Members of the orchid family are popular among gardeners because of their colorful blossoms. Their need for fertilizer is fairly standard among the many different cultivars, but their watering requirements vary greatly, depending on the climate and whether they have air roots and grow on other plants or whether they grow in soil.
General Rule for Watering
Water orchids when the planting medium is dry. Plants suspended in air dry out quicker than those grown in potting mixes; water them more often. Orchids planted in bark need to be watered more often than those grown in potting mixes. Orchids growing in clay pots need to be watered more often than those in plastic pots.
The American Orchid Society advises you to poke your finger into the potting medium. If it feels wet, the orchid doesn't need watering.
Low Water Orchids
Varieties of orchids that grow on other plants are "air rooted." They store water in a kind of bulb. Water these orchids about every five days; increase this to every three or four days in mid-summer heat. Water every 10 to 14 days during the shorter, cooler winter days. Let these orchids dry out slightly between waterings so the air can circulate between the roots. Better to water too little than too much.
Moderate Water Orchids
Orchids in the Phalaenopsis family are often grown in potting mixes in windows and under artificial light. They store some water in their leaves. Water them thoroughly and not again until they are nearly dry. Do not let the roots remain bone dry for more than one or two days. In a dry climate, water every two to three days in the summer. In a Northern climate, water about once every 10 days. Do not let the roots sit in water, which could lead to fungal rot.
High Water Orchids
Orchids in the families Haemeria and Paphiopedilums root in the earth. They like moisture and can tolerate damp soil for days. Many of these orchids are planted in peat that holds more water than bark mixes.
Most orchid species evolved in moist climates and they like a humidity level between 40 percent and 60 percent. If you mist them to increase the humidity, do it in the morning and use distilled water. Tap water can leave deposits of salt on the leaves. Plants kept soaking wet are susceptible to fungal diseases and bacteria. A good alternative to misting is to place the pot on a wet tray of gravel or stones. Water evaporating from the gravel or stones will give the plant all the humidity it needs.
Feed orchids with a soluble fertilizer. If your plant is growing in a mixture of peat and bark or in osmunda, use a 20-20-20 liquid fertilizer. You can also use a special 30-10-10 orchid fertilizer.
Water before you fertilize. Do not use fertilizer containing urea.
Orchids grow naturally in soils or bark with a minimum of nutrients. Do not fertilize more than once a month.
Horticulturalists at the University of Georgia say that over-watering and over-fertilizing are the two main causes of orchid death.
To avoid fungal diseases, water early in the morning. This helps water to evaporate from the crown by nightfall. The crown is where the plant meets the roots, and it is susceptible to fungi.