Rainbow said: ... I agree that flushing the plant's soil media with rain or filtered water from time to time is a good thing.
Because of previous experiences, I shy away from using chemical fertilizers...they have a high salt content. Two of the fertilizers I use now are bone meal incorporated into the soil media at transplant, and fish emulsion liquid about every 4 weeks. As far as I know, these do not have salts.
Many people agree with you!
And some say that
feeding plants organically requires soil organisms like fungi that do not thrive in pots, and generally don't live in soilless mixes. Do you have real
soil in your pots or a soilless / soulless mix? Of course, if you are growing in SOIL in pots, the soil needs organic matter, and feeding only soluble chemicals would starve the soil life and "kill" the soil.
I know of one guy who puts real soil into pots, and keeps it "alive" enough that worms also live in his pots!
One web site claimed that fish emulsion is already "broken down" as sold, hence does not need fungi to digest and release it. If that meant that proteins were already broken up into amino acids, it would be VERY salty (in the sense of total ions, not NaCl). Like beef bullion. I don't know.
Organic fertilizers might release their nutrients more slowly than soluble chemical fertilizers do, reducing the risk of "burn".
And probably many people read the instructions for soluble fertilizer, add the 1/4 tsp called for, think "That's not much!" and then
add 2-3 times as much, killing the plant and blaming the chemicals. I notice that every experienced or commercial grower mentions that they dilute chemicals 2 - 4 times more than advised on the label. And that they often water with straight water, and also know to flush out their pots periodically.
So MIS-using chemical fertilizers may be more to blame for many people than the fertilizers themselves.
The nutrients mostly ARE the salts that we want to avoid accumulating, except for Na and Cl. Maybe Ca in some soils. The soluble "chemical" fertilizers are just more concentrated.
If you loaded up on enough organic fertilizer to
equal the amount of mineral nutrients in (for example) a 1/2 tsp of soluble Miracle-Gro, I think that even fish emulsion would release almost as many (nutritive) salts as the soluble fertilizer does. Maybe over a longer period of time, and hence with less risk of burn.
My opinion is that BOTH kinds of fertilizer should be used with the same concerns:
(1) don't add too much
(2) pick nutrient ratios close to what your plants need, or the excesses will accumulate as toxins
(3) don't use any brand that contains much NaCl, or that won't publish that measurement on the box.
I searched briefly for NaCl content of different fertilizers (chemical and organic) but didn't find useful sources. I know that in some regions, even manure is considered a slainity risk, so cow poop DOES have enough NaCl to be a potential problem.
Many Internet sites talk about
organic fertilizers "not adding salinity". I question that. If they add any N, P or K, or Mg, Ca, Fe, or SO4, they add ions, which are salts, which is what is meant by "salinity".
If they meant "no NaCl", I wish they would say that and give numbers, since EVERYTHING has some NaCl and most organic matter has a fair amount. Our own blood approximates sea water's salinity, though I suspect most plants contain less NaCl than we do. Instead those sites talk as if plant nutrients were not ions, and hence were not salts. That's plain wrong. If fish emulsion truly did not add any ions (salts), it could not add any plant nutrients.
So as soon as I see words like that on a website, I question everything else they say too. Maybe they are just making unstated assumptions and glossing over unstated issues, but the words are as plain wrong as they are frequently stated.
There must be SOME truth to the idea that organic fertilizers don't burn plants as often as "chemical" fertilizers do, because SO many people believe and repeat the myth "organic ferts add no salinity".
I speculate that no one CAN get
all the salt (NaCl) out of fish, but I might be wrong. And I think that high-end soluble hydroponic fertilizers very carefully limit the amount of unwanted ions (mostly Sodium and Chlorine) they include, because total ionic content is a huge concern in hydroponics.
Also, in outdoor gardening, I agree with you. I would rather add compost than fertilizer outdoors, IF I have enough compost.
There is a way that soluble fertilizers might add more (non-nutritive) salts than organic emulsions.
Maybe some cheaper soluble fertilizers use cheap salts that include Sodium or Chlorine or other ions that are not taken up by the plant. THOSE would accumulate in pots more than they would from organic emulsions containing smaller amounts of Sodium or Chlorine.
Also, plants only take up what they need, in the
ratios they need them. If the emulsion fertilizers have very well-balanced N-P-K
in the ratios that your plants need, few will be "left over" after the plant has taken up what it needs. IF some soluble chemical does NOT match your plants' needs, then the limiting nutrient will ALL be consumed and the excessive nutrients will be "left over" and accumulate like ions that the plant does NOT like to take up.
