Does Fertilizer Go Bad (& a couple other ?s)
 

Apologies in advance for more fertilizer questions. I have searched the forum to the best of my ability but I have not been able to find answers to these particular ones.

My orchid collection is small, only twenty-some plants. I have been using the MSU formula, but I find that even when I buy a small container, by the time I get around to using it up (maybe a year or more?), it has changed color and is stuck together in clumps. It does have the moisture-absorbing packet in it.

My first question is: Does fertilizer go bad after a time, or become less potent? Is what I have described an indication that the fertilizer has degraded in some way?

Second question: I have heard and read many times that we should only be using 1/4 or so of the recommended amount of fertilizer. For clarification, does this apply even when using fertilizer specifically formulated for orchids? Or maybe that reduced amount is meant to apply only to those who fertilize frequently (weekly, weakly), and if we are only fertilizing once or twice a month, the directions on the container are proper?

Finally: I have used up my current supply of MSU fertilizer and I'm reluctant to buy more since it takes me so long to use it up. I currently have in my cupboard the following liquid fertilizers, all Schultz brand:

Plant Food Plus, 10-15-10
African Violet Plus, 8-14-9
Cactus Plus, 2-7-7

Is it safe to use any or all of these on my orchids?

I don't think that even when it cakes up, that fertilizer goes bad... it is a mixture of inorganic salts that tend to absorb moisture but don't change chemically. I have a 25-pound sack of MSU that I'll probably be working on for the rest of my life (and I have a large collection...) I keep the sack (with a clip to keep it closed) inside a plastic bucket with a tight-fitting lid and it stays nicely dry. For using it, I put a littlle in a small jar with a tight-fitting lid, which takes me a couple of months to use up. In that amount of time, it does pick up a bit of moisture - I start with powder but end up with little balls of fertilizer. But I treat it the same when measuring.

As far as amount is concerned, doesn't matter whether the fertilizer is labeled for orchids or not... fertilizer is fertilizer. You use a small amount (1/4 to 1/2 of what is on the label) because orchids require only a little bit, but want it more often. Just as you would prefer three modest-size meals per day rather than a huge banquet once a week with nothing in between, orchids are similar in their needs. In nature, they hang from trees and get a very small amount of nutrients washing down on them with rain, nearly every day. I'm no expert on the fine points of fertilizer, but looking at the formulations, I'd guess that the Plant Food Plus is the closest to the usual orchid formulations... a bit heavy on the phosphorus that the orchids don't need much of but won't hurt. (Might help with hard, high-pH water since phosphorus is probably phosphate, a bit on the acidic side) The other two are light on nitrogen, which is the nutrient that would be most useful. They're not "unsafe", just may be less "satisfying".

It happens to me also but I keep using it. Like Roberta said, it's just a mixture of inorganic salts. Some salts change color when hydrated (water absortion). That's why it turns pink.
The fact that it forms clumps may change the concentration but, as the clumps make its volume higher, the concentration will be lower, which is better than higher. Anyway, it will result in minor concentration changes so no issues will come out of that.

Store it in your freezer. It won't clump.

The only part of this I won’t “blanket” agree with is the “use 1/4 to 1/2 the recommended dose” stuff. It’s a little too loosey goosey for me.

Pick a target nitrogen loading and use that amount, no matter the formula.

Ah-ha! I will definitely try that next time. Thanks for the replies, all of you. I won't worry about fertilizer granules changing color or texture.

Ray, I've read many of your site's feeding articles, and I'm trying to digest all of the information. No pun intended. :)

Mountaineer ----- if that fertiliser you have are granules ------ and not liquid, then one way to get a rough idea about how much to use is with the simple calculation shown at this link here. The value of 'T' could be just set permanently as 0.01. And then you just have to put in how much water you are going to use ------ such as 500 mL or 1000 mL etc. And "N" will just be the number on the packet .... (from the N-P-K specifications).

I think that even if a fertiliser is in a liquid form ------ the formula should still be workable ..... except just switch the units of the quantity "F" from mL to gram for the amount of fertiliser needed ----- as an approximation.

I personally do what Roberta does as well. I just know roughly what the manufacturer of my orchid's fertiliser recommends for orchids ------ written on the bottle. And then I just really do just use one-quarter or even one-third of what they recommend. And once we have a measuring device (eg. teaspoon, or syringe for liquid etc) ------ we can just use that as a reference ...... and mix more or less the desired concentration every time.

Although - if ever in doubt, or for serious control of fertiliser concentration ----- we can certainly use the formula too.

I use Akern Rain Mix that comes with a small spoon (1 gr). The recommended dosage is 1 gr. per 2 l of water so I fertilize in every watering with half that dose. Depending on the genus and the season, I may use 1/4 dose, full dose or none.

It’s the mass of nutrients applied that’s important, and that is controlled by the concentration of the solution applied and the frequency of application.

Just think of it like counting calories when eating. You can eat several small meals or one large meal, in order to reach 2000 calories, for example.

I have found that applying 75-125 ppm N per week is a good overall concentration to shoot for. (Yeah, I know it’s a concentration, not a mass, but as we really have no idea how much of the applied solution is absorbed by the plant, it’s an acceptable control.)

6/%N in fertilizer = teaspoons/gal for 75 ppm N
8/%N for 100
10/%N for 125.

Multiply by 1.15 if you prefer your measurements in ml/L.

At the risk of embarrassing myself, I'm just going to say it. I am not good at advanced mathematical formulas.

My main question was about the age of fertilizer and whether that made it any less potent, and I understand now that it does not.

In my question about the weekly/weakly philosophy, I was just wanting clarification. The answers here reaffirm for me that actual amounts as far as teaspoons per gallon are going to vary based on the composition of the fertilizer I am using and how often I use it.

I have tremendous respect and admiration for those of you with advanced scientific knowledge and math skills, and I do appreciate the replies. :)