The Main Nutrients an Orchid Plant Needs to Grow

Photosynthesis

• The orchid family (Orchidaceae), like most plants, converts carbon dioxide from the air and hydrogen from water into starches and sugars to power plant growth, with help from the sun. To accomplish this process, called photosynthesis, an orchid requires three other essential ingredients to manufacture its food. Nitrogen, phosphorus and potassium, the N-P-K of fertilizer labels, must all contribute to photosynthesis in the right proportions. Nitrogen metabolism plays a major role in stem and leaf growth. Deficiencies can stunt growth, but too much delays flowering. For flower formation, phosphorus must be present. Although the plant's use of potassium is not fully understood, it appears to function as an enzyme activator. During the growing season, fertilize orchids once or twice a month with a diluted 20-20-20 solution.

Macronutrients

• Together with the elements essential to the photosynthesis process, three other items, designated as secondary macronutrients, are used in large quantities by orchids for food conversion and growth. Sulfur, like nitrogen, functions as a structural component of the amino acids which supply proteins to the plant. Orchids rarely suffer from a sulfur deficiency, because it is so prevalent in the atmosphere. Essential for the germination of seeds, magnesium is critical to the structure of the chlorophyll molecule. Since it can be leached out while watering, you must supply magnesium when feeding. Apply as a foliar spray to correct deficiencies. The third macronutrient, calcium, has many tasks, such as activating enzymes, directing movement of water in cells, and allowing plants to absorb nitrogen and other minerals. If your water supply does not contain sufficient calcium, you may have to supplement.

Micronutrients

• Akin to vitamins for humans, a group of minerals and elements play a small part in plant health factors. These micronutrients may act as catalysts to bring about certain beneficial activities in orchids. Perhaps the most needed are iron and zinc. Iron, in the form of ferrous sulfate or chelated versions absorbed through the plant's roots, must be present for the production of chlorophyll. Particularly important to carbohydrate metabolism, protein synthesis and stem growth, zinc can be obtained as simply as mixing your fertilizer in a galvanized bucket. Other micronutrients include boron, cobalt, molybdenum, copper, manganese and silicon. Orchid experts disagree on whether these barely required elements ever need to be added as supplements. Many argue that most, if not all, appear as impurities in fertilizer solutions already.

Winter Nutrition

• As light levels and temperatures begin to fall in autumn, going into winter, orchids' nutritional needs change. Reduce the frequency of watering and fertilizing during the cooler season. In general, feed with a fertilizer low in nitrogen and high in potassium -- something like a 10-5-20 ratio. Dendrobium phalaenopsis and Dendrobium canaliculatum hybrids particularly benefit from a low-nitrogen formula. Orchids that bloom in the winter and early spring, like those in the Phalaenopsis genus, favor a couple of applications of bloom boosters, with a 10-50-10 ratio, in October and November. To further prepare winter flowerers, many growers recommend spraying with an Epsom salts (magnesium sulfate) solution to prevent loss of lower leaves and to enhance blooming.

Growing Orchids Outdoors

• A diverse group of orchids can be grown outdoors. As all members of the orchid family are protected by the Convention on International Trade in Endangered Species of Fauna and Flora, purchase plants only from reputable sources that guarantee their plants are not collected from the wild. Though considered tropical plants, certain orchids can thrive as far north as U.S. Department of Agriculture plant hardiness zone 3. The tiny amitostigma orchid (Amitostigma keiskei) will grow in pockets of moss on a vertical wall or in the top of a retaining wall in USDA zones 6 to 10. Sterile soil on the acidic side provides nutrients for the lady slipper orchid (Cypripedium acaule) in USDA zones 3 to 7. On the other hand, marsh orchids (Dactylorhiza spp.) require slightly alkaline, well-drained soil in USDA zones 5 to 8.