What is the best potting mix or soil to use for Kimberly Queen ferns?
The Gardener’s Answer
Hi, Peggy: Kimberly Queen ferns (Nephrolepis obliterata) are hardy to zone 9 so they are considered tropicals for those of us gardening in Kentucky, although they are quite easy to over-winter if you have the space. In terms of soil, this will depend on if you are growing your fern in a container or in the ground. These upright sword ferns are great in containers or planted in a bed. Either way, it is important that the soil is well-drained. In all reality, they are not too picky when it comes to soil as long as it allows for proper drainage. In a container, use a high-quality container medium such as Pro-Mix. If the ferns are growing in the garden, just make sure the clay is not too compact so the roots can breathe. If your clay is compact, working in compost or an expanded slate material such as Permatil will help break up the clay and allow for better drainage. These ferns prefer the soil to be consistently moist, not sopping wet, but they should not be allowed to completely dry out between waterings. Moisture requirements will depend on how much sun the fern is exposed to. These ferns can handle a lot more sun than other ferns can. In fact, they are happy to grow in full sun. They can become very large, reaching 3 feet tall and wide at maturity. Make sure your containers have good drainage and you can feed your ferns once a month with your favorite fertilizer. Liquid or granular is fine.