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Simplifying Organic Growing: The Best Starter Fertilizers

Formulating an organic growing medium for starting vegetable and herb seeds can be a challenge, depending on what a grower is looking for. When it comes to starter fertilizer charges, most growers prefer having them incorporated into their certified organic growing medium.

The question is: how long does it need to last? It is easy to provide a starter fertilizer that can feed vegetable and herb seedlings for up to 3 weeks for heavy feeders (e.g. peppers, tomato and basil) or 5-6 weeks for light feeders (e.g. lettuce, greens).

However the grower must have a plan for fertilizing his crop after those first weeks of growth, when the initial nutrition charge is gone. This the challenging part.

Most professional growing medium manufacturers provide these types of starter fertilizer charges.

Longevity of Starter Fertilizer: The starter fertilizer charge in professional growing media may come from one or more of the following sources: animal or poultry manures (Figure 1), soybean meal, alfalfa meal, bone meal, blood meal, seaweed or fish by-products. For light feeders, it is possible for a starter fertilizer charge to last from sowing of the seed until it is ready to be transplanted into the field or garden. However, heavy feeders will require additional fertilizer applications during the production cycle. If there is not enough starter fertilizer in a growing medium, should more be added?  This can be done, but it is not recommended.

Sustane 4-6-4 Plus Humates by PROMIX

Figure 1. Poultry manure products are often used as a starter fertilizer charge in a certified organic growing medium. Source: Premier Tech Horticulture.”


First, incorporating extra starter fertilizer in the growing medium increases the electrical conductivity (or soluble salts), which can burn or kill sensitive light feeders (Figure 2). There can also be large pH fluctuations as nitrogen mineralization and nitrification occur during the first few weeks after producing the growing medium. Second, as Paul Fisher reported, high fertilizer levels can burn the roots of young heavy feeders. This initial root damage can slow plant growth and development, causing a delay in crop timing. However, once the plant recovers, the high fertilizer can then sustain active plant growth. Clearly, adding more starter fertilizer is too risky as it can cause plant damage.  

romaine burn sign fertilizer

"Figure 2. Typical fertilizer burn symptoms on root system of romaine.
Source: http://ucanr.edu"


Winning Combination: Short-Term Starter Fertilizer and Liquid Feeding: The starter fertilizer charge is not a “one rate fits all” for all crops. As stated for light feeders, most starter fertilizer charges may provide enough nutrients to sustain a crop in a seed tray or pack through the entire crop cycle. For heavy feeders, liquid fertilizer applications are required to maintain normal plant growth. The most common recommendation found in the literature is applying a constant feed drench with 1 tablespoon of fish emulsion per gallon of water. Typically, it should be applied 2-3 weeks after sowing when much of the starter fertilizer is used up. This rate will vary depending on the analysis of the fish emulsion and stage of plant growth (more mature plants need more fertilizer than seedlings). Research found in one case that after 6 weeks, leafy greens used only 15% of the applied nitrogen from a poultry fertilizer (it was believed that the nitrogen was tied up in complex organic molecules).

For more information, contact your Premier Tech Horticulture Grower Services Representative:

BLOE         PEEJ             LAWL

Ed Bloodnick
Horticulture Director
US-South East

JoAnn Peery
Horticulture Specialist
US-Central, Canada-Central

Lance Lawnson
Horticulture Specialist
US-West, Canada-West

     
BUET PARS      CHEJ

Troy Buechel
Horticulture Specialist
US-North East

Susan Parent
Horticulture Specialist
Canada-East, US-New England

Jose Chen Lopez
Horticulture Specialist
Mexico, Latin & South America

 

Sources:

PRO-MIX® is a registered trademark of Premier Horticulture Ltd.

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