Fertilizer Change During Flower Spike

[Ray]

Originally Posted by Bloomer001

I'm feeding about 125 mg N weekly in 2 doses.

May I ask how you are determining the mass you're applying?

Don't forget that "exposure time", extent of root growth, and velamen volume are other important factors.

Starting at the extreme of a bare-root vanda in a slat basket: their "exposure time" is only during the actual application of the fertilizer solution, and the amount that can be absorbed is limited to the volume of the velamen layer on the roots.

Now go to a cattleya in a pot of coarse bark. The exposure time is the time of application, just like the vanda, but is also extended by the time that roots are in direct contact with solution held within the medium. Bark doesn't wick very well, so once those "contact points" have been extracted, that period ends. The total volume of velamen is probably reduced compared to the vanda, so that reduces the immediate uptake, even while the exposure time is extended.

Then there's an oncidium in sphagnum - the medium holds and wicks the fertilizer solution well, and the plant has lots an lots of much finer roots (and greater overall surface-to-volume ratio) to make contact with it, but the velamen is relatively thin. If we assume the velamen-to-vasculum transfer rate is similar for the three, it seems likely the oncidium will take up more of what is applied.

[estación seca]

Many people here have posted many times what are good ranges of nitrogen concentration in the applied solution for Phalaenopsis orchids. These recommendations are not considered high nitrogen.

[Roberta]

Like everything else "orchid" the "right" answer is likely "it depends". There has been a lot of study on techniques to optimize growth and blooming for commercially-produced Phalaenopsis - it's a huge cash crop. Every factor (light, temperature, fertilizer formulation-concentration-frequency, water, and timing of variations in all of those) is optimized for that monoculture crop, The goal is to get lots of blooming plants to market fast, especially for flower-buying holidays.

For those of us who grow examples of the rest of the 800-900 orchid genera (not counting the human-made ones) under a range of conditions suitable to them and manageable for us, the "rules" that work for those mass-produced Phals likely are not appropriate in that broader "orchid world". It's both "less complicated" in that one can get very good results with less-than-optimum conditions, and "more complicated" in that different orchid types have different needs, often very different at different times of the year, and one's success is likely to improve with understanding of the differences.

[Bloomer001]

I agree with you Roberta, I'm learning that growing culture is the primary factor -- and is far more important than fert selection. I read your "101 culture notes" prior to potting these orchids. Your note re air circulation is 100% accurate. The orchid in the green pot is the smallest by far. The green pot orchid is in an internal plastic pot with holes, but the external green pot restricts air circulation compared to the open red tin that the other 3 orchids are planted in. I believe this factor caused the green pot orchid to grow about 30% less than the others in the red tin, with all other factors being roughly the same. When I repot next spring, I'm going to find a pot that allows more air circulation.

Coincidentally, the first flower is beginning to open today!

[Roberta]

If you have the space to get some of these outside once the weather warms up, they'll love it. Air circulation provided by Mother Nature tends to be better than anything what we mere humans can manage, and the natural variation in light and temperature also can work wonders. For me, Phals and such need to stay in, but I have found that the orchids that could grow indoors or outdoors do better when they get outdoors. (Of course, I can get away with more "outdoors" than you can, but come spring/summer your "outdoors" will be viable too.)

[thefish1337]

One thing to consider is that all the initial progenitor cells are formed well before before they become flower cells. If you want to experiment with this you need to make sure these cells can divide initially and to their genetic potential... this is why calcium is so important to plant growth and performance.

For example, major deficiencies of calcium cause Cattleya growths to blacken abort. Intermediate or minor deficiencies will almost always limit the size of the growth and interrupt reproductive processes aka flowering, pollination, seedpod formation (this is true for most flowering plants).

If you want to experiment with this on Phals experiment with different nutrition regimes based on your observations of when critical growth periods. I'd also check the literature because there is a lot of phaleanopsis research due to its economic importance.

[Dimples]

The bottle does say “approximate” and if my math is mathing, it’s close enough. I wouldn’t worry about it.