Organic fertilizer for indoor plants?

prairiemoon2 z6 MANovember 17, 2007

Hello again.. :-)

My plants could use a little boost. They are doing okay but could be doing better. I am considering repotting in fresh soil and fertilizing, but I don't want to use a synthetic fertilizer. The only thing I can think of is Fish emulsion/kelp but the odor indoors is not pleasant to my family. Any other ideas?

Thanks again.. :-) pm2

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tapla (mid-MI z5b-6a)

If you have strong convictions about wanting to remain 'all organic' in your growing endeavors, I wouldn't try to dissuade you, but if you're not, I would.

Chemical fertilizers are immediately available for plant uptake, while organic fertilizers are not. They need to pass through the gut of microorganisms before they can be broken down into elemental forms that plants can use. From this, you can see that their value to plants is intricately Dependant on microorganism populations, which are boom/bust in containers, guaranteeing that nutrient delivery will be erratic. Nutrient levels, pH, temperature, moisture levels, soil composition, soil structure and oxygen levels all affect their populations. Further, when microorganism populations are low, organic fertilizers tend to build up to much higher concentrations in properly irrigated plants than chemical fertilizers do. If this occurs, when cultural conditions return to favorable, the microorganisms can release large amounts of N into soils, so it's easily possible to get a delayed burn reaction from organic fertilizers - and you may never even realize why it occurred.


    Bookmark   November 17, 2007 at 9:55AM
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Hi, I would add some worm casting to your potting soil for natural nutrients. It's true they won't use it as quickly but they will when they need to. You could also spray them once every 10 days with liquid worm casting. I could tell you where to find this if you would like to e-mail me. Patty

Here is a link that might be useful: pattysplants

    Bookmark   November 17, 2007 at 10:37AM
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joel_bc(z6 BC)

I tried organic approaches with houseplants for many years, then gave up. The "smelly" problem was part of it, but not all. I'm going to be interested, though, in what other peoople will post on this thread.

Al's discussion is interesting. Possibly some of what he's written was part of my situation. I'm an organic gardener (outdoors) and I was trying to make decent potting soil from garden soil (including the mineral soil) plus compost, and often with a bit of vermiculite in it. Then fertilizing with a bit of rotted manure or fish emulsion.

Problems included soil that did not drain very well in the day or two after watering, or - on the other end of the timeline - soil that would cake when it got a bit dryish. I had lots of stunted plants and plant death.

I switched to a growing medium that I mix myself: 40% coir, 40% finely ground bark, 20% perlite. This soaks up water nicely (better, for instance, than peat moss), but also drains nicely. And I use Miracle Gro in the water every few weeks. The one thing I( can't figure out is why the makers of M.G. have not included any calcium in the formula. Plants need it. So sometimes I put a couple of nutritional calcium supplements into the blender with some water, then put the result into the watering can along with the M.G.

Good luck with your plants.


    Bookmark   November 17, 2007 at 12:38PM
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tapla (mid-MI z5b-6a)

Some comments about this thread:

* I forgot to mention that when using organic fertilizers, you can expect a much higher incidence of gnats and other insects whose life cycles include a stay in our soils. There will also be that hydrophobic crust that forms on top of soils and frequently makes water absorption problematic.

* I don't use anything in containers I feel will adversely affect drainage or aeration. I make it my responsibility to guard those physical properties judiciously, so I don't use compost or worm castings. I feel that there are a number of supplements and fertilizers, both organic and chemical, that will nicely and efficiently supply the minor elements while having no impact on soil structure, so I use those. It's a personal decision, but it's rooted in soil physics.

* I pretty much agree with Joel's assessment of his soil problems.

Also, fertilizer manufacturers often don't add Ca or Mg to fertilizers because they are sufficiently present in nearly all prepared soils, used to adjust pH northward. If you are making your own soils, you should add dolomitic lime as a Ca/Mg source if you suspect the initial media pH is low. If you think pH is neutral, use gypsum as a Ca source. If you use dolomite, no additional Mg is needed. Using gypsum as a Ca source is one of the few instances where you can feel confident that continued supplementation of Mg (Epsom salts is fine) is actually needed to balance out the Ca:Mg ratio. Mg should be supplied at approx 1/10 the rate of N and 1/4 the rate of Ca.


    Bookmark   November 17, 2007 at 2:27PM
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joel_bc(z6 BC)

Al wrote "* I forgot to mention that when using organic fertilizers, you can expect a much higher incidence of gnats and other insects whose life cycles include a stay in our soils."

Oh, yeah... and I forgot to mention that, too. Gnats, and I think it was flea beetles too. Don't know of they did any substantial plant damage, but they showed themselves from time to time.


    Bookmark   November 17, 2007 at 5:36PM
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prairiemoon2 z6 MA

Al, that was a great explanation. Like Joel, I keep trying to grow plants indoors without using synthetic fertilizers and most of the time I don't use fertilizer at all and then the few times I have, I have used fish emulsion/kelp. I never feel like my plants live up to their potential and that is why my renewed interest in fertilizing more consistently. Really the amount of light I have may be part of it too.

I am in agreement that without the micro organisms in the soil, how would the organic materials break down and become available. I always wondered when you are using a soil-less mix, how you can have an organic process anyway. Not to mention the difficulty in finding potting soil without synthetic fertilizers unless you mix your own.

So sounds as though you grow indoors organically, or do I have that wrong? Do you mix your own soil?

One of the reasons I am reluctant to use synthetics is that I imagine the possibility of the synthetic fertilizer being returned to the room the plants are in when the plants transpire. At least I imagine that I am subverting one of the reasons I grow indoors in the first place, which is to improve the 'quality' of the indoor air. The other reason is that it just doesn't feel right to use synthetics indoors when I only use organic outside. I think it's time I worked it out once and for all and made up my mind one way or the other.


    Bookmark   November 17, 2007 at 7:47PM
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I think this stuff is organic. I recently started using very low doses of the Pro Grow and Liquid Karma varieties. The products themselves smell pretty bad, but i haven't noticed a lingering smell on the plants.

Here is a link that might be useful: Botanicare

    Bookmark   November 17, 2007 at 9:14PM
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tapla (mid-MI z5b-6a)

So sounds as though you grow indoors organically, or do I have that wrong? Do you mix your own soil?

I do mix all my own soils and haven't used a prepared soil in over 10 years. I use almost exclusively a chemical fertilizer with a 3-1-2 ratio. Usually, it's 24-8-16 or 12-4-8 with micronutrients. I do supplement my containers outdoors with fish emulsions when temperatures are over 55*, but never use it when temperatures are cool. Indoors, I use nothing organic (see above - messy & increases likelihood of soil insects, causes hydrophobic layer atop soil).

I'll leave you to worry through the organic/inorganic decision, but don't let the transpiration thing sway your thinking. The gasses that escape through the transpirational process can contain no chemicals or dissolved solids. When water changes phase from a liquid to a gas, it leaves all impurities behind. Along with Oxygen and Carbon Dioxide, plants emit a couple of other by-product gasses, but none of the dissolved solids from fertilizer make it into the air.

Good luck. ;o)


    Bookmark   November 18, 2007 at 12:17AM
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dampflippers(Tyne & Wear UK)

what about the seaweed based fertilisers?

    Bookmark   November 18, 2007 at 5:20PM
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tapla (mid-MI z5b-6a)



    Bookmark   November 18, 2007 at 6:06PM
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watergal(z6/7 Westminster, MD)

This has been a very useful discussion, but no one has suggested yet that this is not the ideal time to fertilize, especially in northern areas where days get short and cold. Tropical plants tend to go somewhat or completely dormant under these conditions. Giving them nutrients when they aren't growing won't do them much good and could harm them.

I personally stop fertilizing around October or November and don't start again until February or March. And that's for the plants I care for professsionally. My plants at home get even less fertilizer - you know the old saying, "The shoemaker's children have no shoes" and all that!

I've only started working towards being organic over the last few years, but I don't think I'd ever want to use organic fertilizer indoors for the reasons already mentioned. (Come to mention it, I guess I don't use organic fertilizer outdoors much either, except for some bone meal for my bulbs. I do compost though.) I am more intent about reducing my use of nonorganic chemical pesticides. I use neem oil, and bought some insecticidal soap to try next time, and I'm about to experiment with using beneficial insects in my indoor grow room.

    Bookmark   November 18, 2007 at 7:24PM
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I was checking out a common fish emulsion manufactorer (NH) website ealier. They had the chemical analysis listed on the website and apparently there is

    Bookmark   November 19, 2007 at 9:42PM
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I agree with the 'No Fertilizing' policy in cold, dark, climates..It's really best to wait until days grow longer and/or new growth forms.
But if someone feels a need to perk up a plant, though if there's no sun in the area, all your plant will get is spindly growth, I'd go with Fish Emulsion..
If not in soil, then use as a foliar spray..There are fish emulsions now sold that have much less 'fishy' smell than others..Ebay and sells this product.
I add 1-2 drops of Superthrive per gallon of water..Since it's not a fertilizer, and not to be mistaken for one, there shouldn't be any problem. Toni

    Bookmark   November 20, 2007 at 6:28PM
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