When you think of ferns growing in the forest, you are probably envisioning the western sword fern (Polystichum munitum). Characterized by bright green, blade-like fronds that can grow up to 4 feet long. This common fern is native to North America and grows abundantly in forests and wetlands throughout the area, although it is also popular amongst gardeners as a low-fuss addition to the landscape. It does well in shady locations which makes it a popular choice for filling out gardens beneath trees or for shade gardens. While western sword ferns are typically grown outdoors, they can also be successfully grown indoors as houseplants, or in planters and containers that are overwintered indoors.
|Common Name||Western sword fern|
|Botanical Name||Polystichum munitum|
|Plant Type||Evergreen, rhizome|
|Mature Size||2-4 ft. tall, 2-4 ft. wide (outdoors); 1-2 ft. tall, 1-2 ft. wide (indoors)|
|Sun Exposure||Partial, shade|
|Soil Type||Moist but well-drained|
|Hardiness Zones||5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b|
|Native Area||North America|
Western Sword Fern Care
Western sword ferns are generally low-maintenance, easy-to-care-for plants as long as they are grown in the correct conditions. They grow happily outdoors in USDA zones 5 to 9 where they are accustomed to warm summers and cold winters, and they do best in consistently moist, humid conditions. As with all ferns, western sword ferns do not bloom and spread via spores rather than seeds. These spores can be seen on the underside of the fronds and appear as small brown spots that are symmetrically clustered together.
This common fern grows best in partial to full shade. While small amounts of direct sun throughout the day are fine, avoid prolonged periods of full sun which can burn the delicate fronds. If you are growing a western sword fern indoors, choose a location that receives bright to medium indirect light.
The western sword fern can adapt to a range of soil conditions as long as the soil is well-draining. It prefers acidic to slightly acidic soil and is often found growing naturally under pine trees and other evergreens where other plants can’t tolerate the acidic soil.
Western sword ferns should be watered regularly to ensure that the soil stays evenly moist, but not wet. If you are growing a western sword fern indoors you will likely need to water it at least once a week. These ferns are not drought-tolerant and a lack of water can quickly lead to the fronds developing dry, crispy edges and dying off.
Temperature and Humidity
The western sword fern is an evergreen fern that grows natively in USDA zones 5 to 9, tolerating winter temperatures as low as -20 degrees Fahrenheit (-28.9 degrees Celsius). It does best in humid conditions and enjoys warm summer temperatures. If you are growing a western sword fern indoors you will likely need to provide it with some extra humidity, either with a pebble tray beneath the pot or a humidifier placed nearby.
For the most part, ferns are light feeders and the same goes for the western sword fern. That being said, these ferns can benefit from a couple of applications of fertilizer during the spring and summer when they are actively growing. Choose a balanced fertilizer such as a 20-20-20 and dilute it to half-strength before applying.
These ferns can grow as many as 75 to 100 fronds per plant and will sometimes require some pruning in order to reduce crowding of the leaves, usually for aesthetic purposes. In the fall when the fronds begin to die off for the winter, do not remove the old fronds as they provide protection in the early spring months for the new growth.
Propagating Western Sword Ferns
Western sword ferns reproduce through spores, and through rhizomes. When it comes to manually propagating these ferns, they are most easily propagated through division of the rhizomes as the spores are small and difficult to work with. The best time to divide a western sword fern is in the early spring before the plant has fully sprouted.
To propagate Western Sword Ferns, follow these steps:
- Unearth a healthy cluster of rhizomes, and using your hands (or a sharp knife if required) separate a portion of the rhizomes from the main clump.
- Move the newly separated plant to its new location and water it thoroughly after planting.
- Avoid fertilizing the new plant for at least 6 months after separating, and ensure that it is well watered for the first couple of weeks after transplanting.
Potting and Repotting Western Sword Ferns
When grown in containers, western sword ferns should be repotted once a year to give the roots more space, refresh the soil, and encourage healthy growth. These ferns are best repotted in the early spring months before the fronds fully unfurl. Choose a container that is one size larger than the last, and be careful not to break too many of the delicate roots during repotting.
Western sword ferns only require overwintering if they are being grown outdoors in containers. While the rhizomes can survive through the cold weather in the ground, they are at risk of freezing completely in isolated containers and planters and should be moved indoors for the cold winter months.
Generally, western sword ferns are highly resistant to pests and diseases, although there are a few common garden and houseplant pests that can still pose a problem for these ornamental plants. Keep an eye out for signs of mealybugs, aphids, and fern mites which are all sap-sucking pests that will cause damage to the leaves of the fern; as well as nematodes which will cause damage to the roots of the fern which can lead to stunted growth and deformations of the foliage.
Common Problems with Western Sword Ferns
For the most part, western sword ferns are problem-free. The most common issues that arise with these plants are usually related to improper watering or fertilization.
Fronds that are browning and crispy around the edges are usually an indication that the fern is not receiving enough moisture or humidity. Ensure that the soil is not drying out between waterings and provide extra humidity if possible. However, browning tips can also be a result of over-fertilization, so cut back on fertilizing if you think this could be the cause.
Yellow Wilted Leaves
Fronds that are yellow and wilting are most commonly a result of overwatering and are most commonly seen in ferns that are grown in containers, either indoors or outdoors. Ensure that your container has drainage holes and double-check that the soil you are using is well-draining.
Do western sword ferns spread?
Western sword ferns spread through rhizomes over time.
How quickly do western sword ferns grow?
As with most ferns, western sword ferns are fairly slow-growing. It will usually take a couple of years before a western sword fern is large enough to be divided.
Should I apply epsom salts to my western sword fern?
Epsom salts can be used as a liquid fertilizer for ferns, providing magnesium sulfate which can speed up plant growth. However, it is not a necessary part of fern care, and consistent fertilization with a regular balanced fertilizer should be enough for a western sword fern.