[Market-farming] Organic fertilizer in seed starting medium?

Shoemaker, William H wshoemak at illinois.edu
Fri Apr 8 21:05:06 EDT 2016

Sorry about the previous post with nothing in it. Hit the wrong key with my left finger.

Marlin, one of the things I was taught as an undergrad in horticulture is that most seeds have all the nutrition they need to develop into an established seedling. That means a plant with leaves that are fully engaged in photosynthesis, probably the 4-leaf stage. So if you have a good growing medium that has very little nutrition in it, say 75% peat moss + 15% vermiculite + 10% rice hulls, your healthy seeds should produce healthy seedlings. That said, some good fertility applied before they reach this stage will be taken up and used when they reach this stage, and will help the seedlings continue to grow well into healthy, mature transplants. A compost tea applied at the two-leaf stage should be planty (sorry, I like puns). So I wouldn't invest too much in fertility in the growing media itself, unless it is compost you use as part of your growing medium. I do like that approach because compost slowly releases nutrients in a steady stream, creating a sustainable flow of whole nutrition to your young plants. It also establishes a microbe biome in the medium which goes to the field with your plants.

So I came to believe that what I learned as an undergrad was true. Fresh seeds are powerhouses designed to get the seedling into an established state without outside support. But once developed into a real seedling, they need, and benefit from that support.

Isn't Spring wonderful?!!


William H. Shoemaker

Retired fruit and vegetable horticulturist

University of Illinois

wshoemak at illinois.edu<mailto:wshoemak at illinois.edu>

From: Market-farming [market-farming-bounces at lists.ibiblio.org] on behalf of Marlin Burkholder [burkholders at glenecofarm.com]
Sent: Friday, April 08, 2016 7:41 PM
To: Market Farming
Subject: [Market-farming] Organic fertilizer in seed starting medium?

Looks like I have done it again!

A year or too ago I posted on MF about have trouble getting seeds started after mixing an organic based fertilizer (Plant Tone I think) into potting soil I was using for seed starting and for pricking week old seedlings over into grow out flats.  Plants would germinate satisfactorily, then stop growing.  After a week or two of wondering why the slow to no growth I would check a few seedlings and find few to no roots.  As I recall someone mentioned that plant proteins contained in some organic fertilizers can be toxic.

The first time it happened about five years prior to the time I last posted about it, I had used a premixed OMRI approved “ready to plant into” medium bought at a local garden center.  Every thing I planted into that stuff failed and I got my money back when I went back to the garden center and bitched.

The time I used Plant Tone I mixed according to instructions on the bag, about a 1/2 to one cup into about a cubic foot of medium.  I assumed that organic materials are more forgiving of less than precise mixing procedure but apparently got bit.  Last year I decided for the next go round to use nothing but chemical salt based materials, Miracle Grow or something similar, and got along better.

Well guess what!  I succumbed to temptation again and bought a five pound bag this spring to use in my starting mixes.  You know, it had kelp, bone meal, alfalfa meal, fish meal, micorizae, several other beneficial organisms whose names I can’t remember etc.--all the good stuff, along with the promise that the plants would love it!  When two seedling flats of peppers tanked, I blamed it on a small amount of germination mix I had left in an aluminum baking pan for about a week which I had used to cover seeds.  The one I had covered with material other than what was in the aluminum pan did not have impressive germination, but the seeds that did come up were healthy.  Then the tomato seedlings I had pricked over into to grow out flats started to go down hill.  A watering with Miller’s Nutri Leaf didn’t revive them.  This afternoon I repotted 180 plants into clean potting soil watered with nothing but Nutri Leaf.  I will do the other half of my tomato seedlings on Monday and hope for better luck.  After over 20 years of plant starting this thing is getting embarrassing and extremely frustrating.

Is it wrong to use fertilizer in seed starting mix?

Marlin Burkholder

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