been great effort by many people to show hydroponic growing as something that can be done by anyone with little knowledge, it has come to my attention that many novice and commercial gardeners fail because of their inability to properly interpret the chemical phenomena around them. One of the variables that is primordial in hydroponic culture and that is grossly oversimplified in most literature about hydroponic gardening is the treatment of pH. For this reason, I decided to create this pH FAQ post in order to answer (in a basic but scientific way) the questions most people have (or should have anyway) about the science of hydroponics.

How can I correct pH changes ?

Bases or acids can be added to hydroponic solutions in order to increase or decrease the pH value of a solution. Bases and acids should be added as solutions and the amount added must be recorded in order to know how nutrients are changed. For example, if a potassium hydroxide solution is added to increase the pH of a solution, the amount of solution added needs to be recorded in order to know how much potassium was added to the solution (since this is a nutrient). Common acids to lower nutrient solution pH values are nitric acid, phosphoric acid and citric acid. I would recommend the use of citric acid to reduce pH and potassium carbonate to increase pH.

What is the ideal pH value ?

It depends on the specific plant you are cultivating. Most crops grow very well with pH values between 5.5 and 6.0, although there are some plants which require more basic or slightly more acid pH values.

How can I stop pH from changing ?

Please refer to the article I wrote about controlling the pH of your nutrient solution with buffers in order to effectively prevent pH variations inside your hydroponic nutrient solution.
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When researchers first started to study how plants grow and what plants exactly need to develop, they found out that plant needs are very different from our own. We, as humans, need minerals, vitamins, carbohydrates, proteins and fats amongst other substances. However, plants seemed to require a small assortment of inorganic substances from which they synthesized a very large variety of organic materials.

Many hydroponic growers are confused by the fact that nutrient needs and nutrient solution compositions are provided in the form of elemental concentration. That is, hydroponic solutions are often described in the form “N 200 ppm”, “K 100 ppm”, etc. Compositions are expressed as the amount of milligrams present of a given element per liter of solution. Nonetheless, this does not mean that the element is present as a pure substance.

For example, the fact that a hydroponic solution contains 100 ppm of Nitrogen, does not mean that the solution contains nitrogen as elemental nitrogen, that is, N2 gas. This in fact, does not express the form in which nitrogen is present, it may be present either in the form of NO3(-), NH4(+) or other molecules. This has caused some confusion since some people are unaware that hydroponic nutrients are mainly inorganic salts that, when dissolved in water, form ionic substances which are the actual nutrient assimilated by the plant.

It is important then to have a clear mental perspective about the way in which things are expressed and the way in which they really are. For example, you can have a hydroponic solution with 100 ppm of P. That is, a hundred milligrams of phosphorous present per liter of solution but in no way does this express the way in which phosphorous is present within the solution. Phosphorous may actually be located as a large assortment of ions, either H2PO4(-), HPO4(2-) or PO4(3-).

The reason why nutrient solution concentrations are often expressed as mere element concentrations instead of actual available form concentrations is because it is much simpler to think about the sum of all the available forms of a nutrient than each nutrient form by itself. In the light of the previous example, it is much easier to say 100 ppm of P than to state a specific concentration of each ion, given that (in this case) all ions are indistinguishable for the plant.

The really important thing about this is that the grower should have a clear understanding of the nature of hydroponic nutrients. Nutrients are really ions, which are formed by the dissolution of salts in water. So when you go out to buy nutrients for your hydroponic solution you should look out for inorganic salts of the desired elements ! (below, an image that graphically shows ion dissolution)
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