In Hawaii, a place many consider a gardening paradise, the idea of growing plants in a greenhouse or other protective structure seems out of place. While some of us think of greenhouses as grand glass-and-cast-iron conservatories associated with botanical gardens and the ultra-rich of the Industrial Revolution era, greenhouses have a far longer history.
The concept of greenhouses began more than 2,000 years ago in Rome, where the emperor desired to have cucumbers year-round, despite bright summer sun and cold winter temperatures. The solution involved protecting plants in structures covered with translucent panels of mica and other materials that allowed light to be transmitted to the protected growing space during cold winter days. Plants were grown in containers and moved inside or outside as needed. During the summer months, plants were protected with cloth shading.
As Europe emerged from the Dark Ages and began to explore the tropical world, explorers returned with plants and animals that required a tropical environment to survive. The development of greenhouses to fill this need slowly emerged. In the process, early horticulturists and botanists learned how to control the plant growing environment. These early greenhouse designs required lots of hands-on human intervention in order to maintain a suitable environment. Opening and closing windows and vents; moving plants; and stoking fires to warm the facility were the jobs of many caretakers.
During the 1400s, growers in Korea used greenhouses, in which temperature and humidity could be controlled, to grow mandarin oranges.
A key development contributing to the modern age of greenhouses and their wider availability was the ability to manufacture glass sheets in sufficient quantities and quality suitable for construction. Beginning in the 17th century, greenhouses were built larger and more ornate, first in England and the Netherlands then throughout the rest of Europe.
We grow plants in greenhouses and under cover in Hawaii to protect them from insects, diseases, sun, rain, adverse temperatures and wind. Backyard orchid hobbyists were among the first in Hawaii to build wood and glass houses to maintain their prized collections. You may still see many of these old greenhouses in yards of older neighborhoods.
In greenhouses, you are able to control plant growth and harvest time by regulating light and temperature. You can screen out many of the unwanted pests that plague plant and fruit production. You are able to screen out fruit flies which oviposit on many fruiting vegetables, butterflies and moths whose larva enjoy munching and boring through your plants and other insect pests. Remember, though, if the plant needs insects for pollination, screens will prevent them from doing their job. Consider self-pollinating plants, parthenocarpic setting fruits or manually pollinate the crop.
Many diseases need free water to start the infection process. A cover can protect the plants underneath from rain and dew reducing the amount of chemicals needed to otherwise control problems when they develop. This is especially true for bacterial and fungal diseases.
When considering a greenhouse for your garden, important considerations are the intended use, size needed, cost and zoning. A home gardener can purchase greenhouse kits or build them from various designs and materials. Many are built with polyethylene plastic sheeting or polycarbonate panels — much cheaper than glass — over a metal or wood frame. With the right greenhouse and a little practice you will be surprised by all of the different plants you can grow to beautify your home and eat well.
For more information on this and other gardening topics, visit the CTAHR electronic publication website at ctahr.hawaii.edu/Site/Info.aspx or visit any Cooperative Extension Service office. Nagata can be reached at email@example.com.