Growth Control of Perennial Ferns

Production of hardy ferns is becoming increasingly profitable as demand for these herbaceous perennials increases. However, growth management, especially of the larger species, in one-gallon pots can be very difficult.

At the request of a grower, we tested the use of the plant growth retardants (PGRs), Concise (uniconazole, Fine Americas, Inc.), Dazide (daminozide, Fine Americas, Inc.), or a tank mix of Dazide plus Citadel (chlormequat chloride, Fine Americas, Inc.), on two of the larger species.

We tested lady fern (Athyrium filix-femina) which is a very vigorous fern with an upright growth habit that can reach 2 to 4 feet tall and ostrich fern (Matteuccia struthiopteris), which has a vase shape with a more spreading habit than the lady fern and can get up to 6 feet tall under ideal field conditions.

Fall planted ferns were fully rooted with some shoot growth when donated to us by the grower in April. All plants were cut back uniformly to about 10 inches and PGRs were applied about 10 days after pruning. In addition to an untreated control group, PGR applications consisted of Concise foliar sprays at 30 or 60 ppm, Concise drenches (10 fl. oz. per pot) at 1 or 3 ppm, Dazide foliar spray at 5000 ppm, or a Tank Mix of Dazide:Citadel at 5000:1500 ppm applied as a foliar spray. All PGRs were applied twice, once at 10 days after cutting the plants back and again 18 days later. Plants were grown in an unheated cold frame mid-April through mid-June. Growth was measured at 0, 2, 4, and 6 weeks after the initial PGR treatment.

There were no statistically significant effects of the PGR applications on any of the growth measurements on either fern species. Although lady fern treated with Concise sprays at 30 or 60 ppm appeared to a bit “tighter”, the average plant height and width of the sprayed plants were actually slightly greater than those of the untreated plants (Photo 1). We found similar results with the Concise drenches, the Dazide sprays, or the Tank Mix spray applications.

With ostrich fern, there were no statistically significant differences in plant growth with any of the PGR applications and the appearance was not improved by the PGR treatments (Photo 2). In fact, we saw significant symptoms of phytotoxicity in response to all Concise applications (Photo 3). Although evident on both fern crops, the symptoms of twisting fronds was more pronounced on ostrich fern and still evident on the treated leaves at six weeks after initial treatment. These symptoms were not observed on plants treated with Dazide or the Tank Mix.

So, our initial study on growth regulation of two of the more vigorous hardy ferns did not identify successful PGR application protocols. As we’ve said before, PGR efficacy is affected by a number of factors. This paper reports the results of a single trial. We would like to encourage you to conduct your own trials. And, please share your results with us!!

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