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Ostrich fern spreads by runners, horizontal underground stems that travel out from an established crown just below the surface and turn upward to form a new crown a foot or two (30 to 60 cm) away. A healthy plant sends out several of these each season. By the third or fourth year a single crown has become a small colony, and by the sixth it is a solid patch.
That means you rarely need to propagate deliberately. You harvest what the colony has already produced: lift the outer crowns, plant them where you want them, and the parent bed closes the gap again within a season or two. Every new bed you make can come from the first one, and beds made this way establish faster than bought crowns because the divisions are larger and travel a short distance.
The outer crowns are the ones to take. They are the youngest and most vigorous, they lift with less disturbance to the bed, and removing them relieves crowding at the edge rather than tearing a hole in the middle. Leave the center of an established colony undisturbed.
Dividing: do it while everything is dormant
Divide in autumn once the fronds have browned off, or in very early spring before the coils start to lift. Both work. Autumn division gives roots the cool damp months to establish before the plant has to support fronds, and is the better choice on ground that stays moist through winter. Early spring division suits cold areas where a newly planted crown might be heaved out of the ground by hard frost.
Do not divide during the growing season. A crown lifted with fronds out loses most of them, cannot replace them until the following spring, and often takes two years to recover. If you discover an escaped runner in midsummer, mark it and come back for it in autumn.
Water the bed the day before you dig if the soil is at all dry. Crowns lifted from damp soil hold their roots together and the runners come up intact; crowns pulled from dry ground shed most of their fine roots as the soil falls away.
- Find the runner, then follow it Clear the mulch and scrape gently with your fingers to expose the runner connecting the new crown to its parent. It usually sits one to two inches (3 to 5 cm) down and runs almost horizontally.
- Cut the runner cleanly Sever it with a sharp spade or knife about four inches (10 cm) from the new crown, leaving that stub attached to the division. Cut once, cleanly, rather than tearing.
- Lift with a full root ball Drive the spade in a hand's width outside the crown all the way round and lever the whole block up. Aim to keep a ball of soil about eight inches (20 cm) across and six inches (15 cm) deep around the roots.
- Trim and inspect Remove dead frond bases and any soft or blackened root. A good division has a firm crown with visible buds on top and pale live roots below. Discard anything with a soft or hollow crown.
- Replant at the same depth, immediately Set the crown tip level with the soil surface, spread the roots outward, firm the soil and soak the ground. Divisions dry out fast, so do not leave them lying about; if you must delay, heel them into damp soil or wrap the roots in wet material and keep them in deep shade.
- Do not pick from a division for two springs A divided crown throws a reduced flush its first spring. Every one of those coils must be allowed to unfurl so the plant can rebuild. Start picking lightly in the third spring.
How many divisions a bed can give
There is a limit to how hard you can plunder a colony. Taking the outer crowns is fine; taking so many that the bed thins out costs you fiddleheads for years. The rule of thumb is the same discipline as picking: take a quarter to a third of the crowns in a bed in any one autumn, all from the outer edge, and leave the rest to fill back in.
A four-year-old bed of six original crowns typically has fifteen to twenty crowns in it by autumn, so four or five divisions is a comfortable take. A bed planted last year has nothing to spare. If in doubt, count crowns in autumn two years running; a colony that gains crowns year on year can support division, and one that is static cannot.
| Bed age | Typical state | Divisions you can take in one autumn |
|---|---|---|
| 1 to 2 years | Original crowns only, first runners forming | None |
| 3 years | A few new crowns at the edge | One or two, edge only |
| 4 to 5 years | Colony closing up, clear outer ring of young crowns | A quarter of the crowns, all from the edge |
| 6 years and older | Dense patch, center may be crowded | A third of the crowns; thin the center as well if coils are shrinking |
| Any age, escaped runners | New crowns in lawn or borders | All of them, and they are free plants |
Spores: possible, slow, and mostly not worth it
Ostrich fern does not set seed. It reproduces from spores carried on the separate fertile fronds, which are short, stiff, dark brown structures that stand up in the middle of the crown and persist through winter after the green fronds have collapsed. Spores are released from these in late winter and early spring.
Raising ferns from spores is a genuine indoor propagation project: sow onto sterilized damp compost in a covered container, keep it in bright shade at around 65F (18C), and wait. A green film of prothalli appears over the surface in a couple of months, tiny fronds follow some weeks after that, and it is roughly two years before you have anything worth planting out and several more before it produces a pickable crown.
Since a division gives you a plant that is already years old, spore-raising is a curiosity rather than a practical route to a fiddlehead bed. Divide instead, unless you specifically want the experience of raising ferns from spores.
Record the parent crown for every division you make, along with the date and where you planted it. Five years on, when one bed is producing noticeably better than another, that record tells you whether it is the site or the stock, and which crowns to take your next divisions from.