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Plant care

Forked Spleenwort (Northern Spleenwort) care

Asplenium septentrionale

Also called Forked Spleenwort, Northern Spleenwort, Grass Fern.

RHS H5USDA 4-8Mildly toxic to petsIndoor 5–20 cm tall and 10–30 cm wide.

Watering rhythm

Medium indirect light (a couple of metres from a window)

Sparingly — water only when the growing medium is dry

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Light

Medium indirect light (a couple of metres from a window)

Soil

Well-drained, gritty, slightly acidic to neutral

Humidity

Low to moderate (30–60%)

Temp

-20 to 25°C

Pet safety

Mildly toxic to pets

Mature size

5–20 cm tall and 10–30 cm wide.

Care at a glance

Light

The Goldilocks zone. Not the south-facing windowsill (too hot, too direct), not the back of the room (too dim, growth stalls). Tolerates partial shade to semi-open conditions; unlike many ferns it can handle periods of brighter indirect or even dappled direct light in its rocky habitat, but scorches in prolonged direct summer sun. If you can't decide, a free phone lux-meter app aimed at the leaf at noon should read between 800 and 1,500 lux.

Watering

Watering forked spleenwort: sparingly — water only when the growing medium is dry. The number that matters isn't the day of the week — it's how dry the top 2-3 cm of the pot feels. A finger in the soil tells you more than a watering app. After every watering, tip the saucer. One of the most drought-tolerant spleenworts; treat it similarly to an alpine, allowing the substrate to dry between waterings, and dramatically reduce watering in winter to avoid crown rot.

Soil and pot

Forked Spleenwort grows best in well-drained, gritty, slightly acidic to neutral. Requires a sharply drained, gritty mix — a 50:50 blend of horticultural grit and loam-based compost is ideal; unlike wall rue, it prefers near-neutral to slightly acidic rather than alkaline substrates (pH 5.5–7.0). A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Forked Spleenwort sits happiest at around Low to moderate (30–60%) humidity and -20 to 25°C (-4 to 77°F). Naturally adapted to exposed, rocky cliff environments with free air movement; does not need elevated humidity and suffers in stagnant, persistently damp air. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed forked spleenwort sparingly. No feeding required; excess nutrients cause atypical, lush growth that is out of character and susceptible to disease in this naturally lean-growing species. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on forked spleenwort in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Crown rot from poor drainage — The greatest cultivation risk; the crown will rot if the substrate stays wet in winter — use a very gritty mix, ensure container drainage holes are unobstructed, and keep in a sheltered spot during prolonged wet winters.
  • Vine weevil larvae — The compact root system of small crevice ferns is particularly vulnerable to vine weevil grub damage; apply Steinernema kraussei nematodes in early autumn when soil temperature is above 5°C.

Propagation

Spore propagation is the primary method — sow fresh spores on moist, gritty, near-neutral compost in a sealed propagator at 15°C in a shaded position; division is rarely practical given the slow rate of growth and minimal clump size. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Forked Spleenwort is mildly toxic to pets. Asplenium septentrionale is not individually listed in the ASPCA Toxic and Non-Toxic Plant database. As with other Asplenium species not individually assessed, a mildly-toxic precautionary classification is used in line with general fern-class cautions (thiaminase content, unconfirmed carcinogenic compounds per PFAF). Incidental contact or minor nibbling is unlikely to cause serious harm, but ingestion should be discouraged. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Forked Spleenwort care — frequently asked questions

What is the common name for Asplenium septentrionale?

Asplenium septentrionale is most commonly called Forked Spleenwort, but it is also known as Forked Spleenwort, Northern Spleenwort, Grass Fern. The names refer to the same species, so care instructions for Forked Spleenwort apply identically to anything sold as Northern Spleenwort.

How much light does forked spleenwort need?

Forked Spleenwort grows best in medium indirect light (a couple of metres from a window). Tolerates partial shade to semi-open conditions; unlike many ferns it can handle periods of brighter indirect or even dappled direct light in its rocky habitat, but scorches in prolonged direct summer sun.

How often should I water forked spleenwort?

Water forked spleenwort sparingly — water only when the growing medium is dry. One of the most drought-tolerant spleenworts; treat it similarly to an alpine, allowing the substrate to dry between waterings, and dramatically reduce watering in winter to avoid crown rot. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is forked spleenwort toxic to cats and dogs?

Forked Spleenwort is mildly toxic to pets. Asplenium septentrionale is not individually listed in the ASPCA Toxic and Non-Toxic Plant database. As with other Asplenium species not individually assessed, a mildly-toxic precautionary classification is used in line with general fern-class cautions (thiaminase content, unconfirmed carcinogenic compounds per PFAF). Incidental contact or minor nibbling is unlikely to cause serious harm, but ingestion should be discouraged.

What USDA hardiness zone does forked spleenwort grow in?

Forked Spleenwort is rated for USDA zone 4-8 and RHS hardiness H5. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Forked Spleenwort deep-dive guides

Every aspect of forked spleenwort care, each with its own calibrated guide:

Featured in these plant shortlists

Forked Spleenwort qualifies for 6 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Forked Spleenwort is also known as Forked Spleenwort, Northern Spleenwort, and Grass Fern.