Forrest Rose Information Specialist 573-882-6843 RoseF@missouri.edu Jan. 20, 2004 Greenhouse hobbyists find challenges in ‘ultimate toy’ COLUMBIA, Mo. – The modern practice of greenhouse gardening began when the European nobility sought ways to grow exotic fruits like pineapples and oranges, which were brought back by early explorers. Now, there are more than 3 million hobby greenhouses in the United States alone, said David Trinklein. “For the avid plant lover, a hobby greenhouse is the ultimate toy.” “Hobby greenhouse gardening is challenging but rewarding,” said Trinklein, professor of horticulture at the University of Missouri. “Recognizing the basic difference of growing outdoors versus indoors can help meet those challenges.” Although greenhouse plants “basically have the same needs for water, mineral elements and sunlight, the way in which these needs are supplied does vary from outdoor production,” he said. First, almost all greenhouse plants are grown in containers, which have many advantages but make proper watering more difficult, Trinklein said. “The growing medium in a container is removed from contact with the soil, which makes drainage much more difficult from a container than from a bed. That fertile garden loam that might produce excellent results in an outdoor or greenhouse bed would likely yield disappointing results when used in a container.” This “perched water table effect” means gravity can’t overcome the water-holding capacity of the soil in a shallow pot as opposed to deeper soil in a bed, he said. “The result is a medium that remains wet far too long after watering, depriving a plant’s root system of oxygen and leading to the possibility of root diseases.” Most greenhouse growers use a soilless growing medium made up of large particles that give it far less water-holding capacity than soil. These mixtures, which often contain Sphagnum peat and other ingredients such as vermiculite and perlite, “are ideal for container production,” Trinklein said. “Additionally, they are considered to be pathogen-free and chemically inert.” Soilless growing media are sometimes generically labeled “potting soil,” even though most contain no soil. “Check the label carefully to be sure that no soil is contained in the mix,” Trinklein said. “Look for Sphagnum peat as one of the ingredients; this type of peat is superior to other types.” One shortcoming of soilless growing media is that, unlike field soil, it does not hold many elements essential for plant growth and nutrition. “Continuous liquid feeding is perhaps the most common alternative fertilization method,” he said. The CLF method is the application of a diluted nutrient solution every time the plant is watered. Several appropriate water-soluble formulations, often labeled as “peat-lite,” are commonly available, Trinklein said. “Another caution is to never water plants with water-softened water because of the high salt content involved. This can be a problem if hobby greenhouses are attached to homes with water softeners.” Greenhouses also lack nature’s “system of checks and balances that helps to keep insects and diseases from becoming huge problems,” he said. “We disrupt that system when we set up a controlled environment in a greenhouse. We often inadvertently supply plant pests with everything they need to flourish and exclude their natural predators.” The first line of defense is to exclude pests from the greenhouse, Trinklein said. “Good sanitation practices along with insect screening on all greenhouse openings can go a low way toward eliminating the need for pest control measures.” Carefully inspect any new plants introduced into the structure for stowaway pests, and monitor the plants regularly to detect the presence of insects or diseases, he said. “There are ‘sticky’ cards available for insect monitoring that make this task a bit easier.” If pest populations get so high as to require treatment, some growers turn to biological controls. “Most greenhouse owners still rely on chemicals to combat pest problems,” he said. “Newer, safer chemicals are available today that lessen the risk to people, plants and the environment.” If a plant is seriously infested, he said, “discarding the plant might be a better management practice than trying to rid it of the pest.” For more information about greenhouse gardening as a hobby, log onto http://agebb.missouri.edu/hort/meg/archives/v9n12/meg1.htm. Source: David Trinklein (573) 882-9631 Return to Current News Releases College of Agriculture Food and Natural Resources AgEBB