Hydroponic Nutrients

Well class, here we are again, armed with our newly found knowledge of pH and conductivity. In this issue we are going to look at nutrients: where they came from, what types there are, and the very important topics of nutrient purity and nutrient strength.

So where did this concept of hydroponic nutrients originate? If we look back in history, hydroponics has been around in some form since the Hanging Gardens of Babylon (the first historical reference to hydroponics). However, we are going to look at the beginning of modern hydroponic nutrients, which began in the 30s with a man called Dennis Hoagland.

Dennis Hoagland was a prominent American researcher in the field of plant mineral nutrition in the 1930s. He developed the world’s first complete and fully balanced nutrient solution. He did this to further his research into the mineral nutrition of higher plants and found that by growing plants in a water-based culture (the purest form of hydroponics) he could effectively document plant responses to mineral deficiencies. He could also record how plants responded to optimal nutrition. By this process of element inclusion and exclusion, Dennis Hoagland finally arrived at a complete mineral nutritional formula for use in hydroponics, called, oddly enough, Hoaglands Solution.

Hoaglands Solution is still the basis for all modern nutrient formulations, and because of this, Dennis Hoagland is regarded as the father of modern hydroponic nutrient solutions.

Nutrient Types

When looking at the huge range of hydroponic liquid nutrient concentrates in your local store you will essentially find two main types: single part (pack) concentrates and two or more part (or multi part) concentrates.

Let’s first look at a multi part (pack) concentrate. Why do they put it into two different packs? The answer to this is very simple: to avoid the precipitation or lock out that occurs when certain mineral elements are placed together in concentrate. The elements separated are the phosphates and sulfates from the calcium source. This is done because calcium reacts with those elements, forming new compounds, i.e. gypsum salts. These new compounds are typically seen as a white precipitate or sludge in the bottom of the bottle (look at most one parts and you will see this).

Multi-part nutrients also offer the advantage of flexibility. When using a multi-part concentrate you can alter the ratios to suit certain conditions. For instance, you could add a little more nitrogen and calcium or extra micronutrients if the conditions warrant it. So you have flexibility as well as a non-precipitated solution to give to your plants.

Single parts, on the other hand, place all the elements together in one bottle. The trade off for this convenience can be lack of full availability of elements and lack of flexibility.

Available now are one-part concentrates that have no precipitation. These are a much better choice, as all the elements contained within the bottle are available to your plants. A very easy way to test whether you have a good one-part nutrient is to shake the bottle vigorously and then decant some into a glass or clear container. After an hour or so, carefully and very slowly pour the solution back into the bottle. If you notice any significant precipitate or sludge on the bottom, then nutrient reaction or lock out has occurred. It is important to know this because when these elements combine and precipitate, they are almost always permanently unavailable to the plant.

If you look at the label on a bottle of nutrients you will see some brands with chelated micronutrients and others without. But what are chelates? And how do they work? A quick reference to the original Greek meaning (claw-like) gives us an accurate explanation. Chelates are molecules that hold (with their claws) other elements within them. Another way of looking at chelates is as a cage with the micronutrient held inside the cage. In respect to plants, chelates function at a number of different levels. Firstly, they protect the element (inside the claw or cage) from undesirable solution, and secondly, they make elements more available to the plant by acting as transporters.

To explore the protection concept further, let’s look at micronutrients that are commonly chelated in nutrient concentrates. Micronutrients, especially Copper, Manganese, Zinc and Iron, are particularly susceptible to unfavorable conditions (i.e. pH shifts, UV light etc). Under these conditions they will become unavailable to the plants, or fall out of solution, making them unavailable for absorption (because they aren’t there!). By protecting our micronutrients with chelates, we make them significantly more available to the plants over a wider range of conditions.

As for the chelates’ role in element transportation, think of them as little microscopic four-wheel-drive trucks carrying a load of goods to the plant. These trucks can pass through any condition or difficult terrain in order to distribute their goods. In other words, chelates carry the elements through the root membrane even when prevailing root conditions would make absorption or transportation quite limited. So chelates are very important to the hydroponic gardener. They make life a lot easier for the plants and for us (no headaches!).

Now that we know a little more about chelates and micronutrients we come to the very important, but often overlooked, issue of element or formulation purity. So what is chemical element purity, and how can a consumer ensure this purity? To help explain this, let’s examine what makes a chemical pure or impure. We can then look briefly at a couple of different chemical grades or standardized chemical purity levels.

The most important factor that makes a chemical or element pure or impure is the relative amount of that element (or elements, in a compound) compared to other elements that are not required. For example, if a chemical, let’s say Phosphorus, is said to be 99.5% pure, this means it contains 99.5% of the required element (phosphorus in this case). The same would be true for a compound like Potassium Nitrate (which contains both calcium and nitrogen). It would contain 99.5% of the multiple elements. The remaining 0.5% would be made up of other elements that are present but not required (i.e. impurities).

It is these other non-essential elements that often pose problems for the hydroponic grower because many are toxic to plants, even in minute quantities. Some common impurities found in many chemicals are Lead, Mercury, Cadmium, Arsenic and Perchlorates. Perchlorates are extremely detrimental to the growth of particular plant species, even in the smallest amount. The other elements listed are all heavy metals. They slow the metabolic processes of the plants, thereby slowing the growth of the plant and hence the yield, which is definitely a very bad thing! This being said, it should be remembered that not all impurities have direct detrimental effects on plants.

As a consumer, the purity question can be overwhelming. Fortunately there are four types of chemical grades (standards) that put this information into perspective. These grades outline the types of chemicals many manufacturers of nutrients use, while clarifying the relative purity of these chemicals.

The four types of chemical grades we need to look at in hydroponics are Fertilizer or Industrial Grade, Technical Grade, British Pharmaceutical Grade and Laboratory Reagent Grade.

Fertilizer or Industrial grade is the lowest (worst). This grade is typically less than 90% pure and contains the largest amount of impurities.

Technical grade is better. It is typically around 90% to 95% pure, but it can still contain quite a lot of impurities, including detrimental elements.

British Pharmaceutical grade is the most preferable grade of material. It is approximately 99% pure, and it is tested to be free of any heavy metals and perchlorates. The standards for this grade are more stringent because these products are typically used in the manufacturing of foodstuffs and pharmaceuticals (which explains why the common slang name for British Pharmaceutical Grade is Food Grade).

Laboratory Reagent Grade is above 99.5% purity, but sometimes it does not undergo specific heavy metal and perchlorate testing.

Many manufacturers make their nutrient concentrates from fertilizer and technical grades because they are significantly cheaper (around one-quarter the price). Paying a little more for a nutrient that is formulated with high purity elements is quite often a wise and prudent choice for the hobbyist gardener who is concerned with the performance of his or her plants. Also, consider that any impurities will also have an effect on the measured conductivity of your made up solution. It will take a greater quantity of an element that contains more impurities to achieve the desired amount of that element. Simply, this means that you are unnecessarily raising your overall conductivity to achieve the correct element levels in your nutrient solution.

So, we can now see that chemical purity is very important. Those that say it doesn’t matter are either very ignorant or have something to hide. I think it would be fair to say, that if a company was using British Pharmaceutical grade chemicals in their product, they would be advertising the fact, given that they offer so many more benefits and cost so much more. Think about this next time you’re about to choose your nutrient product for use in your garden.

Case Study:

Why does my nutrient seem so much weaker now that I use a high purity brand?

Customers often ask this question when they start using a high quality, high purity nutrient brand. Let’s look at why the nutrient reads lower. We will then discuss whether this lower nutrient strength is a detriment or a benefit to your plants.

Firstly, if we remember our discussion on chemical grades we know that high purity grades, i.e. British Pharmaceutical, contain very few impurities. It will therefore take less of that element to arrive at the amount required for optimum growth and development.

For example, when Company A - a manufacturing company that uses high purity ingredients - adds 50 gms of Nitrogen to their nutrient concentrate, they would typically need to add 110 gms of Potassium Nitrate**(a compound element typically used to add nitrogen and potassium to hydroponic nutrient concentrates.) Another manufacturer that uses fertilizer or technical grade chemicals (Company B) would typically have to add 122gms of Potassium Nitrate to get the same amount of required nitrogen. Those other 12gms of unrequired elements are still going to show up on your conductivity meter.

Now we need to look at a plant’s rate of water/element uptake when the nutrient concentration goes much beyond 1300ppm. The amount of water that the plant can uptake when your nutrient strength goes much beyond 1300ppm is dramatically reduced (osmotic stress), especially in high light levels (higher still with CO2 enrichment), and temperatures of over 25 degrees. This is because the plant needs to transpire more when provided with optimal growing conditions (transpiration is the loss of water through the leaves, used to cool the plant from excess temperatures generated by its metabolic processes and the outside environment). To do this, the plant needs to take up more water, but by running a high ppm level the plant is now limited to how much water it can uptake (osmotic stress). It therefore limits its intake of nutrients and slows its metabolic processes to compensate.

Let’s look a little further now. Say we are using Brand X from Company B (lower grade ingredients), which, when made up according to directions, comes to approximately 1600 ppm in tap water. Compare that to the results of Brand Y from Company A (high purity ingredients), which comes to 1200 ppm. Now, both nutrients have a similar amount of mineral elements (check any nutrient bottle to confirm this), but the plants running on Brand X can only take up 40 to 60% of the water that the plants running on Brand Y can. This is because Brand X required more overall ingredients to arrive at the same levels of required elements, so it is now running at a higher ppm level.

Let’s say that during the day the plants running on Brand Y consumed 100 liters of nutrient solution (this is for ease of calculations only, and may not represent all situations). In the 100 liters of nutrient solution there was, for demonstration purposes, 25mg of copper. The plants running on Brand Y have taken up, in one day, 25mg of copper.

Now let’s look at the plants running on Brand X. Because their base strength is higher (1600 ppm), they can only take up approximately 60% of the water (nutrient solution) that the Brand Y plants did. This is due to the constraints of osmotic stress. Now, brand X also contains 25mg of copper per 100 liters of solution, but because of its base strength, the plants can only take up 60 liters of solution (60% of 100 liters). What this effectively means is that the plants on Brand X only took up 15mg of copper (60% of 25mg) in that same day.

Yes, that’s right, the plants on Brand X actually took up less copper at a higher base strength than the Brand Y plants did at a lesser strength! This will equate out for the rest of the microelements as well. Not only that, but the same holds true when comparing the major elements (i.e. nitrogen, calcium, potassium, phosphorus, etc.)

Remember this and think back to what was just outlined:

A good nutrient should be formulated to allow the plants to take up maximum nutritional value from the solution, provided those plants are growing with high light levels and temperatures of over 25 degrees (typical indoor conditions). The nutrient strength, therefore, must be relative to the environmental conditions surrounding your plants. As a rule of thumb, a well-constructed nutrient formula (when made up according to directions) should read between 900 to 1100 ppm on your conductivity meter, exclusive of the starting value of your water. If your nutrient solution reads much higher, then that will typically mean that you are either using a product constructed from lower grade ingredients or that the nutrient is not formulated correctly for typical indoor conditions. Either way, your plants will not be getting the amount of elements and water they require for maximum growth.

On a final note, you typically should not be running your plants on a nutrient solution much above 1300ppm (inclusive of the starting value of your water), even when using a good quality brand. Remember that more is not always better, and in some cases, more can actually mean less!

Well, class, that’s it for today’s lesson. In the next issue we will look at the root system of your plants and dispel some common myths. Until then, keep on growing, and go for that Maximum Yield!