Water makes up as much as 90% of the mass of a plant- even more in some crops, such as lettuce. To get to that level our crops will “drink” a lot of water- as much as three gallons to make one single tomato. For these and other reasons, the quality of your feed water plays an instrumental role in the success of your garden.
Where to start
For hydroponics, you will need two tools: a pH meter, and a total dissolved solids (TDS) meter, also known as an electrical conductivity (EC) meter. A meter is only as good as its calibration; calibrate your meters using the instructions provided with the meter, using calibration solutions from your hydroponics store. If you don’t feel like calibrating your meter before each use, do it once a week- and then do a “cal check,” testing against your calibration solutions before use. TDS meters are more robust than pH meters, and the probe on pH meters is prone to burning out or breaking.
Tip: pH probe life can be extended by cleaning and storing as recommended by the manufacturer.
The “hardness” of your water is determined by the concentration of salts dissolved in it as it comes from the source. Hard water requires the roots to expend more energy to uptake the water and nutrients used for plant growth. Obviously, using better water gives your plants a head start. If your water comes from surface sources such as a reservoir or river in a moist climate, its hardness may be quite low (under 100 ppm), and this hardness may be due to ions such as calcium and magnesium that plants can actually use. If your water is very hard- over 150 ppm or so- you may want to buy purified water or install a reverse osmosis (RO) unit in your home or greenhouse. Don’t use a water softener- they add salts that make for better suds in the shower, but not better plants in the garden!
Tip: Water quality may change throughout the year. Check it regularly for best results.
pH is a measurement of how acid or alkaline a solution is. For most plants, a pH between 5.0 and 6.0 is adequate. Plants in deepwater culture are more sensitive to pH outside the appropriate range, while soil and coir are more forgiving. Your meter and probe should be calibrated with pH 4.0 and 7.0 solutions since you will be measuring within this range.
Once you have added nutrients to your water, based on the manufacturer’s recommendations, mix well and test the pH. A pH outside the acceptable range can be adjusted by adding the proper solution, such as pH Up or pH Down. Be careful not to use too much- a little goes a long way. Dose, mix thoroughly, and test again. A pH outside the recommended range is one of the leading causes of problems in hydroponics. A pH that is too high or too low quickly causes deficiencies, meaning more headaches for you. Remember- the pH may change as plants grow and change the water chemistry. Testing and adjusting the pH between water changes will help keep your plants growing at their best.
Tip: pH papers are an inexpensive backup for your pH meter. Those fragile probes tend to break at the worst possible times!
Chlorine (or chloramine) may be added to tap water in order to kill potential pathogens. Aerating your water for a period of 24 hours or running the water through a charcoal filter will help remove the chlorine. Also, boiling water for approximately 15 minutes will drive away any chlorine present. Potassium metabisulfate will remove both chlorine and chloramine when dissolved in water.
Plants tend to thrive within a specific temperature range- so do the roots! If your reservoir is on a cold concrete floor, it can shock the roots every time your plants are watered. A sheet of plywood as insulation can help keep the chill away.
– Aaron J. Hicks