During propagation of cuttings, a large amount of water is typically applied, leading to a high volume of water and nutrients leached (we measured up to 49249 gallons leached per acre over a 4-week crop cycle in commercial greenhouses). In order to develop best management practices for propagation, and to reduce environmental impacts, our research aims to understand how to best manage leaching and applied fertilizer concentration during plug and cutting production.

One finding is that after 1.5 container capacities (about one soil volume) of water is applied, nutrients in the soil are mostly replaced by the applied fertilizer solution. That means it is very easy to leach out pre-plant fertilizer under mist. Ph.D. graduate Kate Santos found that tissue nutrient levels tend to drop during the rooting of cuttings, and that petunias can take up nutrients through the leaves even before roots form.

Management approaches include ensuring adequate fertilizer is applied during the stock plant phase to have moderate to high initial tissue nutrient levels in cuttings, applying a low fertilizer concentration in the mist, and recharging nutrients after plants are removed from mist. The long-term goal is to model changes in nutrient concentration (EC) and pH in plug trays with different fertigation practices. M.S. student Angelica Cretu is running experiments on leaching preplant fertilizer from commercial and research media in plug trays, and also recharging nutrients. A further step is to investigate the effect of water quality and fertilizer solution on pH drift under mist propagation conditions.

University of Florida: Paul Fisher, William Argo, Angelica Cretu, Kate Santos

Water relations of unrooted cuttings from harvest through propagation

1. Stomatal functioning from the harvest of cuttings on the stock plant through the postharvest environment and in the first days or weeks of propagation (until root initiation).

2. Quantifying water uptake potential through severed stem tissue. This value forms a baseline for water uptake. If evaporative demand exceeds this rate, then mist is required to reduce evaporative demand and to supply water through the leaf blade.

Developing models and control strategies for mist management

1. Develop an evapotranspiration model based on potential water uptake, stomatal behavior and environmental measurements to predict water demand for cuttings in propagation.

2. Use an Argus climate control computer to compare our evapotranspiration model to traditional static mist control strategies.

In the past year, Matthew Blanchard (Ph.D. candidate) quantified how temperature and the photosynthetic daily light integral (DLI) regulate plant development of over 25 herbaceous ornamental crops. Plants were grown at temperatures ranging from 57 to 79 °F (14 to 26 °C) under two DLIs in two different experimental periods. Data were collected on time to flower and flowering characteristics, such as flower number. We are currently analyzing the data and creating mathematical models that will be used to predict effects of temperature and DLI on production time. We will use this information with the USDA's Virtual Grower computer program to estimate heating costs given different production scenarios, different locations, and different times of the year. In the next year, we will grow crops at various fluctuating day/night temperatures to validate our generated models. Plant models will also be integrated into the Virtual Grower software.

We determined the length of the juvenile period and the minimum number of inductive photoperiods necessary for floral induction of more than ten bedding plant crops. Additionally, we have evaluated the effects of the number of inductive cycles and timing of exposure to the inductive photoperiod on crop quality parameters. This will allow us to develop production schedules that reduce production time without compromising crop quality.

Media-pH affects plant health and nutrition.  Micronutrients such as iron and manganese are taken up in toxic levels at low pH (below 5.8) by iron-efficient plants such as seed or zonal geraniums and marigolds, and inorganic iron is insoluble at high pH (above 6.4) causing deficiencies in iron-inefficient species such as petunia or calibrachoa.

Current research on pH management is focused on two areas: lime and fertilizers.  Post-doctoral researcher Jinsheng Huang is working on a range of laboratory protocols (the LimeR series) for media companies that measure the reactivity of different lime sources, which affects how quickly lime reacts to achieve a target pH; unreacted residual lime in growing media, which affects buffering to pH change; and how much lime is required for a particular batch of substrate.   The benefit is to assist media companies to help design well-buffered growing media.  We are continuing to model lime reaction, and refining protocols to estimate the lime requirements of different batches of growing media in order to achieve a target pH.

The potential acidity or basicity of a fertilizer written on the fertilizer bag is based on a model developed in the 1920's for soil application of solid fertilizer.  Many of the assumptions of this model do not apply to greenhouse culture (in other words, the numbers are wrong!).  Ph.D. student Connie Johnson is undertaking research to estimate the pH effect of fertilizers in container production.  The benefit is to better match fertilizer selection with water quality for a stable pH.  We are running hydroponics and growing media experiments with geraniums and impatiens to compare reported acidity of fertilizer with actual measured pH response.  A draft model of fertilizer acidity and basicity is being developed based on the charge balance principle where cations (such as ammonium) are acid and anions (such as nitrate) are basic.

University of Florida: Paul Fisher, William Argo, Jinsheng Huang, Connie Johnson, Rick Vetanovetz

Ph.D. candidates Matthew Blanchard and Daedre Craig have evaluated the use of an experimental formulation of paclobutrazol to control internode elongation of floriculture crops. We are presently repeating the work on different annual crops to determine if there are differences among application strategies (spray versus drench).

In addition, we have continued work with abscisic acid (to be marketed as ConTego in 2010 by Valent BioSciences) to evaluate its potential use on bedding plants to increase the postharvest tolerance to drought conditions. Experiments with these and other plant growth regulating compounds will continue throughout the next year.

Jinsheng Huang and Paul Fisher (University of Florida) present an overview of how lime reacts in container media, and introduces a series of laboratory protocols to predict pH response and lime buffering. A model is discussed that aims to integrate our current state of knowledge, and to allow R&D departments of media and fertilizer companies to explore the likely combined effects of different lime types, lime rates, and substrates.