Photo: Michal KlajbanCC BY-SA 4.0via Wikimedia Commonsresized / cropped
Thread Fern Plant Care
Blechnum filiforme (A.Cunn.) Ettingsh.
Updated · Sources · How we source care data
Icarus is a genus of ferns in the family Blechnaceae, subfamily Blechnoideae, with a single species Icarus filiformis, according to the Pteridophyte Phylogeny Group classification of 2016 (PPG I). The genus is accepted in a 2016 classification of the family Blechnaceae, but other sources sink it into a very broadly defined Blechnum, equivalent to the whole of the PPG I subfamily.
Every 7–10 days
Bright indirect to low light
60–75°F
50–70%
At a glance
How do you care for Thread Fern?
Water Thread Fern every 7–10 days, letting the top layer of soil dry out between waterings, and give it bright indirect to low light. It prefers temperatures of 60–75°F (16–24°C) and 50–70% humidity. Fertilize it every 6 months during the growing season.
What Is the Thread Fern?
Thread Fern (Blechnum filiforme) belongs to the Blechnaceae family within the Blechnum genus. Thread Fern is also known as Icarus filiformis.
Thread Fern displays a low rosette, spreading growth habit, reaching up to 1.5 ft tall with a spread of approximately 2 ft. Thread Fern produces non-flowering.
Leaf size: approximately 12 inches.
How Often Should You Water a Thread Fern?
Blechnum filiforme requires watering every 7–10 days. Allow the top layer of soil to dry between waterings to prevent root rot. Reduce watering frequency during winter when growth slows.
Watering Frequency
Every 7–10 days
Let soil partially dry between waterings
What Light Does the Thread Fern Need?
Thread Fern thrives in bright indirect to low light. Avoid placing Thread Fern in direct, harsh sunlight for extended periods, as this can scorch the foliage.
Light Requirement
Bright indirect to low light
What Temperature and Humidity Does the Thread Fern Prefer?
Blechnum filiforme grows best at temperatures of 60–75°F. Thread Fern prefers humidity levels of 50–70%. A pebble tray or humidifier helps maintain adequate moisture around the plant.
Temperature
60–75°F
Humidity
50–70%
What Soil Mix Works Best for a Thread Fern?
Rich, well-draining soil with high organic content. Good drainage is essential for Thread Fern to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Thread Fern?
Feed Thread Fern every 6 months during the growing season (spring and summer) with a balanced fertilizer diluted to the strength on the label.
Pause feeding in autumn and winter, when growth slows, and never fertilize dry soil — water first.
Fertilizing
Every 6 months
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Thread Fern?
Repot every 2-3 years in spring. Choose a pot one size larger than the current container, and ensure it has drainage holes to allow excess water to escape.
How Do You Propagate a Thread Fern?
Thread Fern can be propagated through spores, division of rhizomes. Similar propagation techniques also apply to blechnum castaneum plant care, which shares the same genus.
Is the Thread Fern Toxic to Pets and Children?
Pet safety not verified
The ASPCA does not list Thread Fern, so we can't confirm whether it is safe for cats and dogs. Keep pets from chewing it as a precaution.
This is a general caution, not veterinary or medical advice. If your pet ate a plant, contact your vet or animal poison control.
See all plants toxic to cats and plants toxic to dogs.
What Pests and Diseases Affect the Thread Fern?
Thread Fern is susceptible to mealybugs, scale insects. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.
Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.
What USDA Hardiness Zone Does the Thread Fern Need?
Thread Fern grows outdoors in USDA Zone 13a. It survives winters down to planting zone 13a. In cooler regions, grow Thread Fern as a houseplant or bring it indoors before the first frost.
Hardiness Zone
Zone 13a
Keep exploring plants
Thread Fern is one of many species covered in the complete plant care and identification guide, which groups plants by genus, attribute, and popularity.
It belongs to the Blechnum genus — compare its care with other Blechnum species on PlantoScan.
Blechnum is part of the Blechnaceae plant family — browse all Blechnaceae genera and species.
Thread Fern copes with lower light than most plants — browse the full list of low-light plants.
More Blechnum Species
Other Blechnum species in PlantoScan's care catalogue share similar watering, light, and soil preferences:
Sources
- Scientific name & taxonomy: Blechnum filiforme (A.Cunn.) Ettingsh., family Blechnaceae (first published in Denkschr. Ak. Wien 24: 21, t.6, f.5. 1864) — World Flora Online record, IPNI name record.
- Pet toxicity: Pet safety not verified: the ASPCA does not list Thread Fern, so we can't confirm whether it is safe for cats and dogs. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Photo: Michal Klajban, CC BY-SA 4.0, Wikimedia Commons — original.
- Hardiness zone: USDA Zone 13a, calculated from the plant's minimum temperature.
- Care values(watering, light, temperature, humidity, soil, fertilizing): PlantoScan's plant database, filtered by automatic plausibility checks — values that fail them are hidden. How we source and check plant data.
Spotted a mistake? Email info@upvision.media with the page link — we check and correct reported errors.
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