Effects of controlled-release fertilizer and supplemental magnesium on leatherleaf fern frond yield and quality

Robert H. Stamps, Annette L. Chandler


There are economic and environmental reasons to reduce fertilizer application rates, especially nitrogen, during the production of leatherleaf fern (Rumohra adiantiformis). However, because the market demands that the fern fronds be dark green in color, there is interest in determining which nutrients besides nitrogen might be the most important in producing green coloration and what effects they might have on frond vase life. Chlorophyll a and b are the pigments responsible for the green color of fern fronds. Magnesium (Mg) is an integral component of and the only mineral constituent of the chlorophyll molecule. Thus, supplemental Mg applications (50, 100, and 150 lb/acre per year) were made using polymer-coated kieserite (MgSO[sub4]·7H[sub2]O) to established leatherleaf fern beds being fertilized at two nitrogen application rates, 200 and 250 lb/ acre per year, using a 15-2.2-12.6 (N-P-K) controlled-release fertilizer (CRF) containing Mg (2%) and micronutrients. The fern was growing in a shadehouse and irrigated from overhead. Initially, the fertilizer application rate had a slight effect on frond color; however, supplemental Mg had no effect. Treatments had no effect on frond chlorophyll content (inferred from SPAD values). Frond tissue analysis showed that Mg content increased with increasing supplemental Mg application rates but Mg and fertilizer treatments had no effect on frond calcium, copper, iron, manganese, or zinc content. Fronds from plots treated with the higher CRF rate were heavier than those treated with the lower CRF rate. Initially, vase life increased with increasing supplemental Mg rate but Mg rate had no effect at subsequent harvests. These results substantiate recommended Mg application rates.


rumohra adiantiformis; chlorophyll; elemental content; foliage color; spad value; vase life

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283