I've used Neptune's Harvest fish-based liquid fertilizer pretty much exclusively in my years of seedstarting. Since I've not strayed, I have no comparative evidence that it works better/worse than synthetic ones, but I've had pretty good success. I don't know the NPK off the top of my head, but it's all rather low.
Rob

-- posted by Lushgardener

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Top 6. Feb 12, 2004 12:14 PM

» kdjoergensen - Re: How about organic fertilizers?

In response to message posted by Lushgardener:

How effective an organic fertilizer will be depends a bit on what it contains?

Does it contain all micro and macro nutrients? Has the manufacturer provided a guaranteed analysis showing what is in the bottle?

As you may know, plants require that all essential nutrients are available (macro as well as micro). If even one is missing, plant growth will be affected, irrespective if this is nitrogen or boron.

The reference to macro and micro thus only refer to the amount required (all are essential elements which means the plants need them all). Does the organic fertilizer contain all essential nutrients ?

Organic nitrogen is not available for plant uptake and must first go through a process called mineralization before the plants can take up the nitrogen.

Mineralization is a process by which microbes in the soil convert organic-N to ammonium and nitrate (in that order).

Luckily, the key requirements for good microbial activity is warm soil, good aeration and consistent moisture (often found in indoors or greenhouse growing areas) so chances of conversion actually taking place - and fast - are good.

First the organic nitrogen is changed into ammonium (NH4+) which is available for plant uptake, in fact, due to positive molecular charge, it is very readily taken up by the plants.

Unfortunately, as I mention in my article, high levels of ammoniacal nitrogen can be a problem for some bedding plants, and it usually causes stretching in most - a condition we are trying to avoid.

Microbes do exist which will convert the ammonium into nitrate nitrogen (NO3-). Unfortunately, nitrate leaches easier than ammonium (ammonium nitrogen is retained by the CEC properties of the growing media) and chances are that your plants will end up taking up majority of the nitrogen as ammonium.

In my article I gave an example using urea, which - by the way - is also an organic source of nitrogen, although it is manufactured and not harvested (organic = contains carbon, not the same as harvested from nature).

You CAN grow good bedding plants using primarily ammonium and/or organic fertilizers (including urea), but I believe you can grow BETTER plants if you use a nitrogen source containing primarily nitrate nitrogen.

I would save the organic fertilizer for outdoors during the hot summer months.

In my opinion, the choice of inorganic vs. organic fertilizer often has nothing to do with consideration for the specific crops, but rather an emotional or conscious decision on behalf of the grower to use organic products as opposed to inorganic, or more correctly, use harvested vs manufactured products.

In some cases, choosing harvested organic seaweed fertilizers may seem the 'green thing' to do until you discover that the harvesting methods may have damaged ocean life whereas nitrate fertilizers produced in a local factory saved jobs. I can not guide to the "right" decision, but from purely a crop point of view, I can say that I am not convinced organic fertilizers necessarily are the best choices.

Kenneth

-- posted by kdjoergensen

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