Challenges in the Greenhouse Production of Rosmarinus officinalis L.

Rosmarinus officinalis L. (rosemary) is popular as a culinary herb, landscape plant, and potted florist's crop. Little research has been reported on the greenhouse production of this plant. Effects of irrigation rate, fertilizer concentration, and growing media on root and shoot growth were investigated for R. officinalis 'Athens Blue Spires'. In the first experiment, rooted cuttings were potted and received fertilizer treatments of 100, 200, or 300 mg?L-1 nitrogen (N) from 15N-2.2P-12.2K water-soluble fertilizer for twelve weeks. Two irrigation regimes were imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 30% or 20% volumetric soil moisture content. Root and shoot dry weights showed irrigation rate did not effect roots, but the higher irrigation rate produced larger shoots at all fertilizer concentrations. The largest roots and shoots were a product of the lowest fertilizer concentration. In the second experiment, rooted cuttings of the same cultivar were potted and received fertilizer treatments of 50, 100, 150, or 200 mg?L-1 N from 15N-2.2P-12.2K water-soluble fertilizer for 2, 4, 6, or 8 weeks. Plants were harvested at the end of each treatment. A third irrigation regime was imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Root and shoot dry weights showed neither irrigation nor fertilizer were significant at week two, six, or eight. Dry weights showed irrigation was significant for roots at week four with the lowest irrigation rate producing the largest roots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. Irrigation was also significant at week four for shoots with the lowest irrigation rate producing the largest shoots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. In the third experiment 'Athens Blue Spires' rooted cuttings were potted in five different soilless media [Fafard 52 (24% peat, 60% bark, 8% perlite, 8% vermiculite); Fafard 3B (45% peat, 25% bark, 15% perlite, 15% vermiculite); Scott's Sierra Perennial Mix (25% peat, 65% bark, 10% perlite); Scott's Metro Mix 700 with Coir (25% coir, 50% bark, 10% perlite, 15% vermiculite); and a nursery mix (89% pine bark, 11% sand)]. Plants were irrigated for fourteen weeks with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 30% or <20% volumetric soil moisture content. Growing media affected shoot dry weight with the highest-percentage peat media (Fafard 3B) producing the largest plants. All were of marketable quality. Irrigation rate did not affect root dry weight, but the higher rate produced larger shoots in each of the five media. The fourth experiment examined the growth of R. officinalis 'Tuscan Blue' rooted cuttings when planted in five different growing media [Fafard 52, Fafard 3B, Scott's Perennial, Metro Mix 560 with coir (30% coir, 15% peat, 40% bark, and 15% perlite), and 100% pine bark]. A third irrigation regime was imposed - plants were irrigated with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Treatments lasted for 2, 4, 6, or 8 weeks and plants were harvested at the end of each treatment. Dry weights showed neither media nor irrigation was significant for roots or shoots at weeks four or eight. However, at week two, media significantly affected root dry weight with the heaviest roots produced by the two perennial mixes (Scott's perennial and Fafard 52). Growing media affected shoot dry weight at week six with the highest-percentage peat media (Fafard 3B) producing the largest plants at the low and high irrigation rate. Irrigation also affected root dry weight at week six with the two lowest irrigation rates producing the heaviest roots in all media.