Due to replacements for broken plants, I find myself with a plethora of ferns. While I have plenty of shade beds for all of them, I thought I'd like to do 1 or 2 large containers with some of them. I have 24" diameter double wall containers, which are 20.5" inner diameter, and 18" tall. I estimate their capacity to be ~20 gallons.
The plants I have are 3" potted Dryopteris erythrosora 'Brilliance,' Athyrium niponicum 'Ghost,' Athyrium niponicum 'Pictum' and bareroot Matteuccia struthiopteris.
Winter hardiness...these are all listed at a low range of zones 2-5, with 'Brilliance' being the least hardy. I'm in zone 7. I could move the pots to a protected area for winter, but will that be necessary? My experience with other plants indicates a loss of 2 zones of hardiness for containerized plants. Will ferns behave the same way?
My soil mix would be a blend of finished and partially finished compost with some MiracleGro Potting mix. Is this a sufficient medium?
What sort of groupings and spacings would you recommend for these ferns? I also have both medium-height and short shade-loving grasses, like Chasmanthium, Deschampsia, Luzula, Sesleria and Carex muskingumensis which could be added, in addition to 'Palace Purple' Heuchera.
Any ideas, warnings or advice would be greatly appreciated.
I'd plant them in the container and not worry about the borderline fern, D. erythrosora 'Brilliance'. I haven't grown that cultivar but I have the species and it comes thru our 7b winters with no problems.
Mir-Gro soil is good for most ferns. Sometimes I add a little bit more fine wood chips to keep it well-aerated.
Give them some room to grow and fill out, so not too close at first.
Do watch to see that your ferns don't dry out during the winter. I have lost more to that than to cold with containered ferns.