One of the questions we hear most often is “Why aren’t my orchids blooming?” Although there’s no single, simple answer, there are a few general principles that may help you understand how to improve your orchids’ flowering. After all, it’s the flowers we want no matter how interesting or exotic the plants may be!
All plants need a certain amount of light for growth and flowering. Most orchids need fairly bright light to flower well, and if your plants aren’t blooming this may be an important consideration. Different types of orchids require different light conditions, ranging from virtually full sun exposure for some to moderate shade for others. The plant itself can give you a hint of its needs: if the foliage is dark green, the plant probably isn’t getting enough light. Normal healthy orchid leaves are usually light to medium green, although some Phalaenopsis have naturally dark leaves. Plants with stiff, nearly succulent foliage will generally want brighter light than plants with soft, thin foliage. If you think your orchids need more light, move them gradually into a brighter spot.
The terete and semi-terete vandas need full sun for at least half a day (more if possible) to flower well. Strap-leaf vandas, as well as their cousins the ascocendas and closely related vandaceous plants, prefer a little shade in the middle part of the day but otherwise the brightest light available.
Most cattleyas, oncidiums and dendrobiums bloom best with slightly shadier conditions. In their natural environment they grow on the branches and trunks of trees, fairly high in the canopy, where the light is quite bright but not direct. These plants will usually adapt to early morning sunshine if they are protected from direct sunlight after about 10 or 11am.
Phalaenopsis and most paphiopedilums need bright shade, without exposure to any direct sunlight at all. Although these orchids are often recommended for indoor growing, they won’t grow well (let alone bloom) in the dark.
Orchids also need good nutrition. Fertilizer in the right amounts at the right times can make a big difference in the way your plants grow and bloom. When the plants are actively growing, a weekly application of a dilute, balanced water-soluble fertilizer with minor elements will help produce healthy leaves and roots. A balanced fertilizer is one where the three major components (nitrogen, phosphorous and potassium, or NPK) are present in equal, or nearly equal, proportion. All fertilizers have a three-number formula representing the proportion of these three important nutrients. For example, a fertilizer with “20-20-20” or “10-10-10” on the label is balanced, while one labeled “10-50-10” or “30-10-10” is not.
Some products labeled as “orchid food” have a 30-10-10 formula. This formula is much too high in nitrogen (the first number) for most orchids unless they are being grown in a bark-based potting medium. Nitrogen is necessary for growth, but too much of it produces lush green leaves and suppresses flowering. If you’re using a high-nitrogen fertilizer on orchids growing in a non-bark medium, this may be another reason your orchids aren’t flowering. We recommend a balanced fertilizer alternated with a “bloom booster” formula during the growing season. The “bloom booster” formulas will have a high middle number, such as 10-30-20. We typically use the bloom booster every fourth feeding.
The plain truth is that some orchids only bloom once a year, and there’s nothing you can do to change that pattern. Most species orchids, and even a good number of hybrids, have an annual growth cycle that produces flowers at a specific time of the year, just as other plants in our gardens and landscapes do. The time of flowering is related to natural cycles of light, moisture and temperature in the environment, and for some orchids a change in one or more of these factors is necessary to trigger flowering.
Most sympodial orchids – those plants with pseudobulbs, such as cattleyas, dendrobiums and oncidiums – are adapted to habitats with seasonal variations of rainfall and temperature. Often there is a very distinct wet/dry season, although the length and intensity of each season may vary a lot. Orchids adapted to these conditions generally have a very distinct growing/resting cycle which coincides with the seasonal changes, and flowering typically occurs at the beginning or the end of the growing period. While growing, these plants need regular watering and fertilizing, but when they stop growing, water should be reduced and fertilizer eliminated. Applying too much water or fertilizer to a “resting” orchid can interrupt the plant’s normal cycle.
Temperature during the resting phase may be important as well. Some dendrobiums require a cooler period during their rest. For a more detailed discussion of the temperature requirements of different groups of dendrobiums, refer to our “dendrobium” culture sheets. There are too many different types of dendrobiums to generalize about their care.
Most monopodial orchids, on the other hand, grow more or less continuously during the year. Phalaenopsis, vandas, ascocendas and related orchids fall into this group. Their native habitats have less seasonal variation in moisture and temperature, so these plants need year-round watering and fertilizing even though most of the species and many hybrids bloom seasonally. The large-flowered white and pink phalaenopsis typically bloom in the winter, in response to a short period of cooler weather in the fall. Two weeks or so with night temperatures from about 55F to 65F will often trigger a flowering cycle.
In any genus of orchids, a hybrid with a complex pedigree of many different ancestral species may not follow any particular pattern for flowering. Sometimes the combination of spring-flowering species and fall-flowering species produces hybrids that flower several times a year, as the plants respond to different environmental signals.
One last consideration: orchids must grow to a certain size before they bloom. This varies with the type, of course, but sometimes the only thing you need to do is have patience. If you purchase seedling orchids, remember that these are immature plants and may require several years’ growth before they are mature enough to bloom.
If your orchids aren’t blooming, check to see that they have the right light conditions, temperature regime and appropriate fertilizing and watering schedules. If everything seems correct and a mature plant still refuses to bloom, you may need to stress it just a little. If you’re fertilizing regularly, stop doing so for a month; reduce watering somewhat, or move the plant to brighter light conditions.