A native of the Eastern part of North America, christmas fern can be found in wooded areas and streambanks. It enjoys a slightly shady habitat and, while Polystichum acrostichoides can grow in colonies, it can also be found singly. The common name of Polystichum acrostichoides is due to the fact that the evergreen fronds are often still green at Christmastime.
I. Appearance and Characteristics
Polystichum acrostichoides, commonly denominated Christmas fern, is a perennial, evergreen fern native to eastern North America, from Nova Scotia west to Minnesota and south to Florida and eastern Texas. It is one of the most common ferns in eastern North America, being found in moist and shady habitats in woodlands, stream banks and rocky slopes. The common name derives from the evergreen fronds, which are often still green at Christmas.
Christmas fern has a tufted, clumping habit, with its fronds arising from a central growth point. It can form colonies, but frequently grows singly or in twos or threes. In winter, the fertile fronds die; the sterile fronds remain through the winter, and are often flattened to the ground by low temperatures and snow cover. The frond is supported by a dark brown- to black-colored stipe, or stem, which is typically a quarter to a third of the overall frond length. Coarse, light-brown-to-tan scales cover the stipe, and are typically about 5-millimetre-long (0.20 in) and translucent. The coiled, developing fronds (“crosiers”) are scaly, greyish and prominent in early spring.
Fronds are 30-to-80-centimetre-long (12 to 31 in) and 5-to-12-centimetre-broad (2.0 to 4.7 in), dark green and rather leathery in texture; their undersides may be covered in very sparse hairs. They have 20 to 35 pairs of pinnae. Each pinna is typically 4-centimetre-long (1.6 in) and has a finely serrulate or spiny edge, and is oblong to falcate in shape. The fine teeth or spines on the edge of the pinna are oriented towards its tip. Each pinna has a small, triangular, “thumblike” lobe at its base. The light brown spores are produced on fertile pinnae, at the frond’s tip, which are conspicuously smaller than the sterile pinnae further down the frond. These fertile pinnae can be described as “acrostichoid”, given that the sporangia occupy most of the lower surface of the pinna.
Christmas fern resembles the Pacific Coast sword fern, Polystichum munitum, although forming less expansive tufts and differing from it and from almost all other ferns in that fertile pinnae of the Christmas fern are noticeably reduced in size relative to the sterile pinnae, while being located on the same frond.
P. acrostichoides is known to hybridize with Polystichum braunii in areas where their ranges overlap.
Christmas fern is popular in cultivation as an ornamental plant for gardens, including natural gardens, as it is easy to cultivate in a range of environments and soils. Being evergreen, it is sometimes used in winter-oriented garden design.
This fern can conserve soil and allay erosion of steep slopes. The fronds are semi-erect until the first killing frost, after which they lie prostrate on the ground and effectively hold in place the duff layer of the forest floor, enabling the gradual decomposition of the duff into humus, which in turn builds the soil.
II. How to Grow and Care
Sunlight
Like other ferns, Christmas ferns do best in conditions that mimic the shady forest floor of their native habitat, the temperate woodlands of North America. They can tolerate full shade but prefer dappled light, the sort of sun that filters through a forest canopy. If they get too much sun, their deep green fronds fade, and the plant becomes stunted. In Southern climates, the fronds burn if they get too much sunlight. Christmas ferns can tolerate more light than most other ferns if the soil is kept moist.
Temperature and Humidity
Christmas fern needs cool, shady conditions. This isn’t a good plant for hot, dry regions. Frost-tolerant Christmas fern thrives in temperatures of 50°F to 70°F, with humidity levels of at least 50 percent.
Watering
Getting the moisture levels right can be the key to flourishing ferns. A once-a-week watering schedule during the growing season is usually more than enough to maintain even moisture. You don’t want to let the soil get waterlogged, and while they’re mildly drought-tolerant, allowing them to dry out too much won’t encourage the healthiest-looking plants.
Soil
Christmas ferns are pretty forgiving regarding soil conditions, providing it’s well-drained. The only soil type they aren’t keen on is dense clay, as they’re prone to crown rot if left in standing water, particularly in the winter. They’ll perform best if the soil is rich in organic matter and moist, but they can tolerate dry, infertile conditions. Mulching around the plant boosts nutrients and helps to hold in moisture.
Fertilizing
When it grows in organically rich soil, Christmas fern only needs to be fertilized once a year—in the spring—with fertilizer for acid-loving plants. Fertilizer for azaleas and hydrangeas works for this fern, too. Follow the product instructions for quantity and frequency.
Planting Instructions
Plant Christmas fern in spring after the last frost or early fall before the first frost. Dig a hole as deep as the root ball and twice as wide to give the roots (rhizomes) room to grow. Add compost or organic material to the hole and position the root crown barely above soil level. Space your plants 18 inches apart to give them room to reach their full size. Mulch the ferns to keep their roots cool and the soil moist. It can take several years for Christmas ferns to become established.
Pruning
Unfussy Christmas ferns don’t need pruning. Just remove dead, damaged, or yellowing leaves throughout the year as they appear. Don’t trim the foliage in the spring when new fiddleheads appear, or you’ll damage the fronds’ ability to feed the plant via photosynthesis.
Propagation
When you already have healthy mature plants, it’s super easy to add more Christmas ferns to your collection by propagating them through root division in the early spring. If you want more of a challenge, try sowing ripe spores. Follow these steps to increase your chances of success:
- Spores darken and naturally fall off the underside of the fronds when they’re ripe. This usually occurs around October. Don’t try picking them off before they are ready, as they’ll likely be unviable.
- Gather spores from the fronds with narrower tips (these are more likely to be fertile).
- You can cut off a frond and place it between two sheets of white paper. The spores will drop off over the next 24 hours if fully ripe.
- Make sure you separate any accompanying chaff before sowing the spores. Gently tipping and tapping the paper usually causes the chaff to fall away while the spores remain.
- Dust the spores onto the top of a sterile, moist potting mix suitable for ferns, ensuring they make good contact with the mix.
- Mist the potting mix and, when fully moist, cover the container with plastic and place it in a tray with a couple of inches of water.
- Position the tray in a spot with plenty of warmth and access to indirect sunlight.
Replace the water regularly. Don’t let the soil waterlog or dry out.
- It could take two or three months, but be patient and look for the appearance of a carpet of prothalli (heart-shaped shoots)
- Gently transplant clumps into individual pots filled with moist potting mix when the prothalli are around 1/4 inch tall and leave them uncovered.
- Once the prothalli are around 1 inch tall and fronds begin to appear on them, you can gradually harden them off in preparation to transplant them to their spot in your garden.
- Wait until they are at least 4 to 6 inches tall and the danger of any frost has passed before transferring outdoors.
Potting and Repotting
Christmas fern can grow indoors, but you must provide plenty of humidity and keep the plant out of direct sunlight. Put a potful of Christmas fern in a steamy bathroom by a window that gets morning sun for good results, or add a humidifier to the room where the plant is located. This fern doesn’t need annual repotting—every two years is usually sufficient.
Pests and Diseases
This might be a trouble-free plant when the conditions are right, but keep an eye out for the issues below—they’re usually a sign that you need to switch something up.
Yellowing Leaves
If the fronds on your fern look a bit pale and lose their lush green color, it might be getting dry and sun-scorched. Don’t forget these plants do well in shadier spots.
Dropping Leaves
They might be more drought tolerant than some fern species, but Christmas ferns like even moisture to thrive. Check the soil if you spot leaves dropping on the fronds, and consider upping your watering schedule (without waterlogging).
Browning Tips
Crown rot is one of the most common issues for Christmas ferns. It’s usually a result of waterlogging caused by poor soil drainage or overwatering. If you start to see the tips of the fronds turning brown, this can be an early indicator that rot is setting in.
III. Uses and Benefits
Christmas fern is easy to cultivate, reliable, and a good choice for areas where soil erosion is a concern. This elegant fern is popular in woodland gardens, shade gardens, and areas where soil quality is poor, like next to walls or on slopes. Hostas, astilbes, and bleeding hearts make great companion plants, as they provide some color.
IV. Christmas Fern Companion Plants
- Hosta
Hosta is one of the most frequently grown garden plants. Hosta, also known as plantain lily, has big, heart-shaped leaves that look tropical, but this plant is cold-hardy and easy to grow. The tough, shade-loving perennial lights up shady spots in the landscape in summer and spring and comes in a seemingly endless range of color variations. Hosta thrives in the same growing conditions as Christmas fern, so it makes a good neighbor in the garden.
- Astilbe
Astilbe is a gorgeous plant thanks to its fern-like bronze and green leaves and colorful plumed blossoms in pinks, reds, purples, and whites. This showy perennial thrives in the same shade and moist soil as Christmas fern, so they are good garden neighbors. Astilbe’s dramatic, spikey flowers attract pollinators that would otherwise pass by a border of ferns.
- Bleeding Heart
This old-fashioned perennial is a cottage garden favorite. Its heart-shaped pink or white blooms are among the first flowers to come up in the spring, and they look lovely paired with the feathery fronds of Christmas fern. Bleeding heart thrives in the same shade and moist soil as Christmas fern, so they go together well. Try ‘Gold Heart’ because its chartreuse foliage and pink blooms contrast nicely with the deep green, leathery fronds of Christmas fern.
