The difference between a merely good orchid and a spectacular specimen plant is fertilizer.
Like any other plant, orchids need fertilizer to thrive. It's true that they need less than most other plants—and too much fertilizer can quickly burn an orchid’s sensitive roots—but there is no doubt that well-fed orchids are healthier, hold their leaves longer and bear more flowers.
Use a High-Quality Fertilizer
There are lots of opinions on which fertilizer is best, and a whole industry has sprung up to sell specialized orchid foods. You can quickly get lost in the advanced chemistry of various fertilizer claims, but here's the skinny: one nitrogen molecule is very much like another nitrogen molecule. In fact, the quality of your water matters more than your brand of fertilizer. So when it comes to fertilizer, buy a high-quality, balanced fertilizer that contains the three major elements (nitrogen, phosphorus, and potassium), plus all the minor nutrients (sulfur, calcium, magnesium, iron, manganese, boron, copper, zinc, molybdenum, and chlorine). Use a low-urea or urea-free fertilizer because urea is not a truly available source of nitrogen for epiphytic orchids.
This is an old rule of thumb among orchid growers: "Water weekly, weakly." You can judge the strength of commercial fertilizer by the concentration of the major nutrients. In general, you'll probably be safe using a standard 20-20-20 fertilizer at quarter strength, and a 10-10-10 fertilizer at half strength. Follow the label directions on specialty orchid fertilizers.
Overfeeding will not benefit your plants. Synthetic fertilizers contain mineral salts, such as potassium, calcium, and others. Over time, these salts build up in your pot and potting medium and can seriously harm the plant. Additionally, overfed orchids often grow too quickly, making them weak and susceptible to disease. Finally, many kinds of orchids actually bloom worse if they're overfed. Find the fine line and stick with it.
Feed During the Growing Season
Many orchids—dendrobiums, for example—go into dormancy over the winter months. Others, such as Cattleya, slow way down in their growth. There is little purpose in feeding a dormant plant. Start fertilizing again once the plant shows signs of fresh growth in the spring.
To Bloom-Boost or Not?
It's increasingly easy to find specialized bloom-boosters that offer slightly different nutrient balances or micronutrients designed to enhance orchid flowering. These are tempting, but unless you're a professional grower, there's little benefit to these products. First, most home orchid collections carry multiple genera that flower at different times of the year. Second, different genera have different flowering requirements. When you get down to it, a high-quality, well-balanced fertilizer is just as effective at producing blooms as a booster, and it will benefit all your plants, not just the bloomers.