Why is the solution pH important?

The reason is that plants have adapted to absorb some nutrients best at slightly acidic pH values. A pH value below 4 will cause the stress of most plants roots and low nutrient absorption. At pH values over 7.2 many elements like iron will start to form insoluble precipitates. As long as the pH is in the range of 5.8 to 6.8 most plants will draw up all needed nutrients from the solution.

How can the pH be measured?

For most people, a liquid colorimetric pH test kit works well and costs from $5 to $ 10. A type of pH indicating paper is also available, but is not as accurate as the liquid test. Serious pH measurement is accomplished using electronic meters that can resolve the pH to the nearest 0.1 of a pH unit. They need calibration against a solution of a known value, which is known as a buffered pH reference, or simply "pH buffer." The pH buffer solutions come in three ma_jor values: pH 4, pH 7, and pH 10. The pH 7 buffer is the most important for Hydroponic work, as we want to be just below 7 for most crops. The glass electrode tips of the electronic meters are very fragile. They should be stored in a slightly acid storage solution to prevent the microscopic pores from clogging with dissolved minerals.

Why do my pH readings fluctuate?

This occurs for several reasons. The first is that after adding acid to a raw water source that is high in carbonates and bicarbonates the pH will go much lower, but after a few hours may "bounce back" to a level higher than before the acid was added. This is due to a complex reaction involv­ing carbon dioxide that is dissolved in the water and then carbolated. Another reason is that the plants will actually change the pH of the solution as they take up nutrients. It just means the plants are growing! Yet another reason is that the roots exude organic acids during growth, as well as CO2 which becomes carbonic acid when dissolved in water.

How can I adjust the pH of the nutrient solution?

Most gardeners will have alkaline tap water with a pH of 7.5 to 8.5, depending on the water source. About I teaspoon (5ml) per 10 gallons of water is a good general starting point. Add the acid before adding the nutrients. The three most common acids are sulfuric (15%), phosphoric (30%) and dry powdered citric acid. Vinegar can be used on a small garden, but excessive amounts would be needed for a large reservoir. People living high in the mountains and using well water may have acidic water to start with. In that case, pH upwards adjustments could be made with potassium hydroxide or potassium bicarbonate. Many nutrient formulas will react quite strongly toward the acid side after some time. This is why it is important to check the pH at least every other day for commercial crops.

Is there an organic method of lowering pH?

Yes. Citric acid or vinegar could be used to lower the pH of the nutrient solution. Vinegar is usually only used on very small gardens, since fairly large amounts of it must be used to stabilize hard alkaline water to the correct pH. Powdered citric acid is available which can be used in very small amounts to lower the pH. Generally, I teaspoon of citric acid will treat about 20 gallons of hard tap water.

Irrigation____________________________

using Hydroponic Systems (definitions)

The way water is delivered to the plant is a function of the type of Hydro­ponic system used. The type of Hydroponic system is relative to what type of crop is grown, what materials are available, and the budget. The Hydroponic gardener has many options in this area. There are many types of Hydroponic systems, along with hybrid types or variations of each one.

1.  Ebb & Flow irrigation, also known as "Flood and Drain," is where the growing media is in shallow trays that are watered by flooding the whole tray from one end. A slight slope in the tray leads the water to the other end of the tray where there is a small drain that leads back to the nutrient tank where the pump is located. The drain is known as an "overflow drain" because, due to the design, it will only let water rise to a certain level before it overflows the top of a tube which prevents the tray from overfilling and spilling onto the floor. The root area obtains fresh oxygen when the tray drains because fresh air fills in the voids in the rooting media as the water drains out; a very productive and reliable method!

2.  Drip irrigation is well known, even in conventional soil farming and gardening. In Hydroponics this technique involves pumping the nutrient solution up from the nutrient tank and then sending it by tubing to an individual drip emitter for each plant. Drip irrigation usually requires a little more work to set up, and the drippers may be prone to clogging. Most growers use this technique on longer season crops, due to the labor involved when changing crops, and the maintenance.

3.  Nutrient Film Technique is an advanced Hydroponic growing method first pioneered in England. The basic concept involves a plastic trough or gutter that is irrigated by a constant-but-low volume of water on one end, which flows by gravity to the other end, and back to the reservoir. The plants are held about 3 inches or so above the bottom of the gutter, and the roots form a mat at the bottom of the channel. The water level is very shallow, only a few millimeters at most. This shallow layer of water makes it impossible to submerge the entire root structure, with only a thin film of water coating the upper mass of roots (hence the name). This is now the main Hydroponic farming method in Australia and New Zealand. There is almost no growing media used, other than that used to start the seed or cutting before it is placed into the system. This means production costs are very low, with media costs greatly reduced. This method is NOT recommended for beginning gardeners, as the whole crop could be lost in one day. Constant attention to the crop is required.

4.  Wick systems make use of capillary action to draw water up into the root area. There are several variation, but essentially there is a pot suspended over a tray of water. The pot has a few pieces of wick material (rope) set around the plant roots, passed through the bottom holes in the pot and into the water below the pot. As the plant uses water, more water is drawn up the wick by capillary action. There is a special variation of this technique invented in Europe called "Hydroculture," which does not use any external wick. Instead special fired clay pebbles with very high capillary action are used in a special open-mesh container inside another pot acting as a reservoir. The pebbles draw water up from the very bottom of the container as the plant needs it. This method is excellent for house plants!

5.   Aeroponic systems are the most complex and technical of all the Hydroponic methods. They suspend the plant so that the roots hang down into a chamber that is sprayed or misted by nutrient solution. The spray may be constant or intermittent, depending on the system. Most commercial aeroponic systems use high-pressure pumps that are operated intermit­tently, either by a timer, or according to demand. The demand is calculated by sensors that turn the pump on as needed. The maximum interval is no more than 30 minutes. The roots will start to stress after 30 minutes with no spray or mist.

6. Raft systems, also similar to what is known as deep channel systems, use a deeper layer of water than NFT. The water is usually a few inches deep. Plants are set into foam blocks which have a hole in the center for the roots to go through, so they can dangle down in the solution. Fresh oxygen is provided by constant circulation of the solution. This method has been used to grow lettuce in warm tropical climates as part of what is called "aquaponics" (the raising of fish), using the same water to grow plants hydroponically. The foam helps insulate the water from the heat of the sun. The nutrient reservoir in this case is actually a fish tank! The ancient Aztecs used a similar method which enabled them to produce an extremely large yield of food in a small area. They used all parts of the food chain including algae, insects and mussels.

Irrigation_______________________________

Using Hydroponic Systems (Q & A)

Which type of Hydroponic system is best for the beginner?

For fast growing plants, such as lettuce or tomatoes, the Ebb and Flow method is very reliable, with excellent growth. Aeroponic systems require more attention, but also produce outstanding yields. Slow-growing plants, such as house plants, do very well in the hydroculture system of passive Hydroponics (no pump or electricity needed). Wick systems are inexpen­sive to build for schools.

What about drip irrigation?

Drip irrigation is good for long term crops, such as tomatoes or cucum­bers, in the greenhouse, which may grow for eight months or more. The drip emitters require constant attention to make sure they are not clogged. A filter of at least 100 mesh should be installed on the feed line to keep dirt out.

When using drippers, how much irrigation is enough?

Generally, as long as there is enough water to saturate the media and also give at least 10% runoff back to the storage tank, then that would be the minimum irrigation required for a drip irrigation system.

How can I control the precise amount of water delivered by a drip system?

The easiest method is to use a very short-cycle timer. The pump and the size of the drip emitters are a constant, so just controlling the time that the pump is on will control the volume of water delivered.

How much irrigation is required for Ebb & Flow systems?

The minimum flood level for most media is about 1 inch. The capillary action of the media will draw water to the top of the media. The irrigation cycles could be for as long as 30 minutes of pump on time. The off time between cycles could be from one to six hours. The most common cycle we use is 30 minutes on and 90 minutes off, which repeats from daylight to dark.

What about watering at night?

Whatever system you use there is no need to irrigate at night for almost any climate conditions. Night watering should be avoided since it encour­ages mold and fungus infections. The only exception would be the aeroponic type system, or NFT system in very dry conditions.

Should aeroponic systems be constant or intermittent?

We have found that it is OK to run the aeroponic irrigation around the clock, but that there is no need to mist at night. Large commercial aeroponic systems may use sensors in the root chamber to determine if irrigation is needed.

Should NFT systems be run during the night?

We recommend no irrigation at night time, as it tends to encourage leaf molds and stem bacteria. Only if climate conditions are very hot and dry would a nighttime irrigation cycle be of any possible help.

Should NFT systems be operated constantly during the day?

Most NFT systems run constantly during the day. Some of our customers report that by shutting off the pump for 20 to 30 minutes root health improves The pump must not be off for more than 30 minutes or the plants will start to experience water stress at the top leaves of the plant.

When should the nutrient in the reservoir tank be changed?

The water in the holding tank should be drained at least every other week. For maximum growth the nutrient tank should be changed every 7 to 10 days. Flush out the media with clear water to eliminate salt buildup at the top of the media.

What should I do with the old nutrient solution?

It is still an excellent source of nutrients for soil plants that are growing outside. Please use the water to irrigate so that the remaining nutrients will be used by the soil, rather than going down the drain to be treated at the sewage treatment plant.

What about algae and mineral deposits that buildup on the growing trays and reservoir?

Prevent algae growth by preventing light from getting to the reservoir (cover it up). To prevent algae on top of rockwool cover the top with plastic film, or sprinkle a little "Pyroclay" on top of the rockwool. The algae does not hurt while growing, but may become a problem if it dies off and starts to decay. Use a stiff bristle brush and scrub the trays to remove mineral deposits. Use some citric acid (with gloves!) to dissolve stubborn calcium deposits, and rinse thoroughly before refilling.

Air and Climate _________________________  

(temperature, humidity, airflow,CO2 enrichment, and ventilation)

What climate is best for most plants?

The best climate for most plants is a temperature between 68° and 85° F (20° to 30°). The preferred humidity range is 50-70% relative humidity. Air circulation is needed to remove the stale moist air from the plant leaves, and replace it with dryer air, higher in _CO2 content, so that growth may continue as long as there is light.

Why is the humidity specified as "relative" humidity?

The term relative humidity relates to the fact that as air temperature increases so does the ability of air to hold moisture. The rule of thumb is that for every 10° F rise in air temperature, a given volume of air will hold twice as much water. That is why dew forms droplets of water on the outside of a cold glass on a warm day.

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