Gardeners in cold climates have learned to extend the growing season by building greenhouses. As early as 30 AD, mentions of greenhouses appeared in the writings of the famous Pliny the Elder, Roman scholar and scientific authority of his time.
Pliny described specaria as garden beds equipped with wheels covered with glazed frames to protect plants in cold weather. In Latin, specularium refers to a transparency that lets light into a building. The word is derived from Lapis specularis, a variety of gypsum rock that splits into sheets almost as clear as glass. Today it is called selenite.
Specularis were erected on the island of Capri around AD 30, specifically to provide a year-round supply of melons (Cucumis melo) for the powerful Emperor Tiberius Caesar.
Although glass was discovered long before, it was only used to make beads and small vials until 100 AD when the Romans started making glass windows. Masters of glassblowing, they honed a technique for splitting a long balloon of molten glass into two halves, which they flattened into separate panes.
The Middle Ages were strewn with pitfalls and troubles. It was not until much later – a millennium later – at the beginning of the Renaissance that the Italians developed the concept of modern greenhouses.
Innovation was driven by collections of exotic plants acquired from explorers returning from journeys to distant lands. The Italians called their greenhouses Giardini botanici, botanical gardens in Latin. They erected them to house these exotic plants and study their medicinal properties.
With the Age of Exploration, the Roman concept of greenhouses spread eastward. In 1459, a cookbook written by Jeon Soon, a Korean royal physician, described greenhouses equipped with temperature control devices, improving Italian design with artificial heat and ventilation.
In the 16th century, greenhouses spread to the Netherlands, England and France. There, the royal courts housed important collections of exotic plants acquired from the explorers they sponsored.
The buildings, a symbol of wealth and prestige, were imposing and luxurious monuments of glass and stone built for the enjoyment of monarchs while serving as places of scientific study in herbal medicine.
The greenhouse in the park of the Palace of Versailles is just one sumptuous example. The largely glazed building, commissioned by Louis XIV, is nearly 500 feet long and 50 feet high. The high price of glass and the cost of maintaining an optimal climate inside made these structures accessible only to the upper class, governments and scientific institutions.
However, rapid advances in technology during the Industrial Revolution led to improvements in manufacturing and design that lowered the cost of glass and lowered taxes on glass and windows. As a result, greenhouses became affordable for middle-class plant lovers.
Similarly in the United States, the high price of glass made greenhouse ownership a privilege reserved for the upper class. The federal Direct Tax Act of 1798, a property tax repealed in 1847, took into account the number and size of windows and taxed accordingly, allowing only the wealthiest to be able to afford a greenhouse.
During the early years of the republic, some of America’s most famous greenhouses were built by wealthy families with connections in international trade. One of the oldest is the Lyman Estate Greenhouses (go.uvm.edu/lyman-estate) in Waltham, Massachusetts, built in 1798 for Theodore Lyman, a Boston shipping magnate and avid horticulturist.
The Lyman Estate greenhouses are still in operation and contain many exotic specimens acquired by Lyman himself. They are open to the public and admission is free.
Today, materials and construction techniques are constantly improving, making greenhouses accessible to all budgets. Plastic films and fiberglass offer new possibilities for glazing. Framing materials include aluminum and galvanized steel. More efficient air conditioning systems are available, from passive solar designs to sophisticated heating, cooling and ventilation systems.
Many affordable options for greenhouses are available to homeowners. They come in various shapes and sizes. Now is the time to plan if you are considering a greenhouse to house your seedlings before the last frost.
Nadie VanZandt is a UVM Extension master gardener from Panton.