Hydroponic Nutrients and Mediums
Setting up a hydroponic system can be fairly straightforward. Growing the plants and managing the system present much greater challenges that take time and experience to master. Balancing nutrient solutions, pH, and EC can be difficult. There is a wide array of ready to mix nutrient solution concentrates available. Nutrient solutions can also be custom made by mixing stock solutions of the individual components.
Nutrient Solution Composition
Nutrient solutions generally contain nitrate, dihydrogen phosphate, sulfate, potassium, calcium, and magnesium. These ionic nutrients must be balanced to maintain a pH of 5.5-6.5 in order to be absorbed by the roots of the plant. The plant’s rate of nutrient and water uptake will be affected by the amount of oxygenation applied to the roots or growth medium. Most nutrient solutions use synthetic nutrients. Because hydroponic systems do not contain the soil microorganisms that convert natural nutrients to sources that can be used by plants, a form of the nutrient that can be readily utilized must be supplied. Refined natural nutrient solutions are gaining popularity, but most hydroponically grown plants are not cultivated organically.
Most nutrient solutions are labeled with N-P-K ratios that represent the proportion of nitrogen to phosphorus and potassium, the three major nutrient elements. More important than the actual N-P-K numbers is the ratio of the nutrients. Concentration should be increased as the plant matures, but ensuring that the plants in the vegetative growth phase are fertilized with a nutrient mix that has ½ to ⅔ the concentration of phosphorus to nitrogen is even more important. A nutrient solution or combination of solutions with an N-P-K ratio around 7-5-5 would be appropriate and can be diluted less to increase concentration. Flowering plants have more need for phosphorus that is used to develop flowers and resins, than for nitrogen which fuels overall plant growth and biomass production. Nutrient mixes with half the concentration of nitrogen to phosphorus, such as a 3-10-10 solution, are best for floral growth in the plant.
Different strains of the plant will have slightly different nutrient preferences and cultivation times. In general, plants will complete their growth and flowering within 9-13 weeks of hydroponic growth. Most manufacturers of nutrient solutions provide feeding schedules and mixing guides for growers to use.
Adjusting and Monitoring pH and EC
Measuring and monitoring can be done using a pH meter and EC meter. The electrical conductivity (EC) will measure the concentration of nutrients in the water, and the pH will measure the acidity or alkalinity of the solution and water. A TDS (total dissolved solids) meter can also be used to measure the nutrient solution in parts per million (ppm) but EC is a more standard measurement. For the plant, an EC reading of 0.8 to 0.2 is ideal for the plant’s young life cycle, with levels increasing with maturity. An EC of 2.0 would correspond to 1000 ppm and represent the range of nutrient concentration for floral growth in a mature plant. EC can be converted to ppm by multiplying the reading by 500 or 700 depending on which of the two ppm scales is being used.
Increasing or decreasing the nutrient solution concentration will alter EC. To adjust pH, a solution like pH Up or pH Down can be used if it falls out of range. Some growers choose to regularly adjust pH to a certain number, but most adjust only when it falls outside of the desired range (5.5-6.5). Most hydroponic nutrient solutions recommend fully changing after 7-10 days and topping off lost water volume daily. The best time to adjust pH is during the weekly solution change. There is little need to correct it day-to-day.
Soilless Growth Mediums
Some hydroponic growth mediums have mineral properties that can alter pH and EC. If rockwool, perlite, or coir are being used additional adjustments may be needed. Calcium and magnesium levels can be especially influenced by coir. Since the coir will readily take up calcium and magnesium before it can reach the plant, it is usually necessary to increase levels in the nutrient solution significantly to ensure plants do not become deficient. By ratio, coir will absorb calcium and magnesium at about twice the rate of sodium and potassium. Monitoring calcium and magnesium levels in the passed nutrient solution will let growers know if more supplementation is needed and indicate when the coir has reached holding capacity and levels can be decreased. The coir should be fully buffered when ~100 ppm of calcium can be detected in the drainage. Pre-buffered coir can be used to reduce the need to significantly adjust nutrient levels. Growers who are new to hydroponics may opt to start with inert mediums like clay balls to avoid these concerns.
Precautions for Hydroponic Systems
It is always important to make sure growth medium and growing systems are sanitized before use. Likewise, distilled or reverse osmosis purified water should be used and filtered in recirculating growth systems. Along with algae, oxygen and nutrient depletion, and flow disruption, hydroponic systems can be threatened by pathogens like the pythium fungus. Pythium is a major threat in warm climates where solution temperature is maintained under 25°C. Some root death will occur naturally as plants mature and flower, but early or excessive root death is another problem that hydroponic growers must be observant of.
Common Soilless Mediums
- Coco coir
- Rice hulls
The innovation of plastics significantly advanced hydroponic cultivation by making it affordable and eliminating the need for concrete tanks and beds. Technological innovation in developing pumps, timers, plumbing, and other equipment further advanced hydroponics by automating systems which further reduced costs and labor involved in growing plants hydroponically. Today’s hydroponic greenhouses can be highly automated for environmental control and robotic harvesting and transplanting. Greenhouses in arid regions may even combine their hydroponic systems with desalination units to allow sandy land to be farmed hydroponically.
Benefits of Hydroponic Greenhouse Production
Virtually any plant can be grown using hydroponic methods. Adjustments to types of nutrient solutions and rooting mediums can be made to cater to particular plants. Some common hydroponic crops include strawberries, celery, tomatoes, cucumbers, peppers, lettuce, herbs, and other leafy greens.
- An alternative for plant production in locations with poor soil quality that will not support cultivation
- Hydroponic greenhouses are an option in areas prone to environmental pests or diseases that would reduce production
- Hydroponically grown plants, especially vegetables tend to be larger and produce more biomass
- Some plant species are bred exclusively for hydroponic greenhouse production and cannot survive outdoor conditions
- Hydroponic greenhouse species are often also bred to resist pathogens
- Increased control over pH and nutrient application and more efficient nutrient use with no loss of nutrients to leaching
- More efficient use of water than growing in soil (depending on site conditions)
- Higher planting density and yields per acre
Disadvantages of hydroponic cultivation include high initial costs of equipment, the potential for pathogens like fusarium and verticillium, and complex nutrient problems. While manual labor is somewhat reduced, hydroponic growing requires more technically skilled labor to care for crops. Growers must be knowledgeable in nutrient use, formulation, and signs of deficiencies. Oxygen levels can also create complex problems in hydroponic systems, requiring care and monitoring that plants do not become waterlogged. Advances in disease-resistant plant varieties and devices for monitoring and testing nutrients have helped to address these issues and make hydroponic cultivation a more attractive option.
Hydroponic Plant Roots
Roots of hydroponic plants may not have root hairs like normal plants. Because nutrients are so readily available, large and hairy root systems are not needed to scavenge for water and nutrients. Since root growth requires the plant to expend energy to the roots instead of the aerial plant, it can be a disadvantage for hydroponic plants to put lots of energy into root growth. Large root growth can also compromise hydroponic systems by blocking drainage and disrupting solution flow.
Hydroponic plant roots need to be kept between 20°C and 30°C. Temperatures below 20°C will induce undesirable morphological changes like increased branching and thickening of the roots. Oxygen balance is also essential to prevent root death. At high temperatures, oxygen does not dissolve well in water, and the plant’s need for oxygen increases. To avoid starving the plant of oxygen, the nutrient solution needs to be bubbled to aerate it, or a sufficient portion of the roots must be left exposed to the air.