This article provides a guide to achieving success with organic soils in raised beds, specifically addressing the common issue of yellowing plants, which indicates a nitrogen deficiency.

 

The Nitrogen Challenge in New Organic Soil

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• Organic Soil Composition: Organic soils are primarily made from composted materials (plants, wood chips, bark, peat moss, manures) mixed with minerals like sand. These materials are rich in nutrients, including nitrogen, from dead plant matter.

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• Microbial Nitrogen Lock-Up: When new organic materials are added, microscopic organisms in the "living" soil rapidly break them down. To do this, these organisms require a lot of nitrogen for quick energy. This process temporarily removes available nitrogen from the soil, locking it up inside the microbes' bodies.

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• Result: Plants suffer from a temporary nitrogen deficiency, turning yellow, even though the total nitrogen content of the soil is high. Over time, as the easy-to-digest materials are consumed, many microbes die and release the nitrogen back into the soil, creating a long-term "food bank" for the garden.

 

How to Ensure Success (Add Nitrogen)

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• Fertilize Immediately: To get lush, green plants from the start, we recommend that you add a fertilizer containing nitrogen. The first number on a fertilizer bag (e.g., the '5' in 5-4-3) represents the nitrogen percentage. This allows the microbes to do their work while still leaving plenty of available nitrogen for the plants.

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• Re-Fertilize with New Material: When adding new organic materials (manures or mulches) to existing beds, remember to boost the fertilizer again, as the new material will spur a fresh surge of microbial growth and nitrogen lock-up.

 

Key Takeaways on Organic Soils

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• Why Nitrogen Isn't Added During Mixing: Nitrogen is not added to bulk organic soils during initial mixing because the rapid decomposition would create intense heat, posing a fire risk in bulk piles of new soil. Even if it didn't ignite, the nitrogen would be quickly absorbed by the microbes before the end-user could utilize it.  To counter this, our Premium Bedding Mix has added chicken manure which is high in readily available nitrogen, but it’s always best to fertilize new soils when building raised beds as this too can quickly be used up in raised beds.

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• Longevity: A quality organic bedding soil can last for decades in a raised bed (e.g., 20 years or more), remaining loose, rich, and productive.

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• Superior to Sand/Gravel: Organic soils are far superior to heavier materials like topsoil (when used alone), sand, or gravel for two main reasons:

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1. Weight and Compaction: Organic soils are much lighter and do not compact like mineral materials, making them easier to work.

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2. Nutrient Storage: Organic materials have a high surface area with plenty of "holes" (cations) to attach and store nutrients. Topsoil, sand, and gravel lack these storage areas, causing added fertilizer to easily wash away without being banked for the future.