Sanitation
Growing with hydroponics means making time to start cleaning. The best environment for hydroponics is a clean one. Dirty growing environments equals problems. to get the best yield from your crops and minimize problems for your plants.
Clean, Clean, Clean and then sanitize with at least a 10% solution of bleach and water, then rinse well with good water. Hydrogen peroxide is also an option for sanitizing hydroponic systems and has the same function as chlorine in hydroponics–that is, it kills undesirable organics, but goes into the atmosphere from a liquid in about 2 hours and leaves no residue in the water; the same cannot be said for chlorine, which is residual and may harm plants if the concentration is too high.
Problems can spread rapidly through a hydroponics growing system. Sanitizing all equipment between crops can save a lot of trouble with bacteria and viruses which can spread through the whole crop in a very short time.
Keep pets and pests both away They can introduce contaminated particles of organic matter as well as physically damage the plants.
Loose dirt and wind blown organic matter can also cause plants problems.
All piping must be kept clean by periodic pumping of the water/hydrogen peroxide mix, all debris must be removed, the reservoir must be cleaned with the water/hydrogen peroxide mix and brushed when the nutrient is replaced.
Nutrient solutions are salts which will build up in vessels, piping and tubing they need to be flushed regularly.
Rotting plant material (roots, stems, leaves, and flowers) makes an ideal environment for pathogens and pests, so no dead plant material should be in the grow area. If there ever is an infestation of insects or pathogens, all plants must be removed and the system cleaned thoroughly before starting new plants
Bacterial and Viral
Bacterial and viral diseases can spread very quickly throughout a system, especially if a closed system is being used, where nutrient solution is recirculated. Although UV and ozone water purifiers can be used in hydroponic systems, they can be very expensive and have adverse effects on the minerals in the solution. If raw, incoming water is from a contaminated surface source, UV and ozone treatment may be necessary to assure pathogen-free source water. If using ozone time must be given for the ozone to dissipate before adding nutrients.
Basic sanitation is necessary for “Workers” , clothing and shoes which should be free from soil and other contaminates; shallow trays of bleach solution for workers to clean off their shoes before entering the growing areas. Sanitree suits are an option for added protection. Hands and tools must be cleaned regularly to prevent spread of disease. Smoking or chewing tobacco must be strictly forbidden, and workers should wash their hands after handling tobacco to prevent transmittance of viruses.
Insects
It is commonly assumed that hydroponic agriculture systems are relatively free of insect pests and plant diseases because the technology is mostly enclosed. Unfortunately, this is not true. Pest populations can increase with alarming speed because of the lack of natural environmental checks.
The frightening ability of some insects to develop resistance to pesticides has revived worldwide interest in the concept of biological control: the deliberate introduction of natural enemies of pest insects, particularly when used in association with horticultural practices, plant genetics and other central mechanisms.
Climate
It is nearly impossible to create a complete climate control, what is most important is to have air flow around the plants. Plants have been around for a very long time and tend to take care of themselves with a bit of aid they can be made to produce very efficiently.
Good circulation is necessary for proper cooling, heating, CO2 replenishment, and removal of undesirable gases, such as ethylene. Your circulation system must work together with your heating, cooling, and CO2 systems in order to obtain peak efficiency.
Many different methods of circulating air have been developed. The vent-tube system is used quite a bit, and consists of a fan-jet connected to a perforated plastic tube running the length of the greenhouse at ceiling height. The fan forces air through the tube, which moves the warm air in the roof space downward to displace the cooler air at the floor level.
A horizontal airflow system is more efficient, and can move a larger amount of air around the plants. Large fans, hanging above the crop, are set up facing one direction in one section, and in the opposite direction in the adjacent section. A more complicated system is a vertical airflow system, which uses fan-jets to move air along the roof, downward at the end walls, then along the floor through the crop. This system provides the best mixing of air and brings warm air down into the plants.
There are a number of layers of air in a green house, depending on the temperature and the moisture held in the air. Micro climates are also formed by the plants. Ideally you want to move the air though the plant giving the plant plenty of co2 and removing the moisture been transpired by the plant, keeping the plant either warm or cool depending on the conditions.
Generally speaking cool moist air will be at floor level this is where the root zone should be, keeping the root zone cool where less evaporation occurs. The lower the better it is for the root zone.
When using a forced air system you have to treat your incoming air either by heating or cooling to give the right amount of air exchange that is required.
The vents can then be controlled the windward vents closed completely leaving the leeward vents slightly open to allow the system to vent (to breath).
The best way to get air to flow around a plant is to blow dry cool or heated air upwards around the plant not the root zone creating a circular motion of air around the plants. In other words if you were heating you would suck air from the roof space and blow it upwards around the plant, if cooling you would suck air from the floor space. This would be the most efficient method as natural air flow due to moisture content and temperature would aid the air circulation process
This is not always practical as the ducting and cooling/heating units require a lot of space thus limiting plant access. They will be bumped into and damaged creating a lot of maintance. Also having fans which require electricity at floor level where water is present creates a danger for workers.
The only viable option is to place the ducts and cooling/heating units at ceiling height and force air downward then sucking air upwards keeping a circular motion of air flow.
Humidity is generally taken care of by the circulating air flow and by the cooling or heating units. Air exchange also will effect the humidity levels.
Screens do not play a major role when heating but when cooling is needed they can play a major role. They need to be employed as soon as radiation reaches a certain level or if there is a rise in temperature. They will help in forming a buffer zone keeping hot air above and letting the hot air from below passing though and forced out.
Roof sprinklers can play a major role in achieving a lower temperature at night. Using roof sprinklers during the day can be wasteful as a lost of water due to evaporation can be costly. If used at sunset the system can be cooled quickly to help in achieving a lower night temperature and less water is wasted.
It is near impossible to create a complete climate control, what is most important is to have air flow around the plants. Plants have been around for a very long time and tend to take care of themselves with a bit of aid they can be made to produce very efficiently.
Temperature
Temperature - The amount of thermal energy. In a gas like the atmosphere temperature is a measure of the average speed of the molecules. Scientists would say temperature is a measure of the average Kinetic Energy of the molecules. The faster air molecules move, the more kinetic energy and the higher the temperature.
Both day and night temperatures influence plant vigor, leaf size, leaf expansion rate, and time to fruit development. Under low night temperatures, the rate of leaf growth is slower, and leaf size is reduced in young plants. Day and night temperatures should be carefully monitored. A general rule of thumb for most horticultural crops is for night temperatures to be approximately 5.5° C (10° F) lower than day temperatures. For most plants, day temperatures should be 21° -26° C (70° -79° F) and night temperatures around 16° -18.5° C (61° -65° F), although many new varieties do best with little difference between day and night temperature (check with your seed company for recommended growing temperatures). For seedlings, the temperatures should be constant, 20° -22° C (68° -72° F), then gradually acclimate the plants to the diurnal temperatures before transplanting.
Optimum temperatures for the crops you are growing are 16-28 deg. C (a little higher for peppers than for tomatoes), with plant stress becoming notable at around leaf temperatures of 32-34 deg. C and above.
With good air movement, and healthy plants being given sufficient water and at a correct EC, the plants will transpire and cool themselves so that temperatures in the canopy are often much lower than that outside.
So, while outside temperatures may be 34 deg. C (90 deg. F), the canopy should be lower than this and the plants growing well. Its a good idea to invest in an infrared thermometer that you can use to measure leaf temperature directly and use this as your guide rather than outside temperatures.
If the leaf temperatures on your plants are higher than the air temperature in the system, this indicates the plant is under thermal stress and has shut down photosynthesis.
Ideally, the leaf temperature should be 1 -2 deg. C lower than the air temperature indicating the plant is photosynthesizing, transpiring, and therefore cooling itself.
High temps in excess of 30° C to 35° C will cause many different types of damage to the plants, such as inhibition of growth and even death. The physiological nature of heat damage is thought to involve a de naturation of some protein component of plant cells. Fruit abortion may occur at these temperatures as well. Temperatures lower than optimum will alter the plant metabolic systems to slow growth and again hinder growth and yeilds.
While the solution temperature of 80 deg. F is acceptable, you will need to be careful for the plants to have a very high water demand under high temperature conditions. When this occurs, the plants can remove a great deal of water from the nutrient solution, thus concentrating the nutrients and increasing the electrical conductivity (EC) to levels that will stress the plants and cause a number of growth problems.
Running the EC fairly low in high temperatures is a good idea and keep a constant check on the EC in the root zone (in the media surrounding the roots, rather than in the solution reservoir).
It can be difficult to keep EC levels at the correct range when the plants are taking up a great deal of water one day and a lesser amount the next day.
During high temperature the irrigation solution temperature can rapidly reach a high level which can cause the solution to hold less oxygen. This can cause serious oxygen deficiency which in turn can make plants susceptible to root diseases, such as Pythium.
Also, keep a check on the temperature in the media around the root zone during the warmest part of the day (in fact, monitor this over several hot days) to check that the roots are not "cooking".
During high temperature 12 hours a day of good light levels and reasonable temperature control is fine for the plants you are growing. It would not prove to be economical to provide supplementary lighting for another 2-4 hours per day as the cost would not be paid back in extra yield and you would need to supply a very high intensity lighting system.
During high temperature CO2 enrichment would not be practical either as you will need to keep constant ventilation and continual air movement through the crops so that moist air is removed and humidity levels kept down below 90 percent (to prevent many fungal diseases). CO2 would be rapidly lost to the outside. CO2 will be constantly replaced if the ventilation system is working well, so the plants will not suffer from CO2 depletion.
Under high temperature conditions, it is likely that even if you could enrich with CO2 to over 1,000 parts per million (ppm), that this would not give a large increase in yield (CO2 enrichment is more beneficial under winter conditions).
Fogging systems can be an alternative to evaporative pad cooling. They depend on absolutely clean water, free of any soluble salt, in order to prevent plugging of the mist nozzles. Like fan and pad cooling, fog cooling is only really efficient in low humidity environments.
Temperatures can be measured easily with a minimum/maximum thermometer. Several thermometers should be placed throughout the greenhouse, and should be calibrated against each other and a quality thermometer at least twice per year. In large commercial operations, computer controlled systems are common. Such systems can provide fully-integrated control of temperature, humidity, irrigation and fertilization, carbon dioxide, light and shade levels.
Humidity
Humidity refers to the amount of water vapor in the air.
In order for a plant to actively grow, it must be allowed to transpire freely during photosynthesis; this means plenty of available water, low to moderate humidity, and good air circulation. Humidity influences calcium uptake and hormonal distribution by controlling transpiration, ion pumping, and stomatal opening and closing. High humidity coupled with low air movement reduces transpirational cooling, and can lead to heat overload for the plant.
People tend to think of humidity in terms of relative humidity, which is the ratio of the amount of water vapor in the air to the amount of water vapor the air could hold at that temperature, expressed as a percent. Plants, on the other hand, perceive humidity in terms of vapor pressure deficit (VPD). VPD is the difference between the vapor pressure in the air and the vapor pressure inside the leaf. Water moves by diffusion from the roots through the plant and out the leaves as transpired vapor, thereby being "pumped" up the plant as the vapor moves from the higher pressure inside the leaf to the lower pressure in the surrounding air. Low VPD (high humidity, greater than 80%) is often responsible for nutrient deficiency symptoms, such as blossom end rot (calcium deficiency) because the plant is not transpiring, therefore it is not drawing water, or nutrients, into the roots. High VPD (low humidity, less than 50%) can also lead to the same symptoms, because water and nutrients are pumped too quickly through the plants, depositing nutrient ions in the leaves rather than properly in the fruit.
Humidity can be measured with a sling psychrometer. Other equipment such as a humidistat can measure relative humidity to an accuracy within 4%.
Most plants can function adequately in relative humidity’s of between 55and 80%, which corresponds to VPD’s of 1.0 to 0.2 kPa. For tomatoes, the ideal humidity should be between 65 and 75% during the night and 70 to 80% during the day. Tomato yields and fruit quality are lower at lower VPDs (higher humidity). Leaf size can also be reduced, and flower and fruit abortion can be significantly increased under high humidity conditions. Glassiness and "gold fleck" in tomato fruit is also attributed to high atmospheric humidity.
Relative Humidity.
Do not allow relative humidity to drop below 50 percent. Low humidity causes dry pollen, excessive plant transpiration and water stress. Where resistant varieties of plants are used, overhead fine mist nozzles coupled to a hygrometer can help keep relative humidity high. The nozzles should apply a very fine mist that does not wet the plants
Misting and fogging systems are used by some growers to increase humidity and decrease temperatures. However, if used improperly, these systems can greatly increase the incidence of mildews and plant diseases, not to mention corrode metal structures.
Since 1802 when John Dalton demonstrated that air is a mechanical mixture of gasses we have known that air in no way "holds" water vapor. Being a mechanical mixture of gasses means the molecules (nitrogen, oxygen, carbon dioxide, water vapor and others) merely occupy the same space. In a large jar containing marbles of 5 different colours, the blue marbles do not hold the red marbles and the red the yellow, the marbles of different colours just coexist in the jar.
This is a bit misleading because in the jar the marbles are stacked on top of each other, in the atmosphere there is plenty of space between molecules so most of the space is mostly empty space. So if anyone asks you what the atmosphere is mostly - it is mostly empty space.
Oxygen and nitrogen alternately do not have "hook & loop" areas or little hands to grab and hold water vapor molecules. It comes down to energy.
A liquid water molecule evaporates from a body of water or from the sweat on your skin if it gains enough energy to break free of the attractive forces holding the molecule to neighboring water molecules. The energy comes from collisions with neighbors and if a molecule gains enough energy it can rocket free of the water. The liberated molecule is then water vapor zipping around with zillions of other molecules in the air.
It has nothing to do with a magical power of the air molecules above. In science there is no magic, nearly everything when investigated at a fundamental level is elegantly simple, rational and quite amazing.
There is always plenty of space between air molecules for water vapor molecules to fit. If we imagine oxygen and nitrogen molecules enlarged to about the size of two joined tennis balls at sea level and about 50°F (10°C) there is an average distance of about 4.75 feet (145cm) between air molecules.
It is important to realize that the molecules are zipping around in all directions at hundreds of miles per hour and many collisions are taking place all the time. If a "snap shot" is taken at an instant in time and all the distances measured the average inter-molecular distance between tennis ball size molecules at sea level will be 4.75 feet. (145cm). Even at 50°F (10°C) there is plenty of room for more tennis balls to fit. When the air is heated to 80°F (27°C) the average distance between the tennis-ball size molecules increases to about 5.5' (168 cm), not a great increase in average inter-molecular distance. NERGY
When thinking of humidity always think in terms of energy and there is only so much energy to go around and not all of it is available to do the work of evaporation. The remainder goes to the other molecules in the air - each gas in the mechanical mixture gets its fair share.
There is a connection between humidity and air temperature, but the connection has nothing to do with warm air "holding" more water vapor. Think of air as a kinetic energy delivery system. Warmer air moving into a region has more thermal energy than the air it is replacing. At the molecular level we say the average kinetic energy of the molecules is greater in the warmer air and the thermal energy of the warmer air is transferred to water molecules as the faster moving air molecules collide with the slower molecules in the water. The faster moving air molecules lose energy and the slower moving water molecules gain energy and begin to move faster and collide with each other more violently. Some of the water molecules will gain enough kinetic energy ( or speed or thermal energy - all three are the same) to escape the liquid and become a free moving gas molecule. If the newly arriving air is colder the opposite occurs.
A liquid molecule of water is closely surrounded by many others, all moving about, twirling, swirling and gliding around each other in an incessant dance. Almost all the kinetic energy a liquid molecule needs to evaporate is gained from collisions with its surrounding liquid neighbors.
Air does deliver some thermal energy to the liquid, but because the number of molecules (molecular number density) in the air above the interface is about 1000 times less than the number of molecules in the liquid, by far most of energy for evaporation will come from the liquid.
A molecule evaporates when sufficient kinetic energy is gained through collisions with its neighbors for it to overcome the attractive forces between the liquid molecules. These forces include hydrogen bonds and Van der Waals force. As the molecule escapes it takes with it kinetic energy, leaving the water surface with a diminished total kinetic energy.
A molecule condenses when it is moving slowly enough and is pulled back to the water surface by the attractive forces, i.e. its velocity is insufficient to resist the pull of the various forces of attraction. The molecule plunges into the water, transferring energy to the molecules near where it hit the surface and is once again liquid.
It is easy to see why evaporation cools a surface and condensation warms it - when you think energy
Relative humidity expresses how much of the energy available for evaporation has been used to "free" liquid water molecules from its neighbors. A relative humidity of 50% means half the available energy has been used to evaporate water from the ground, streams, lakes anywhere else it is and 50% is still available to do more evaporation.
As the temperature rises during the day the amount of available energy increases. If by early afternoon the amount of available energy doubles (and it does in summer very often) Without changing the number of water vapor molelcules in the air the relative humidity drops to 45% Because there is twice the amount of energy available - remember relative humidity is what percent of available energy has been used and because it doubled during the day the percent used is half the original! relative humidity is relative to what .... relative to the amount of energy available to do the work of evaporation. Because the amount of energy increased as the sun warmed the atmosphere the percentage of the energy available that was used decreased, i.e. the relative humidity, all the while there was no change in the amount of vapor in the air. So when you hear someone say its feels worse than 52% relative humidity today, they do not understand the concept of relative humidity because 92°F and 52% is a very humid afternoon. Because the concept is confusing a better measurement is the dew point temperature.
Dew point temperature is a measure of humidity. If air is cooled eventually enough energy will be removed for water vapor to begin to condense. When we say condense it just means some of the molecules slow enough so that the attractive forces between liquid molecules are strong enough to make the molecules stick together.Remember the water vapor was originally liquid water and to get it to evaporate you had to add energy. As long as a molecule is moving fast enough (faster = warmer) it will remain vapor, but as a molecule cools (cooler = slower) at some point it will slow enough so it will stick to other water molecules. When that happens scientists say the molelcule condensed.
In terms of relative humidity, as the parcel of air is cooled, the relative humidity increases, when the relative humidity reaches 100%, the air parcel has cooled to the dew point temperature. At a relative humidity of 100% the dew point temperature always equals the temperature. The greater the difference between temperature and dew point the lower the relative humidity.
Dew Point Vs. R.H.
Unlike relative humidity if dew point increases, it is only because the amount of moisture in the air increases. If relative humidity changes it can be because of the temperature change or moisture change, or both.
Remember - think energy - if the air cools less thermal energy is available so the proportion utilized for evaporation is greater. For example if the relative humidity is 45% and half the thermal energy is removed because the air cools at night the relative humidity will rise to 90%, without changing the amount of moisture in the air. When using dew point temperature as a measure of humidity any change is strictly due to moisture change.
Dew point can never be higher than the temperature. At saturation, i.e. 100% relative humidity the temperature and dew point are the same.
Calculate Dew Point
Relative humidity gives the ratio of how much moisture the air is holding to how much moisture it could hold at a given temperature.
This can be expressed in terms of vapor pressure and saturation vapor pressure:
RH = 100% x (E/Es)
where, according to an approximation of the Clausius-Clapeyron equation:
E = E0 x exp[(L/Rv) x {(1/T0) - (1/Td)}] and
Es = E0 x exp[(L/Rv) x {(1/T0) - (1/T)}]
where E0 = 0.611 kPa, (L/Rv) = 5423 K (in Kelvin, over a flat surface of water), T0 = 273 K (Kelvin)
and T is temperature (in Kelvin), and Td is dew point temperature (also in Kelvin)
So, if you know the temperature, you can solve for Es, and substitute the equation for E into the expression for relative humidity and solve for Td (dew point).
Plants do not like moisture on their leaves, dew point is important in the system.
If a plant can be made to increase the amount of water it takes up thus the amount of nutrients better results are achieved. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem. When air temperature is increased the metabolic functions increases changing the osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots primarily driven by water potential differences and capillary action.
Transpiration occurs through the stomata apertures where a plants leaf surface is dotted with these openings, and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells (together known as stomatal complex) that open and close the pores. Plants regulate the rate of transpiration by the degree of stomatal opening. The rate of transpiration is also influenced by the evaporative demand of the atmosphere surrounding the leaf such as humidity, temperature, air movement and incident light.
To keep the plant from going into heat stress cooling the plant though the root system is a very effective method.