The difference between 'slow release' and 'controlled
release'
Osmocote releases plant food AT THE RATE THAT PLANTS NEED
IT.
Unlike many slow-release fertilisers, the release of fertiliser
from the Osmocote prills is controlled by soil
temperature (not by soil moisture, as many gardeners
think).
- When the weather is warm in the active growing seasons of
spring, summer and early autumn, plants need more food and the
Osmocote prills release fertiliser more quickly.
- In winter when soil and air temperatures are lower, plants need
less food because their growth rate is reduced, so less plant food
is released from the prills.
How does controlled release work?
Osmocote prills are made up of many thin layers of soy coating,
all of which contain tiny fissures.
Water is absorbed into the prills to dissolve the fertiliser
inside, but cannot be released until the prills expand sufficiently
to allow the fertiliser to escape through the tiny cracks.
When the soil is warm and plants are actively growing, the
coating expands and fertiliser is released. When it's cold and
these minute cracks close up, less fertiliser is released.