Mineral Nutrition for Slipper Orchid Growers

AnTec Laboratory - Bob & Lynn Wellenstein

Everyone's conditions are very different, and you must balance the various factors of your growing with each other. What is stated

here are the factors we take in to consideration regarding mineral nutrition: it is hoped that there may be aspects discussed that may be

useful to you. We suggest that careful experimentation on small numbers of plants be carried out before anyone makes any major

change in their growing conditions. Also, everyone does not have the same goals in growing, and may not be interested in trying to

tease every last bit of potential out of their plants. As a result, we’ll also discuss some options to consider if you want to grow these

plants without going into the details of matching your fertilizer with a water quality analysis.

allowing the media to dry completely will aid in salt elimination, but can also lead to rotted roots, so using a more open mix than you

normally would and watering more frequently may also be of help, letting you water without the mix completely drying out but still

keeping some air supply at the roots. If you are seeing what appears to be symptoms of a mineral deficiency, or dehydration of the

plants, remember that to check the most obvious and most common cause first, loss of roots due to rots.

Dose response generalization

If you have a water analysis in hand, you can then match

your fertilizer better to your needs. If you have 30 – 50 ppm

or more calcium available in the water, then you should

choose a balanced fertilizer without calcium. If you have 20

plants. Otherwise, use a balanced fertilizer for the rest of the

macronutrients sparingly (try to keep TDS of irrigation mix

[water plus fertilizer] at 350 ppm or lower, and the chances

that you will encounter nutrient deficiencies is small. The

only further caution is to check the pH of your water

fertilizer mix and make sure that it is in range for the types

of plants you are growing (see Use of Calcium Based

Supplements for Paphs for more details). However, if your

goal is to grow the plants as well as possible, we’ll try to

provide you with some tools here to fine tune your program,

sense. Please note that the response curve for many micronutrients is very steep, being absolutely essential in very small quantities, but

many, such as boron, are also very toxic in quantities that are only slightly higher. I have heard hydroponic growers cite a rule of

thumb for micronutrients that "twice optimal is toxic." The obvious corollary is use extreme care if you are supplementing the micro

or trace elements. Another caution is that many plant hormones that are commonly used as supplements have similar dose response

curves as the microelements, so again use care to follow label instructions, more is not better, at best you are wasting your money at at

worst you may be damaging your plants. While the dose response curve for macronutrients is somewhat more forgiving, we still want

to stay fairly close to the optimal area in choosing our fertilizer levels.

You need to consider mineral nutrition of your plants as a combination of your water and the fertilizer you add. What we currently feel

is a reasonable range of nutrients for a steady feed program (combined level provided by both the water and the fertilizer) for Paphs is

provided in the following chart, but please remember that the absolute values that you should use will be affected by light levels, day

Nitrogen (NO

3

Potassium 60 100

Calcium 30 50

Magnesium 15 30

Phosphorus 30 50

Sulfur 15 25

Boron trace < 0.8

Iron > 0.5 2

Manganese > 0.2 2

and magnesium levels is somewhat easier, you simply have to supply them at the level you want. Several commercial fertilizers are

available that provide one or both of them, but many have neither. Your choices are to select one of the fertilizers that contain

sufficient levels, or to feed calcium nitrate once every 2-3 weeks and Epsom Salts (magnesium sulfate) at another feeding every 2 – 3

weeks. Even some of the fertilizers that have these two elements in them contain them at sub optimal levels for use in pure water, so a

periodic feed of calcium nitrate and Epsom Salts may still be indicated even with them. If you are working with water with higher

concentrations of these elements you may need to choose a fertilizer that does not contain them to maintain as much balance as

possible in your program. As discussed earlier, if you have extremely high water salinity, you may have to fertilize at well below the

sub optimal levels to avoid salt build up problems for your plants roots.

Water/ fertilizer pH is another commonly overlooked area, and an area where I think many folks could drastically improve their plants

health. Various elements are available at different levels depending on the pH of the solution they are dissolved in, with some

start with. Fertilizers differ in their alkalinity or acidity depending on composition. You may be able to match a fertilizer to your

condition to arrive at an acceptable pH, for example an acidic fertilizer used with pH 8.0 municipal water may end up at a range in the

high 6’s. It is important to know the pH of your final irrigation mix, and make adjustments if necessary to get it into an appropriate

range. We use potassium hydroxide to raise our pH, phosphoric acid is commonly used to lower pH. Vinegar is commonly mentioned

as useful for lowering pH, however we do not have experience with it. It is also possible to use a limited amount of potassium silicate

to raise your pH, follow label directions to avoid using too high a level. Do not try to raise the pH levels of fertilizer concentrates that

contain calcium or magnesium and phosphorus, you may cause precipitates to form. The pH adjustment of these fertilizers must be

made in the diluted form.

The charts below summarize additional information regarding mineral nutrition. The relative numbers of atoms in plant tissue is a

generalized approximation based on molybdenum being 1, to give a rough’ idea of the relative needs of the plants for each of these

tissue as the plant mobilizes the element from the more expendable older tissue to the newer growing areas. Conversely, if it is not

translocatable, then the deficiency will show more in the new growing areas of the plant. Another diagnostic indicator to pay attention

to is the location of the symptoms, are they marginal, interveinal or generalized on the leaf? Again, I’d like to point out that the most

likely cause of a mineral deficiency (unless you are not fertilizing at all) is the loss of the roots of the plant, leaving it unable to take up

the needed nutrient levels.

Element Symbol Form

Most

readily

available

Unavail-

able pH

Relative No.

Atoms in

Plant Tissue

Carbon C CO

2

35,000,000

Oxygen O O

2

, H

2

O

30,000,000

Nitrogen N

3

-

6.0 – 8.0 <4.5, >9.5 1,000,000

++

Magnesium Mg

++

6.5 – 9.0 <4.5, >10.5 80,000

Phosphorus P

6.5 – 7.8 <4.8 60,000

Copper Enzyme component, electron

carrier protein in chloroplast

Stunted, misshapen growth. Symptoms of magnesium or

iron deficiency

entirety.