When to Repot and Propagate Boston Fern

Best time to repot: spring

UW-Madison Extension recommends repotting or dividing a Boston fern every few years in spring, and Clemson Extension says early spring for overcrowded ferns. The reason is simple. In spring the plant is coming out of its winter rest and starting to push new fronds, so it roots into fresh mix quickly. In winter it is semi-dormant, and a pot of fresh, wet mix around a resting root ball invites rot.

Signs it needs repotting

Illinois Extension lists signs that apply to most houseplants, and they fit Boston fern well:

• Roots grow out of the drainage holes or show on the surface of the mix.
• The pot is packed with roots and very little mix.
• The plant wilts between normal waterings, because the root-filled pot can’t hold enough water.
• New fronds come in smaller than usual.

A fern that dries out by the next day even in mild weather has almost certainly outgrown its pot.

Pot and mix

Go up one pot size, or divide the plant and return a piece to the same pot. Use a mix that drains freely but holds moisture. Clemson suggests equal parts packaged houseplant mix and peat moss or leaf mold, while UW-Madison suggests peat and vermiculite. Make sure the pot has a drainage hole. Set the plant at the same depth it grew before, water it well, and hold off on fertilizer for a while. Clemson says to wait six months before feeding a newly repotted fern.

When and how to propagate

Divide in spring, at repotting time. Slide out the root ball and cut it vertically with a sharp knife into halves or quarters, keeping as many fronds as possible on each section. Pot each piece in fresh mix and keep it evenly moist while it settles in.

The plant’s runners root wherever they touch soil, so you can also pin a runner onto a small pot of moist mix during the growing season and cut it free once it has rooted. Spores are not a practical option at home, because named cultivars do not come true from spores.

When to move it outdoors

UW-Madison says potted Boston ferns can go outside once all danger of frost is past. The last frost date alone can be too early, though, because nights often stay cold for a few more weeks. Illinois Extension’s rule for houseplants is to wait until nights stay above 50°F.

Start in full shade, such as a covered porch or the north side of the house. Illinois Extension notes that sudden strong light burns the leaves of houseplants moved outside. Take the pot out of its saucer so rain can drain away. Outdoors, a fern in a basket can dry out in a single hot, windy day, so check it daily.

When to bring it back in

UW-Madison says to move the fern inside, or protect it, when temperatures dip into the low 40s °F. Purdue Extension’s general advice is to bring houseplants in before temperatures drop to 55°F, and Illinois Extension uses 50°F. Moving the fern when nights are in the low 50s °F gives you a margin and makes the shift indoors less abrupt. On warm days you can carry it in at night and back out in the morning.

Check it for pests before it comes inside. Look over the fronds and the undersides of the leaflets for scale, mealybugs and mites, and look for slugs on the pot. Rinse the plant with a firm spray of water. Clemson warns that many pesticide sprays injure ferns, so test any product on a few fronds first. Purdue suggests checking well ahead of the move, since it can take several treatments to clear pests. Indoors, expect some leaflet drop as the plant adjusts to lower light, and water less as its growth slows.