When to fertilize with blooming fert?

[Orchid Whisperer]

The horticulturalists I know at the University of Georgia and State Botanical Garden of Georgia, agree with fertilizers that have roughly equal N and K, less P. This includes orchids. I have a research article, experiment with Dendrobiums, that supports this.

I agree that lower fertilizer, in general, seems to be better for orchids. The only time I provide it more often is in the spring with new growth.

[Ray]

Originally Posted by Orchid Whisperer

The horticulturalists I know at the University of Georgia and State Botanical Garden of Georgia, agree with fertilizers that have roughly equal N and K, less P. This includes orchids. I have a research article, experiment with Dendrobiums, that supports this.

And yet... Brandon Tam, the orchid specialist at the Huntington Botanicals Gardens in California, who has garnered a whole bunch of awards, only feeds with calcium nitrate.

OW - I'd love to see that article, if you can share it.

Frankly, I think it'll be a while until we "know for sure" about any of it, as orchids are so flexible and undemanding of nutrition.

I'll be one of the first to acknowledge that tissue analysis may not paint an accurate picture of the plants' needs, as it is well-established, for example, that phosphorus is actively taken up in excess and stored away in vacuoles, where it sits unused. Plus, if tissue analysis was entirely valid, we could conclude that people need lots of fat and cholesterol!

[Roberta]

Originally Posted by Ray

And yet... Brandon Tam, the orchid specialist at the Huntington Botanicals Gardens in California, who has garnered a whole bunch of awards, only feeds with calcium nitrate.

Also, Brandon has found that Paphs actually do better with well water (which is loaded with calcium bicarbonate, TDS between 200 and 800 ppm) than with RO. Other orchids get RO, but the Huntington's world-class Paph collection gets that well water.

[Ray]

Shifting gears a bit, I think that part of the issue we orchid growers face is the inability to know just what the plants are actually getting - mass wise - when we feed them.

If we take poinsettias as an example (which used to be the biggest floral cash crop in America before orchids became popular), the difference is obvious:

It is a very well-established fact in the industry that it takes one-half gram of nitrogen to get a plant from rooted cutting to "full flush" for Christmas sales.

The growers know the volume of the pot, the retention of the medium, the time-to-harvest, and their expected frequency of irrigation, so having selected a formula they prefer, can calculate the nitrogen concentration that will provide that sum over the growing season.

Does anyone have even a guess of the retention of an orchid medium, and how it may change over time? I doubt it.

From testing I did many years ago, I learned that LECA tends to have a retention of about 50%-60% of its dry weight. So I know that if I fill a pot with saturated LECA and weigh it, my liquid content is about a third of that, so I could easily calculate how much fertilizer is store, but I don't know diddly about how much a plant takes from that, because the root system isn't nearly as extensive as that of a terrestrial plant.

[Orchid Whisperer]

Ray, I'm away from home right now, but should be able to find the dendrobium article later on

[Orchid Whisperer]

Originally Posted by Ray

And yet... Brandon Tam, the orchid specialist at the Huntington Botanicals Gardens in California, who has garnered a whole bunch of awards, only feeds with calcium nitrate.

OW - I'd love to see that article, if you can share it.

Frankly, I think it'll be a while until we "know for sure" about any of it, as orchids are so flexible and undemanding of nutrition.

I'll be one of the first to acknowledge that tissue analysis may not paint an accurate picture of the plants' needs, as it is well-established, for example, that phosphorus is actively taken up in excess and stored away in vacuoles, where it sits unused. Plus, if tissue analysis was entirely valid, we could conclude that people need lots of fat and cholesterol!

Ray, here is a link to that article:
Nitrogen, Phosphorus, and Potassium Requirements for Optimizing Growth and Flowering of the Nobile Dendrobium as a Potted Orchid in: HortScience Volume 43 Issue 2 (2008)

[Ray]

Thanks. That was very interesting. To my understanding of the data presented, for that particular Dendrobium nobile hybrid, there was an optimal N level, P was necessary, but not in great quantities nor did more help. There was also a minimum K level, but again, more really didn't aid much.

I thought it was interesting that increasing K resulted in better leaf retention in the hybrid, but they cited just the opposite to be true in cymbidium.

All of that science confirmed some of my thoughts, and while it did suggest there are different nutritional parameters for D. nobile hybrids, it still didn't prove a thing about General orchid nutrition.

[Orchid Whisperer]

Ray, my interpretation of the article focused on 3 things.

1. With N application, there was no benefit gained by supplying more N than 100 ppm (parts per million), and most of the improvement came from supplying just 50 ppm (compared to plants receiving zero N). Plants given 200 ppm showed no improvement over 100 ppm, and at 400 ppm, were somewhat smaller. Plants that received N until flowering had fewer flowers than plants that stopped receiving N earlier during growth.

2. Variation in K showed the same pattern of effects on plant health as variation of N, at the same concentration levels (severe leaf loss at zero ppm, improvement at 50 ppm but still leaf loss, improvement in plant vigor plateaued at 100 ppm, remained similar at 100 to 400 ppm levels). Other studies cited: 200 ppm K resulted in fewer leaves in Cymbidium than at 50 to 100 ppm K; 50 ppm K is sufficient for Phalaenopsis, Cattleya and Cymbidium.

3. There was not much benefit to providing more than 25 ppm of phosphorus.

So, overall, for the Dendrobium, less P required than the higher rates of N and K needed, supplying N-P-K in concentrations of 100-25-100 ppm gives the most benefit without wasting fertilizer. For Cymbidium and Phalaenopsis, you can probably provide 100 ppm N and 50 to 100 ppm K, but not lower than 50 ppm K. Cattleya apparently is fine with N and K of 50 ppm each.

Ray, orchids are so varied in terms of how they grow, where they grow, light preferences, whether they go dormant, etc., that I doubt any single study could say anything about general orchid nutrition. The article does generally support higher N, low P, higher K fertilizer requirements.

To the original poster, I would skip "bloom boosting" fertilizer, which usually adds more P than the plant will need.

In terms of timing, I find that providing fertilizer early in the growth cycle seems most important, I don't fertilize much at all in late summer (we are a warm climate here in the southeastern USA, but we are warm-temperate, so there is a cool to cold season when my plants are brought indoors, and don't grow very much). There is some variation in that timing depending on the type of plant; the article I provided a link to is most useful for growers of Nobile-type Dendrobiums.

[Ray]

I generally agree with your assessment, except for the K requirements, based upon my observations, tissue analysis, and anecdotal evidence like Brandon's. But again, while that's been holding true for me for the last 8 years, I also had success for at least that long with MSU RO, which is much higher in P & K than K-Lite. However, the article is about nobile dens, which I don't grow.

I did note that they watered "as needed when the medium was dry", but are not more specific than that, so it may very well be that my, much lighter applications are totaling closer to theirs that it seems.

Since moving here to coastal southeast NC and growing my plants outdoors in the long, warm spring/summer/fall, I don't see as much of a mid-summer slowdown as I did in the greenhouse in PA, but while I keep my feeding concentration the same, the winter (indoor) frequency is greatly reduced.

[Orchid Whisperer]

Ray, since I have a lot of different types of plants together (limited space to spread out, limited time), I find that my fertilizer schedule and watering tends to be of the "common denominator" type. Or put another way, the "Rolling Stones" type, where the plants don't always get what they want, but they get what they need, because everything gets treated the same, with a few exceptions.

I mostly stick to a "Cattleya" pattern, because that is mostly what I grow. Plants that don't care for that tend to be give away, and I avoid taking on Catasetums and the like.