The question of whether human cremated remains act as a good fertilizer is a common inquiry for those seeking a natural final disposition. While it seems logical that the mineral content of ashes would nourish the soil, the direct use of untreated cremains is generally not recommended for promoting plant life. Cremated remains contain elements plants need, but their specific chemical composition and concentration create an environment toxic to most soil and plant ecosystems. Understanding the makeup of these remains and their effect on soil is important for anyone considering incorporating them into a garden or memorial planting.
Chemical Makeup of Cremated Remains
The substance returned after the cremation process is not the soft, dark powder typically associated with wood ash, but rather pulverized bone fragments. The intense heat of cremation, reaching between 1,400 and 1,800 degrees Fahrenheit, vaporizes all organic material and leaves behind the skeletal structure. This remaining material is primarily inorganic compounds, with the main component being calcium phosphate, which accounts for over 70% of the total mass.
These elements are derived from the hydroxyapatite mineral structure of bone, which is highly stable and survives the extreme temperatures. Cremains also contain trace amounts of other minerals, including sulfate, potassium, and sodium, which are present throughout the body’s tissues.
The final weight of cremains is typically between six and nine pounds, depending on the individual’s bone density and body mass. Although these minerals are technically nutrients, their chemical form after processing is not readily bioavailable for plants, and their concentration poses a significant challenge to soil health.
Understanding the Soil Impact (pH and Salinity)
The chemical makeup of cremated remains creates two primary issues that make them unsuitable for direct use as fertilizer: extreme alkalinity and high salt concentration. Untreated cremains have a highly alkaline pH, often ranging between 10 and 12, which is comparable to substances like bleach. This high pH level drastically alters the chemistry of the surrounding soil, which typically thrives in a more neutral range of 5 to 8.
Extreme Alkalinity and Nutrient Lockup
Introducing a highly alkaline substance can lead to a condition known as nutrient lockup. When the soil pH is elevated, many essential micronutrients, such as iron, manganese, and zinc, become chemically bound and insoluble. Although plants require these elements for growth, the change in soil chemistry prevents their roots from absorbing them, creating a nutrient deficiency despite the presence of the mineral.
High Salinity and Salt Burn
The other major concern is the high concentration of soluble salts, particularly sodium. Cremains can contain sodium levels up to 2,000 times higher than what is considered tolerable for healthy soil. This excessive salt content causes “salt burn” in plants, which occurs when the high salinity in the soil draws water out of the plant’s root cells through osmosis.
This dehydration can damage plant tissues, inhibit photosynthesis, and ultimately kill the surrounding vegetation, especially seedlings and young plants. Studies have demonstrated the severe consequences of this imbalance, with one showing that 90% of seedlings died within three weeks when exposed to untreated cremated remains.
Practical Methods for Safe Incorporation
To safely incorporate cremains into the environment, the two problems of high alkalinity and high salinity must be addressed through dilution and amendment. Scattering a small amount of cremains over a very large area can dilute the concentration enough to prevent localized harm to established plants. Burying large volumes in one place or near a plant’s root ball will likely damage or kill the flora.
Using Buffering Agents
A more effective method involves mixing cremains with a specialized soil mixture or buffering agent designed to neutralize the harmful properties. These commercial products work by lowering the pH and diluting the sodium content to a safe level. The recommended process involves blending the cremains with the neutralizing agent and allowing the mixture to sit for a period, sometimes up to 90 to 120 days, before introducing it to the garden.
Alternative Incorporation Methods
For those wishing to avoid pre-treatment, several alternatives exist:
- Deeply bury the remains far away from the active root zone of plants.
- Place the remains in a biodegradable urn with a neutralizing liner.
- Select memorial tree species that are tolerant of more alkaline conditions.
- Water the area deeply after incorporation to help leach the water-soluble salts down past the roots.