Fertilizer "water" longevity

staze(8)June 24, 2013


Having seen this post http://forums2.gardenweb.com/forums/load/houseplt/msg0314403013336.html but nothing on my question, I thought I would ask.

Once you've mixed the fertilizer with water, say, Foliage Pro 1/4tsp per gallon (weakly weekly, etc), but you don't use the full gallon(s), how long can it sit around without any serious detriment? Week?

Obviously the nutrients aren't going to evaporate, but I wouldn't be surprised if prolonged light, or O2 exposure (or heck, bacterial/fungal growth) could be an issue.

Thoughts? Al?

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I've always wondered this as well. I remember when I was a kid my mother used to have orchid food mixed up in a bottle. She used it on her orchids for years, although they never would flower for her (probably because she didn't really know what she was doing). A few years ago I found one of these bottles with fertilizer still in it and it looked ok, not cloudy or any sediment in. It was probably over 10 years old. Don't know what happened to it. Probably was thrown out. It's still in the back of my mind if I could mix up fertilizer in water bottles and just keep it on hand so I don't have to mix every time I fertilize.

    Bookmark   June 24, 2013 at 4:33PM
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pirate_girl(Zone7 NYC)

I'd go the other way, I only mix up fertilizer as I need it. If I don't quite finish using it, I'll finish it up next time.

Doesn't seem a good idea (to me) to mix it up & then leave it for extended periods of time.

    Bookmark   June 24, 2013 at 5:29PM
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Makes sense. Though, thinking about it, hydroponics uses "mixed" fertilizer for some time, just topping things off due to evaporation and use by the plants. I don't think they ever just toss the whole lot and start new unless you get some nasty growth.

My main wonder was if there's any harm in say, a week of having it mixed (time between waterings).

Was hoping Al might comment. =)

    Bookmark   June 25, 2013 at 2:35AM
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pirate_girl(Zone7 NYC)

Well, certainly I'm not Al (Hiya Al). I'm sure a week will do no harm at all. If you'd wish to be doubly certain, dilute it even more.

    Bookmark   June 25, 2013 at 7:26AM
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tapla (mid-MI z5b-6a)

Most organic fertilizers, like fish emulsion, have antibacterial agents in them that only work at high concentrations. As soon as you dilute the FE, the concentration of the bacterial agents isn't sufficient to prevent the nasty stuff from growing, and it goes smelly very quickly. It doesn't so much reduce its effectiveness as it does reduce your ability to tolerate the evidential odor that tells of its going bad.

Soluble synthetic fertilizers are sort of the same, but it takes longer for them to go bad. I've found though, that once a synthetic mixture has gone bad in a container, the next batch goes bad much faster unless you sterilize the container between batches.

In the winter, I fertigate about every 4 days. When I'm done, I refill 5 - 1 gallon jugs with water (now, it's RO water, but was formerly tap water) and mix the FP into the water, so it rests about 4 days before it's used. I don't often get 'stuff;' growing in the water, but when I do, it's like a mildly gelatinous mucus suspended in the water. It's never created any problems with the soils I use, but I wouldn't be to surprised if it might not bring problems if the soils used didn't breathe properly.

Finally, if you do intend to 'store' mixed fertilizer solution. I'd be looking for a cool and dark spot to hold it until it can be used. The best way to deal with this is to get more plants so you use more fertigation solution and turn the whole thing into a nonissue. ;-)


    Bookmark   June 26, 2013 at 9:21PM
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dellis326 (Danny)

Most hydro-growers change out the nutrient solution on a regular schedule, every 4 or 6 weeks for example, some more often, some less. They only top off between those times. There is also some form of circulation of the solution so it isn't just sitting.

If you're going to mix and store a fertilizer solution, keep it in the dark or store it in dark containers so you don't end up with a jug of greenwater or a bacterial slime. Not necessarily harmful but it will weaken the mix.

    Bookmark   June 26, 2013 at 10:52PM
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Great info, thanks. I wasn't planning on storing so much as having left-overs after watering, but shoot, after reading this, maybe I will consider... I know Spray-N-Grow calls for letting it "mature" but I don't think for anywhere near a day or more. =)

When you were using tap, did you leave the containers open? I only think of the dissolved Chlorine in most municipal water. Or do you figure it would just collect at the top of the jug and get released when you opened it and poured it out.

Though really, most plants aren't going to care about Cl2 as much as hard water.

Thanks again! And yes, more plants... the problem is, I have a wee-one on the way (less than a month), and the wife is encouraging fewer plants around rather than more. =)

    Bookmark   June 27, 2013 at 2:51AM
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tapla (mid-MI z5b-6a)

You can tell a lot more about products you purchase for the purpose of nutrient supplementation by looking at their analysis than by taking for granted the veracity of their producer's claims. In the case of Spray-N-Grow, the only nutrients listed as being in the product are iron and zinc at .1% and .05% respectively. It does contain miniscule amounts of cobalt, nickel, molybdenum (micronutrients), but also contains unwanted heavy metals in the form of cadmium, mercury, lead, and arsenic. I doubt you can find any analysis of what's in the product at the Spray-N-Grow site because once you see what IS (and isn't) in it, you'll have a clearer picture about whether or not it could be of any value. IOW, making the analysis readily available would surely reduce sales. Eleanor's VF-11 is a similar product that is unbelievably over-priced, based on its analysis of NPK @ .15-.85-.55 (note the decimal points). This means it has 15/100 of 1% N, 85/100 of 1% P, and 55/100 of 1% K. One or 2 drops of a weak fertilizer having NPK %s of approximately 1-6-4 in a gallon of water would be about as potent as Eleanor's.


When using tap water, I filled 1 gallon milk jugs and left the top open. It wasn't so the chlorine would gas off - I knew it wouldn't. I did it in case there is any truth in the idea that cold water from the tap can shock roots. I've asked the question of dozens of horticulturists, and none have been able to say it can, or think of a physiological reason it might. Cold water on my containers in mid summer seems to be a significant plus, because it DOES reduce root temps quickly, so I try to water around the 5-6 PM time slot in summer.

Enlist the little one early as a helper .....


    Bookmark   June 27, 2013 at 3:53PM
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Thanks very much! I do plan on recruiting him as a helper. =)

I can honestly say, I never noticed there's basically no info on Spray-N-Grow... reminds me a bit of Superthrive, without the crazy writing all over it. At least Superthrive smelt like B1.

On a side note to all of this, with things like FP, is there concern about light stability (should the container it's in, or for example, your gallon jugs, be kept out of sunlight)? I ask because I put some of the FP in a little (brown) glass bottle with a dropper, since the dropper dispenses 1/4tsp easily. It was either that, of find some disposable plastic pipettes for measuring out such a small quantity.

I've just started using FP, so we'll see how that goes.

Thanks again for all the help.

    Bookmark   June 28, 2013 at 2:41AM
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doh, you pretty much answered that already and I forgot. Ignore that last question.

Thanks Al! Happy 4th!

    Bookmark   June 28, 2013 at 2:46AM
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I switched from Miracle-Gro soluble fertilizer to Foliage-Pro recently, and when I left the leftover weak solution stand on the counter till the next watering, bushy mold grew on the surface of the half-full water bottle in a few days. It was a "duh!" moment for me - I effectively encouraged to grow whatever microscopic stuff was in my tap water - water, humidity, high summer temp and fertilizer were all right there in the bottle.

I mix smaller batches now and leave the leftovers in the fridge till the next watering - then I put the chilled fert water outside for a few hours for warming up before using.

Learning as I go along!

    Bookmark   July 3, 2013 at 10:06AM
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