One teaspoon per gallon of fertilizer!

[MateoinLosAngeles]

Reading SVO culture guide for Catasetinae, Fred Clarke recommends 1 tsp/gallon of any fertilizer during active growth.

My understanding is this is at every watering. This would mean around 200 ppm N on every watering with the fertilizer I use. So potentially 600 ppm N a week, 1800 ppm N a month.

Am I getting this wrong? All my orchids get about 300 ppm N a month, which is 3,600 ppm N a year.

I understand Catasetinae really do most of their growth in an intense 3 to 4 month period. 1800x4 is 7200 ppm N during their growing season.

Is this reasonable or am I missing something?

[StephaneL]

I've been growing mine at 150 ppm of nitrogen at every watering from the first watering in the spring until about October, and then progressively decreasing at the end of the season. At the top of their growing season (August and September for me), I water them almost every day with this regiment. They seem to appreciate.

[MateoinLosAngeles]

Originally Posted by StephaneL

I've been growing mine at 150 ppm of nitrogen at every watering from the first watering in the spring until about October, and then progressively decreasing at the end of the season. At the top of their growing season (August and September for me), I water them almost every day with this regiment. They seem to appreciate.

Nice. Seems like we have similar climates. I might be a bit warmer and drier which would even justify more watering.

Thanks for the tip!

[Ray]

In order to do a reasonable comparison, we need to couple the concentration with the volume retained and root exposure.

A 200 ppm N solution contains 200 mg N in a liter.

If you pour a liter of solution on the plant, depending upon the medium and pot volume, it might only retain 50 ml or less, meaning no more than 10 mg N is retained.

Then you can consider the volume of velamen on the entire root system, and what minuscule percentage that is of the pot volume, which makes up the “instantaneous absorption volume”, or the huge majority of the nutrient uptake. Yes, some is more slowly “fed” to the roots by the potting medium, but I suspect it’s not a great deal (if it was, mineral buildup would be a non-issue), and knowing how limited an orchid’s root system is relative to that of a terrestrial plant, it suggests that the plant is getting but a tiny fraction of the mass of nutrition applied.

The “exposure time” factor is a variable folks don’t really think about. A bare-root vanda, for example, is literally only exposed to nutrient solutions as they are applied. I think that is one reason vandas have a reputation of being “heavy feeders”. It’s not that they need more food to grow - granted some are relatively fast growers - as all plants need the same mass of nitrogen to add a fixed mass of tissue, but because they’re just not getting much at each feeding.

At the other end of the spectrum is something like semi-hydroponics, where the exposure of roots to nutrition is constant.

[smweaver]

It does seem to me like that's quite a lot of fertilizer for an orchid. Other than growing on the side of a cliff in the middle of a colony of seabirds, how would any orchid ever receive this much fertilizer in the wild?

I appreciate your explanation of the science involved, Ray, and what variables need to be factored into a calculation of how much fertilizer any given plant is able to make use of. But I have several plants that often get placed--pot/basket and all--in a bucket of water to sit for a good thirty minutes or so when I fertilize them. So I think they may be, in this case, getting a lot of exposure time to the fertilizer (which is, actually, why I do this for the heavier feeders).

Also (and I know you indicated that it depends on, among other things, the potting medium), wouldn't watering something grown in pure NZ sphagnum, which retains a lot of applied nutrients, be burned, over time, by this rate (1 teaspoon per gallon)? I'm not sure how successful you would be attempting to periodically flush salts out of NZ sphagnum (although i'm certainly no expert, so perhaps this is effective with moss) if the substance has been exposed to this much fertilizer.

Good conversation to have, and an interesting topic.

Steve

[estación seca]

Fred gets lots of awards on his plants.

[Dimples]

Another thing to consider is the amount of light and temperatures the plants are getting. I grew professionally in large greenhouses less than 3 miles from SVO and the outdoor climate + whatever level of shade and airflow needed for the specific crop results in indoor greenhouse conditions that are perfect. So, SVO can use a lot of fertilizer and get a lot of benefits from it because the plants can effectively use it. If someone tried to do the same thing with lesser conditions, they would be wasting some of the applied fertilizer because the plants just can't use it. The extent of the waste would be determined by the growing conditions. A little less light, minimal waste. A lot less light, a lot of waste. Throw the balance too far off and damage could occur over time unless mineral buildup is managed.

Not saying don't follow the SVO recipe, just pointing out that what works for a commercial greenhouse isn't going to translate to the experiences of every hobby grower.

[StephaneL]

Originally Posted by smweaver

Also (and I know you indicated that it depends on, among other things, the potting medium), wouldn't watering something grown in pure NZ sphagnum, which retains a lot of applied nutrients, be burned, over time, by this rate (1 teaspoon per gallon)? I'm not sure how successful you would be attempting to periodically flush salts out of NZ sphagnum (although i'm certainly no expert, so perhaps this is effective with moss) if the substance has been exposed to this much fertilizer.

I grow mine in sphagnum moss and I also was worried about mineral buildup when I calculated the concentration recommended by Fred Clarke (I must have watched the same video than MateoinLosAngeles). However, at the height of their growing season they drink all the liquid I provide to them extremely rapidly. I fully saturate the moss with water and it is almost dry the next day. My hypothesis is that since the water is absorbed by the plant, rather than drying in the medium, the mineral buildup is minimal.

With regard to Dimples's comment, I'll add that I have them in a southwest window and they get up to 7 hours of direct sun every day.

[Roberta]

I make life easier for myself... Catasetinae during the growing season need a LOT more fertilizer than most of my orchids. So I add some time release fertilizer (such as Nutricote or Dynamite) to the pots. They get the light fertilizer that everybody else gets (which would be inadequate) but the time-release gives them the extra boost that they need without extra effort on my part. (I use it for my Cymbidiums for the same reason)

Orchids need fertilizer in proportion to their growth, because the minerals are what are needed to grow new tissue. (To just "exist" they provide their own carbs with photosynthesis). Most orchids grow very slowly, so don't need much fertilizer. Catasetinae on the other hand basically "reinvent" themselves every year, and grow so fast that you can see day-to-day increase. They're growing more like a tomato plant than an orchid... and so need to be fertilized accordingly.

[MateoinLosAngeles]

Originally Posted by Roberta

I make life easier for myself... (...) So I add some time release fertilizer (such as Nutricote or Dynamite) to the pots.

Aah!! This is so smart, Roberta. Thank you