- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 133
compact shoot growth. In these cases, photoperiodic lighting can be
used to extend the day length (usually 12ā13 h dā^1 ) to stimulate shoot
growth and stem elongation. Examples of such genera and species
include at least some cultivars ofEchinacea(Runkle et al. 2001),Leu-
canthemum(Runkle et al. 1998a),Phlox paniculata(Runkle et al.
1998b), andRudbeckia(Runkle et al. 1999).
In many cases, additional tools must be used beyond non-inductive
photoperiods to assist in maintaining vegetative stock plants of herba-
ceous perennials, such as repeated spray applications of ethephon
(Glady et al. 2007) and trimming techniques that remove flowering
shoots and promote young vegetative shoots (Faust and Grimes 2004;
2005). Recent breeding efforts have been so successful at stimulating
flowering of previously long-day species, such asCoreopsisandGail-
lardia, that vegetative cutting production is very challenging regardless
of the photoperiod provided and amount of ethephon applied.
- Plant Nutrition.Stock-plant-production facilities are often located
in regions with volcanic soils, so the greenhouses rely on locally mined
volcanic rocks as the primary source of growth medium. The rock is
screened to various sizes ranging from 2 mm to 3 cm diameter pieces.
Coir coconut fiber or peat moss may be added to increase the water-and-
nutrient-holding capacity. If no coir or peat moss is added, the highly
porous volcanic rock essentially creates a hydroponic irrigation system.
In this situation, drip irrigation is used predominately and may run up
to six to eight times per day. A complete fertilizer comprised of all essen-
tial nutrients is injected into the irrigation water resulting in a constant
liquid fertilization program that delivers a nitrogen concentration rang-
ing from 100 to 300 ppm (Gibson 2006). Some water and volcanic rock
sources may have excessively high levels of minor nutrients, such as
manganese, boron, or copper, so the fertilization programs are appro-
priately adjusted.
Nutrient management is often monitored by daily measurement of
the leachate that drains from the base of the stock-plant containers dur-
ing an irrigation event to evaluate the pH and electrical conductivity to
which the plants are being exposed. Leaf-tissue analysis is also a use-
ful tool for monitoring stock-plant nutrition. The standard technique
is to sample the entire cutting, including leaves and stem, since many
species have relatively small cutting size. Tissue analysis labs provide
a range of acceptable levels of individual nutrients within plant tissues.
Cuttings, which are comprised of the most dominant shoots within the
plant canopy, are removed weekly from the stock plants along with a
significant quantity of the nutrients that the plant had previously taken