Are you doing everything right, but your flowers still don’t last as long as they should? It could be your water. By Terril A. Nell, Ph.D., AAF Research Director, American Floral Endowment
Flowers live or die based on the availability of water to stems, leaves and blooms. Indeed, water stress may be the most significant factor affecting vase life in cut flowers. Flowers die prematurely when the amount of water being absorbed is lower than the amount lost from the leaves, stems and blooms. Research has shown that several factors can lead to reduced water absorption, including bacteria, air blockages and water quality, especially water pH. Poor water quality can reduce the amount of water absorbed. Without water, individual cells cannot function. This is particularly critical for cut flowers that must get water from a bucket or vase solution. Flowers open by using water to enlarge the petal cells, just as air inflates a balloon. New petal cells are not produced after harvest, so a continuous flow of water is needed by the flower if it is to open fully and remain viable for seven days. Sugars from flower foods in bucket/vase water supply energy to supplement the flower’s naturally occurring sugars.
Some people assume that all water is the same regardless of the source, but water quality varies by geographical location or even from one well to another. Four water quality parameters may affect the life of flowers: pH, alkalinity, hardness and total dissolved solids.
pH is a measure of the acidity or alkalinity of the solution and may range from 0 to 14. A pH of one is extremely acid while a pH of 14 is extremely basic (also referred to as alkaline). A pH of seven is neutral. The pH of water affects the ability of flower stems to absorb water. Water with a pH between 3.5 and 5 are best for water absorption and vase life. Flower foods and hydration solutions are designed to lower water pH to these levels.
Research has demonstrated clearly and consistently that solution pH impacts water absorption. Flowers and stems that attained the greatest increase in fresh weight (pH 3) had the best keeping quality while flowers that had little increase in fresh weight (pH 7) had the poorest keeping quality. It is no wonder that the flowers at pH 3 lasted longer since they absorbed about 70 percent more water than stems held in water at pH 6 and lasted longer. Additionally, blockage decreased nearly fourfold over the same pH range. All these positive impacts of low pH were due to ability of water to be absorbed easier at low pH. But, there is another factor: bacterial growth.
Bacterial growth in the vase or bucket solution lowers water absorption by blocking or partially blocking the base of the stem where water is absorbed. Bacteria in the vase water has been related to scape (leafless stem) bending of Gerbera and reduced longevity in many other crops.
One solution to controlling the growth of bacteria is reducing the pH; lowering solution pH strongly may inhibit bacterial growth. In other words, by lowering the pH, the growth of microbes is reduced, which helps to keep the stems clear so more water can be absorbed. Commercial hydration and flower food solutions contain a buffer to lower water pH to the desirable range.
One other factor that solution pH affects is the presence of minerals that become crystalized in the solution. For example, in water with a pH higher than 7, iron, if present, precipitates out of the solution and will clog the cut stems. In water with high amounts of iron and failure to reduce the solution pH to less than 7 will result in nearly complete blockage of the base of the stem by iron in three days. And, of course, the flower wilts due to lack of water absorption.
The following characteristics of water are related to water absorption or ability of the water to be buffered. To have the ideal pH for cut flower water absorption, it is necessary to lower water pH between 3.5 and 5. Most water sources have a pH above 6, so hydration solutions and flower foods contain an acidifying agent to lower the pH.
The ease or difficulty of buffering water pH depends on the amount of calcium carbonate (chalk) in the water. Calcium carbonate is measured in units of concentration, such as parts per million (ppm) or mg/liter. An alkalinity level between 60 and 180 ppm is best. Water with this level of alkalinity is easily buffered with the acidifier contained in commercial hydration and flower food solutions. As the level of calcium carbonate rises, the pH is more difficult to buffer.
Water contains naturally dissolved calcium and magnesium. Hardness is a measure of the amount of calcium and magnesium (parts per million) in the water. Total hardness is the sum of the calcium and magnesium levels. Generally, hard water contains high alkalinity levels, thus making the water difficult to buffer. Water with high levels of hardness will require special treatments to remove the calcium and magnesium. While water softening systems will remove these minerals, they should not be used in the flower industry. Water softeners replace the calcium and magnesium with sodium, and sodium can be toxic to flowers. The most effective methods for reducing hardness are either deionization or reverse osmosis.
Total Dissolved Solids (TDS)
Another measure of water quality is the level of total inorganic salts and organic matter present in water. Flowers do poorly in water containing high levels of salts.
Also, be aware that a couple of salts, such as fluoride, can be harmful to flowers.
Have Your Water Tested
The only way to determine the quality of the water in your store or other facility is to have it professionally analyzed. The results of your water test will guide decisions about treating the water to achieve optimal outcomes. In most locations, use of commercial flower hydration and flower food solutions will provide positive results and excellent vase life without additional modifications. Testing does provide you with peace of mind that your water, with the correct solutions and handling practices, will provide your customers with highquality, long-lasting flowers.