Spanish Moss Cold Hardiness II

Tillandsia usneoides that spent much (but not all) of the winter of 2015-16 outdoors in Mansfield, Connecticut.

A while back I wrote about the cold hardiness potential of Tillandsia usneoides (Spanish Moss). Last winter was a very warm one, and for a while it looked liked some experimental clumps of T. usneoides, the hardiest bromeliad, might make it through a whole year outdoors in New England. A specimen brought indoors on February 10, 2016, perked up in a cool greenhouse with no sign of frost damage.

However, one of the worst cold snaps in recent years started just a few days later, with five days around the weekend of February 13 not seeing temperatures above freezing at all. The arctic outbreak reaching a nadir with a day with high temperatures only reaching 10°F (-12°C), lows of -10°F (-23°C), and howling winds. Although this was only a brief interlude in a record warm season, it was enough to kill all the T. usneoides material that was left outdoors.

Periods of more than a week with constant sub-freezing temperatures, or absolute low temperatures below 0°F (-18°C), seem to cause severe or fatal damage to unprotected Spanish Moss. This winter in Connecticut we've already experienced enough cold weather to cause almost total dieback, but I wonder if some year soon we'll have conditions where T. usneoides survives an entire southern New England winter, and resumes normal growth in the spring?

Tillandsia usneioides Flowering

Tillandsia usneoides was in bloom in the UConn greenhouses the other week. The flowers are minute and greenish and easy to overlook, but do emit a slight sweet smell. "Spanish Moss" is indeed not a moss (nor is it from Spain), but a flowering plant in the pineapple family, the Bromeliaceae.

Greenhouse flowering of T. usneoides is unreliable; looking back, I don't see any records of Spanish Moss in flower at UConn since 2004. Intriguingly, the blooms this spring all seemed to be on the clumps of T. usneoides that I had left outside for a portion of last winter in an impromptu hardiness trial. The plants grow perfectly well, vegetatively, when kept in a tropical greenhouse year round, but it is possible that a cold vernalization period triggers flowering. I can't be sure that cold was responsible, though, since a number of other factors were different with the outdoor Spanish Moss. It spent the entire summer of 2014 outside, which means it received rain water rather than tap water, and probably less water and nutrients overall than the non-flowering greenhouse material. Maybe I'll try keeping some plants refrigerated next winter, and see if a cold period alone encourages blooming.

Spanish Moss Cold Hardiness

Tillandsia usneoides grown outdoors in Connecticut and brought inside on December 24 (left) and January 12 (right).

 Tillandsia usneoides, or Spanish Moss, is a rootless epiphyte with inconspicuous greenish flowers, in the family Bromeliaceae (the pineapple or bromeliad family), and one of the emblematic plants of the American South. It is native to an enormous geographical range in the tropics and warm temperate regions of the New World, from coastal southeastern Virgina and possibly Maryland, down almost to the southern tip of South America in Argentina and Chile. The whitish appearance of the plants is the result of a dense coat of umbrella-shaped (peltate) hairs, which are involved in trapping and absorbing the rainwater and trace nutrients.

Tillandsia usneoides grows naturally in locations that experience considerable frost, and would appear to be the most cold hardy of the epiphytic angiosperms (flowering plants). I have grown Spanish Moss outdoors in the branches of trees in Mansfield, Connecticut many times and it always does quite well from spring to fall. Plants that are left out over the winter have never survived, though, even in mild years.

This winter I had left out a number of clumps of extra T. usneoides, but after they had been thoroughly frosted I decided to bring some in to the UConn greenhouse to see if they could be revived. Plants retrieved on December 24 looked a little dehydrated at first but recovered quickly in the greenhouse, with negligible die back. November-December was warmer than normal, but the plants had experienced numerous hard freezes, some multiple-day stretches of sub-freezing temperatures, and absolute lows of about 10°F (-12°C).

Another clump brought inside on January 12 experienced much harsher weather, including week long periods with daytime highs below freezing and absolute lows of -2°F (-19°C). Although this plant probably lost well over 90% of its shoots, a smattering of stem tips with a couple of leaves and internodes have definitely survived and are resuming growth in a cool but frost-free greenhouse. Still, the plant was clearly near the limits of survivable conditions.

Three different collections of Tillandsia usneoides: typical USA form, gathered in Charleston, SC by R.W.A. Opel (left); fine Carribean form from the Dominican Republic (center); robust form from Peru (right).

As might be expected from a plant with such a wide native range, T. usneoides is variable in appearance from place to place; the photo above shows three forms collected in different localities but grown in the same greenhouses. This year's hardiness tests were carried out with cultivated Spanish Moss originating in the southeastern USA; in previous years I have tried the Peruvian material outdoors, but it succumbed rapidly during the first hard frosts in autumn. So, there seems to be some genetic variability in winter hardiness in T. usneoides. It might be interesting to experiment with outdoor cultivation of material from the northern limits of the range of Spanish Moss, Virginia or the inland edges of the Carolina Low Country. Success would seem unlikely in Connecticut, regardless of the wild source of the plants, but I wonder if some adventurous gardener might be able to establish T. usneoides in a mild, protected coastal location in New Jersey or Long Island, or possibly even the more maritime parts of Massachusetts, say Martha's Vinyard or the Outer Cape.

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Addendum: I rescued some more clumps of T. usneoides from outdoors in mid-February, after more extended periods of sub-freezing weather. Some shoots still looked pretty green initially, but this was the green of a package of frozen spinach; everything was clearly brown and dead a few days after thawing out. 

Connecticut Cactus & Succulent Show this Weekend

Hatiora herminiae, an epiphytic cactus from Brazil.

2014 is the year of the 31st annual Connecticut Cactus and Succulent Show and Sale, to be held in its usual location at Naugatuck Valley Community College. The event will run Saturday April 5, 10:00-5:00 and Sunday April 6, 10:00-4:00. More information is available from the Connecticut Cactus and Succulent Society. Parking is abundant and admission is free.

It's always a fun time, and every year we get a large number of repeat guests coming in from all over the Northeast, to see an extensive judged show, numerous vendors, informative lectures and demonstrations, auctions filled with rare plants and rare bargains, and (primarily?) to meet and chat with other fans of unusual desert plants.

Tropical Succulents Talk

Myrmecodia platytyrea ssp. antoinii, an epiphyte from Southeast Asia with a symbiotic relationship with ants.

At next month's meeting of the Connecticut Cactus and Succulent Society, I'll be giving at talk about "Tropical Succulents." I'll be covering plants that grow in dry microhabitats in otherwise moist tropical forests, which sometimes have well-developed water storage tissues. Most of these rainforest succulents are epiphytes that grow without soil, clinging to branches high in the treetops. I'll have examples of myrmecophytes (ant-house plants) like Hydnophytum and Myrmecodia, orchids, jungle cacti like Rhipsalis and Selenicereus wittii, some unusual peperomias and hoyas, and others.

The meeting will be at Lauray of Salisbury, which will have a wide array of interesting succulents, begonias and orchids on sale. The trip through the Litchfield hills to Lauray should be nice in early October, too; I'd expect the fall foliage to be near its peak.

Epiphyte Tree at UConn Greenhouses

One of the big events this past fall here at the University of Connecticut greenhouses has been the completion of an epiphyte tree in the entryway, which had previously been somewhat cramped and lacking in focus. The new entryway provides space for tours to assemble, and a point of interest to draw visitors in.

Epiphytes are plants that live on the surface of other plants, using their hosts for support but not acting as parasites. About the only epiphytes that occur naturally here in Connecticut are tiny mosses and liverworts that grow on tree trunks, but in tropical climates trees may be festooned with diverse communities of orchids, bromeliads, ferns and others.

The UConn epiphyte tree was put together over the summer, with many hours of volunteer help from the Connecticut Orchid Society. It is constructed around a skeleton of steel pipes clamped together into a hexagonal trunk, with additional pipes jutting out above head level to create branches. The trunk is covered with panels of expanded metal, which do a good job of rounding out the angular underlying structure. All of the basic structural materials were recycled from old bench parts from the greenhouses.

Clint Morse and members of the C.O.S. assemble the epiphyte tree's internal skeleton.

Probably the most time-consuming part of the construction of the epiphyte tree was covering it with bark. We used natural cork oak bark, which is harvested—sustainably, without killing the trees—in the western Mediterranean region. The C.O.S. and greenhouse manager Clint Morse laboriously fit pieces of bark together, sometimes cutting them to fit or softening them with steam in a large autoclave to mold them into the right shape, then wired them in place. Gaps were filled in with slivers of bark glued in place, or clumps of coconut fiber. The branches of the epiphyte tree were covered with special ordered bark tubes (taken whole from smaller cork oak trunks).

Some of the initial plantings were done as the bark was being fit into place, using epiphytes already established on pieces of cork. More plants were wired or glued into place later, and these should anchor themselves and spread with time. We’re still working on fine-tuning the tree and its plantings, but stop in and check it out if you’re in the area!