And, there are surely others. Whatever the reason, here are some points to consider before getting started.
1. How many square feet will the growing area be? This impacts the number and size of lights, size and location of nutrient plumbing, electrical feeds and fans and size of conditioned water reservoir.
2.
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What growing systems will be used? This affects the composition, volume and frequency of nutrient refills to replace transpiration. In general, run-to-waste is not suitable for small system automation. It is best to stick with re-circulating or static systems.
3. Is management of pH required? This requires a sensor for each controlled system and components to dispense pH reagents.
4. Is management of nutrient conductivity required? This requires a sensor for each controlled system.
5. Is regulation of environmental factors such as temperature, humidity and/or CO2 important? The location must have sufficient power and drainage for heaters, air conditioners, humidifiers and dehumidifiers. This also affects the number of sensors and requires hardware to control the associated equipment.
While this may seem like a lot to consider, many of the items must be considered when setting up a manual hydroponic system. In manual systems, the sensors are pH meters, conductivity probes, thermostats and humidistats etc. The ‘control systems’ are single purpose devices such as timers.
Wouldn’t it be nice to have all these duties managed by a computer leaving the planning, administration and harvesting for the gardener? If you are considering automating your hydroponics system, please carry on reading.
Main growing area
The author’s garden is designed to use one 600 watt lamp creating a growing area 4 feet by 6 feet. Walls are lined with Mylar to capture as much light as possible and a seedling starting shelf with T5 fluorescents is attached. There are three types of growing system: static pots (capillary), aeroponics (spraying the roots) and Ein-Gedi (a combination of aeroponics and deep water culture). Nutrient management is common for the aeroponics and Ein-Gedi systems and is circulated through a pH and conductivity sampling chamber. pH and conductivity management are discussed in more detail later. Nutrients refills for the pots on the left do not require real time pH and conductivity control. Figure 1 is a photo of the main growing area. Notice the refill solution solenoids in the bottom left of the photo.
a
Figure 1: Growing Area
Seedling propagation
An integral component of a complete hydroponics system includes seedling propagation. For the author’s system, an ebb and flow seedling propagation area was constructed. T5 fluorescent light timing, ebb and flow cycles and nutrient replenishment are managed by the software. Seedlings are started in commercial plugs and transferred to the main growing system as appropriate. For the aeroponics and Ein-Gedi systems, seedlings are inserted into Styrofoam ‘donuts’ which are in turn inserted into mesh pots.
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Figure 2: Seedling system
Nutrient mixing and distribution
Figures 2 shows the nutrient mixing and transfer system. The foil covered bottles are a three part commercial nutrient, pH up and down reagents and pure water to flush out the dispensing tubes. A reservoir holding 70 liters of pH adjusted water is at the back. Because the nutrient mixing system is above the growing area, gravity is used to transfer mixed refills to the channels.
So, how does a refill get requested and processed. Each channel is fitted with a float switch that triggers after transpiration of a set quantity of nutrient mix. For this system, two liters is generally transpired each day by each channel. After receiving a request for a refill, two liters of water is transferred from the reservoir to a mixing vessel. Predetermined amounts of each nutrient component are added using an accurate peristaltic pump. The amount of each nutrient added is determined by the growth stage of the plants: vegetative, flowering or fruiting. There is a solenoid valve for each nutrient component that opens when required. After each component is transferred, the lines are flushed with pure water to prevent a reaction with the next component. An air stone stirs the mixture and it is transferred to the plant containers via another solenoid valve. The number of solenoid valves required is governed by the number of channels and nutrient components. One pump is required for the reservoir and one for the nutrients. One float switch is required for each channel, for the mixing vessel to signal when it is full and for the reservoir to signal when it is low.
c
Figure 3: Nutrient mixing and transfer system
pH Management
One of the most important issues in hydroponics is controlling nutrient pH. There are numerous theories, articles and postulations on the subject of pH. If one accepts that pH should be controlled within a narrow range for various plant species, it can be tedious to manage it manually. As a Chemical Engineer, I subscribe to the control approach. Automatic control is, therefore, a welcome addition to the system. There are two requirements for a pH control system: an electrode with a computer interface and a pH reagent dispensing mechanism.
Numerous pH electrodes are available for hobby and industrial use. These are connected to a computer using a pH transmitter. Earlier, the pH reagent bottles were shown as part of the nutrient mixing system. The nutrient mixing system doubles as a pH reagent dispenser. A small amount of water (50-100 m l) is pumped from the reservoir to the mixing vessel, pH reagent is added, lines are flushed and the mixture is transferred to the channel. One additional solenoid is required for each pH reagent. The control software for this function should have safety features to help prevent over compensation and oscillation between pH up and pH down doses. Large changes in pH over short time periods can prove detrimental to the health of many plants.
d
Figure 4: pH and Conductivity sampling chamber
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Figure 5: pH management graph
Conductivity Management
As with pH, there are many theories and practices relative to nutrient conductivity management. Some practices, however, tend to be commonly accepted. One such practice is to alter the conductivity of the nutrient for different stages of plant development. This is usually accompanied by a change in the photoperiod. Another is to maintain the nutrient concentration at a given level during a growth stage through addition of a refill solution as transpiration progresses. Unless one has access to a laboratory, it is not possible to know precisely what the concentration of each component of a nutrient solution is at any given time. Fortunately, most plants can tolerate a reasonable range of nutrient component concentrations. A scheme the computer can administer is to change the nutrient makeup from stage to stage. Using a conductivity electrode and computer interface, the nutrient concentration is continuously monitored. When the nutrient volume is depleted by a set amount, the concentration of the refill formula is calculated using the currently measured nutrient reservoir concentration. In this way, it is possible to avoid totally exchanging the nutrient on a periodic basis. Unlike pH, the operating range for conductivity is less critical. Adjustments do not need to be made on demand but can wait until a refill is required. Frequency of refilling can be changed by modifying the volume added on each refill.
f
Figure 6: Conductivity management graph
Timers
Timers are an indispensable part of hydroponics systems. At the very least, one is required for the main light. Others may be required for nutrient pumps, fans etc. Mechanical and standalone electronic timers offer limited flexibility for frequency and length of cycles. Computer managed timers provide much more flexibility to an automated garden. There is no practical limit to the number and/or duration of on/off cycles (within the constraints of the attached device). Light cycles can be progressive mimicking Mother Nature’s sunrise/sunset anywhere on the planet. And, there is no need to physically reset timers after power outages. With a suitable uninterrupted power supply for the computer, cycles will be resumed automatically when power is restored.
Conclusion
Automating a hydroponics setup is rewarding and can add to the pleasure of the hydroponic gardening experience. The data gathered by the computer can be studied, analyzed and used to continuously improve subsequent growing cycles. Hardware and software is now becoming available. As set out earlier in the article, automation is not an all or nothing proposition. With a little planning and careful selection of components, the system can be built as time and economics allow. If DIY help is required to hook up some of the components, everyone has a friend who can help. Who knows, they may like the challenge and take up hydroponics gardening themselves. Automated systems will increase and everyone will benefit from new discoveries.