As summer arrives and temperatures rise, many water-soluble fertilizers containing crystalline water tend to cake or dry out and turn white when the weather gets hot. Examples include nitrogen-magnesium fertilizer, medium-element water-soluble fertilizer, copper(II) sulfate pentahydrate, magnesium sulfate heptahydrate, and zinc sulfate heptahydrate.
Typical signs: softening in heat, moisture absorption, water exudation; after cooling or standing, they harden and cake again. Repeated thermal expansion and contraction worsen the caking. Drying and efflorescence turn the granules white.
One reason for caking in water-soluble fertilizers is that crystalline hydrates become unstable when heated, losing their crystalline water, which becomes free water and binds the powder together into lumps.
1. Core Cause: Crystalline Water “Escapes”
Many single-nutrient water-soluble fertilizers contain a certain amount of crystalline water (e.g., nitrogen-magnesium fertilizer, medium-element water-soluble fertilizer, copper(II) sulfate pentahydrate, magnesium sulfate heptahydrate, zinc sulfate heptahydrate):
- At room temperature: Crystalline water remains securely “locked” in the crystal structure, keeping the crystals loose and non-caking.
- When temperature rises: Crystals are heated → structure loosens → crystalline water is released → becomes free water. (This water comes from the material itself, not external humidity.)
2. Why Does Caking Occur?
- The released free water forms a moisture film on the surface of the granules;
- Powder particles become wet and stick together;
- With temperature fluctuations and moisture evaporation, recrystallization occurs, hardening into lumps.
Summer Fertilizer Storage Methods
1. Seal and Protect from Moisture: After use, any remaining fertilizer from an opened bag must have its inner bag tightly sealed and be placed in a sealed bucket or thick plastic bag. Avoid moisture absorption in humid weather or environments, which can then lead to caking when exposed to high temperatures.
2. Environmental Control: Choose a cool, dry, and well-ventilated warehouse. Avoid direct sunlight. It is recommended to keep the temperature below 30°C.
3. Keep Off Floor and Away from Walls: Use pallets or wooden boards to elevate the fertilizer, preventing ground moisture from rising. Stack at least 30 cm away from walls to ensure air circulation.
4. No Mixing: Fertilizers must not be mixed or stored with seeds or pesticides to avoid cross-contamination, which could cause phytotoxicity or fertilizer damage.
Post time: May-20-2026
