A guide to growth fertilizer?

[Wolfrott]

One of the major orchid nurseries here sell their growth fertiliser, as well as gardening warehouses offering the more generic stuff.

Naturally they come with instructions, but how often do you recommend uing it? Any experiences to share?

[Stray59]

It really depends on the fertilizer, but the rule of thumb I follow is to fertilize "weekly, weakly", I currently use 1/2 the suggested strength of MSU formulation, alternating with a 1/2 strength fish emulsion once every other watering, and I spray the entire plant, not just the roots as the leaves and stems will absorb the nutrients too. If you are using a salt-based fertilizer (the blue or green crystallized products) you have to regularly "flush" the media with clear water to get rid of any build-up, and watch using too strong of a mixture as many orchids will burn pretty easy. Personally, I am trying to move more into organic fertilizers, but for now this works great for me.
Remember that some orchids only want to be fed when they are in the growth stage, needing a rest after blooming - many Dendrobiums fit this category.
There are different fertilizer formulations that help with inducing better blooming or stronger growth available in garden centers, and I have had good success with them in the past, but now I just stick with what works for me right now -.
Hope this helps some....it'll be interesting to see what others are using.

[Wolfrott]

Thanks very much! Yeah, I am using not the blue groth/bloom powder, but the white one. I have been applying the weakly/weekly recommendation, but wanted to check if it was actually sound advice or not

It is always great to get feedback and compare how we all look after our flowers!

[bil]

Personally I like Ray's philosophy of 'very little, all the time.'
I use about 0.2g per litre of K Lite, and I use that every time I water. No danger of burning the roots, and it is more like they get in nature.

[Subrosa]

You should also consider what media you grow in when selecting a fertilizer. If you use a bark product you'll want to go with a fertilizer with a higher nitrogen content. Nitrogen is the first number in the 3 number code used to rate fertilizer. Some manufacturers make both "growth" and a "bloom" formulas. For bark you would want the extra nitrogen in the "growth" products.

[Ray]

Originally Posted by Subrosa

You should also consider what media you grow in when selecting a fertilizer. If you use a bark product you'll want to go with a fertilizer with a higher nitrogen content. Nitrogen is the first number in the 3 number code used to rate fertilizer. Some manufacturers make both "growth" and a "bloom" formulas. For bark you would want the extra nitrogen in the "growth" products.

I don't know if I can agree 100% with that, but I suppose it does depend upon a number of variables.

Yes, microorganisms consume cellulose (actually, their metabolites break it down), and their populations are spurred on by the application of nitrogen (I'll tell you of my Exxon Valdez cleanup experience some day), but in this day and age, with the better potting media materials available, and a general tendency of growers to repot their plants far more frequently than in the early days of collecting, that doesn't necessarily mean you need to adjust your feeding to accommodate them.

The population if "µ-bugs" if fresh medium certainly doesn't warrant that, but I think it becomes more of a factor as the medium breaks down, harboring a far greater population, but by then, we've probably repotted anyway (or should have).

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Back to the original query, for a moment...

I think the best thing to do is to choose a target nitrogen concentration - chosen based upon application frequency - and stick to that, no matter the formula.

I water 3-4 times a week in summer, always with fertilizer, so I shoot for 25 ppm N. To achieve that, I divide 2 by the %N on the label of any formula, with the result being the teaspoons per gallon (2.6/%N gives ml/L).

If I fed only once a week, I'd probably go with about 100 ppm N, so I'd use 8/%N for teaspoons/gallon (10.4/%N for ml/L).

[Stray59]

Wolfrott:
As you can see there are a lot of different views on fertilizer as there is on just about anything else related to orchids. I was going to suggest that you look up Ray's responses on this subject as he has done a LOT of testing and research, but of course when I wanted to locate his posts on this subject, I couldn't locate one of them!
Ray- thanks for chiming in and providing your formula. - I have been considering the "every time you water" approach, but I was hesitant as I have burned my orchids in the past and am a little "fertilizer-shy" for it. Now I just have to drag out my calculator and try to de-code your formula! Thanks for sharing your knowledge here.....very appreciated!
Good post - Wolfrott you kind of have to decide what works for you, but as you can see the overall general approach is a weak fertilizer solution, given frequently.
Let us know what you decide to use.

[Ray]

Stray - that "formula" is VERY much a gross estimate. It's better for liquids than powders, as powders can have greater differences in bulk density, so a set volume isn't going to be the same mass for all, and fertilizer formulas are in weight percent - yet, at the concentrations I'm referring to, that error is insignificant.

[RNCollins]

Originally Posted by Ray

Back to the original query, for a moment...

I think the best thing to do is to choose a target nitrogen concentration - chosen based upon application frequency - and stick to that, no matter the formula.

I water 3-4 times a week in summer, always with fertilizer, so I shoot for 25 ppm N. To achieve that, I divide 2 by the %N on the label of any formula, with the result being the teaspoons per gallon (2.6/%N gives ml/L).

If I fed only once a week, I'd probably go with about 100 ppm N, so I'd use 8/%N for teaspoons/gallon (10.4/%N for ml/L).

If you go to Ray's website and enter your fertilizer numbers into the worksheet it will give you the ppm (parts per million) of Nitrogen, Phosphorus, and Potassium. I'm too lazy to do the math so I just use Ray's formula.

Fertilizer TDS Calculator - First Rays LLC