Whenever the question of fertilising (feeding) arises at gatherings of orchid growers, a wide variety of unsubstantiated regimes is often proposed. In my opinion most are sadly lacking in their ability to satisfy the orchid’s requirements. A well-grown orchid should flower two to four years after removing the seedling from flask, depending on the genus. Its physical appearance will vary depending on its parentage but it should possess a large first pseudo-bulb and progressively larger subsequent bulbs. All leaves, from the very first one, should be healthy and intact. In order to achieve this state, optimal culture, including a balanced feeding regime, is required at all times.
To many, this involves the application of an NPK-fertiliser (one that supplies the elements nitrogen, phosphorus and potassium) regularly. If there is any doubt that something may be missing, then perhaps two or three different fertilisers are used in rotation. This approach often results in a multi-bulbed plant with numerous back-bulbs, and inflorescences with a lower number of smaller flowers than could be expected. The fertiliser provides the major chemical elements but other essential elements have to be found from breakdown products and impurities. This approach is unlikely to provide a constant supply of nutrients in the required amounts, resulting in chemical deficiencies and a malnourished plant.
Optimal plant growth requires an adequate supply at all times of Carbon, Hydrogen and Oxygen together with twelve other nutrients, six macro (Nitrogen, Phosphorous, Potassium, Calcium, Magnesium and Sulphur) and six trace elements (Iron, Manganese, Zinc, Copper, Boron and Molybdenum) in an environment that is conducive to their constant availability to the plant’s roots. Carbon dioxide and water are fundamental in photosynthesis. Water and oxygen are vital for healthy roots, which are in turn vital for the absorption of water and nutrients by the plant. Air (which contains carbon dioxide) and water provide the carbon, hydrogen and oxygen, and are taken for granted, but they must be constantly available.
The twelve nutrients listed above (nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron, boron, manganese, zinc, copper and molybdenum), whilst required in vastly different quantities, are none the less equally important one to the other. The use of the term, balanced fertiliser, in the context of this article, refers to a fertiliser that contains all of these nutrients in their correct proportions and in a form that is readily available to the plant. There are definite desirable relationships between the proportions of nitrogen and potassium, phosphorous and magnesium, calcium and magnesium and the various trace elements. If these are not maintained within certain limits, deficiencies result and plant performance suffers. A plant will perform to its genetic potential only if adequate amounts of each of these nutrients are present. As soon as the first one is totally consumed, performance is impaired. At this stage, mobile elements may be translocated from the older part of the plant to maintain the growing point, to the detriment of the older part of the plant, which suffers leaf loss and the consequent production of back-bulbs. Immobile elements cannot be translocated, causing further development of the plant’s growing points to cease immediately.
I prefer a single fully balanced fertiliser, applied at the same strength all the year round on all orchids, from those just out of flask to adult plants, whether they are in the ‘growing’ or ‘flowering’ phase. To accommodate any variation in one or more nutrients throughout the year, I simply feed at an appropriate strength and frequency to ensure that sufficient fertiliser is present at all times to cater for this, even if there is excess of some nutrients at times. This system fulfils our aim of producing healthy, mature orchids that flower well.