Thoughts on fertilizer. - Orchid Board

Team Ferret · #1 09-05-2007, 08:32 PM

This question comes up often, “how much should I fertilize”, or something close. When the answers come it is everything from “weakly weekly” to a rather high dose at 125 ppm N. This has added to my confusion until I took a long hard think about it. So I am going to throw this out for discussion, but I don’t claim that this is correct.

What I am thinking is the difference is the basic culture. The volume of water, relative to what will evaporate and how it will evaporate, is key to how much fertilizer that can be added. I will throw out some examples with the understanding that this is in general and some orchids just don’t like high amounts of fert.

Bare root culture such as with Vandas. A very low volume of water will be absorbed by and cling to the roots. What isn’t absorbed evaporates completely in a short period of time relative to humidity, temperature and airflow. Any nutrients not absorbed will precipitate out of the evaporating water on the roots and be deposited on the root itself. When this residual salt reaches a level that is damaging to the roots, and I don’t know what level this would be at, the roots are damaged. So to prevent root damage on a Vanda, you would fertilize with a very weak solution.

Bark or mix that a lot of orchids grow in would allow for a bit more fertilizer because the evaporation rate is slower and the volume of solution present is greater than the example above. As moisture evaporates or is absorbed by the roots, more moisture/solution is supplied by what remains in the medium. To this the “weakly weekly” feeding makes sense because as the water evaporates the residual fertilizer remains in the medium which would be rehydrated at the following watering.

Non S/H rock culture (we could include sphag moss here), depending on the type of rock used, even more fertilizer could be used because there is more volume of solution available. Many of the “rocks” available are porous and wick solution to and away from the roots. Ill skip to S/H and this will make much more sense.

Semi Hydro culture at 125 ppm N or greater. Because there is a relative large volume of solution which is wicking up as the top evaporates would prevent the fertilizer from precipitating onto the roots until the concentration of the fertilizer is too great to continue to be suspended in the water. If we start with a volume of 1 pint of solution at 125ppm and over two weeks that evaporates to ½ pint, we should be at 250ppm, which should still easily remain suspended in the solution and not burn the roots.

I think where this gets tricky with new growers like myself is when we have a culture that can handle moderate or high doses of fertilizer but the orchid has new roots that the ends are exposed and not buried in the medium. Fert solution that remains on these roots when watering/feeding will evaporate and the salts will precipitate on the roots and burn them. I learned this one the hard way but cured it with a clean water misting after watering with fert solution.

Ok, so these are my thoughts as to why there are many answers to the question, “how much fertilizer”. If I am correct here, it will serve to explain that all of the answers are correct given that they are properly matched to the culture.

Dave

dennis · #2 09-05-2007, 09:18 PM

Bark or mix that a lot of orchids grow in would allow for a bit more fertilizer because the evaporation rate is slower and the volume of solution present is greater than the example above. As moisture evaporates or is absorbed by the roots, more moisture/solution is supplied by what remains in the medium. To this the “weakly weekly” feeding makes sense because as the water evaporates the residual fertilizer remains in the medium which would be rehydrated at the following watering.

when you grow in bark you should use a higher concentraed amount of nitrogen as to help supplement the loss from the decaying bark. bark uses nitrogen as it decays. a 125 ppm is a good place to start with due to the fact that we do not give the most ideal conditions to grow these, anything more would be a waste as the plant would not be able to absorb any more due to the less than desireable conditon. if you could achieve the perfect condition for each variety that you grow then you could up it to 250ppm due to the fact that the plant would be able to grow at its maximum ability

John · #3 09-05-2007, 10:20 PM

Good discussion. Can you translate ppm into tsp/gal? What are your thoughts about using 10-50-20 at some stage instead of 30-10-10?

John

Andrew · #4 09-06-2007, 12:30 AM

Quote:

Originally Posted by John

Good discussion. Can you translate ppm into tsp/gal? What are your thoughts about using 10-50-20 at some stage instead of 30-10-10?

John

For what it's worth PPM = mg/L. Regarding the 10:50:20 idea. Why such a high concentration of phosphorus? To be honest, I've never seen orchid bloom formulations in my part of the world with a P value higher than 20ppm [P2O5] - most are around 10-15ppm [P205]. Even general purpose blooming fertilizers designed for annuals don't get much over 30ppm [P2O5]. FWIW K values in our orchid bloom formulations range from 20-30ppm [K2O].
Andrew

Team Ferret · #5 09-06-2007, 02:08 AM

Good example Dennis. The bark medium would need a higher N % based on the biology of the decomposing bark. The same N % in a sphag moss or rock culture would be too much. Would I be wrong in this understanding?

As I understand it, divide 10 by the % of N (nitrogen) content of your fertilizer. That number would be the amount of teaspoons per gallon to get a 125 ppm N concentration of fertilizer in your watering solution. Do a search on this board for 125 ppm or MSU, you will find lost of useful info. However, this concentration is 2 to 4 times the amount 70% of the folks on this board would recommend. This, if I am correct, is based on their culture of the orchids they have.

I don’t think orchids need a phosphorous boost to flower. This is because they slowly build up and store the “chemicals” they need to flower. The 30-10-10 is a good general fertilizer for bark based medium. In fact, I have seen that a lot of growers use a weak fertilizer of 30-10-10 daily and add slow release 13-13-13 fertilizer to the medium. But, for those who grow in a medium that has no or little “nutritional” value use something more along the lines as 2-1-3, or close to that ratio. I use a hydroponic nutrient that has a 10-5-13 with minor and trace elements.

Dave

John · #6 09-06-2007, 02:49 PM

The reason I brought up the 10-50-20 was that several years ago JR Peters sold and promoted it to inhance flowering. A quick search on the web showed 10-30-20, 30-10-10, 3-9-6 and 7-5-6 formulations. The 3-9-6 was to "promote enhanced flowering both in color and size of bloom". (These were all labeled for orchid use) I have been using the 30-10-10 year round, generally in the summer every other week at 4-5 tablespoons to 40 gallons and maybe once a month at a lower rate in the winter. I would be open to try something else if it would offer better results. I am using bark and moss. Any thoughts?
John

Ross · #7 09-06-2007, 05:45 PM

Dave, I am hoping Ray jumps in here 'cause there is tons of misinformation. First of all 125ppm Nitrogen is not high concentration at all. I know this is what Ray uses as do I at every watering. I have seen him discount "bloom boosting" mixes or regimes and I personally have seen my orchids increase their blooming with no increase in phosphorus. Same mix all year. As for S/H versus bark, I've heard that plants in bark need more nitrogen. This has not been my experience this year. I have mounted plants on sticks, bark, tree fern, slats, shingles, vanda baskets and plastic and all get the same treatment. I have potted plants (I use waterlily baskets) in coarse bark, fine bark, "special" mixes from suppliers, diatomite, sphagnum, perlite, charcoal/sphagnum/bark, and many other mixes. I have seen no differences in performance, just in ability to grow due to increased air flow, etc around the roots. I have followed the advice on Ray's site and it works for me. Your results may vary - you live in a different climate.

markr · #8 09-06-2007, 07:12 PM

Quote:

Originally Posted by Team Ferret

This question comes up often, “how much should I fertilize”, or something close. When the answers come it is everything from “weakly weekly” to a rather high dose at 125 ppm N. This has added to my confusion until I took a long hard think about it. So I am going to throw this out for discussion, but I don’t claim that this is correct.

What I am thinking is the difference is the basic culture....

Hi,

I think the recommendation of 125 ppm N is a compromise - I'm perhaps putting words in Ray's mouth (fingers?) but that's how I understood his recommendation. When one has many different plants in a variety of media and growing techniques, 125 ppm is a decent way of catering to all of them without the headache of tailoring different fertilizer concentrations to each plant. This concentration is meant to be used at every watering, not once a month or something.

Also, to support something rsfrid wrote, I don't think 125 ppm N is particularly high - higher than recommended in older books but for the last several years experts have been recommending higher and higher concentrations. Isn't 250 ppm N the recommended concentration these days for Phalaenopsis grown in lower-latitude greenhouses?

Team Ferret · #9 09-06-2007, 07:53 PM

All things being considered and in the grand scope of orchid culture, 125ppm is high. Of the fertilizers I have on hand it is twice the recommended amount. It is confusing to the newbees, who are the ones who use this resource for education, to read 125ppm as a low dose of fert only to read the next post recommending “weakly weekly” as being ¼ to ½ the recommended dose of fert. And please re-read my thoughts on high phosphorous fertilizers, I agree with you and Ray.

Please understand that I am rehashing the fert info that is posted here by other members. The goal here is to sort out the facts about fertilizers with the culture they are recommended for. When a person asks a fert question and the answers come without the culture info they are recommended for, confusion sets in. It has happened to me and I am seeing it every time the question is asked by a new grower.

I agree that more N is not needed in a bark medium that is new or lacks fungi and bacteria that would use the N to decompose the bark. Funny thing is that I have not read anywhere where anyone is “seeding” their bark mix with fungi or bacteria so that the plant can use the decomposed matter. Isn’t this the point of having a bark based mix? However, I do read a lot about folks disinfecting and cleaning their mediums. So would any beneficial pathogen survive enough to decompose the bark and thus consume N? This brings us full circle to that I agree, more N is not needed.

No doubt that Ray knows his stuff and S/H is a good culture. But we should be mindful that S/H is quite removed from traditional cultures. To simply say that one should use 125 ppm at every watering in a culture thread is not completely in line with the rest of the thoughts in the thread. The reason I say this is that the word “watering” means a little different for S/H. In S/H the plant is continuously being watered. The “watering” spoken of in regards to S/H is really a flush and re-establishing of the level of solution in the reservoir. So yes, fert is used for every watering but that is what, every two or three weeks? The term “watering” for traditional cultures is actually watering of the dry medium and plant. These two “waterings” are completely different in function.

I am no expert at orchid culture and I am not busting chops. I am however expert at a lot of other things. What I am seeing in the orchid community, not just here, is incomplete culture information. This is no different than racing, shooting, religion, etc. Let’s face it, we are awash in product information but not in technical information. Making heads or tails of this mess is hard. All I am doing, for my sake and the other new growers, is to hash this stuff out in one place. I greatly appreciate the comments. Keep ‘em coming.

Dave

Ross · #10 09-06-2007, 08:56 PM

Dave, my thoughts on bark are that decomposing bark soaks up nutrients to be sure. But we try to avoid decomposing bark! Bark is simply a medium to use for root structure. It could be rock or anything else (as I tried to illustrate in my previous post). If the discussion revolves around what plants use and need in the natural environment, that is one thing. But I think most folks here simply want some medium to root the plants in and get then to thrive. Thus Ray's observations (wish he'd join in here!) that steady supply of Nitrogen is better over blasts of high Nitogen followed by low Nitrogen. All I know for certain ( and I am convinced of this) is that his observations regarding constant supply of 125ppm Nitogen works for me.