Garden Detective

Sword ferns can thrive in containers

Sword ferns grow along the Crystal Springs trail in Huddart County Park in Woodside. These ferns also grow well in pots in the cooler areas of the garden.
Sword ferns grow along the Crystal Springs trail in Huddart County Park in Woodside. These ferns also grow well in pots in the cooler areas of the garden. Sacramento Bee file

Is it practical to plant ferns such as Autumn Fern and Western Sword Fern in containers? Will they grow to maturity as long as the container is big enough? I ask because here in Cameron Park (Zone 9) we have rocky soil and I’m not sure that these ferns would make it by planting them in the ground. Any input is welcome and appreciated.

Joe Coradetti, Cameron Park

According to UC master gardener Carmen Schindler, the sword fern is a beautiful, flexible and very low-maintenance addition to the garden. It is appropriate for USDA Zones 3 through 8, but also will grow in Zone 9.

With fronds that resemble its name, the sword fern is a long-lived evergreen fern that can become 4 feet tall and 7 or 8 feet wide in ideal conditions. However, it is more likely to grow to 2 or 3 feet tall and 4 to 6 feet wide. In a mature plant, as many as 100 dark-green, lance-shaped fronds may grow from the rhizome at the plant’s center. Each frond may reach 4 to 6 feet long and will live for several years.

The sword fern will reach its grandest proportions under classic fern conditions – moist, loamy soil with nearly full shade. However, it does quite well in dry shade, part shade and in soil with low to moderate nutrient levels. The sword fern prefers year-round moisture, but once established, the deep and fibrous roots make it quite drought resistant, especially when shaded.

When ferns are grown outdoors during summer, they should be located in the cooler areas of the garden, usually in deep shade or on the north side of the house or a garden structure. Avoid exposing ferns to full sun in summer. A humidity level of 30 percent is about as low as most ferns will tolerate. Forty to 50 percent is certainly a more desirable range.

Put pots of ferns or other plants in saucers or trays filled with gravel and water. This increases humidity around the plant. Always maintain the water level just below the surface of the gravel so the bottom of the pot won’t be standing in water. Some indoor gardeners add charcoal chips to the gravel. This helps keep the water clean and odor free. For best results, replace the gravel periodically or wash it thoroughly at three-month intervals as algae, etc., start to develop in the water or on the gravel. Sanitation is important in keeping down diseases and mosquitoes.

When you grow ferns in decorative tubs, ceramic or cache pots without drainage holes, it is not recommended to place gravel in the bottom of the container. A better approach is to plant the fern in a clay pot and set inside the decorative container. Then put sphagnum moss in the space between the two containers. Keep the moss moist. This helps increase humidity and prevents rapid drying of the soil.

Years ago, clay pots, wooden boxes or moss baskets were the most popular fern containers. Today, however, many gardeners use plastic pots. Growing plants in plastic pots is a bit different than other containers because moisture and air cannot move through plastic. This means you have to water the plants less often.

Regardless of the pot you use, drainage holes are necessary. In potting, place gravel or clean pieces of broken pots over the drainage holes to prevent clogging. Also, make certain the pots are thoroughly clean. If you’ve used the pots for other plants, you should scrub them thoroughly with a strong detergent and hot water. It’s also a good idea to soak the pots in a solution of one part household bleach and nine parts water. This eliminates disease problems. In mixing and handling the bleach solution, exercise caution. You may injure your skin and eyes if you handle the solution improperly.

When using new clay pots, soak them in clean water overnight, preferably longer. This rinses away any chemicals and thoroughly moistens the pot. Periodic washing of the pots is desirable, too. This helps remove scum, soil, accumulated fertilizer salts or other materials that might clog air spaces in clay pots.

Ferns require well-drained soil. Sandy soils or humus soils with good surface drainage are preferred. Growing mediums vary considerably. Good mixtures drain well because of different components such as coarse sand, gravel and charcoal. A typical mixture contains equal parts of peat moss, peat humus, leaf mold, ground sphagnum moss and manure. A soil mixture for ferns must hold adequate but not excessive moisture, contain organic matter and be well aerated so air can move through the soil. Regardless of the mixture you use, be sure it is thoroughly mixed. Damp ingredients are easier to mix and pot.


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