Thoughts on fertilizer.

[Ross]

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.

[Team Ferret]

I think we are hitting the same nail, just from two different directions. In other words, I agree.

Dave

[quiltergal]

Just a comment about semi-hydro. I flush and refill the reservoir on a weekly basis. Letting it go longer has drawbacks. The plants will use what they need from the "cocktail" as needed, so as time goes by "cocktail" changes because the plant has used more or less N or P. In order to maintain the integrity of the "cocktail" it needs to be replaced weekly. You may have started out the week with 125ppm N but by the end of say week 3 who really knows how much N is left?

I also agree with Ross. I have lots of different plants in different media that have different culture requirements. Right now it takes me over an hour to get everything watered on a weekly basis. As someone else stated the 125ppm is a compromise. I shudder to think how long it would take me to water if I tailored the ppm N to each and every plant. While 125ppm may not be perfect for every plant it's close enough for all my plants to thrive and bloom.

[Andrew]

Dave,
I agree about the phosphorus, which was partially why I was curious why so many US growers seem to use high P formulations to get their orchids to bloom. My understanding was that phosphorus is predominantly used in nucleotides and phospholipids and therefore is necessary for dividing cells. Sure this means plants need it to flower but they also need it for leaf and root growth. I was under the impression (from a few papers I've seen on non-orchid nutrient uptake) was that phosphate requirements are usually fairly stable throughout the growth/flowering cycle and that most complete fertilizers supply more than enough. Where I've seen recommendations for high P ratios, it's usually where rapid root growth is favoured (seedlings, root crops etc). Both orchid and non-orchid bloom fertilizers on my side of the world focus on relative potassium concentrations, which to my mind is much more understandable.
Andrew

[Ray]

I'm going to have to "peck" at all of this info in a very fragmented fashion, so bear with me.

Some of what I've read in this thread differs from my understanding, but it might be something of a difference in interpretation, more than anything else. Take the vanda feeding, for example. While I agree that the roots will only absorb "so much", I don't buy the "feed it weakly or the residues will build up" to bad levels. For one, vandas are very heavy feeders, so need a lot of fertilizer. Secondly, In 40 years of growing, I have never seen buildup occur directly on roots. The surrounding medium is far more sponge-like, so can accumulate the minerals in a far higher concentration. When the water evaporates from them, that's when and where the precipitation occurs. Any tiny amount of deposited minerals on a bare vanda root will redissolve and wash away next time it's watered.

How wet or dry the root zone is has just the opposite effect on need for fertilizer concentrations than what was mentioned. Fertilizers are only absorbed by the plants as mineral ions, which means they must be in solution. We must also keep in mind that a plant needs so much mass of nutrition to survive, grow and bloom. If I put fertilizer solution in a very fast drying medium, the plant may extract those nutrient ions only while they are still in solution (wet), so may only (just for example's sake) get a few percent of the applied minerals. If, on the other hand, the medium stays wet longer, the plant has the opportunity to absorb more of what's there. From that we would have to conclude that a wetter medium needs less fertilizer, not more. And that leads me to the concentration question.

125 ppm N is something of a compromise as MarkR mentioned, but it is anything but a high concentration. Back when Miracle-Gro and Mir-Acid were the norm, feeding was usually done infrequently but at much higher concentrations - 350-500 ppm N being more the range. Dr. Yin-Tung Wang at Texas A&M - someone who actually does a lot of good scientific work, rather than relying on anecdotes - has shown that a regular diet of 250-275 ppm N gives phals optimum growth and flowering in his greenhouse conditions.

I was probably part of the dissemination that weaker was better, as I used to grow at 50 ppm N and recommended that, but I have found my plants to grow better at the higher rate. Keep in mind that the 125 ppm N level was determined in another scientific study at Michigan State - the study that the "MSU Fertilizer" formulas came from - and that while it may be something of a compromise to account for the differing nutrient needs of different plants, it is a reduced level to account for the fact the PAR (photosynthetically active radiation) in northern latitudes is reduced compared to those closer to the equator.

While on the subject of the MSU study, one of the more significant things that came out of that, in my mind anyway, was the killing of the phosphorus-as-a-bloom booster myth. Plants need very little phosphorus, and any in the fertilizer in excess of that is a waste. What they proved was that it's the excess of nitrogen that slows or prevents blooming, not that phosphorus enhances it. The conclusion was that by adding a lot of inexpensive phosphorus-containing minerals to the formulation, one dilutes the nitrogen down to not-stopping-blooming levels.

[Ray]

I wanted to add another thought in relation to semi-hydroculture.

The comment was made that we might start with a pint of 125 ppm N solution, but after a time, it will beccome a 250 ppm N solution at half the volume, due to evaporation.

Unfortunately, that ignores the actions of the plant.

After it has been poured into the pot, the plant starts to absorb nutrients from the solution, which reduces the concentration in the reservoir. Yes, the plant absorbs some of the water as well, but keep in mind that there is a great deal of osmotic pressure in this process, and I'd bet the gradient in the concentrations of the mineral ions is greater than that for the water.

I would guess that - unless the temperature is so high and humidity so low that the evaporation rate is extreme - the mineral concentration in the liquid goes down over time and does not concentrate.

However, waste products are also being dumped in the root zone by the plant, and they dissolve in the liquid present (s/h or otherwise), changing the chemistry to some unknown elixir, so we are doing good by watering relatively frequently and flushing/refreshing that solution.

[Team Ferret]

Everyone, thank you for posting to this thread. Ross really had me rethinking this topic. So, here is what I have learned from this thread (please correct me if I have misunderstood);

It is clearly understood that orchids don’t need more phosphorous.

That 125ppm is not a high concentration of fertilizer. This understanding is in spite of book and online recommendations of ¼ to ½ strength fertilizer solution which would be 30 to 50 ppm.

Based on the presented abstract of scientific research, the use of higher concentrations (250 to 500ppm) won’t hurt the orchid, and if grown in southern latitudes nearer the equator would actually benefit the orchid.

Mineral salts from the fertilizer rarely if ever build up on the roots, even in bare root culture.

Feeding is not as big of an issue as I was understanding, or misunderstanding.

My conclusion is that I should feed my orchids how I feel is best and if I am not happy with the rate of growth I can increase the fertilizer to a reasonable rate (I am assuming up to 250ppm here in FL). Although not mentioned, I do understand that the amount of fert is only part of the equation. Light, humidity, air movement and overall plant health must support the target growth rate.

I know I should chill a bit about growing orchids. Its supposed to be a hobby for me, you know something to help me RELAX. I have worked with metal and mechanical stuff my whole life and can’t tolerate mistake or failure. Most of the time with metal you get a second chance to get it right, but with living things you don’t. So I am breaking my head trying to get this growing stuff right. What I forget is that plants are alive and can take care of themselves, given that they have the basics.

Once again, thank you for this discussion.

Dave

[Ross]

Originally Posted by Team Ferret

That 125ppm is not a high concentration of fertilizer. This understanding is in spite of book and online recommendations of ¼ to ½ strength fertilizer solution which would be 30 to 50 ppm.

Dave, sort of. I think what several of us said is yes 125ppm is not a high concentration but it might NOT be up to snuff for certain 'chids like some of the Phals. But it's a good compromise when one doesn't have the time or patience (like me) to adjust mix for a varied collection. In other words, it's "good enough" to get the job done. Works for me so far.

Originally Posted by Team Ferret

Feeding is not as big of an issue as I was understanding, or misunderstanding.

My conclusion is that I should feed my orchids how I feel is best and if I am not happy with the rate of growth I can increase the fertilizer to a reasonable rate (I am assuming up to 250ppm here in FL). Although not mentioned, I do understand that the amount of fert is only part of the equation. Light, humidity, air movement and overall plant health must support the target growth rate.

I think I agree. I pretty much went with the MSU recommendations since Michigan State is here in Michigan (and has a great football team this year, thanks for asking!) As for higher concentrations, I guess I'd want to know why I was doing that before I just assumed anything. You may be right.

I definitely agree on the other factors. I've made two major changes over the last year or so. I've gone to a steady feeding regime. Plants get fertilizer with every watering. Some every day, other as long apart as 3-4 days or a week. But each one gets totally submersed, totally flushed, whatever, depending on the container or mount.

Not sure what you mean by "target growth rate" but for me it is whatever the plant seems to look like in nature. So I pour over photos in books and on line and decide how I want the growth to "maximize". For instance, my Dendrobium anosmum canes are 1/3 longer this year than any year previously. That's close to 48" long!

Thanks for the thread. It was a goodie

[Vanessa]

By George I think you've got it! Good luck Dave and enjoy your hobby to the fullest. I really learned a lot from your post and the ones that followed.

[Ray]

Your second-to-last paragraph brings up another interesting point, Ross.

If you look a orchids in nature, you are unlikely to see consistently optimal or "maximized" growth. The vagaries of nature interfere too much.

In the wild, they only get a good feeding if it rains, and if it rains too much, that food - washing down from the forest canopy - is very dilute. Wind desiccates them and knocks them down. The sun parches them, especially if that shading branch overhead breaks. Critters chew on them, and the temperatures can vary all over the map.

A captive species - if given the right culture - will most often be far superior to its wild cousins, primarily due to the consistency of culture.