It occurred to me that my cuttings are not really all that different than the cut flowers that can be purchased at florist shops. Florists often use specialized plant food or preservatives to prolong the life of cut flowers.
My local florist uses a product called Chrysal. I purchased several packets at $0.25 CAD a piece and added the prescribed amount to the water. It seems to have worked. The cuttings with Chrysal have lasted longer than the cuttings without the additive (although I haven't specifically quantified what the difference is).
Cut flower additives (Wikipedia):
According to the Brooklyn Botanical Garden, different additives can be
used to prolong the lives of fresh cut flowers. Experiments were
performed with various substances mixed with water, including aspirin,
vitamin pills, vinegar, pennies, and flower food to test their effect
on cut flowers' lifespans.2 Each plant was placed in the same
environment and the same type of plant was used in each vase.
This research found that the best additive for flowers was the
retailer-provided "flower food" that is usually given with a bouquet.
Plants are known to thrive in an environment where there are few
bacteria, plenty of food for energy, and water uptake is encouraged.
Flower foods contain an acidifier that helps to adjust the water's pH.
With a lower pH the water and food conducting system within the flower
can work at maximum efficiency. The sugar in the food will be used by
the plant as an energy source, which had been lost when the flower was
cut away from its root. With these nutrients the plant will be able to
fully develop. Finally, there are stem unpluggers that will make sure
that the flower can easily take up water and nutrients that can later
be used to take care of the needs of the rest of the plant.3 This
combination gives the fresh cut flowers everything that they need to
survive longer. When tests were carried out in St. Mary's College
C.S.S.p, Rathmines, Dublin, however, results showed that glucose was
more effective at prolonging the life of cut flowers than the
commercial plant food. The experiment was carried out as part of the
Junior Certificate Science Examination set by the Irish State
Examinations Commission 2008.
Cut flower longevity (Wikipedia):
Once flowers are removed from the plant they continue to grow slowly,
but have a diminished capability of receiving the nutrients that are
vital for their survival. In most countries, cut flowers are a local
crop because of their perishable nature. In India, much of the product
has a shelf life of only a day. Among these are marigold flowers for
garlands and temples, which are typically harvested before dawn, and
discarded after use the same day.
The majority of cut flowers can be expected to last several days with
proper care. This generally requires standing them in water in shade.
They can be treated in various ways to increase their life. According
to James C. Schmidt, a horticulturist at the University of Illinois,
originally putting cut flowers in a sterilized vase is important to
extending the life of the flowers. Vases can be cleaned using a
household dish detergent or a combination of water and bleach. Using
these disinfectants ensures that there will be less bacteria growing
within the vase that could potentially cause the plant to wilt and die
at a faster rate. Schmidt also claims that cutting the flowers
diagonally with a sharp knife under running water ensures that they
can immediately take up fresh and clean water. Re-cutting the stems
periodically will ensure that there is a fresh surface from which the
stems can take up water. This will allow the flowers to last even
longer. Other ways to care for vase flowers includes keeping flowers
away from ceiling fans and air-conditioning vents as this can lead to
dehydration, keeping flowers away from fresh fruit of vegetables,
using filtered water rather than tap water so as to avoid both
chlorine and fluoride, and keeping flowers away from your