Peters 20-20-20 + TE Professional
 

I could buy a 20-20-20 (with trace elements) fertilizer.

What is a safe solution to make for watering orchids?

Peters advice:

Continues feeding: 0.5 - 1.5 gram/liter
Occasional feeding (for example once a week) 0.8 -2 mg/liter.

I assume I have to make a much weaker solution to water orchids safely with it.

Any input is highly apprecieated.

With a 20-20-20, I’d start with 1/2 teaspoon per gallon for a starting point. I don’t know the metric equivalent.

Ray has the math formulas, so he’d be able to advise you on target ppm nitrogen.

Use this calculator from Ray's site: calculator

You should aim for 100 ppm N.
Note that some orchids don't like to be fertilized in every watering. Which plants do you have?

At the same site you'll find plenty of info about feeding and more or less everything else related with orchids.

A really simple rule of thumb for weekly feeding is 100 ppm N. If you divide 9.2 by the %N in any fertilizer, the result is ml/L for that product.

The plants I have are on this list. I’m waiting for a Cymb. sinense to join my pack 😉

https://i.imgur.com/0Jkblzq.jpeg

---------- Post added at 08:56 PM ---------- Previous post was at 08:51 PM ----------

Thank you, that’s an easy formula to remember. Going to check out your website.


I often read to water the orchids before fertilizing. True?
I always dunk the pots, bark or bark with bits of sphagnum and let water run through the pot with fertilizer or Kelpak in the end, to avoid salts buildup.


Should I invest in a TDS/EC meter? They aren’t crazy expensive.

Do not water before fertilizing. Proper concentrations of fertilizer will not harm roots. Watering first fills up velamen with plain water, and less fertilizer will be absorbed. Fertilizer applied after a plain watering is mostly wasted.

TDS meters don't measure total dissolved solids. They measure electrical conductivity, proportional to the number of charged particles in the solution. Unless you know exactly which chemicals are in the solution these meters don't yield useful data. Total dissolved solids are measured by evaporating a known quantity of water and weighing the minerals left behind. There aren't any meters that can do this.

Your water company publishes an annual water quality report. It will tell you what is in your water. It may report total dissolved solids, water hardness, or give amounts of each chemical species present. You can add the amount of fertilizer you plan to use and calculate TDS for yourself.

Luckily I never water before fertilizing, pfew. Sometimes it's hard to distinguish good practices from the not so good on the internet. Reliable sources can be hard to recognize.

I found the yearly report for 2023, thank you for guiding me towards that report.

I don't know how your water is down in Limburg, but over here in the southern tip of the Veluwe area our water is so pure that I use fertilizer meant for rain/RO water. Otherwise I have to add calcium and magnesium to standard NPK fertilizer, and it's just easier to use Akerne's Rainmix.

I also rotate the Rainmix fert with 20-20-20, so that I can use up what I have left, and both at a dosage of 50ppm N (which is 0,25g/L for the 20-20-20).

Hi Camille,

we have lots of calcium in our tapwater. I don't recall the amount calcium & magnesium from when I still had a dense planted fish tank. But I never had to supplement one of these.

When I looked at Rainmix I concluded I can't use it here unless I resort to reversed osmosis mixed with some tapwater. And that is not going to happen as I don't have a area to install a reverse osmosis unit. Ideally that would be near the bath tub. I wouldn't be the first one to forget it's running and flood for instance the bathroom or worse.

I dosed 20-20-20 at 0,5 gram/liter. Do you think I should dose less concentrated? Or only dose less as long as the plants don't show active growth?

I can't wait for spring!

I'm following both Ray and Akerne's advice, which happen to come out to roughly the same thing. Ray suggests 100ppm N per week, and I usually water twice a week most of the year so that's 50pp per watering. Akerne's dosage (works out to 60ppm N) is because according to them it is sufficient for the majority of orchids, and no periodic flushing of the substrate is required at that dosage.

Your dosage is still fine (was sort of the 'standard' when I started on OB) but you might need to flush with tapwater every 4-5 waterings.