How to Propagate Ferns

How ferns reproduce — and why it matters for propagation

Ferns reproduce by spores, not seeds. This means fern propagation works differently from most garden plants. The three reliable methods for US gardeners are division (fastest), runner offset separation (for stoloniferous types), and spore sowing (slowest but most productive).

Ferns produce spores in structures called sori — the brown dots or patches visible on the undersides of fertile fronds. Each sorus contains thousands of microscopic spores. When conditions are right, spores germinate into a tiny intermediate structure called a prothallus. The prothallus produces the egg and sperm. If fertilization occurs, a new sporophyte (the fern plant we recognize) develops. The whole process takes months.

For most US gardeners, understanding spore biology is interesting but not necessary. Division and runner separation give faster, more reliable results. Spore propagation makes sense when you want many plants of a specific variety, or when dividing a particular species is difficult due to its root structure.

Method 1: Propagation by division

Division works for clump-forming ferns with fibrous or rhizomatous root systems. It is the fastest propagation method — a divided plant is already an established plant.

Division timing:

• Best: early spring when fiddleheads are just emerging (March–May depending on zone)
• Acceptable: late summer after the heat peak, at least 6 weeks before first frost
• Avoid: midsummer heat stress and winter dormancy periods

Suitable fern types for division include:

• Autumn fern (Dryopteris erythrosora)
• Male fern (Dryopteris filix-mas)
• Japanese painted fern (Athyrium niponicum)
• Ostrich fern (Matteuccia struthiopteris)
• Lady fern (Athyrium filix-femina)
• Christmas fern (Polystichum acrostichoides)

Step-by-step division process:

1. Water the fern thoroughly the day before dividing. Moist soil makes root separation easier and reduces transplant shock.
2. Dig up the entire clump with a garden fork, working 6–8 inches out from the base to avoid cutting roots.
3. Lift the root ball and set it on flat ground or a tarp.
4. Examine the root mass. Identify natural divisions — sections with both fronds and a solid piece of the root system.
5. For small clumps: pull apart by hand or use two garden forks inserted back-to-back to lever sections apart.
6. For large, dense clumps: use a sharp spade, serrated knife, or pruning saw. Make clean cuts. Jagged tearing increases disease entry points.
7. Each division needs at least 3–5 healthy fronds and a solid piece of root.
8. Replant divisions immediately at the same depth as the original plant. Do not bury the crown deeper than it was growing.
9. Water thoroughly and keep consistently moist for the first 4–6 weeks.

Division spacing by fern type:

For specific care details on one of the most popular division candidates, see autumn fern.

Method 2: Runner offset separation

Boston ferns and other stoloniferous species produce horizontal runners that develop small plantlets at their tips. Separate these when the offset is 2–3 inches across and has a visible root system.

Runner-producing fern types include:

• Boston fern (Nephrolepis exaltata) — the most common houseplant fern in the US
• Sword fern (Nephrolepis cordifolia)
• Rabbits foot fern (Davallia spp.)
• Staghorn fern (Platycerium spp.)

Separating Boston fern runners:

Boston ferns produce multiple thin stolons that hang over the pot’s edge or spread across soil. Each stolon develops a plantlet at the tip.

1. Wait until the plantlet at the stolon tip is 2–3 inches wide and shows clear root nubs.
2. Prepare a small 3–4-inch pot with moist potting mix.
3. Pin the stolon to the surface of the new pot’s soil using a bent wire or a hairpin, keeping the plantlet in contact with the soil. Do not cut the stolon yet.
4. Keep both pots consistently moist. The plantlet roots into the pot within 3–4 weeks.
5. Once rooted, cut the stolon between the parent plant and the new pot.
6. Grow the new plant in bright indirect light at 60–80°F. Humidity above 50% helps Boston ferns root strongly.

This layering technique is lower-stress than cutting the offset before roots form. It gives the new plant an established connection to the parent during the rooting period.

Staghorn fern pup separation:

Staghorn ferns (Platycerium) produce offsets called “pups” at the base of the plant. Wait until a pup is at least 4 inches wide — smaller offsets lack enough stored energy to establish independently. Use a sharp, clean knife to separate the pup where it connects to the parent. Mount on a board or plant in a mix of orchid bark and sphagnum moss.

Method 3: Spore propagation

Spore propagation produces many plants from one frond at no cost beyond time and patience. It takes 6–18 months from collection to a transplantable plant. The technique rewards gardeners who want rare cultivars or large quantities of a single species.

Collecting spores

1. Check fern fronds in late summer. Fertile fronds (those with sori) on the undersides are ready to harvest when the sori turn from green to brown. Brown, slightly fuzzy sori are at the right stage — before they open and release spores.
2. Cut a fertile frond at the base.
3. Place the frond face-down on a sheet of clean white paper inside a large paper bag or on a clean tray.
4. Leave undisturbed indoors in a dry location for 24–48 hours. Spores fall from the sori and collect on the paper.
5. Fold the paper carefully to collect the spores. Store in a sealed paper envelope (not plastic — moisture condenses and damages spores) in a cool, dry location.
6. Spores remain viable for several months to a few years depending on species.

Sowing spores

1. Sterilize the growing medium. Mix equal parts perlite, peat or coir, and fine potting mix. Pour boiling water through it, or microwave the moist mix for 90 seconds, to kill competing fungal spores. This step is critical — unsterilized mix grows mold before fern prothalli can establish.
2. Fill shallow seed trays or 4-inch pots with the cooled, sterilized mix. Press flat.
3. Sprinkle spores thinly on the surface. Do not cover — fern spores need light to germinate.
4. Water from below by setting the container in a tray of water until the surface is evenly moist. Do not water from above — spores wash away easily.
5. Cover the container with a clear plastic lid or plastic wrap. This creates the high-humidity environment fern prothalli need.
6. Place under fluorescent or LED grow lights at 12–16 hours per day. Keep temperature at 65–75°F. Do not use direct sunlight — it heats the enclosed container too much.

Germination timeline

Pricking out and potting up

Once sporelings reach 1–2 inches tall and can be individually handled, separate them from the mass. Use a fine skewer or toothpick to lift clumps of 3–5 sporelings with their roots. Transfer to individual 2-inch pots filled with a moist, fine-textured potting mix. Return to the high-humidity environment for 2–4 more weeks before gradually acclimating to normal humidity.

Humidity and light for all propagation methods

All fern propagation methods fail in dry air or direct sun. Humidity above 50% — ideally 60–70% — and bright indirect light are the two non-negotiable requirements.

US indoor environments in winter drop to 20–30% relative humidity, especially in forced-air heated homes. New fern divisions and all spore-germinated plants need supplemental humidity during establishment:

• Pebble tray with water beneath the pot
• Misting 1–2 times per day (less effective but better than nothing)
• Clear plastic bag tent over the plant for 2–3 weeks after division
• Dedicated plant humidifier for serious propagation setups

Direct sunlight bleaches and kills new fern fronds. North or east-facing windows in US homes provide appropriate indirect light for establishment. Under grow lights, keep new plants 12–18 inches below the light source to avoid heat stress.

For indoor growing setup options, see best grow lights and best soil for indoor plants.

Troubleshooting

New divisions wilting after transplant: Normal for 1–2 weeks. Keep consistently moist and shaded. Wilt from transplant shock recovers without intervention if the roots are intact.

Spore tray growing mold instead of fern prothalli: The medium was not sterilized, or moisture is too high. Discard moldy trays. Start over with boiling-water-sterilized mix and better ventilation under the cover.

Runners not rooting after 6 weeks: Check that the plantlet is actually in contact with moist soil. Secure with a bent wire or staple. Increase humidity around the runner connection point.

Divisions not growing new fronds after 8 weeks: The division may lack enough root tissue. Check whether the root section is attached and undamaged. Keep in a humid, shaded location another 4–6 weeks before assuming failure.

Fern propagation by species: quick reference

For details on how fern species perform as garden plants across US hardiness zones, see spider plant babies for a related look at how common houseplants produce offsets, and how to propagate pothos for a comparison of division-style propagation in a popular houseplant.