fertilizing indoor seedlings ?

mandolls(4)April 11, 2011

I have been following the advice of members on the growing from seed forum re: weak dilution's of fish fert on my seedlings under lights.

However............As I read more and more, it seems that organic fert needs real soil micro organisms in order to be taken up by the plants. I am raising these seedlings in a soilless mix, so how is using an organic fertilizer an advantage? Wouldn't it actually be more productive to use a chemical fert until I get them in the ground?

I do plan on using organics in the garden, but do you all use them in soilless mixes under lights?

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Dan Staley

so how is using an organic fertilizer an advantage?

Its not in that situation.


    Bookmark   April 11, 2011 at 9:47AM
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dchall_san_antonio(8 San Antonio)

If your seeding medium has been watered more than one time, it already has microbes in it. If it contains any peat moss or compost, then it is teeming with microbes.

If your medium is strictly that white stuff, then you might soak some compost in water for a few minutes and water that water through your seeding medium to transfer the microbes from the compost to the medium. Then I would water it with diluted milk and/or the other liquid ferts you can find.

    Bookmark   April 11, 2011 at 10:00AM
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gjcore(zone 5 Aurora Co)

I try to stay organic as possible but I'm not against all use of chemical fertilizers. I do use some Miracle-Gro very diluted on seedlings as well fish fertilizer.

This year I've also started a couple new things. I've been adding some presoaked alfalfa pellets to the top edges of the seedling containers after they start their 2nd set of true leaves. The other thing is I use 2 layers in my seedling containers. The top layer is a mostly peat commercial starter mix and the bottom part is potting soil. It seems to be working out pretty good so far.

    Bookmark   April 12, 2011 at 9:43PM
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joel_bc(z6 BC)

Indoor seed starting... Some people believe strongly in using a sterile "potting soil" or other fairly inert growing medium, and then (after the germinated seedlings get their second leaves) watering with dilute fertilizer. Others say, nah, mix a bit of compost &/or rotted manure in with the potting soil. To which the inert bunch say "well, you can promote damping-off, or even burn yer little seedlings."

How do people here see it?

    Bookmark   April 13, 2011 at 12:47AM
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Fish fertilizer is pure nitrogen unless it's some kind of combination with other ingredients. It's not at all enough for seedlings in potting soil. They need all the macro and micro nutrients. There should be liquid organic options available many places.

The best seaweed fertilizers contain lots of kalium and some nitrogen. It does depend upon the variety of seaweed harvested. The varieties that can be harvested on the beaches on low tide is usually the most nutritious, with the highest content of nitrogen and kalium. They lack phosphorous completely.

Biproducts from potato and sugar industry are often made into easily absorbed fertilizer for plants, and are great for seedlings. Here I get a fermented type that looks a bit like molasses, and are a biproduct when they extract sugar from sugar beets, and I get very good results from it. It contains all NPK, micro organisms and micro nutrients. There are similar fertilizers made from biproducts of wine production and even paper production, when fermeted they
have easily absorbed nitrogen and kalium. I'm not so shore about the phosphorous, or if there are anything comparable to the super phosphates. However, plants grow very well with these molasses type fertilizers. I really like the stuff made from sugar beets. These are a type of brown thick liquid that can smell funny, but not particularly unpleasant.

Joel_bc: I think it depends upon the seeds. Orchid growers have much better results sowing in sterile planting medium, but with most garden plants there's no benefit.

    Bookmark   April 13, 2011 at 7:56AM
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joel_bc(z6 BC)

In the OP on this thread, mandolls wrote: "I have been following the advice of members on the growing from seed forum re: weak dilution's of fish fert on my seedlings under lights."

This year, I used a commercially bagged, perlite-containing "organic potting soil" - and was a bit disappointed in the results, due to the fact that I did not put any compost or rotted manure into the mix. However, I want to contribute this...

I did a seedling-growth comparison with trays of heritage tomato seeds and jalapeno pepper seeds. I planted some trays where I mixed about 15% volcanic-rock powder in with the potting soil. The seedlings in those trays grew twice as big and twice as healthy in the same period of time as those in some in trays for comparison. In the comparison seedling trays, I used the same potting mix, the same seed, the same light, and the same watering schedule & technique - just no crushed volcanic rock. The time between planting and germination appeared to be identical - all the differences occurred after germination of the seeds.

The volcanic soil (or rock powder) that I've tried is much finer than fine sand. I have to conclude there is some property of this amendment that is responsible for the pronounced difference in the health and development rate of the seedlings.

    Bookmark   April 17, 2011 at 9:23PM
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Dan Staley

I have to conclude there is some property of this amendment

Likely high cation exchange capacity.


    Bookmark   April 18, 2011 at 9:41AM
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(I don't mean to single out anyone on this thread.) On this forum, people always say, "I try to garden as organically as possible" and then give an example of when they don't think that is possible, which is often the teensiest obstacle.

I always want to say, "No, you don't. I try to garden as organically as possible, which I've learned, is very, very possible." I would prefer it if people would just frankly say, "I'm not wholly committed to organic gardening, although I admire the concept, in theory."

This isn't actually a completely true post, though, I admit. I use amendments that are not organic. I use newspaper, I use manures from animals whose habits I know nothing about, and I buy inorganic seedlings from nurseries. I don't call myself an organic gardener, but I have never encountered---as a person who believes that gardens (or at least my garden) should be managed organically---a situation in a garden that cannot be ignored or a plant substituted or a crop not grown or leaf damage regarded as the minor problem it usually is.

And what people forget about organic gardening is that one of the theories is that the main reason that it doesn't always go well, is that you've got your next door neighbor killing off all the beneficials, all the natural predators, that organic gardeners need to depend on for their methods to truly succeed.

I admit (with shame) to using peat-based Pro-mix to start seedlings. I fertilize with fish/seaweed based products and---my favorite---worm castings from my worm bin.

    Bookmark   April 18, 2011 at 10:01AM
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Chemical fertilizer will burn tender young seed roots.
I know persons who mix a trace of bone or blood meal in their seed mix & Never lost a seed.
But I am not that brave, I add N-P-K after the plant has at least two true leaves.
I know a natural gardener who uses liquid fertilizer the day after transplanting.

    Bookmark   April 18, 2011 at 11:48AM
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My original question was based on what I have read about "chemical" fertilizers causing imbalances in the soil of a garden bed, while organic fertilizers are more likely to build the soil, making it better and better over time.

However when fertilizing seedlings in plastic cups with a soilless mix, I am not concerned with long term "soil" imbalance. I am concerned with strong healthy seedlings. I am not using large quantities of fertilizer of any kind, and dont believe that a very diluted dose of 20-10-20 (an orchid fert that I had on hand), is anymore likely to burn anything than a diluted fish/kelp fert. I havent added fert to anything that isnt already transplanted, and then not immediately.

I am interested in organic gardening, which is why I read in this forum, but I certainly dont claim to be an organic gardener with a capital "O". I do like to think that I am improving my little spot on the earth, not just sucking it dry, but I also drive a car, and use fossil fuels to heat my home, shop at Wallmart.etc etc.

John - I am curious about the "volcanic soil" you tested. I googled around but didn't hit on anything that was being sold to gardeners.

    Bookmark   April 18, 2011 at 9:41PM
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Yes, I understand. I was reacting to a different post, but really I was reacting to hundreds of "organic" gardeners who will say, I try to garden organically, but....
Actually, a friend who wants to be an organic gardener told me that she had to finally succumb to using a chemical pesticide because she had spider mites. And what I wrote here is what I wanted to say, but didn't, to her.
I don't care if people are or aren't organic gardeners (Well, I do, but that's not an issue with me.).

And it's okay to fudge on the organics if that's what you want to do. I wasn't griping. I just always feel like pointing out that all you have to do to garden organically is just to do it. I guess what it is is, I know a lot of gardeners who panic when they see leaf minor damage or aphids on a plant stem. I have never lost an outdoor plant to aphids. Well, maybe some nasturtiums, but that's what they're for.

I guess I'm having my own private tangent. Yes, fish emulsion fertilizers (all nitrogen fertilizers) can burn a plant in the same way that chemical fertilizers can.

    Bookmark   April 19, 2011 at 11:08AM
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tapla (mid-MI z5b-6a)

Mandols - FWIW, I pretty much already follow the plan you laid out in your opening post, with excellent results, consistently. Setting ideology aside and focusing on efficacy, I can attest to the fact that I have never been able to achieve results in any form of container culture that satisfy me, by trying to duplicate garden conditions in containers - mainly because growing anything in conventional containers is much closer to hydroponic growing than growing in the garden. I adhere almost completely to the adage that you should feed the soil instead of the plant ..... in the garden, but when it comes to containers, and that includes seed starting, I have never found anything that works better than a very well-aerated medium in conjunction with a soluble fertilizer that has all 12 of the essential nutrients (in a favorable ratio) plants normally get from the soil.

BTW - it's much more likely that a grower will 'burn' roots or end up with ammonium toxicities or other complications when using blood meal and various other meals as a N source than it is when applying adequate doses of N from nitrate or urea sources.


    Bookmark   April 19, 2011 at 4:45PM
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Thanks for the response Al - its probably through reading your various posts on container soils that got me thinking that it would make more sense to use non organics inside on my seedlings, I just hadnt seen it suggested anywhere by people who were planning on moving the seedlings to an "organic" garden.

I suppose that for some fundamentalist organic gardeners, simply growing in plastic cups under fluorescent lights could be the first step on the road to hell.

This is only my second year with a veg garden and my first year of successfully (so far) growing seedling under lights. I still have lots to learn. What I love about this forum is that so many people have completely different sets of "rules" that they swear by. I get to "weed" through it all and figure out what works for me.

There is no way I am putting diluted milk on my seedlings, the smell of the fish fertilzer is bad enough, but sour milk under lights sounds awful.

    Bookmark   April 20, 2011 at 7:08AM
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tapla (mid-MI z5b-6a)


    Bookmark   April 20, 2011 at 5:15PM
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gjcore(zone 5 Aurora Co)

anapat, I'm sorry for using "Whenever possible". That was a bad term to use. Also it seems it's a bad thing to mention non-organic ways here. I won't do that again here.

    Bookmark   April 24, 2011 at 8:45PM
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gjcore, even I (and I'm a fan of me) thought I sounded deranged in the above post. I always worry that people don't give organic gardening a chance once they encounter a problem. I didn't mean to jump on you.

    Bookmark   April 26, 2011 at 1:44PM
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I have experimented on a few different soils/soiless mixes to find that both converted the organic fert to a usable form......so I guess they both contained microbes....just my experience...not that I would take it to the bank. Found some biodegradable seed starting pots the other day with organic fert built in them....have started some squash in them. Kind of interesting and seem to work fairly well.

    Bookmark   April 27, 2011 at 10:11PM
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