How to interpret your post harvest water analysis report
After flowers have been harvested, they get dehydrated. Post harvest water is used to 'jump start', and hydrate the flowers. The quality of the water used to hydrate the flowers is important and determines the final quality and vaselife of the flowers. The quicker the hydration process, the better. De-hydration stresses the flowers, reduces the vaselife and promotes ethylene production which stops the flowers opening in the vase and reduces quality. Ethylene is a gas and will affect the quality of the surrounding cut flowers.
As a general rule of thumb the 'starter' water for post harvest rehydration of flowers should be of drinking water quality before post harvest treatments are added. Post harvest water must be tested in a laboratory to determine suitability.
This is a measure of the acidity or alkalinity in the water. The ideal pH for post harvest water is 5, with a minimum limit of 4, and a maximum limit of 6. A lower pH keeps the Xylem, the water conducting vessels, working at maximum efficiency. Lower pH water is more hydrophyllic, which means that the water molecules stick to each other more easily and move up the xylem faster. A lower pH is essential for effective chlorination to kill the bacteria. At high pH's chlorine becomes ineffective as a bacteriocide.
In general a lower pH water will give a longer vaselife. Most flowers prefer a pH of 4-6, however some flowers require lower pH's.
EC and TDS
The EC (electrical conductivity) and TDS (total dissolved solids) are a measure of the amount of salts in the water. A guideline for an EC of <1.5 and a TDS of < 1000 ppm have been set. Ideally the EC should be < 1 for a longer vaselife. High EC's affect the movement of water into the stems and the rate of re-hydration. Very high EC's may even draw water away from the plants. EC can be reduced by using clean water from rain or reverse osmosis. Very low EC's have no buffering capacity and may have a negative effect on vaselife.
Total Suspended Solids (TSS)
TSS should be below 25 ppm. The presence of suspended solids will interfere with the disinfection process. The solids may move into the xylem of the stems and block the water flow into the flower completely. The lower the TSS, the better the vaselife. TSS can be reduced by filtering.
The turbidity is a measure of the cloudiness of the water. It is recorded in NTU - Nephelometric Turbidity Units. Turbidity is a key water quality indicator. For post harvest water a low turbidity <5 ntu, is essential for a long vaselife. A higher turbidity indicates the presence of suspended solids that can block the xylems and prevent water uptake. Turbidity also indicates the presence of suspended particles, microbes, and/or organic matter that can increase chlorine demand and prevent effective disinfection of the water. Turbidity can be reduced by flocculation and filtering.
Total Bacterial Count (TBC)
Total bacterial counts in colony forming units (cfu's) are conducted at 22 Celsius and 37 Celsius. Bacterial can grow in the post harvest water feeding off the sugars that are added to the water, or come from the plant stems. Bacterial will enter the plant xylem during water uptake and grow and breed in the stems, blocking the water uptake during post harvest rehydration AND more seriously during rehydration after shipment. Bacteria will greatly reduce vaselife of cut flowers. A maximum tolerance for most flower handlers is 1000 cfu/100 ml. However the lower the bacterial count the better.
Total bacterial counts can be reduced by proper hygiene systems and disinfection, and by starting with clean water.