Do you need CalMag supplementation with MSU?

[NewBloom]

I first started fertilizing with an MSU fertilizer (13-3-15 8Ca-2Mg). When the MSU finished, I switched to Dyna-Gro's Grow 7-9-5 with the calcium magnesium being 2 and 0.5 respectively.

Lately, I've been considering adding cal-mag or Epsom salt to my feeding program once a month. I would use it one week a month without adding any other fertilizer. Some of my rescue phals have new leaves where the growth just stopped. Do you think the 2 Ca and 0.5 Mg in the Grow were too low and created a deficiency?

I will switch back to MSU when the Dyna-Gro runs out. Is Cal-Mag supplementation necessary when using a MSU fertilizer?

I also have crushed oyster shell for my cyms. Would using that take the place of a liquid cal-mag product?

[Ray]

One of the best ways to control your feeding regimen is by managing the the nitrogen loading of your solutions - that's the way large-scale nurseries do it, so it must be OK.

That said, it takes approximately two teaspoons of the "Grow" to match one teaspoon of the MSU formula. That means that it would therefore be equivalent to one teaspoon of a 14-18-10-4Ca-1Mg.

The particular MSU formula you referred to is intended for use with water containing NO dissolved minerals at all, and fed at 125 ppm N, it is designed to give a sufficient amount of Ca and Mg for most orchids. That said, the fact that the "Grow", if applied at the same 125 ppm N, only has half of the Ca & Mg content, does not mean that you would experience any nutrient deficiency issues. I used it at 50 ppm N for about 10 years, and was very pleased with the growth and flowering of my plants.

What water supply are you using? The fact that you used the RO version of the MSU stuff suggests pure water, and if that's the case, switching to the Dyna-Gro product in an unbuffered water supply will result in an extremely low solution pH, and THAT might affect the plants.

[NewBloom]

Hi Ray,

I use tap water with the orchids. The MSU fertilizer is RepotMe's Raniwater/RO/Tap water formula.

In the last month I realized I had been using the Grow at a weakened mix.

I had been applying the Grow at 1/4 per gal water at each feeding--with 1/8 tsp Pro-tekt--because I'd misread the Dyna-Gro culture sheet. It suggests 1/2 tsp per gallon for catts, phals, dens and onc. Only for the cyms does it suggest 1 tsp/gal.

Ray are you recommending that I "bump up" the Grow to 2 tsp/gal where the company says to do 1/2 tsp?

According to a spa Ph test strip I got from Home Depot, the water is at 6.2. Today I tested the Ph of the MSU fertilzer after it had been applied to the plant in CHC with some oyster shell as a light top dressing. The Ph also tested in the 6.2 range. I haven't tested the Grow as yet.

Now the phals in question were rescue plants that were in bad shape so that might be part of the growth problem. But I'd say they really improved over the summer and the worst of the lot are the ones that put out new leaves that plateaued.

[BobInBonita]

In my opinion, the pH of your water isn't so much an issue, since unbuffered water will change pH quickly - even dissolved CO2 will form carbonic acid and drop the pH. As soon as minerals (buffers) are added, the pH will tend to stabilize more.

The real issue as Ray asked was the mineral content of your water. Tap water from a "hard" aquifer will have all the Ca and MG you need, wheras some "soft" lake water sources are pretty low.

Remember, most orchids get watered by rain water so their needs are pretty low..

[Ray]

Hi Ray,

I use tap water with the orchids. The MSU fertilizer is RepotMe's Raniwater/RO/Tap water formula.

There is no such thing as a single MSU formula that spans both pure (rain, RO, etc.) and mineral-bearing water supplies (tap, well).

If your water supply is essentially mineral-free, there are no dissolved ions capable of buffering the solution - i.e., "stabilizing" the pH. The addition of small amounts of ionizable species can therefore effect the pH of the solution easily. As Bob mentioned, carbon dioxide absorbed from the air can form carbonic acid and drop the pH. Fortunately, it's a very weak acid, so the addition of almost anything else overwhelms it. The minerals in a typical fertilizer formula intended for mineral-bearing (hence, buffered) water, on the other hand are strong ionizers. Adding the Dyna-Gro "Grow" formula, for example, can result in a solution pH in the 3's or 4's.

That is why Bill Argo developed the "RO" formula - it uses different minerals in a combination that buffers the solution in the correct pH range when added to pure water.

Also to Bob's point, most tap- and well water supplies contain enough calcium and magnesium that it's really not necessary to add much, if any at all with the fertilizer. The only exception to that that I am aware of is NYC municipal tap water, which is so mineral-free that you pretty much have to use the "RO" formula. Pure water, having none of the above minerals, needs to have them supplemented - hence the 8Ca-2Mg in that formula.

Ray are you recommending that I "bump up" the Grow to 2 tsp/gal where the company says to do 1/2 tsp?

To some extent, fertilizer regimen is a matter of personal preference.

In the study that Bill Argo and Jan Szryzen conducted that led to the development of the MSU fertilizers, they found that applying about 100-150 ppm N provides a good diet to a diverse collection of orchids.

If you divide 10 by the %N on the label, the result is teaspoons per gallon for 125 ppm N, so if you round up or down for convenience, you're still in that range.

Dave Neal, owner of Dyna-Gro, believes that feeding very weekly entices the plants to grow more roots, in order to find more nutrition. His logic is more roots=stronger plant. I followed his lead for years, but decided to try the 125 ppm N regimen when Bill approached me about trying his stuff, and I see better growth and flowering.

[NewBloom]

Thank you for the information.

Ray, the formula of: 10 / N% on label...can that be done for any non-MSU fertilizer to calculate the teaspoons per gallon needed to reach 125 ppm? I want to be sure I understood your recommendation.

I'll finish up the bottle of Grow using the modifications.

[LadyOrchid]

As I have found this topic I will ask my question here.
The same situation is with me MSU formula with RO water but sometimes I do think my tap water is ok for my Cattleyas and Vandas. It contains all together around 150/200 ppm.

But I am not sure I understood correctly about Dyna Gro Orchids is it for RO water or tap.

If I can use with my tap water with lower level of N I will have better results. My tap water contains Ca and Mg in good amount.

Do you think Dyna Gro Orchids will do good with my tap water.

[estación seca]

The pH will matter as well. Mineral availability changes with pH. Get a liquid pH measuring kit from an aquarium store. Check the pH of your tap water. Then check the pH of your tap water plus the amount of fertilizer you plan to add. If your pH is in an acceptable range (5.5-7.5 or so?) and the nitrogen is in an acceptable range, that solution should work fine.

Most plants actively take up potassium and phosphorus from the environment. Most plants exclude calcium. It will not penetrate the roots except at the root tip where the endodermis hasn't formed (inner layer of root.) Plants crystallize calcium with oxalic acid in their sap to yield an extremely low level of free calcium - low enough they can use calcium as an intracellular messenger molecule.

[Ray]

Excessive amounts of calcium in the medium or in solution can also inhibit the uptake of other nutrient ions.

I want to expand upon E.S.' statement about pH and nutrient availability, as folks might misconstrue that statement: Within the realm of pH values that are appropriate for orchids, and even a bit on either side, pH has no impact on availability.

The classic chart we've all seen that says otherwise, was created by pouring a single fertilizer formula solution through a single type of soil. Soils, containing clays and very fine organic matter, have sites within them that bind cations. The term used is cation exchange capacity - CEC. What they bind, how strongly, and what they release to the plant's are determined by the pH. Different soils have different CEC's, and depending upon the fertilizer formula, there are any number of combinations of what is available and what is not, because it has been trapped by those sites in the soil.

Fortunately, I suppose, orchid media have almost no CEC, so if the nutrient is in solution, it's available to the plant.

[LadyOrchid]

Thank you so much my guys for your input. All written is more than correct.

How much I know my best choice would be for sure K-Lite but unfortunately I can't find that fertilizer to buy :-(
I think low P and K in formula are very good for orchids.
If you maybe know where I can have this fertilizer please tell me. I will pay shipping that is not a problem at all ;-)