Food for Thought (Fertilizing)


by Ken Slump

Posted by Sys Admin over 3 years ago.

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Hobbyists Often Tailor Fertilizer Needs to Their Orchid Collections

THE WHAT, WHEN AND HOW OF orchid fertilizing provides constant discussion among orchid growers. For many, there seems to be a supposition that if the right fertilizer is used, or the best application regime is followed, all orchid-growing problems will be solved. 

In truth, fertilizing schedules, like most other facets of orchid growing, tend to be unique to each grower. What works for one individual does not always succeed for someone else. This is likely because plants’ nutritional needs are determined by many interrelated factors. Temperature, water quality, frequency of watering, growing medium, type of container, amount and quality of light, age of plant, time of year and kind of orchid are some of the variables that meld to determine a plant’s nutritional needs.

WATER QUALITY  Of all of these, it is probably most important that you know a bit about your water quality before you initiate a fertilizer regime. The pH of the water (its relative acidity or alkalinity) is an important factor, as it can affect the availability of nutrients. A pH of 7 is considered neutral. Below 7 is termed acidic, and anything higher is deemed alkaline. While needs and tolerances among orchids vary, most will grow satisfactorily when the water’s pH ranges between 6 and 8. Simple pH-test kits are available at most pet shops and retailers that sell aquaria and freshwater tropical fish.

In most areas, tap water is fine for orchids. Your local nursery, greenhouse or extension service should be able to advise you whether your local water is suitable for plants. Be aware that water quality can vary within a municipality. Your water may be quite different from that of your fellow orchid grower across town. Note too, that water softened by the addition of sodium is not good for plants. In cases where water quality is unacceptable for orchids, ion-exchange water softeners or reverse-osmosis (RO) systems can solve the problem.

Orchids, like other plants, have some predictable nutritional requirements. Minerals are required for plant growth and flowering. Most of these are absorbed by the roots in the form of mineral salts that may be produced by and found in the medium in which the plant grows.

The three macronutrients needed by plants in large amounts are nitrogen, phosphorus and potassium. When you look at a label on a jar or bag of fertilizer, the three numbers listed (such as 20-20-20, 10-0-0 or 18-6-12) represent the percentages of these three minerals that are found in that fertilizer. They are always listed in the same sequence, with nitrogen first, phosphorus second and potassium third. A fertilizer that contains all three is termed “complete,” even though the percentages of each mineral may be unequal. When the percentages are the same, the fertilizer is called “balanced.”

Nitrogen, essential for good vegetative growth in the plant, is a primary ingredient in proteins and chlorophyll. Phosphorus is essential for many plant activities and has traditionally been considered important for flower and fruit production. Potassium is used by plants to strengthen tissues and helps promote disease resistance.

TRACE ELEMENTS   Other ele-ments required by plants in larger quantities include calcium, sulfur and magnesium. Elements that are needed in small amounts are called trace elements. These include iron, manganese, zinc, boron, copper and molybdenum. For most plants, adequate amounts of trace elements occur in the soil or water supply, but that may not be the case for some orchid growers. Trace elements may need to be supplied, particularly for plants that are grown in inert media or those that receive water that has had all minerals removed.

Most orchid growers subscribe to, or at least have heard the axiom “weakly weekly” as a guide for an orchid-fertilization scheme, and it is not a bad standard. It is important to appreciate that many orchids are adapted to survive in rather marginal environments that are inhospitable

to other types of plants. Copious nutrients are not typically available in such habitats. Consequently, orchids’ nutritional needs are usually small. But like most plants, orchids do respond to supplemental fertilizing by producing stronger vegetative growth as well as larger and more numerous flowers.

MAKING A CHOICE  There are several options from which to choose when selecting an orchid fertilizer. 

First, realize that you do not have to buy a product that is made especially for orchids. Most plant fertilizers contain the same or similar ingredients.

Whether to choose an organic versus an inorganic fertilizer is another consideration. Organic fertilizers are derived from decomposing materials of plant or animal origin. Examples include manure, fish emulsion, bone meal or compost. Inorganic products are produced industrially through chemical processes. These are available in a variety of forms including liquid, powder, granule, and even pellets that are coated for time-release of their nutrients. Despite arguments you may hear to the contrary, the elements found in either type are the same to the plant. Organic products may contain un-known quantities of additional nu-trients necessary for plant growth beyond the specifications on their label, but the convenience of the inorganic products is undeniable.

For most hobbyists, soluble powders or granules seem to be the fertilizer mediums of choice.

 APPLICATIONS  Most growers dissolve the materials to the desired strength and apply it to the plants during regular watering with an injector or siphoning apparatus. Others prefer to water their plants first, and then spray the exposed roots and perhaps the foliage with the dissolved product, in order to avoid burning the plant tissues with too much fertilizer. In many cases, indoor hobbyists with small collections can accomplish the latter technique with a spray bottle.

It is important to read the label carefully when determining dilution strength. You are usually better off to use the products at a weaker strength than recommended. Never forget that the manufacturers make their money by selling product. The sooner you use it up, the sooner you will be back for more. Always keep in mind that orchids are not greedy feeders.

AVAILABLE CHOICES  I have to admit that I am a rather lazy grower, and in recent years I have come to favor time-release pellets for my potted orchids. Their usefulness requires a growing medium that is not overly coarse, so that the pellets do not immediately wash to the bottom or, worse, out of the pot. Temperature and frequency of watering strongly influence how long these fertilizers will deliver nutrients to your plants, and you need to look for the longest-lasting formulation you can find. I seek those that claim to last for six months and have even found a nine-month formula recently. You will likely not find time-release fertilizers made just for orchids; you will have to shop among the products sold for general gardening. Do not worry whether they are labeled for trees and shrubs or flowers and vegetables. Your orchids will not care.

Which strength or formulation to choose is the other dilemma, and this is where every grower seems to have a preference. Some select balanced products (e.g., 10-10-10) while others like a fertilizer higher in nitrogen (e.g., 20-10-10). The higher nitrogen products may be more important for growers using organic media such as bark, since its slow decomposition requires nitrogen too. Some growers like to switch to a “blossom booster” formula (e.g., 10-30-20) when their orchids are in active growth. I follow a policy of switching products and formulas periodically. If there is a deficiency in one, another may compensate for it.

You will also hear advocates for some special fertilizers that may be used for certain kinds of orchids or at a particular time of year. Epsom salts, iron supplements, bone meal, urea-free formulas and other recipes for success all have their advocates, and I have used some of these. Their champions will quote chapter and verse on why they are critical to orchids, but I am not certain of the science behind the claims and have to take them at face value. Whether they make a real difference is sometimes difficult to validate. It certainly may depend on a host of interrelated factors.

I will say that I believe that most of us tend to use plant fertilizers in excess. In my first couple of years of orchid growing, I fertilized seldom, if at all, due to limitations imposed by my orchid growing area. I kept my plants indoors on open wire shelves, and while I could tolerate puddles and water accumulation underneath them on the tile floor, I did not want to deal with the crust and corrosive damage that can be caused by accumulated fertilizer salts. Despite these starvation tactics, I had quite acceptable results. I won my share of ribbons, trophies and awards at orchid shows. With changes to the shelving system, I have given more attention to providing supplemental nutrition but I am still a rather stingy feeder. I suspect most of us could cut fertilizer use in half and see no appreciable difference in our plants’ performance. Nevertheless, it is undeniable that some orchid growers who employ a well-planned and disciplined fertilizer regime do achieve remarkable results.

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