134 J.E. FAUST, J.M. DOLE, AND R.G. LOPEZ
up. As a result, nutrient solutions delivered to stock plants tend to
provide higher concentrations of nutrients compared to finished plant
production.
The electrical conductivity of the fertilizer solution is taken into con-
sideration with respect to the cutting leaf texture and resistance to
physical stress. Higher electrical conductivity solutions produce cut-
tings with smaller, thicker leaves that perform better in the postharvest
and subsequent propagation environment (A.H. Justice and J.E. Faust,
unpublished). These solutions range from 2.5 to 3.0 mS cm−^1 .Solu-
tions with lower electrical conductivity result in higher cutting yield
and larger leaves. Thus, one strategy is to utilize lower electrical con-
ductivity solutions (1.5–2.5 mS cm−^1 ) during the first few months of
the stock-plant production, termed the build-up phase, which occurs
before cuttings are being harvested, then switch to a higher electrical
conductivity solution (2.5–3.5 mS cm−^1 ) during the peak cutting har-
vest season. Nitrogen and potassium are the primary nutrients that are
manipulated to alter the fertilizer solution electrical conductivity.
Foliar calcium and potassium silicate sprays improve leaf strength
and resistance toBotrytisinfection in the postharvest and propagation
environments (Losenge et al. 2011). Calcium chloride foliar applica-
tions have also been shown to improve leaf mechanical strength of poin-
settia cuttings (Samarakoon et al. 2015).
- Plant Growth Regulation.The desired characteristics of stock plants
include a non-flowering, well-branched canopy and individual stems
that are comprised of compact internodes and small leaves. Breeders
have selected annual and perennial species for prolific flowering that
can make it difficult to produce vegetative stock plants which produce
cuttings without flower buds. Foliar applications of ethephon made
weekly during the early weeks of stock-plant production is the pre-
ferred method of aborting flowers (Faust and Lewis 2005a). Ethephon
also has the benefit of promoting branching of some species (Hayashi
et al. 2001). However, ethephon applications need to be terminated
prior to the beginning of the peak season, when cuttings are harvested,
since ethephon causes ethylene to continue to be produced in the plant
tissues for several weeks after application (Leatherwood et al. 2009).
Late applications of ethephon result in increased ethylene production
in the postharvest environment, which exacerbates postharvest prob-
lems such as leaf yellowing and leaf abscission of the cuttings dur-
ing the first days in propagation. Ethephon has the additional benefit
of reducing leaf size, which allows for propagators to place cuttings at
a higher density on the bench. Excessive application of ethephon can