Production and quality of greenhouse roses in recirculating nutrient systems

Greenhouse-grown rose plants were grown in either a non-recirculating (open) nutrient system, or a recirculating (closed) nutrient system with or without one of five amendments. Recirculation had no effect on harvest parameters during the first 8 weeks of the harvest period, but had a negative impact on stem length during the second 8 weeks, and on stem number and length when averaged over the entire harvest duration. Differences were not likely caused by changes in electrical conductivity or macro-nutrient concentrations of the nutrient solutions. Amendments to the recirculated solutions consisted of increased concentrations of Ca, B or Si, reduced pH, or use of an adsorbent resin to remove specific organic molecules. All amendments mitigated the negative effects of recirculation on at least two harvest parameters, but only during the second-half of the harvest period. With the exception of the intentional changes, mineral status of the nutrient solutions were similar in all recirculated treatments. Leaf chlorosis was observed in all recirculation treatments. It is likely that the reduction in rose quantity and quality in recirculation is caused by a combination of factors, some of which were ameliorated through the addition of specific amendments to the solution.