# Fertilizer



## schmiggle (Feb 12, 2018)

Plants are pretty magical. They seem to eat nothing--all they need, at least for a while, is air, water and sunlight. However, after a few months of normal growth, many houseplants seem to grow without growing. They grow new stems and leaves, but they drop old ones; they stubbornly refuse to flower; they seem to sulk, despite no changed conditions.

The reason for this is that plants can't actually just eat air, water and sunlight. Just like you, plants produce proteins, and proteins take atoms other than oxygen, carbon, and hydrogen (the atoms bonded into glucose in the principle reactions of photosynthesis). Plants usually get these nutrients from the medium they are grown in (with a few exceptions I will get to shortly). Plants need these nutrients just as much as they need sunlight, water, and air; otherwise, you are essentially feeding them nothing but sugar, and it's honestly astonishing how long they can go from just that. For long term survival and flourishing of plants, you will need to fertilize.

The traditional division of plant nutrients is into macronutrients--those used in large quantities--and micronutrients--those used in small quantities. However, when using fertilizer, growers tend to worry principally about the three following macronutrients: nitrogen, phosphorous, and potassium. When you see a fertilizer rating, you will notice three numbers, arranged as follows: x-y-z (for example, 10-10-10). What this means is actually fairly simple: the first number is the percentage of nitrogen by volume, the second is the percentage of phosphorous by volume, and the third is the percentage of potassium by volume. For this reason fertilizer ratings are often known as NPK, after the acronyms for these elements on the periodic table. 

Most fertilizers contain the other macronutrients plants need (calcium, magnesium, and sulfur). However, most do not contain the necessary micronutrients--chlorine, iron, boron, manganese, zinc, copper, molybdenum, and nickel (knowing what these are is usually not necessary, but can be useful for seeing if a fertilizer is really complete). Micronutrients are just as important as macronutrients; they are simply not needed in as high quantities. Usually they are present in sufficient quantity in tapwater, and for this reason, I recommend watering almost all plants with tapwater where possible. If the tapwater in your area is unsuitable (usually because it has too many dissolved solids) and you need to use bottled water, I recommend using distilled water and a fertilizer that includes micronutrients, since it's essentially impossible to know the quantities of various dissolved solids in other kinds of bottled water.

Now, the obvious question is: how much and how often should you fertilize? This, of course, depends on what you are trying to grow. Many sources will talk about dilution to "half strength" and then tell you how often to fertilize; I, however, prefer to work with parts per million (ppm), simply because it is universal. Here is an example of where this matters:

I have two fertilizers. Fertilizer A is rated 10-10-10, and fertilizer B is rated 20-20-20. Suppose I dilute to half strength (usually the strength recommended on the package) and fertilize once a week. The plant receiving fertilizer B is receiving a doubly high load of fertilizer! If I use ppm instead, however, I will dilute fertilizer B in twice as much water, thus watering the same amount.

Ppm is measured in terms of volume. As a simple example: suppose I have a 10-10-10 fertilizer, and I dilute one mililitre of it in one litre of water. In that case, I would be dissolving one tenth (10%) of one one thousandth of one litre of nitrogen into a litre, so the concentration of nitrogen would be one ten thousandth, or one hundred ppm. The same math can be done for the concentrations of all of the nutrients.

It is important not to over-fertilize, because fertilizer usually comes in the form of salts, which can burn plant roots if they are present in overly high quantities. What I have used with pretty good success is 30-10-10 fertilizer diluted to 50ppm, with which I water my entire collection aside from carnivorous plants about once a day. However, though I grow a wide diversity of plant species, the ones I fertilize all have one thing in common: they are epiphytic or lithophytic, so in the wild they grow on exposed tree bark or rocks. Thus, they have low nutrient requirements and they grow slowly. My guess would be that most house plants would like a higher concentration of fertilizer, but I don't really know what it is. What I would do is start with 100ppm, see how the plant reacts, and go from there. You can look up signs of over-fertilizing online, and I've already described the signs of under-fertilizing. I've significantly damaged at least one plant through over-fertilizing, so do be careful (although it's worth noting that that one was carnivorous, and many people don't fertilize carnivorous plants at all). 

I know of two groups of plants that don't absorb nutrients primarily through the roots. Carnivorous plants, of course, tend to use their traps, whatever those are; I usually fertilize those traps where possible, although often carnivorous plants do just fine on whatever insects are around (with the notable exception of king sundews). Tillandsias are able to absorb nutrients through their leaf surface (despite the name air plant, they, like all living things, need more than just air to survive), so you can just spray the leaf surface like you do when watering.

If there's any information I've missed, or anything I should clarify, please tell me. I hope this is helpful and not too confusing.

Reactions: Informative 4 | Winner 1


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## Major017 (Feb 13, 2018)

Ok.

Reactions: Agree 1


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## mickiem (Feb 13, 2018)

That sounds like a lot of fertilizer and a lot of water. My home is 10-20% humidity in the winter (and my plants aren't growing as actively) and I only water once a week/ fertilize once a month. 

I am building a vivarium for PDF and bromeliads. Is there a safe fertilizer to use with them?  

I’ve never considered the ppm before. That’s good stuff; thank you.


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## schmiggle (Feb 13, 2018)

mickiem said:


> That sounds like a lot of fertilizer and a lot of water. My home is 10-20% humidity in the winter (and my plants aren't growing as actively) and I only water once a week/ fertilize once a month.
> 
> I am building a vivarium for PDF and bromeliads. Is there a safe fertilizer to use with them?
> 
> I’ve never considered the ppm before. That’s good stuff; thank you.


I should have clarified--I spray on fertilizer, so it's not all that much water. I wouldn't do it for a cactus, though.

It sounds like a lot of fertilizer because it's so often, but if I used as directed I would be using 200ppm, and I would water with it. I have no idea what you use, but most plants get a constant stream of low levels of nutrients in the wild, so I imagine that they're better able to use it the less they get at a time. It also prevents burns and salt stress. 25ppm twice a day is what I was told was good for most orchids, but it's difficult to dilute that much, so I doubled the concentration and halved the frequency. My plants certainly haven't exhibited signs of being overfertilized.

Another thing is that plants with more light and higher temperatures utilize fertilizer faster. I grow all of my plants under lights and many in a terrarium, so this helps with both things.

I don't know what pdf is, but bromeliads need fertilizer. I would use the 50ppm daily if they were mine.


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## mickiem (Feb 13, 2018)

schmiggle said:


> I should have clarified--I spray on fertilizer, so it's not all that much water. I wouldn't do it for a cactus, though.
> 
> It sounds like a lot of fertilizer because it's so often, but if I used as directed I would be using 200ppm, and I would water with it. I have no idea what you use, but most plants get a constant stream of low levels of nutrients in the wild, so I imagine that they're better able to use it the less they get at a time. It also prevents burns and salt stress. 25ppm twice a day is what I was told was good for most orchids, but it's difficult to dilute that much, so I doubled the concentration and halved the frequency. My plants certainly haven't exhibited signs of being overfertilized.
> 
> ...


Thanks, very helpful.  PDF = poison dart frogs, sorry for that omission.  I have never raised a lot of bromeliads and am fairly new with the frogs.  I am concerned the frogs will be harmed by fertilizers.

I usually do 1/4 strength and more frequent than recommended, but I like your ppm advice and I am sure that will be better.  I can't wait to see the plants' reaction.

I have a nice collection of Peperomia but I am still learning.  I know some are succulent, some are epiphytic, some climb etc.  I don't know how to tell the difference and right now I grow them all in pots.  Some have groupy roots that separate themselves from the main root (but are still at the root).  I think these might be epiphytic.  Do you have experience with these?  Maybe I'll take photos and start a new thread....  don't mean to hijack.


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## schmiggle (Feb 13, 2018)

I don't have experience with Peperomia, but epiphytes usually have tough roots without root hairs, so that's how I would tell them from other plants. They will generally need less fertilizer than other plants, although there are certain notable exceptions. However, I would probably just start with a low concentration, see how they respond, and then try increasing it if you think it will be helpful.

I don't know how poison dart frogs would respond to fertilizer. However, in that case you do have the advantage that the plants can use dart frog droppings. My guess would be the frogs would be ok with a bit of fertilizer, since as I said before, the bromeliads wouldn't really grow at all without it. The only non-parasitic plants that don't need fertilizer at all are those adapted to bogs, which are usually either carnivorous (allowing them to self-fertilize, essentially), adapted to survive on minute amounts of nutrients from slowly decomposing organic matter, or have microbial partners that help them fix what nutrients are available. Given that people make bromeliad including dart frog terrariums, it seems to me you're probably OK.


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## The Snark (Feb 13, 2018)

The only contribution here that comes to mind is watch out for nitrogen. @schmiggle You could go into the difference between ammonium nitrate and compounds derived from organic processes, a 101 on how to chemically incinerate your plant, and that most nitrogen fertilizers go unassimilated and gets flushed and rinsed away. It has to be the most abused substance on the planet with chemical companies making a fortune on peoples ignorance.


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## schmiggle (Feb 13, 2018)

The Snark said:


> The only contribution here that comes to mind is watch out for nitrogen. @schmiggle You could go into the difference between ammonium nitrate and compounds derived from organic processes, a 101 on how to chemically incinerate your plant, and that most nitrogen fertilizers go unassimilated and gets flushed and rinsed away. It has to be the most abused substance on the planet with chemical companies making a fortune on peoples ignorance.


It's interesting that you've brought that up, because I've read that it's a myth that plants can't use ammonium. However, as I've discussed above, the best way to avoid burning a plant is to fertilize small amounts at a time. That way a plant is less likely to be overloaded with salts. The same goes for making sure it gets absorbed: fertilize smaller amounts more often, rather than fertilizing large amounts occasionally.

I've never heard of any useful differences between fertilizers derived from organic material and synthetic fertilizers on a small scale. On a large scale, the latter are particularly bad causes of eutrophication, because they're in an immediately usable form and they don't tend to stick around. But I'm pretty sure the fertilizer I use is synthetic. I just dilute it so much that it's harmless to most plants, and I use little enough and in a closed environment that I believe it's basically not a problem. But I would absolutely like to hear what you are thinking of, in case there is something I should fix.


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## The Snark (Feb 13, 2018)

Okay, this from various growers. The fertilizer of choice for nitrogen that can even be sprayed on the leaves is derived from fish poop and offal. No salts, breaks down readily and doesn't enter the environment.

Compare to the idiocy over here where the rice farmers overload the flooded fields twice a year with the chemical crap, the fields drain into the canals and rivers, and the water hyacinth and other plants grows so voraciously it's a long arm back hoe every 5 years to keep up with the overgrowth.


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## mickiem (Feb 13, 2018)

schmiggle said:


> I don't have experience with Peperomia, but epiphytes usually have tough roots without root hairs, so that's how I would tell them from other plants. They will generally need less fertilizer than other plants, although there are certain notable exceptions. However, I would probably just start with a low concentration, see how they respond, and then try increasing it if you think it will be helpful.
> 
> I don't know how poison dart frogs would respond to fertilizer. However, in that case you do have the advantage that the plants can use dart frog droppings. My guess would be the frogs would be ok with a bit of fertilizer, since as I said before, the bromeliads wouldn't really grow at all without it. The only non-parasitic plants that don't need fertilizer at all are those adapted to bogs, which are usually either carnivorous (allowing them to self-fertilize, essentially), adapted to survive on minute amounts of nutrients from slowly decomposing organic matter, or have microbial partners that help them fix what nutrients are available. Given that people make bromeliad including dart frog terrariums, it seems to me you're probably OK.


Thanks, this is very helpful.  Those "groupy" roots are just as you described; tough and without hairs.  I can't believe how hard it is to get information about peperomias!  They are truly awesome plants.


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## MetalMan2004 (Feb 14, 2018)

Anyone here ever use Microlife?  Its incredible stuff.  Its only 6-2-4 but a scoop of it in any pot does wonders!


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## schmiggle (Feb 15, 2018)

MetalMan2004 said:


> Anyone here ever use Microlife?  Its incredible stuff.  Its only 6-2-4 but a scoop of it in any pot does wonders!


Interesting. No, I've never heard of it. How big a scoop are you using, how often do you apply it, and what plants do you use it on? I suspect it works well partly because it's got such low nutrient concentrations.

I will re-iterate that the branding is meaningless--an ion is an ion is an ion--but if it works for you, the only reason I would stop is if you see the same product for cheaper or see the same concentration ratios and feel like diluting.


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## MetalMan2004 (Feb 15, 2018)

schmiggle said:


> Interesting. No, I've never heard of it. How big a scoop are you using, how often do you apply it, and what plants do you use it on? I suspect it works well partly because it's got such low nutrient concentrations.
> 
> I will re-iterate that the branding is meaningless--an ion is an ion is an ion--but if it works for you, the only reason I would stop is if you see the same product for cheaper or see the same concentration ratios and feel like diluting.


It may be more of a southern thing, not sure.  Just google it and read the quick paragraph from the company on it.  In addition to the 6-2-4 its got several species of “beneficial microbes” and micronutrients.

Instructions say 2.5 oz per 5 gallons of container every 3-4 months.  Its virtually impossible to burn plants with it so I just gice every plant a scoop with a little cup.

Its incredible how quickly the plants grow with it compared to regular fertilizer.  This summer once my plants take off again I’ll have to post a picture or two.

The only thing I haven’t used it on yet is my orchids.  I may have to email them to see if and how I should use it with them.


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## pirminiamac (Mar 1, 2018)

This should be a sticky !


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## Storm1028 (Mar 3, 2018)

I grow plants in my tarantula enclosure and I've been using dubia frass and molt for fertilizing my plants. Does any one have experience using dubia frass as fertilizers? Also, for those who keep plants with tarantulas, what do you use as fertilizers that are safe for the tarantula? TIA


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