I have two questions:
1. How should I keep the area under my 0.5m x 1.5m indoor green house flies free? (My greenhouse works with a plant growth light)
2. For how hours in a day should I keep the growth light turned on?
Thank you for your inquiry. The flies that are generally found around indoor housplants are commonly refered to as fungus gnats (Bradysia species). These gnats are small, delicate bodied flies that commonly develop in the growing medium of houseplants. The fungus gnat larvae usually are located in the top 2 to 3 inches of the growing medium, depending on moisture level of the soil. They primarily feed on fungi, algae and decaying plant matter. However, the larvae will feed on plant roots and leaves resting on the growing medium surface. Larvae develop rapidly and are fully grown in two to three weeks.
The most important strategy to minimize fungus gnat problems associated with houseplants is to allow the growing medium to dry between watering, especially the top 1 to 2 inches. The dry-growing medium will decrease survival of any eggs laid and/or larvae that hatch from the eggs as well as reduce the attractiveness of the growing medium to egg-laying adult females. In addition, it is recommended to re-pot every so often, particularly when the growing medium has “broken down” and is retaining too much moisture. Furthermore, be sure to remove any containers with an abundance of decaying plant matter such as decayed bulbs and roots, which provide an excellent food source for fungus gnat larvae. Please refer to the following Toronto Master Gardener Website for additional information on control of fungus gnats: Fungus Gnats. You also might like to refer to the following website for additional information on gnats: https://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html
No matter what type of plants you are growing indoors, you must be sure to give them a dark (rest) period. Plants photosynthesize in the prescence of light and respire in the dark. Photosynthesis is a chemical process in which water and carbon dioxide in the prescence of light energy are converted into sugrs and oxygen. Plants require photosynthesis to manufacture food that is essential for their growth. Respiration is a chemical process whereby the sugars and oxygen are broken down into water and carbon dioxide. The balance of respiration to photosynthesis affects many biological processes, such as growth rates, and the setting of buds and fruit. Plants are usually divided into three categories depending on their preferred day length: short-day, long-day or day-neutral. Short-day plants, such as chrysanthemums, kalanchoe, azaleas and begonias, will thrive on less than 12 hours of light per day. In fact, these plants need to go through a series of even shorter days before they will set buds and flower. Long-day plants require at least 14 to 18 hours of light each day. Most vegetables and garden flowers are long-day plants, and when they don’t receive enough light they get pale and leggy. Day-neutral plants, including foliage plants, geraniums, coleus and African violets, are usually satisfied with 8 to 12 hours of light all year-round. The Toronto Master Gardeners have a number of excellent Gardening Guides on growing plants indoors: Beginners Guide to Growing Indoor Houseplants
Continue to enjoy your indoor garden