Unsealing and Sealing

  I couldn't wait, but probably should have.

  Armies of seedlings have overwhelmed my shelves of grow lights indoors.  Cabbage, chinese cabbage, kale, claendula, broccoli, parsley, lettuce, cauliflower.  Busting out of seed trays jostling under the fluorescent tubes, or pricked out and standing in orderly ranks of 72 or 128.

 And each day the sun grows stronger.  Driving down the road I have to crack the windows to let some air lest I roast.  That delicious bracing air that is beginning to smell of damp soil and life.  These bracing early spring days reach the 30s and 40s, and the breezy air flows around you with that same quality of melting ice:  a cooling fire, a liquid burning cold.

  With more seeds and seedlings on the way, I decided to brave an experiment a few days ago.  Admittedly it was slapdash, thrown together at the end of the day, but I figured it was time to think about a cold frame.  Mine was a cute homely little thing, cobbled together with old bricks stacked together and a recently scrounged sheet of plexiglass.  Was I crazy to hazard some pampered indoor plants in my little contraption on a night forecast to dip to 20?  Yes.  Probably even the best cold frame wouldn't have mattered against the frigid air.

  A cold frame is meant to acclimatize seedlings and plants pampered indoors to the harshness of the outdoors.  Unmediated sunlight, winds, and above all colder temperatures can all stress tender plants.  The cold frame is an enclosed space with a transparent lid that can be opened or closed to varying degrees to gradually expose plants to the environment so they literally develop a "thcker skin."

  The key to the cold frame is forming a good seal when closed for the evening.  This is where my own quick build failed.  The gaps between the bricks allowed air into the chamber, effectively mullifying any protection, so that the morning after I built it I found frost not only on the grass outside but on the inside of the plexiglass lid.  20 degree lows are probably too low for any cold frame to protect delicate indoor plants, but I could improve it greatly by making sure that when the lid is closed the entire environment is sealed.  This could be accomplished with more serious construction or could be done by even simply piling soil or leaves up around the sides of the brick walls so as to form a seal or at least a mediating baffle to slow heat and air transfer.  I could also pack any empty space in the frame with styrofoam packing material I have lying around for insulation.  Another improvement would be to burrow down into the ground so the cold frame's floor is below ground-level (as long as it won't flood when it rains).  In China, greenhouses are constructed as just such giant buried cold frames.  Their floors are six feet below ground level and I'm told even tomatoes grow right through the winter.

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  In some ways the cold frame's opposite is the Wardian case.  This is a transparent enclosed case that is kept sealed rather than gradually opened.  In the early-19th century, Londoners fell victim to a craze for ferns.  Ferns of all kinds were hunted from glens and woods in the countryside (some to near extinction) for the sake of urban fashion, to be potted and shown off in Victorian parlors.  (To learn more about this, extravagant parlor displays, and the milieu which led to the birth of the modern houseplant, check out Tovah Martin's very interesting book Once Upon a Windowsill.)  Unfortunately, this was London of the early Industrial Revolution, choked and benighted by coal smoke, and many ferns promptly crumbled and died.

  Nathaniel Ward, a London doctor, was a fern collector and amateur naturalist.  He one day collected a moth in a glass jar within which he placed some soil and plants.  Though the moth eventually died, Ward noticed that the plants flourished, apparently saved from the "bad air" of London by the sealed nature of the jar.  Soon the fern enthusiasts saved their prizes in "Wardian cases" dressed up as elaborate Victorian mini-glasshouses.  These cases became little temples of green life in the sooty urban expanse.

  The Wardian case not only preserved precious ferns but revolutionized the transportation of plants from one part of the world to another.  Since the late 18th century with the world-crossing botanizing expeditions of Joseph Banks on Captain Cook's voyages (the inspiration for Star Trek.  Captain Cook = Captain Kirk!), Britain's growing navally-based empire saw the value of moving valuable newly dicovered food crops from one colny to another (Captain Bligh's ill-fated voyage, source of "Mutiny on the Bounty," was meant to ship breadfruit trees from Tahiti to Jamaica for a cheap food source for Caribbean slaves).  The stressful months-long sea voyages filled with storms and salt water were nearly always disastrous for plants that were usually potted into barrels, exposed to harsh sea air and winds, and then sometimes even watered by ill-informed shiphands with salt water from the sea when fresh water was a scarce resource. 

  The advent of the Wardian case changed this by enclosing well-packed plants into large glass cases.  The tight seal kept the harsh sea environment out and humidity from plant respiration and soil in.  It also was instrumental in the mass smuggling of Chinese tea plants from China to British-controlled India over the Himalayas, effectively breaking the Chinese hold on Britain's tea addiction.  Plants could now move across the vast expanses of the Inidan and Pacific oceans back to the metropole of London and the imperial center of plant expeditions, the Royal Botanic Garden at Kew. 

  The modern descendant of the Wardian case is the terrarium, where plants nestled in a bit of soil in a glass bowl are sealed away.  Water is cycled and recycled in the closed environment where tiny ferns, mosses, and club-mosses flourish.