Silicon (Si) and Titanium (Ti) Influence Growth of Selected Annual Bedding Plants

Soilless media is used to grow annual bedding plants; however, this media lacks levels of beneficial elements found naturally in soil.  Previous research has shown that silicon (Si) supplementation can improve overall plant growth, as well as inhibit biotic and abiotic stresses in select horticultural crops.  Titanium (Ti) supplementation can also increase overall plant health.  This study investigated the effect of foliar Si and Ti applications on key quality factors of five annual bedding plant species grown in soilless media.  The five plant species selected were geranium (Pelargonium x hortorum), impatiens (Impatiens walleriana), pansy (Viola x wittrockiana), petunia (Petunia x hybrida) and snapdragon (Antirrhinum majus).  Foliar applications of sodium silicate (NaSiO₃) and Ti-ascorbate (Tytanit^®) were used to supply beneficial Si and Ti.  Silicon treatments were 0, 50, 100, 150 and 200 mg Si∙L^-1. Titanium treatments were 0, 25, 50, 75 and 100 mg·Ti∙L^-1.  Several key horticultural traits were affected in the study, depending on the species and concentration of Si and Ti applied.  Silicon treatments affected plant height for all five species, while Ti treatments only affected geraniums, petunias and snapdragons. Plant height increased, then decreased quadratically for geraniums with both Si (P=0.003) and Ti (P=0.001) treatments as well as pansies with Si treatments (P=0.002). Snapdragon plant height increased linearly in response to Si (P=0.024) and Ti (P=0.003) treatments.  The number of days to flower (anthesis) for petunias had a linear decrease with Ti treatments (P=0.01) while impatiens had a linear increase with Si (P=0.005) and Ti (P=0.02) treatments.  Geraniums responded with a quadratic decrease, then increase for the number of days to flower with Ti (P=0.001) treatments.  The chlorophyll content, as estimated with a SPAD meter, of impatiens and pansies had a linear decrease in response to Ti (P=0.05) treatments, while geraniums had the same response to Si (P=0.04) treatments.  Silicon and Ti supplementations were found to affect key horticultural traits of annual bedding plants.  However, this response was species specific and further research is needed to assess the specific impacts of Si and Ti on additional annual crops grown in soilless media.