CO-Horts Blog

Tuesday, February 12, 2019

Cut Flower Challenges

Posted by: Sarah Schweig, Broomfield County Extension

Valentine’s Day is upon us. Love it, hate it, or indifferent, let’s at least appreciate the holiday as an excuse to enjoy fresh flowers! The beauty of cut flowers is ephemeral by nature, and maybe that’s part of the appeal. Still, folk remedies and DIY solutions for prolonging vase life abound. We can explore the science behind these solutions by taking a look at the most common reasons flowers don’t last at home.

Challenge: Insufficient food supply
DIY Fix: Table sugar
This idea here is simple. Plants need sugars to maintain cellular processes. Cut flowers have carbohydrates stored in leaves and stems, and these reserves will be depleted to maintain basic metabolic activity. For flowers that are harvested when fully open, like gaillardia or yarrow, insufficient food supply may lead to early senescence. For flowers that are harvested at earlier budding stages, like gladiolus or peony, insufficient food supply means those flowers may never fulfill their destiny.

Flower food is formulated to provide the ideal amount of sugar (typically glucose), as well as acidifiers (see next problem). However, because sugar is so essential to prolonged vase life and continued development, adding table sugar (sucrose) will do in a pinch.

Challenge: Microbial activity
DIY Fix: Softened water, lemon juice, aspirin, pennies
Unfortunately, plants aren’t the only sugar-lovers living in your vase water. Fresh cut flowers will lose some of those stored carbohydrates where the stems are cut, resulting in a sugary solution that encourages the growth of microbes. While supplemental sugar will support plants, it only exacerbates the microbe problem. Bacteria and fungi block flow of water and nutrients through xylem tissue, and some produce ethylene, which encourages senescence.

The vase life claims of our first DIY fixes are based on the fact that lowering the pH of your vase water will discourage microbial activity. Although hard water tends to be alkaline, chemically softened water contains sodium and should not be used in flower vases. The citric acid found in lemon juice, however, is quite effective and is a common component of commercial floral solutions. While dissolving aspirin in water does lower pH, studies are mixed on whether it has any effect on vase life. Even those studies that report a positive effect on vase life agree that floral solutions are much more effective.

Adding pennies to vase water is based on the fungicidal properties of copper. Pennies have been made from around 98% zinc since 1983, and the copper in pennies is not - and never was - water soluble. We can fully myth-bust this one (satisfying, huh?).

Challenge: Ethylene-induced senescence
DIY Fix: Vodka, gin, whiskey, etc.
Ethylene is a plant hormone involved in ripening and senescence, and thus there is generally an inverse relationship between ethylene and shelf-life. The principle here is that the ethanol, which is contained in distilled spirits, can affect the production of and response to ethylene. Ethanol has been shown to delay maturation in plants in a number of contexts. A study published in HortTechnology investigated adding distilled spirits to water to reduce tipping of paper white narcissus by reducing plant height. At certain concentrations of ethanol, plant height was successfully reduced without apparent toxicity to roots and with no effect on flower size or timing. Ethanol has also been shown to delay the ripening of tomatoes, among other fruits. While there is evidence to support this solution, at-home success would require a high level of precision. Depending on your vase size, the difference between an effective ethanol concentration and a toxic ethanol concentration could be a matter of a few drops!

What You Can Do
There are many practical and effective ways to reduce the effect of ethylene on your cut flowers without the need for laboratory precision. Place them in a spot with good air circulation, away from heat sources. Do not place flowers near your fruits and vegetables, which produce ethylene as they ripen.

Though I generally support the DIY spirit, commercial floral solutions are by far the safest bet for meeting your flowers’ basic needs. One size is not fits all for maintaining cut flowers. Roses and snapdragons, for example, need extra sugar to push blooms open. Sunflowers are highly susceptible to bacterial plugging of xylem tissue and may require a stronger biocide. While it’s tough to get a perfect solution for a mixed bouquet, you can get as close as possible by going with the pros on this one. Floral solutions are readily available and contain, at a minimum, necessary plant food and an acidifying agent to help keep xylem tissue freely conducting water and nutrients.

Another cause of reduced xylem function in cut flowers is embolism. Cut stems under warm water to help prevent these air bubbles from forming. Use clean, sharp tools to prevent crushing the stem tissue. Ensure that leaves growing below the water line, and any fallen leaves or flowers are removed, as this decaying matter will encourage microbial growth.

Eventually, even though you’ve done everything right, you’ll see signs of the battle with the microbes. When water turns cloudy or you notice fuzzy-looking growth on stems, change your vase water and re-cut stems.

How long will your Valentine’s Day flowers last? Try it out, maybe add a penny for good luck just in case, and let us know!

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