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Your water quality can greatly impact the longevity of your cut flowers and the performance of your floral nutrient solutions. Here are some of the basics that you should be aware of.
Soluble Salts
Depending on your geographical location, the water coming out of your tap may contain high concentrations of soluble salts, commonly referred to as "hard water." Soluble salts commonly found in tap water that determine water hardness include calcium carbonate and calcium sulfate. Hard water may also have high concentrations of magnesium. As you might expect, cut flower sensitivity is species dependent. Research has demonstrated that flower life of roses, mums and carnations declines when the salt concentration approaches 200 ppm (mg/liter), whereas gladiolus don't show a decline until the concentration approaches 700 ppm. In addition, the soluble salts in hard water may react with the ingredients in your floral nutrient solution. Precipitation of certain chemical compounds may occur, resulting in cloudy vase solutions.
Alkalinity and pH
Another characteristic of hard water is high alkalinity. The alkalinity of your water will determine its ability to neutralize acids. Alkalinity is commonly expressed as ppm of calcium carbonate and should not be confused with the term "alkaline," which describes a pH above 7.0. Water can have a high pH, but may not necessarily have a high alkalinity. For example, it will take much less acid to neutralize water with a pH of 9.0 and an alkalinity of 70 ppm than it would to neutralize water with a pH of 8.0 and an alkalinity of 200 ppm. The alkalinity of your water can greatly affect the capacity of your floral nutrient solution to lower pH to the 3.5 to 4.0 range that is recommended for sustaining flower life. Also, you may run the risk of overdosing your cut flowers with active ingredient when trying to obtain a pH of 3.5 to 4.0 with water that has a high alkalinity. Instead, add the recommended amount of floral nutrient and determine the pH. It is better to be in the 5.0 to 5.5 range with the recommended amount of active ingredient than at a pH of 3.5 with double the recommended amount of active ingredient.
"Soft" Water
To further complicate matters, water containing high concentrations of sodium ions, or "soft water," has been shown to be even more detrimental to flower life than hard water; therefore, you should avoid using tap water that is run through a water softening system. You will be better off bypassing your softening system and using hard water.
Fluoridated Water
Research has shown that fluoridated water with fluoride concentrations as low as 1 ppm can cause injury to freesia, gladiolus, gerbera, carnations and tulips. Depending on flower species, toxicity symptoms can manifest themselves as foliar and petal burn or failure of flowers to fully open. It has been suggested that the use of a floral nutrient solution containing aluminum sulfate can partially reduce fluoride damage; however, it has also been suggested that the use of a floral nutrient solution may further exacerbate the problem by increasing water uptake.
Water Testing
Getting a reliable water test is the first step in identifying any water quality problems you might have. Approximate tests for soluble salts, pH, and alkalinity can all be done in house using inexpensive handheld meters and testing kits available from horticultural and laboratory supply companies. When doing testing in house, it is imperative that meters are calibrated regularly with appropriate standards. If more detailed testing is desired, a list of testing laboratories can be obtained from the Soil and Plant Analysis Laboratory Registry for the U.S and Canada. Hopefully, the list will include a local university or extension services in your area.
Water Treatment Systems
If your water testing indicates that you have poor water quality then you may want to consider a water purification system such as reverse osmosis or deionization.
Reverse Osmosis (RO)
An RO system is the less expensive of the two. Water will move naturally through a permeable membrane from a solution of low solute concentration to one of higher solute concentration by the process of osmosis. By applying pressure to the solution of higher solute concentration, then water can be forced through the membrane in reverse (higher solute concentration to lower solute concentration) and effectively remove 90% of the solutes.
Deionization
Deionization systems use ion exchange resins to remove solutes which readily dissolve in water in their ionic (charged) forms. The surface of the resin is covered with fixed positive or negative charges. Anion exchange resins remove negatively charged ions (e.g. carbonate ions HCO³¨) while cation exchange resins remove positively charged ions (e.g. calcium ions Ca²+). As the water passes through the resin, anions and cations are removed and replaced (exchanged) with positively charged hydrogen ions (H+) or negatively charged hydroxyl ions (OH¨). These released ions then combine to produce water molecules. The resulting water that is produced is very pure, but the cost can be nearly 5 times that of an RO system.
Fluoride Removal
Fluoride can be removed by RO and deionization, but if your water is not particularly hard and your fluoride levels are high, then you may want to remove fluoride by other means. Fortunately, in most cases the fluoride concentration in fluoridated municipal water is below 1 ppm; however, higher concentrations can occur. Fluoride can be removed from your water using activated carbon filters. An alternative ion exchange process using alumina can also be used; however, the pH of your water must be at least 5.5, which would require the water to be treated with an acid injection system.
Some Final Words
Justifying the cost of a purification system may be difficult, but if your water quality is particularly poor, then the quality of your cut flowers can be seriously compromised. The bottom line is to be sure to get your water tested. Whether it's good or bad, in the end you will gain more control over the quality of your cut flowers and those arrangements you work so hard to create.
Dr. Garry Legnani joined the Smithers-Oasis Corporate Research & Technology team in February 2005. His responsibilities include managing all horticultural and post-harvest activities, as well as greenhouse and flower testing operations at the Kent, Ohio location.
Dr. Legnani received his Ph.D. in Horticulture from Cornell University. He had previously obtained B.S. and M.S. Degrees from Clemson University.
Along with his technical responsibilities mentioned above, Dr. Legnani will be providing helpful and relevant information in the Smithers-Oasis "post harvest 101" web page, where he will offer practical advice on flower care and handling in periodic articles.
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