Actual Performance versus Theoretical Advantages of Polyacrylamide Hydrogel throughout Bedding Plant Production

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add signifi cantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca 2+ and Mg 2+ ). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported benefi cial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species (pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)) was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain refl ectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, fl ower number, fl ower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed signifi cant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was signifi cantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total fl ower numbers and fl ower longev- ity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefi ts from hydrogels confi rms the potential benefi t early in production with little to no benefi t later in production and in post-produc- tion. These data will assist growers in determining if the benefi ts derived from the use of PAM justify the added cost of medium. ideal for use in crop production. These products