How much fertilizer?

[mascia]

Hey everyone,
I always follow the instructions when mixing fertilizer with water, and most times I opt for a more diluted solution, but how much should I use on each plant?

I've been pouring a small cup of the solution on each pot, which seemed fine, but today I watched a video from an experienced orchid grower and he used at least 4 times more fertilizer than me.

Considering most of the water will simply run through the drainage holes if I use a huge cup, does it make any difference? Is there a rule of thumb?

[jkofferdahl]

Well, the YouTube guy is nuts. He's using more fertilizer than probably ALL his orchids need.

A lot of people advocate a routine of fertilizing weekly, weakly. The general method behind this is to mix fertilizer at 1/4 the label directions and use it every week. My experience has shown, and my belief is strong, that even this is too much. Most orchids will do fine with even a quarter of THIS amount. Almost everyone over-fertilizes their orchids.

[Orchid Whisperer]

I use about 1/8 to 1/4 of the strength recommended on the label. I apply to the pot or roots to the point where water is dripping through or the roots start greening up. A couple gallons gives fertilizer to all of my 100 or so plants.

[nogreenthumbs]

Ray of firstrays.com (which appears to be down at the moment) who has a bunch of posts here and has something like 40-45 years of experience posted the following in another thread that I had posted on another orchid forum.

I thought it was really good information.

Originally Posted by Ray

Being an engineer and bit of a nerd, I started delving into the nutritional needs of orchids, and it actually opened my eyes significantly. (Warning! Professorial mode: On)

If you look at the makeup of an orchid, it is 95% water. Of the remaining 5%, about 95% of that is carbon, oxygen, and nitrogen, with the first two coming from water and air; the N it gets from the fertilizer we apply. The remaining fraction of a percent is the rest of the stuff it gets from fertilizer.

Add to that some analyses of the water that drips down on orchids in the wild (their primary source of nutrition), and we see that it is almost devoid of any nutritional value - 15-25 ppm total dissolved solids (TDS) is typical, and that's only when it just starts raining - and we learn that most of that is nitrogen.

So my conclusion from that is that nitrogen is the most important nutrient, but it should be applied very sparingly, as 1) the plants have evolved to need very meager nutrition levels, and 2) excessive N can actually stifle flowering.

I won't go into details (look up "Rubisco" if you're a bit of an intellectual masochist), but in order for any plant to add about a pound of mass - a huge amount in orchids - it must absorb and process about 25 gallons (roughly 95 kg) of water, but only about 5 grams of nutrient elements.

So, about 7 or 8 years ago (I've been growing orchids for over 45 years now), all of that led me to this growing regimen:

• Use a VERY open potting medium, so the roots always have excellent air flow around them.
• Water the daylights out of them: Frequent & Flooding. Water is the driving force behind plant growth.
• Use a very small amount of fertilizer at every watering. I mean really little. Divide 2 by the %N on the labels to get the teaspoons per gallon to use.
• Make sure that "fertigation" solution contains nitrogen, calcium, and magnesium; the other stuff can "tag along". (Your water supply may have enough calcium and magnesium in it, but as a user of RO water, I add it.). I prefer K-Lite, a 12-1-1-10Ca-3Mg derivative of the MSU RO formula.

All of my plants seem very happy with that, and are growing and blooming better than I've ever seen - figures it would take me almost 40 years to figure that out....

When the MSU fertilizer was first released, the developers recommended 125 ppm N for feeding. Figuring they knew what they were talking about, that's the level I used. Later, after doing some research, especially that related to the analyses of the "through fall" and "trunk flow" that orchids to see in nature, and the frequency with which they are fed in nature (whenever it rains), I dropped my concentration to 25 ppm N, and started applying it every time I watered. In later conversations with the PhD that led the development team, he told me that there was no scientific basis for the 125 ppm, but they "tried it, and it worked," so that's what they recommended.

As far as the concentration is concerned all you have to do is a simple mathematical fraction:

2÷13 = 1/6.5, so 1/6 teaspoon/gallon is fine, as is 1/8. Rounding up or down a bit isn't going to hurt anything. By the way, for those of you civilized folks on the metric system, 2.3/%N on the label gives you the ml/L for 25 ppm N.

Something I would recommend to everyone however, is to make a concentrated stock solution, and then use a bit of that solution to let down to your final fertilizer concentration. Many fertilizers, the original MSU for example, are very heterogeneous. Each ingredient is a large flake, small flake, powder or prill, so taking a fraction of a teaspoon or ml and expecting it to be true to the fertilizer formula is questionable. Add to that the fact that powder bulks densities can vary greatly, and it is folly to try to measure them by volume, hoping it equates to mass.

Instead, I recommend that folks make up a concentrate with a larger, known weight of powder. If you're looking for 25 ppm N, for example, that means you want 25mg N per kg (liter) of water in the final solution. As the powder is 13% N, that means you're shooting for 25/0.13=192 mg of fertilizer powder per liter (or 192 x 3.785=728 mg per gallon). But that's kind of tough to measure, so we should make life easier and make a concentrate in which that much is contained in a smaller volume - for example, let's say we want that in 10 ml. 192 mg/10ml = 19200 mg/L, so of you put 20 grams in a liter, that's close enough, and 10 ml of that solution, diluted to 1 liter, gives you your ~ 25 ppm N solution for feeding.

For Imperial measurers, 0.2 pounds of that 13% N fertilizer, when used to make up a gallon of concentrate, allows you to use one ounce to make up that same gallon of 25 ppm N final solution.

Steve, I believe it has been stated already, but fertilizer is probably the least important aspect of orchid culture.

Feed lightly and regularly, and dedicate your time to making sure ALL of the other aspects of culture are correct

I also asked in a PM about "flushing". If you aren't aware (I think someone mentioned it in an earlier post) with heavier fertilizer it can build up in the media and pot and cause problems with the plant, so you occasionally need to use just plain water to wash out some of the stuff that's building up.

What Ray told me about flushing was that if I was fertilizing at 25ppm and using a LOT of the liquid, then I was essentially flushing with every watering so you don't need to do the occasional flush.

As somewhat of a counterpoint to the above, I have another thread here where estación seca posted the following.

Originally Posted by estación seca

I know a lot of people recommend very low doses of fertilizer for many orchids. However, two good Cattleya growers I have met recommend high amounts of fertilizer for Cattleyas in warm, sunny climates: Fred Clarke of Sunset Valley Orchids in Vista, California, and Amy Chung Jacobsen, an AOS judge who lives south of San Francisco, but in a much warmer and sunnier area. Amy specializes in Laelia purpurata, a warm- to hot-growing plant from Brazil.

I have observed June sunshine in the upper Midwest of the US is nowhere near as bright as it is here in Arizona. When I have been in France, Germany and the Netherlands in June it is even less bright. I think orchids are able to produce tissue faster in areas with brighter sun and higher temperatures than they are in more northerly areas. To make this increased amount of tissue they need more water and more fertilizer.

On his Web site Fred Clarke recommends watering his Cattleya seedlings at every watering with approximately 100 parts per million of nitrogen. He uses MSU blend fertilizer. This works out to about 1/2 teaspoon / 2.5ml of powder per gallon / 3.78 liters of water. Fred waters 2-3 times per week in warm weather and once a week in winter. He waters with plain water once a month to leach out salts.

Amy also fertilizes with every watering, but she uses a 20-20-20 blend, also at 1/2 teaspoon per gallon, or approximately 130 PPM nitrogen. She told me we were lucky to have hot weather in Phoenix to grow Laelia purpurata, because we could water and fertilize more often, so our plants would grow even faster.

I am finding much better growth on my Cattleyas since I've upped my fertilizing of my plants in bark to these recommendations. This matches my experiences growing cacti in the Midwest, Seattle, southern California and Arizona - I can fertilize my cacti extremely heavily here in Phoenix, whereas this amount of fertilizer in St Louis would have led to etiolated cacti due to much less sun.

So, I think low fertilizer may be a good idea in cooler and dimmer climates than where orchids are native, because in such places they are not able to use as much fertilizer as they could in warmer, sunnier climates. We are warned excess fertilizer causes weak growth, which predisposes to infections. Cactus people give the same warnings. I think this is about sun, and not excess nitrogen. Cacti getting the sun they really need do not become weak, even with large amounts of fertilizer. Sun in the Midwest of the USA, or in Europe, is sufficient to keep cacti alive, and to bloom many. They neither look as good as, nor bloom as well as, plants grown in better light.

Steve/nogreenthumbs lives in Houston, which is even farther south than Phoenix, so he gets even more light than I do. Prosthechea are in the Cattleya alliance, but most do not grow in as much sun as most Cattleya species. However, realize bright shade in the tropics is much brighter than bright shade in a temperate region. Prosthecheas are still fairly high-light orchids.

Which seems like a very valid point to me.

And if all of that isn't confusing enough, with certain types of orchids that go through a long dormant period followed by an extreme growth period (like Catasetums/Catasetinae) you would throw all of that out of the window and fertilize much more heavily, at full strength or almost full strength based on some things that I've read. But I think those situations and orchids are more the exception than the rule.

Be careful, I think I severly stunted and could have killed my first orchid by over fertilizing earlier this year if I hadn't found these forums.

[estación seca]

When you fertilize, the aim is to soak the roots. The amount this takes varies - if they are mounted, it won't take much. In a pot it may take more.

Some people use a spray bottle rather than a stream of water. In my experience I can wet medium in a pot with less solution when I spray it rather than pour it.

[Orchid Whisperer]

Originally Posted by estación seca

When you fertilize, the aim is to soak the roots. The amount this takes varies - if they are mounted, it won't take much. In a pot it may take more.

Some people use a spray bottle rather than a stream of water. In my experience I can wet medium in a pot with less solution when I spray it rather than pour it.

Exactly.

I meant to include in my post that I am using a pump sprayer to apply fertilizer solution.

[nogreenthumbs]

Originally Posted by estación seca

When you fertilize, the aim is to soak the roots. The amount this takes varies - if they are mounted, it won't take much. In a pot it may take more.

Some people use a spray bottle rather than a stream of water. In my experience I can wet medium in a pot with less solution when I spray it rather than pour it.

Originally Posted by Orchid Whisperer

Exactly.

I meant to include in my post that I am using a pump sprayer to apply fertilizer solution.

I've just been pouring, and you do go through a TON of fertilizer solution to water each plant. Since I only have a couple of plants, that's not too big a deal, but it could get ugly if you have a ton.

I've been thinking about the semi-hydro thing.

[jkofferdahl]

Originally Posted by estación seca

When you fertilize, the aim is to soak the roots. The amount this takes varies - if they are mounted, it won't take much. In a pot it may take more.

Some people use a spray bottle rather than a stream of water. In my experience I can wet medium in a pot with less solution when I spray it rather than pour it.

This is a great point. On days I actually do fertilize, I do a complete watering of the plant and let is dry for about 30 minutes before spraying the roots with the fertilizer solution. Thanks for adding this important point!

[bil]

Go to First Rays' page and read everything he has on fertiliser.
Following his suggestions I use 25ppm N of Klite which is a high N, low PK fertiliser.

I use that on every watering, and get great results. The exceptions are the Stans and Catasetinae which get 150ppm of 30.30.30 at every watering.

Pouring and soaking takes a lot of time, and water, and hence fertiliser.
I too use a spray, and stop as soon as the water runs out the bottom. On average they all get 30 seconds' spray, every day for the mounts and 3 times a week for the pots.

[mascia]

Thanks for all the replies!

I think Ray's approach is really interesting, but I do believe it's hard to compare orchids growing for someone at 40°N with my orchids growing at 24°S or for someone even closer to the equator.

I've only been growing them for a year or so, but between last october and march some my cattleyas literally doubled in size. Plants that only had 7 or 8 bulbs would create 5 new bulbs at the same time. During summer I was feeding with ~150 ppm weekly and was thinking this was too low due to how much energy they were spending on growth. I've never had any issues with root burn or anything of the sorts.

Considering I only watered them 2x a week, 25ppm seems awfully low while they are actively growing.

I think I'll make an experiment and get two nearly identical orchids that will be grown side by side, and try feeding one on every watering and the other weekly or every two weeks, and see the results after a few months.

Has anyone ever done something similar?