The definition of hydroponic gardening is that no soil is used. Therefore all nutrients need to be provided directly through the nutrient solution. This has the advantage of being able to completely control what nutrients are accessible to the plant and in what quantities. Luckily for those of us who don’t have the time or knowledge to make our own nutrient solutions, they are readily available from hydroponics suppliers and online. Nutrient solutions typically come in combinations of two or three concentrate bottles. This is because certain minerals can not be combined in high concentration because the precipitate.
The main components of hydroponics nutrients are calcium, magnesium, potassium, nitrate, sulfate and phosphate. Many micronutrients are also present such as iron, manganese, copper, zinc, boron, chlorine, nickel and molybdenum. Nutrient solutions can also come in single bottle concentrates, which contain chelating agents to keep the iron soluble.
The concentration of nutrients needs to be maintained at a certain level. This is easily monitored with a handheld meter that measures the concentration of minerals in water (measured in parts per million; ppm). With the nutrient solution that I use, a concentration of about 1,000 ppm is ideal. With time, plants use up both nutrients and water. If both nutrients and water are used up at the same time, the volume of water will drop but the concentration of nutrients in the water will remain the same as they are being used up at the same time. If not as many nutrients are being used, for example when plants are still young, the water will be used up more quickly than the nutrients and the concentration will increase. The opposite occurs when plants are growing strongly and require a large amount of nutrients. Regular monitoring and correcting concentration by either adding more nutrients or water keeps this under control. After a reasonable period of time, nutrient solutions need to be completely replaced. This is because individual nutrients e.g. nitrogen would be used up from the solution, even though the overall concentration may be stable. It is recommended that nutrient solutions be replaced every 1-2 weeks. I replace mine every 2 weeks.
The other important aspect of nutrient solutions is pH – the balance between acidity and alkalinity. The importance of pH is in the ability of plants to absorb nutrients. Each mineral is absorbed by plants within a certain pH range. The optimal pH range for absorption of most nutrients is between pH 6 and 7 (see Figure 1). The graph shows that movement away from this pH in either direction results in greatly reduced availability of many nutrients, which results in sub-optimal plant growth.
Figure 1. pH and nutrient availability
Plants also have pH ranges within which they grow best. The ideal growth pH ranges for a selection of plants varies between pH 5 and pH 8 and is shown in Figure 2. For most plants, a pH of 6 is within the ideal range. This is the pH that is recommended by most hydroponics gardeners, and is what I use in my hydroponics systems.
Figure 2. Ideal plant pH ranges
For those gardeners that want to get into the nitty gritty of making their own nutrients or tinkering with compositions, free nutrient calculators can be found with an online search. While it is possible to make your own nutrient solution, the large range of commercially available solutions means that there really isn’t a need for gardeners to go into this level of detail. I have never tinkered with the composition of nutrient solutions, other than to change pH.
Pavel Sluka is the owner of Hydroponics Habitat. You can visit his website at HydroponicsHabitat.com.