Growing Hartford Fern from Spores

Lygodium palmatum sporeling at five months old.

In a previous post I talked about the biology and ecology of the Hartford Fern, Lygodium palmatum, America's lone native species of climbing fern. In this post I will discuss the process of growing this rare and botanically interesting plant from spores, which turns out to be relatively quick and unproblematic, as fern propagation goes. 

Spores: Plant material of Lygodium palmatum is occasionally available from mail order nurseries, but the only regular source of spores that I am aware of is the American Fern Society's spore exchange, currently meticulously curated by Brian Aikins in Washington state. Spores could also be collected from mature plants in late autumn, if one happens to already have access to cultivated plants.

Lygodium palmatum, gametophyte (dark green) with one-leaved sporophyte emerging (light green).

Soil: Hartford Fern grows in acidic soil, so I have used a light, acidic mixture of sphagnum peat moss and perlite for starting spores. I pasteurize small batches of soil in a microwave (on high for about five minutes), which helps to prevent or at least delay contamination of spore pots by algae and moss. 

Sowing Spore: Lygodium spores are as fine as dust and must be sown on the surface of pots of soil, where they will be exposed to light. Temperate zone ferns like L. palmatum are best started in spring; no special pre-treatment, such as cold stratification, is needed. Ideally, spores should be sown thinly, so that the sporelings will have a little space between them, but this is difficult to accomplish. The soil is kept moist to wet by watering from below or with gentle misting, and the whole pot should be kept in a humid, closed environment in a plastic bag or terrarium. Bright but indirect light is best (such as in an east-facing window, or at the periphery of a grow light setup). 

Germination and Sporeling Care: Lygodium spores germinate within a month or so, giving rise to crinkly, dark-green gametophytes. Gametophytes are the haploid (only one set of chromosomes), gamete-producing phase of the plant alternation of generations. The spore sowing mix has very little nutrient content on its own, so misting several times a month with half-strength water-soluble houseplant fertilizer is needed from germination on. 

The gametophytes take several months to mature, at which point they produce sperm and eggs, fertilization takes place, and tiny, light-green leaves start to emerge from the undersides of the gametophytes. These light-green leaves are the young sporophytes, the diploid, spore-producing phase of the life cycle. In ferns, the sporophyte is the large, long-lived phase of the life cycle; what we typically think of as a fern plant. 

The sporelings can be transplanted out to individual pots when the sporophytes have one or two fully expanded leaves and are about a centimeter or two across; this will probably be in summer, about four months after sowing. Transplants should be gradually adjusted to brighter sun and lower humidity, in preparation for overwintering the young plants in a cold greenhouse or sheltered position outdoors.

Lygodium palmatum, 6 month sporeling starting to put out dissected leaves. 

Hartford Fern

Lygodium palmatum climbing on Osmundastrum frond. Windham County, Connecticut, August 13 2021.

One of the most unusual native ferns in my area is Lygodium palmatum, the Hartford Fern or American Climbing Fern. The climbing ferns are about 40 species of Lygodium, the lone genus in the family Lygodiaceae, distantly related to the curly-grass ferns (family Schizaeaceae). The climbing ferns are mostly tropical, with a few representatives in north temperate regions, including Lygodium palmatum, the sole species of climbing fern native to the US.

Lygodium palmatum with fertile and sterile leaflets, climbing on Winterberry (Ilex verticillata).

Climbing ferns are indeed vines--uniquely, I believe, among ferns--which twine around other plants in order to reach sunlight and position their spore-producing structures higher for more efficient spore dispersal. Perhaps even more peculiar than the vining habit of Lygodium, is the fact that the vines are not stems, but very long, indeterminately growing leaves (the only stem tissue in climbing ferns is the underground rhizome from which the twining leaves arise). The fronds grow from a meristem (growth point) at their tip, periodically producing new leaflets (pinnae). Some large tropical species of Lygodium have additional meristems at the base of each leaflet, which can grow out as new vining fronds, especially if the main growing point of the frond is severed. This growth form is a remarkable parallel to the organization of the entire shoot system--with shoot apical meristems, stems, leaves and axillary buds--of just about every other group of plants. 

Lygodium palmatum, fertile leaflet underside with immature sori, in August.

 Mature Hartford Ferns bear two different types of leaflets. On the lower parts of the frond there are broad, palmate (hand-shaped) sterile pinnae, which are strictly there for photosynthesis, not reproduction. The more distal parts of the frond may bear fertile pinnae, which are more branched and end in many narrow pinnules. Fertile leaflets have sori on their undersides, which are clusters of minute sporangia, the capsules that shed spores in autumn.

Lygodium palmatum patch, with Marsh Fern (Thelypteris palustris).

Hartford Fern is associated with wetlands with acidic soil; I have seen it in Red Maple swamp and river floodplains, generally in spots with dappled sun under a somewhat patchy tree canopy ("high shade" as wildflower gardeners say). Lygodium grows on hummocks, banks and other slightly elevated spots in wetlands, seemingly avoiding low places that would have standing water in spring. Associated plants include Cinnamon Fern (Osmundastrum cinnamomeum), Royal Fern (Osmunda regalis), Catbrier (Smilax rotundifolia) and the usual shrubs of acidic swampland such as Sweet Pepperbush (Clethra alnifolia) and Highbush Blueberry (Vaccinium corymbosum).

Lygodium palmatum habitat, Windham County, Ct.

 Red maple swamp with Cinnamon Ferns is not exactly an uncommon habitat in the Northeast; there are probably hundreds of acres of wetland that looks appropriate for Lygodium, in my town alone. But as far as I know, there are no Lygodium populations at all in my immediate area. Hartford Fern is geographically widespread, too, being native to most of the states east of the Mississippi. It's a bit of puzzle, then, just how rare our native climbing fern is; there are apparently fewer than five patches of it in all of New York state, for instance. 

Part of the reason for Hartford Fern's rarity is thought to be the collection of the fern's evergreen fronds for Christmas decorations in the nineteenth century, which led to the state of Connecticut passing legal protections for the species in 1869, the first endangered plant legislation in the United States. Land clearance for agriculture and the flooding of wetlands by widespread construction of dams for mills probably also harmed Lygodium populations in New England. It's possible that there is some non-obvious reason, as well, why most semi-open wet woodlands are not actually suitable for Lygodium, despite looking similar to the vanishingly rare spots where Hartford Fern does grow. In any event, catching sight of our native climbing fern is a special and unfortunately quite uncommon occurrence. 

--

A followup post covers propagating Hartford Fern from spores in cultivation.

 

Midsummer Orchids

Platanthera psycodes, Lesser Purple Fringed Bog Orchid.

 The hazy, hot and humid period in late July in early August is generally a slow time for wildflowers in New England--the spring ephemerals are long past and the late-summer asters and goldenrods haven't started--but there are a number of native orchids that bloom during the height of summer.

 

Goodyera tesselata, Checkered Rattlesnake-Plantain, in late July in Ashford, Ct.

 

 Goodyera, the rattlesnake-plantains, is a large, almost cosmopolitan genus of terrestrial orchids, with two species extant in Connecticut (and one more probably extirpated). Goodyera tesselata is the less common of the two, a small plant with pale, checkered leaves. It favors well-drained, piney woods, and is more frequently encountered to the north of my area. Checkered Rattlesnake-Plantain  is thought to be derived from an ancient hybridization event between two other Goodyera species.

 

Goodyera pubescens, Downy Rattlesnake-Plantain, in late July in Mansfield, Ct.

 

Goodyera pubescens, or Downy Rattlesnake-Plantain, is by far the more common species in its genus in southern New England, and is one of the most frequently encountered wild orchids overall. An observant hiker can spot the green-and-silver variegated rosettes and spikes of white flowers of this charming plant, on virtually any walk through the woods in eastern Connecticut. The rosettes of leaves grow from branching underground rhizomes, and can form large colonies.

Platanthera clavellata, Small Green Wood Orchid, in late July in Mansfield, Ct.

Platanthera is the most diverse genus of orchids in New England, with about 16 species, though many of these are very rare, localized, or "historical" (locally extinct). Many species have had a hard time with development, invasive species (including earthworms and slugs), forest succession, deer overpopulation, a warming climate, and probably in some cases direct picking and digging by gardeners. One species that seems to be doing pretty well in Connecticut is P. clavellata, which is not that uncommon in acidic, swampy woods and on stream banks. It is difficult to spot out-of-flower, with a few nondescript oval leaves, and even in flower is not what you would call showy, so it is quite possible that it is even more frequent than my impressions would indicate.

Platanthera psycodes, Lesser Purple Fringed Bog Orchid, in late July in Tolland County, Ct.

Platanthera psycodes, on the other hand, is rather uncommon in my area, but beautiful and totally obvious when in flower. Flowering plants are waist-high. with lovely violet-pink petals. The flowers are not strongly scented, have long nectar spurs behind the petals, and are pollinated by butterflies. The plants pictured here were scattered along a cold, spring-fed stream, in mucky, acidic soil.

Soils for Succulents

 Basic Cactus and Succulent Mix

1 part potting soil for houseplants

2 parts sharp sand 

1 part vermiculite

1 part perlite

This is a good basic soil for most potted cactus and succulent plants, consisting of ingredients that are easily available from nurseries or hardware stores, at least in my part of the world. The commercial potting soil portion holds some water and nutrients, while the sand drains well and provides inert bulk. Perlite and vermiculite are lightweight expanded minerals that help aeration and drainage, with vermiculite also being able to hold some water and nutrients. 

The sand component is the potentially most variable part of any of these mixes; I've seen a surprising range of stuff sold as bagged sand at the hardware store, even under the same brand name at different times. Ideally I look for sand that is mostly quartz, with rough, irregular grains; in New England this is mostly river sand mined from old glacial deposits. Beach sand is usually not suitable, since it tends to consist of smooth, rounded grains that pack together. Sand that consists solely of very fine grains (granulated sugar sized) is also not good. I've occasionally run into "sand" that was actually some kind of industrial ground-up rock, with a mixture of larger chunks and a lot of powdery material; this has proven disastrous for succulent soil usage.

 UConn Cactus and Succulent Mix

3 gallons soilless potting medium 

3 gallons sharp sand

1 gallon perlite

1 gallon vermiculite

2 gallons calcined clay pellets

1 gallon pumice (or sponge rock or expanded shale)

1 gallon pea-sized gravel

3 tablespoons slow-release fertilizer

This is the cactus soil used in the biodiversity greenhouses at the University of Connecticut, made up in big batches in an electric soil mixer. The soilless medium is currently Jolly Gardener C/B, a peat and composted bark mix; in the past we have used peat/perlite Cornell-type mixes from the ProMix and Fafard lines. Coir-based mediums also give acceptable results with this recipe.  

The UConn C&S mix includes some coarse inorganic components that are a little more exotic than vermiculite and perlite. Calcined clay comes from several manufacturers; we have used Turface MVP and Primera One Field Conditioner. It's similar to kitty litter, but fired at a higher temperature so that it does not break back down into clay when wet. 

Pumice has become somewhat difficult to find in the eastern US in recent years; we have a stockpile that was ordered in bulk from Hess Pumice Products. Pumice substitutes that might be easier to find in the Northeast include sponge rock (an expanded volcanic mineral similar to perlite) and expanded shale, which is manufactured in New York and available under the Norlite, Solite and Espoma Soil Perfector brands. Expanded shales and calcined clay can contain harmful quantities of salt, so be sure to get a material that is intended for horticultural use.

Mineral Soil Mix

1 part sandy-loam soil

2 parts sharp sand

2 parts perlite

2 parts vermiculite

1 part pumice, calcined clay or expanded shale

This is a soil-based mix containing essentially no organic material, for use with more delicate succulents, such as Conophytum. I picked up the basic idea for it while working at Mesa Garden, where, back in the day, just about everything was potted in "Mabel Mix," which was equal parts sand, pumice, and native desert soil, the soil coming from the leftovers from road grading. "Loam" is used here in the soil science sense: a soil composed of silt (mineral particles smaller than sand grains) with some sand and a little clay, not in the gardening sense of "any fertile soil." New Mexico desert loam is hard to come by in Connecticut, but sandy loam subsoil, from a few feet down, with very little organic content, is an acceptable substitute. 

Digging a hole in New England will probably yield lots of rocks, and maybe some loamy mineral subsoil that would make a good base for cactus mix. 

 

 

The general idea with all of these recipes is to produce a potting medium that drains well, isn't too heavy, isn't too rich, but that still holds some water and nutrients. The basic theme is: a smaller amount of organic soil or loam, cut with generous quantities of sand and coarser mineral components. There is much leeway for changing the ratios and substituting or omitting ingredients. The flip side of this flexibility is that there are no miracle ingredients that will effortlessly take your succulent plant cultivation to the next level; there is no substitute for patience and close attention to proper light, temperatures, ventilation, watering and fertilizing. 

Happy 4th of July!

Bald Eagle chicks in northeastern Connecticut.

This July 4th might not quite yet mark a total independence day from COVID, but the pandemic is definitely receding into the background. Willimantic's boom-box parade made a comeback, but was shorter and more subdued than usual, either because of the weather (coolish with occasional drizzle), or lingering coronavirus concerns. 

One of the known area Bald Eagle nests is home to two young eagles this year, which seemed to be just about ready to fledge when I saw them last weekend. They were hopping around in the branches above the nest, and flapping their wings, but not flying. 

Mountain Laurel (Kalmia latifolia) in Bigelow Hollow State Park, Union, Ct.

 This year was a banner year for the Connecticut state flower, Mountain Laurel, with some of the most profuse flowering that I have seen. The peak was probably in mid-June, but the laurels looked fantastic for several weeks, and there are still a few flowers hanging on in cooler spots. Last year there were barely any flowers at all, but for 2021, the laurel thickets have really put on a show.