Growing Orchids in Atlanta - Determining the Right Fertilizer Concentration

Introduction

In years past, we’ve all heard about feeding orchids weakly weekly or diluting the fertilizer to 1/4 strength.  These were probably good generalizations at the time.  Several months ago, however, the Atlanta Orchid Society had a wonderful speaker, Jan Szyren, who gave the society much more specific information about feeding orchids. Not only did we learn that we should use a basic fertilizer (that is, a fertilizer with nitrate as the nitrogen source), we also learned that plants, including orchids, will grow best if fed at a nitrogen concentration of 125 ppm.  Jan introduced us to the Michigan State University Reverse Osmosis fertilizer (MSU RO fertilizer), which was designed to be used with low alkalinity water, the type of water that Atlanta has.  Because low alkalinity water has low levels of calcium and magnesium, the MSU RO fertilizer is supplemented with calcium and magnesium as well as with the micronutrients needed by orchids.

Many AtOS society members are now using the MSU RO fertilizer, and Jan suggested that ½ teaspoon of fertilizer be mixed with each gallon of Atlanta water.  Jan also mentioned that she is experimenting with higher concentrations and her initial results appear good.  After reading the Bill Argo articles about pH and plant nutrition, I’d like to give you some additional information that might be useful. 

Using the MSU RO fertilizer and diluting it at ½ teaspoon per gallon, the nitrogen concentration will be 105 ppm.  If you use 1 teaspoon of MSU RO fertilizer and a gallon of water, the nitrogen concentration will be 210 ppm; so, you should probably add between ½ and 1 teaspoon of the MSU RO fertilizer to each gallon of water so that you get somewhere between 100 and 200 ppm nitrogen.  Little information exists to guide us in deciding what is the correct nitrogen concentration for orchids.  Jan suggested 125 ppm nitrogen because this seems to give the best result for plants in general.  Jan suggested that orchids be fed with every watering and that every 4^th or 5^th watering be without fertilizer so that salts (like sodium) do not build up in the orchid mix.

You might look at the plants in your collection to decide if you should feed at 125 ppm or try something a little higher (200 ppm, for instance).  Large orchids in active growth or orchids that we typically think of as heavy feeders, such as Cymbidiums, might benefit from using nitrogen concentrations close to 200 ppm.  More delicate orchids, such as many Pleurothallids or seedlings, probably will do better at 125 ppm.  My impression is that feeding at a nitrogen concentration of 300 or 400 ppm or higher with every watering is probably too high.  Remember, no one knows for sure what is best so you will have to use some judgment along with personal observation of your orchids to decide what is appropriate.  For now, I plan to feed at every watering with a nitrogen concentration of 150 ppm and omit fertilizer every 5^th watering or so.

Determining the fertilizer concentration 

Since other fertilizers are also used, I would like to give you an example of how to calculate the amount of fertilizer to dilute in water to give you the desired ppm nitrogen.  First, you need to know the nitrogen concentration of the fertilizer.  The nitrogen concentration of the fertilizer is the first of the three numbers.  In the case of a fertilizer that is 20-10-10, the nitrogen concentration is 20%.  Here are the steps to determining the amount (in volume) of fertilizer to add to water:

Step 1  Multiply the desired nitrogen concentration by the gallons of fertilizer you want

Step 2  Multiply the percent nitrogen in the formula by 75

Step 3  Divide the value from Step 1 by the value from Step 2.

Here’s the formula:

Amount of fertilizer to add  =           (Desired nitrogen concentration) x (# gallons of water)     

                                                                           (% nitrogen in the fertilizer) x (75)

Here’s an example if you want 125 ppm nitrogen as the final concentration in 1 gallon of water and your fertilizer is 20-10-10:

Amount of fertilizer to add to 1 gallon of water   =      (125) x (1)            =   0.083 ounces

                                       (20) x (75)

If you want a higher or lower nitrogen concentration, replace the 125 in the preceding formula with the desired nitrogen concentration.

Here’s how to convert 0.083 ounces to a volume measured in teaspoons.

            Volume in teaspoon  =   0.083 ounces   =   0.4 tsp

                                                   0.2 ounces/tsp

Therefore, if you are using a fertilizer that is 20-10-10, just a little less than ½ teaspoon in a gallon of water will give a fertilizer concentration close to 125 ppm nitrogen.  You could easily round this off to ½ teaspoon and the concentration will be just a little above 125 ppm.  If you want a nitrogen concentration of 200 ppm, add about 3/4 teaspoon of the 20-10-10 fertilizer.  If you added 1 teaspoon, then the nitrogen concentration will be about 320 ppm so you can now gauge how to dilute the 20-10-10 fertilizer to give the amount of nitrogen you think you should feed your orchids.

If all of this confuses you to know end, call the manufacturer and talk to one of their technical representatives to find out how to dilute the fertilizer to get the desired ppm nitrogen.  And still another option is to look at Part 5 in the Bill Argo articles on pH and plant nutrition.  Part 5 will be in September 2004 AtOS newsletter and on the AtOS website.  The bottom of Table 1 gives the amount (in teaspoon) of different fertilizers that can be added to 1 gallon of water along with the corresponding concentration in ppm nitrogen.  In this table, the MSU RO fertilizer is the 13-3-15-8 Ca-2 Mg.  The table also lists other fertilizers, too.

Practical Advice About the Concentration of Fertilizer

Here’s the practical advice I promised:
#  Feed your orchids at 125 ppm nitrogen (or a little higher) with every watering, skipping the fertilizer with every 4th or 5th watering in order to flush salts from the orchid mix.

# If you are using the MSU RO fertilizer, use between ½ and 1 teaspoon of fertilizer for each gallon of water,

#Use ½ teaspoon of MSU RO fertilizer for orchids that are “light” feeders,

#Use 1 teaspoon of MSU RO fertilizer for orchids that are “heavy” feeders,

#If you are using another fertilizer, use the formulas in this article to calculate how much fertilizer to add to a gallon of water to get the desired nitrogen concentration,

#Call the manufacturer and have them tell you how much fertilizer to add to a gallon of water to get the desired nitrogen concentration,

# Look in Part 5, Table 1 of the Bill Argo articles (on the AtOS website and in September 2004 AtOS newsletter) to find the amount of fertilizer to add to 1 gallon of water to get the desired nitrogen fertilizer.

Coming up

The next article in this series will describe using pH and EC meters to measure the pH of the orchid mix and the fertilizer concentration.

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            ^[1]  PPM = parts per million and in this case is parts of nitrogen per million parts of water.

            ^[2]  1 US teaspoon holds about 0.2 ounces of fertilizer.

Hydroponics History and Hydroponics Culture

HYDROPONICS

Many people think of hydroponic as growing plants in water, but hydroponics production actually is defined as growing plants without soil. This production system may use a wide variety of organic and inorganic materials. The nutrient solution, rather than the media in which the plants are growing, always supplies most of the plant nutrient requirements. This method of growing has also been referred to as nutrient-solution culture, soil less culture, water culture, gravel culture and nutriculture.

Hydroponics culture is not new. One of the first experiments in water culture was made by Woodward in England in 1699. By the mid-19th century, Sachs and Knop, the real pioneers in the field, had developed a method of growing plants without soil. The term “hydroponics” was first used by Dr. W. F. Gericks in the late 1930s to describe a method of growing plants with roots immersed in an aerated, dilute solution of nutrients.

Today, hydroponics is used in commercial greenhouse vegetable production around the world. There are several advantages to hydroponics culture with some problems. In automated hydroponics culture, some of the watering and fertilizer additions can be computerized, reducing labor input.

Liquid (Non-Aggregate) Hydroponics Systems 

In this system, no rigid supporting medium for the plant roots is used. Liquid systems are, by their nature, closed systems; the plant roots are exposed to the nutrient solution, without any type of growing medium, and the solution is recirculated and reused.

Nutrient Film Technique (NFT)

This hydroponics system was developed during the late 1960s by Dr. Cooper at the Glasshouse Crops Research Institute, Little Hampton, England. The principle of the NFT system is to provide a thin film of nutrient solution that flows through

either black or white-on-black polyethylene film liners supported on wooden channels or some form of PVC piping which contains the plant roots. The walls of the polyethylene film liners are flexible, permitting them to be drawn together around the base of each plant, which excludes light and prevents evaporation.

The nutrient solution is pumped to the higher end of each channel and flows by gravity past the plant roots to catchment pipes and a sump. The solution is monitored to determine the need for replenishment of salts and water before it is recycled. A capillary mat in the channel prevents young plants from drying out, and the roots soon grow into a dense, tangled mat. A principal advantage is that a greatly reduced volume of nutrient solution is required, and this system is more easily heated during winter months or cooled during hot summers to avoid bolting and other undesirable plant responses.

The slope of the channels in NFT needs to be approximately 3 inches per 100 feet. Slopes less than that are not sufficient. Depressions in the channel must be avoided, or puddling of the solution will lead to oxygen depletion and growth retardation. A cold nutrient solution will prevent plant uptake of nutrients. By heating the nutrient solution, growers can lower greenhouse night air temperatures without adversely affecting crop yield and total value. Crops also benefits from a heated solution, especially when plants are small and close to the solution.

The NFT system also allows for economical cooling of plant roots, avoiding more expensive cooling of the entire greenhouse.

Aggregate Hydroponics Systems

Aggregate systems such as vertical or flat plastic bags are “open” and the solution is not recirculated, while porous horticultural grade rockwool may be “open” or “closed.” In a “closed” rockwool system the excess solution is contained and recirculated through the system. Not reusing the nutrient solution means there is less sensitivity to the composition of the medium used, or to the salinity of the water.

Bag Culture 

In bag culture, the growing mix is placed in plastic bags in lines on the greenhouse floor. The bags may be used for at least two years, and are much easier and less costly to steam-sterilize than soil. Bags are typically made of UV-resistant polyethylene, with a black interior, and generally last

for two years. The exterior of the bag should be white in regions of high light intensity levels, to reflect radiation and inhibit heating the growing medium. Conversely, a darker exterior color is recommended in low-light latitudes to absorb winter heat. Growing media for bag culture may include peat, vermiculite, or a combination, with perlite is sometimes added to reduce cost. Examples of lay-flat bags are Plant-in-Bags and Fertile-Bags. Bags are placed on the greenhouse floor at normal row spacing for the crop. It is beneficial to first cover the entire floor with white polyethylene film, increasing the amount of light reflected back into the plant canopy. A covering may also reduce relative humidity and the incidence of some fungal pathogens.

Paired rows of bags are usually placed flat, about 5 feet apart (from center to center), with some separation between bags. Holes are made in the upper surface of each lay-flat bag for transplants, and two small slits are made low on each side for

drainage or leaching. The soil in the bag is moistened before planting. Drip irrigation with nutrient solution is recommended. A capillary tube should run from the main supply line to each plant. Moisture conditions near the bottom of the bagged medium should be examined frequently. It is normally best to be on the wet side, rather than dry.

Rockwool Culture

The use of horticultural rockwool as a growing medium in open hydroponics systems has been increasing rapidly. This technology is the primary cause of rapid expansion of hydroponics systems. Rockwool was first developed as an acoustical and insulation material. It is made from a mixture of diabase, limestone and coke, melted at a high temperature, extruded in small threads, and pressed into lightweight sheets. Insulation rockwool and fiberglass batting are not appropriate for use in horticulture. For use as a growing medium, rockwool must first be modified by a special proprietary process.

As a growing medium, rockwool is not only relatively inexpensive, but is also inert, biologically non-degradable, takes up water easily, is approximately 96 percent “pores,” or air spaces, has evenly sized pores (important for water retention), lends itself to simplified and lower-cost drainage systems, and is easy to heat during winter. It is so versatile that rockwool is used in plant propagation and potting mixes, as well as in hydroponics.

In “open” rockwool hydroponics systems, plants are usually propagated by direct seeding in small rockwool cubes with a hole punched in the top. The cubes are saturated with nutrient solution and are usually transplanted into larger rockwool cubes manufactured specifically to receive the germinating cubes, and side-wrapped with black plastic film. The large cubes are then placed atop rockwool slabs on the greenhouse floor. The slabs are usually 6 to 12 inches wide, 29 to 39 inches long, and 3 inches thick.

The greenhouse floor is covered with white polyethylene film for sanitation and light reflection. A bed normally consists of two rows of rockwool slabs, each wrapped in white film, in rows spaced 12 inches apart. The slabs should have a slight inward tilt toward a central drainage channel. If bottom heat is required, the slabs are placed on polystyrene sheets, grooved in the upper surface to accommodate hot water pipes.

Due to the porosity of the rockwool, and given an appropriately modest irrigation schedule, almost all the solution remains in the slab for plant use. If there is a surplus, it will drain out of the slab and into the shallow channel. Before transplanting, the rockwool slabs are soaked with nutrient solution. The plant remains in the small rockwool cubes in which it was established. Plants are set along the slabs through holes cut in the plastic film. If a root system is well developed in the cubes, roots will move into the slab within two or three days. Each plant receives nutrient solution through individual drippers, with irrigation rates varying by plant demand and environmental conditions.

The advantages of the rockwool system are:

1) Rockwool is lightweight when dry, and is easily handled.

2) It is simple to bottom-heat.

3) It permits accurate and uniform delivery of the nutrient solution.

4) It uses less equipment and has lower fabrication and installation costs; and there is less risk of crop failure due to the breakdown of pumps and recycling equipment.

The disadvantage is that rockwool may be:

1) Relatively costly, unless manufactured nearby.

Nutritional Disorders

Nutritional disorders are plant symptoms or responses that result from too much or too little of specific nutrient elements. Generally, there are no nutritional disorders unique to hydroponics. Plants are more likely to experience nutritional disorders in a closed hydroponics system than in an open system. In a closed system, the levels of impurities or unwanted ions in the recycled liquid, or from the chemicals used, may more easily destroy the balance of the formulation and accumulate to toxic levels.

The most common nutritional disorders in hydroponics systems are caused by:

1.  High levels of ammonium (NH4). This causes various physiological disorders in many crops, and is avoided by supplying no more than 10 percent of the necessary nitrogen from ammonium.

2.  Low levels of potassium (less than 100 ppm in the nutrient solution) can affect tomato acidity and reduce the percentage of high-quality fruit.

3. Low levels of calcium. This induces blossomed rot in tomatoes.

4.  Zinc toxicity, caused by dissolution of the elements from galvanized piping used in the irrigating system. It is avoided by using plastic or other non-corrosive materials.

Symptoms of Plant-Nutrient Deficiencies

Plants usually display characteristic symptoms if nutrients are not present in adequate amounts. Below is a guide to the symptoms that may occur if the level of one mineral nutrient is below the range needed for best plant growth. There may be other reasons, such as ratio of nutrients that may cause a plant to display a definite symptom. If one of the deficiency symptoms occurs, however, a lack of the proper nutrient may be suspected, and the amount of that nutrient increased. Nutrient-related disorders of crop plants can be avoided if crops are closely observed and the composition of the nutrient solution adjusted, particularly in closed systems.

Deficient                                                        Symptoms

Nutrient

Nitrogen  :-  Leaves are small, light green; lower leaves lighter than upper; weakstems.

Phosphorus :-  Dark-green  foliage;  lower  leaves  sometimes  yellow  between  veins; purplish color on leaves or petioles.

Potassium :- Lower  leaves  may  be  mottled  (light  to  dark  blotches);  dead  areas near tips and margins of leaves; yellowing at leaf margins continuing toward center.

Calcium :- Tips of shoot die; tips of young leaves die; leaf tips are hook-shaped.

Magnesium :- Lower  leaves  are  yellow  between  veins  (veins  remain  green);  leaf margins  may  curl  up  or  down  or  leaves  may  pucker;  leaves  die  in later stages.

Sulfur :- Tip  of  the  shoot  stays  alive;  light-green  upper  leaves;  leaf  veins lighter than surrounding areas.

Iron : Tip of shoot stays alive; new upper leaves turn yellow between veins (large veins remain green); edges and tips of leaves may die.

Manganese  :-     Tip of the shoot stays alive; new upper leaves have dead spots over surface; leaf may appear netted because small veins remain green.

Boron :-  Tip of shoot dies; stems and petioles are brittle.

Advantages of Hydroponics

•   Land is not necessary. It can be practiced even in upstairs, open spaces and in protected structures.

•       Clean working environment. The grower will not have any direct contact with soil.

•       Low drudgery. No need of making beds, weeding, watering, etc.

•       Continuous cultivation is possible.

•       No soil borne diseases or nematode damage.

•       Off-season production is possible.

•       Vegetable cultivation can be done with leisure sense.

•       Many plants were found to give yield early in hydroponics system.

•       Higher yields possible with correct management practices.

•       Easy to hire labour as hydroponics system is more attractive and easier than cultivation in soil.

•       No need of electricity, pumps, etc. for the non-circulating systems of solution culture.

•       Possibility of growing a wide variety of vegetable and flower crops including Anthurium, marigolds, etc.

•       Water wastage is reduced to minimum.

•       Possible to grow plants and rooted cuttings free from soil particles for export.

Limitations of Hydroponics

•     Higher initial capital expenditure. This will be further high if the soil-less culture is combined with controlled environment agriculture.

•    High degree of management skills is necessary for solution preparation, maintenance of pH and Ec, nutrient deficiency judgment and correction, ensuring aeration, maintenance of favourable condition inside protected structures, etc.

•       Considering the significantly high cost, the soil-less culture is limited to high value crops of the    area of cultivation.

•       A large-scale cultivator may have to purchase instruments to measure pH and Ec of the nutrient   solution.

•       Energy inputs are necessary to run the system.

•       Yields were found to decrease when temperature of the solution rises during warm periods.