A Hydroponics Primer
Hydroponics, plant cultivation without soil, comprises a variety of growing techniques that is scalable for everything from commercial farms to home gardening. Properly grown, hydroponic produce can compete with field grown crops in appearance, nutrition and taste. In addition, it is a resource-efficient production method that is likely to become a key, if not essential, agricultural system in a world with a hungry, growing population and less available acreage for food production. For the home gardener, hydroponics can be a fun hobby that enables us to garden year round, while helping us better understand some of the below-ground mysteries of soil based gardening.
It is oversimplistic to think of hydroponics one-dimensionally because it encompasses techniques as varied as rooting a cutting in a vase of water to large scale, multi-level, fully automatic environmentally-controlled commercial operation. But regardless of scale, the practices share common techniques and benefits.
Commercially, hydroponics is potentially very sustainable. Growing operations can be located in urban centers, close to markets, eliminating cross country transportation of crops with its attendant carbon footprint. Water can be recirculated, reducing consumption by as much as 90% vs. field growing, thus enabling successful farming even in water-starved desert areas. With proper hygiene, the elimination of soil dramatically reduces the risk of soil borne pests and diseases. Plants are fed using scientifically determined, grower-measured nutrients in solution. There is no problem with over- or under- fertilization or runoff.
Without soil, weeding is a non-issue, eliminating a headache for the home gardener and reducing controversial herbicide use on the farm. In addition, because hydroponic installations can be multi-level and operate year round, output potential per unit area is several times greater than for outdoor soil-grown crops.
There is an ongoing debate about the nutritional and taste characteristics of hydroponic produce compared to soil-grown products. The prevailing opinion is that nutrition is a function of what the crop is fed while growing. Hydroponic systems provide a known and optimized formulation of macro and micro nutrients, and studies have shown it to be equal or even superior to soil-grown produce when properly managed.
The logic is similar in the taste debate, with the potential advantage of picking commercial crops that are locally grown, at a later stage than if the product must be transported long distances to reach market. There is research underway that aims to directly address taste and other characteristics, including health-promoting “bioactive” qualities by finding ways to more closely match a plant’s soil-grown experience hydroponically. For me, for now at least, the jury is still out on home grown summer tomatoes, but otherwise, in my limited experience, hydroponic produce holds its own on taste as well.
In any case, hydroponic food production has many merits and a lot is happening to build on them. At least one respected market research firm placed worldwide hydroponic production at over $21 billion in 2016, growing at a respectable rate of 6.5%. Related research claims that 12% of US tomato production is already grown hydroponically. A google search of anything related to hydroponic growing will yield a long list of books, articles, videos and supplier ads explaining and peddling hydroponic techniques and products. Soilless agriculture is definitely here to stay.
How is it Done?
The common basis for hydroponic growing systems is that there is no soil; instead, plants are supported mechanically or in an inert growing medium. Plant roots are exposed to nutrients carried to them by water in the form of a thin film or stream, a wicking system, an aerated nutrient pool, a flooded and drained tray or a spray. Here are some popular system concepts.
Water Culture: Floating Raft System
Photo courtesy of: hydroponics.name
A basic system used for lettuces, greens and herbs, water culture systems place plants in an inert growing medium in perforated pots, mounted in a styrofoam raft, floating in a nutrient bath. Note that the solution needs to be aerated, manually with a whisk or via an air pump, to provide adequate oxygen to plants. Limited oxygenation restricts this method to short growing cycle crops. It is not suitable for longer season and vine crops.
Nutrient Film System (NTF):
In NTF systems, plants are supported in a growing medium within a trough. A constant flowing thin film or stream of nutrient solution is pumped from a reservoir into the trough. The solution passes through the medium into contact with the plant roots. The trough is angled to use gravity to move the solution back to the reservoir or into a separate container for other use.
Photo courtesy of: homehydrosystems.com
Wicking systems are simple and don’t require power. They are a popular classroom system for this reason. The plant tray is positioned close to and directly above the nutrient reservoir, to minimize nutrient and moisture transport distance. One end of the wick is in the nutrient reservoir, the other in the growing medium. Solution is transported by capillary action. This system is best for smaller, non-fruiting plants with lower moisture and nutrient requirements.
Ebb and Flow or Flood and Drain Method:
Photo courtesy of blogs.cuit.columbia.edu
Plants are supported in an inert medium, in a level tray. Nutrient solution is pumped into the tray, flooding it for a period of time, then allowing it to drain back to the reservoir. The cycles are typically automatically timed and intervals vary by system and plant.
Photo courtesy of: verticalfarm.altavista.org
Rather than bathe plants in solution, aeroponics periodically mists plant roots with nutrient solution. Plants are supported mechanically or in an inert medium while roots are allowed to grow down toward the misting nozzles.
Drip or Trickle Feed Systems
Drip feed systems pump nutrient from a reservoir through small tubes that provide a regular drip irrigation to plants supported in an inert medium. Excess can be recycled and air is pumped into the reservoir to keep the solution aerated. It is important to prevent water pooling at the trough bottom to prevent root rot. Choice of medium should be based on the plant’s drainage preferences.
Choosing a Hydroponic Technique
The crop to be grown is key to determining which system is most appropriate. Lettuces, arugula, bok choy and basil, for example, which have a crop cycle of 1 to 2 months, can be grown in a water culture system. Longer term crops like vining crops and plants that like sandy or well drained soils need a system that regularly drains nutrients and exposes roots to air. Ebb and Flow or Drip systems are more appropriate for these crops. Aeroponic systems can be effective for many crops; however, they are more complex to manage and require a higher process management commitment from the gardener.
There are a variety of soilless growing media used in both seed germination and in hydroponic growing systems. Their common characteristic is that they are inert or very slow to decompose to avoid affecting the nutrient delivery while providing a support structure for the plants.
Most gardeners are familiar with soilless media used for seed germination. Peat, vermiculite and pearlite are typical and these materials are also used in hydroponic applications. Other inert, or slow-to-decompose materials like rock wool, coconut fiber, and a lightweight expanded clay aggregate called “grow rocks” are also widely used. The best choice depends on the hydroponic system, the plants to be grown and medium characteristics like moisture and nutrient holding capacity, aeration, particle size and wicking action. Descriptions of these media and their characteristics are available on line or from hydroponics suppliers.
Options for providing nutrients range from establishing a chemistry lab in your home to purchasing pre-made mixes from a hydroponics supplier. I recommend the latter to start. Purchased solutions must cover the 6 essential macro and 8 micro elements needed by plants. There are different blends for different plants as well as customized blends for vegetative vs fruiting plant stages where appropriate. There is also widespread research underway that attempts to simulate soil-based growing, without sacrificing the precise nutrient delivery of hydroponics. The goal is to optimize the nutrient and flavor quality of hydroponically-grown products. For the beginning home gardener, a standard solution, chosen in consideration of the crops being grown, makes sense. Controlling the nutrient concentration of the reservoir is essential. An electrical conductivity meter is the tool used to accomplish this task.
In addition to the essential nutrients mentioned, plants require water, light and air.
Water used in hydroponic systems must be high quality. Processed city water is generally satisfactory. Reverse osmosis or distilled water is great. Sophisticated home systems may include a filter. The pH of the nutrient solution as well as the growing medium will require use of a pH meter to help keep it in the preferred range for the crop to be grown, generally in the 5.5-6.5 range.
Light is sourced from the sun for outdoor installations or from grow lights for indoor systems. LED lighting is very popular now because of the ability to optimize color mix, the relatively low investment cost, and efficiency.
Air is important both above and below the plants. Aerating the nutrient solution and/or providing appropriate aeration to plant roots is essential. Nutrient application cycles and growing medium choices are central to getting this right. Above the roots, the issues are similar to soil based gardening. Good air circulation and plant spacing both come into play. Inside and in greenhouse environments, air movement, temperature and humidity management are important for plant growth and to minimize the likelihood of insect and disease issues. Fully environmentally- controlled systems account for all these factors. Up-front investment is a function of system sophistication. Thus, higher-priced units automate many of the otherwise manually-controlled factors that influence success or failure of the crop.
Getting Started at Home
Researching this topic was an eye-opening experience, especially discovering the quantity and variety of information and equipment that is available to prospective hydroponic gardeners. The options range from youtube videos showing DIY possibilities to simple herb-growing systems to backyard greenhouses to fully environmentally-controlled furniture-like indoor “hydroponic appliances. ” The home gardener has a multitude of possibilities for taking up the craft.
If your head is spinning from all the possibilities and process management requirements, relax. It is easy to start small with an inexpensive purchased system and packaged supplies to grow greens or herbs and learn as you go. Hydroponics system and material suppliers are happy to answer questions and offer guidance. There is little doubt that the prospect of enjoying fresh, chemical-free, locally or home grown produce and vegetables, year round, will drive the growth of hydroponics. The question is whether we, as individuals, will be buyers or growers.
Hydroponics for the Home Grower, (Howard M. Resh, CRC Press, 2015).
“Home Hydroponics,” Va.Coop.Ext. ext.vt.edu/Pub.426-084.
“Types of Hydroponics Systems,” www.soilless.org/hydroponics/types
“Are hydroponic vegetables as nutritious as those grown in soil?” https://well.blogs.nytimes.com/2016/12/23/are-hydroponic-vegetables-as-nutritious-as-those-grown-in-soil/
Thanks to Babylon Micro Farms, Charlottesville, VA, for the facility tour and explanation of their proprietary “hydroponic home appliance” system.