Nutrient supply and uptake during propagation of Petunia cuttings

Nutrition strategies were found to be highly variable between grower operations surveyed across the country, emphasizing the need for further understanding of supply and uptake dynamics in propagation. The objectives of this research were to (1) survey water and fertilizer management strategies during propagation, (2) survey typical tissue nutrient levels in 44 herbaceous annual unrooted cuttings, (3) evaluate the effect timing of macronutrient supply on Petunia x hybrida 'Supertunia Royal Velvet' cuttings, (4) evaluate the effect of stock plant nutritional status on fertilizer response in propagation, and (5) employ aeroponics design to quantify stem versus foliar uptake. Grower management of the timing and concentration of nutrients applied to vegetatively grown calibrachoa ( Calibrachoa x hybrida) or petunia (Petunia x hybrida) ranged from 0.5 to 80 mg·L -1 Nitrogen (N) in week 1, and from 64 to 158 mg·L -1 N in week 4. Leached water volumes ranged from 4.5 to 46.1 L·m-2 over 4 weeks and contained 0.29 to 1.81 g·m-2 N, 0.11 to 0.45 g·m-2 P, and 0.76 to 2.86 g·m-2 K. Most of the nutrients and water were leached during the first seven days when the highest volume of water was typically applied to cuttings as a method to minimize transpiration until root emergence. Nutrient availability in the root zone at root emergence increased root length from 0.5 cm to 2.8 cm, however excessive application of water during the first week of propagation (greater than 1 container capacity) leached the preplant nutrient charge in the substrate and constant application of complete fertilizer at 100 mg N˙L-1 for 21 days reduced root dry weight. Tissue nutrient decline was observed prior to root emergence and when initial tissue nutrient concentrations were 4.9%N or lower, they quickly fell below recommended ranges prior to root emergence. Nutrient solutions applied in mist propagation rapidly affected tissue nutrient concentrations of cuttings with differences in tissue nutrient concentration apparent by 7 days after insertion into substrate, therefore foliar uptake of both macronutrient and micronutrients was effective in supplementing nutrient supply prior to root emergence and minimized the measured tissue nutrient decline during root initiation.