Slow release fertilizers

Boyce Tankersley
Thu, 19 Feb 2004 06:03:01 PST
Hi Kathy:

I'm working off of memory here. I believe this is the way these fertilizers work, but wouldn't swear to it.

Osmocote is a pelleted timed release fertilizer. The coating varies in thickness. The coating is dissolved (perhaps not the correct technical term) through the interaction of moisture and microbes. Because microbes respond to temperature, the higher the temperature the quicker the release rate. Likewise, the warmer the water the more rapidly the coating dissolves.

We discovered this when using Osmocote to fertilize some high value ornamental plantings in Texas. The fertilizer seemed to 'run out' before the labeled date. As it turned out, this was not really a problem. Plants also increase metabolic rates during periods of high temperature when moisture is not a limiting factor and so can effectively utilize larger amounts of fertilizer, particularly nitrogen - particularly for plants grown in full sun. We switched to a longer lasting formulation (12 month I think) in order to supply the ornamentals with the 9 months of fertilizer they needed.

Never observed any toxicity.

Boyce Tankersley

-----Original Message-----
From: Kathy Stokmanis []
Sent: Thursday, February 19, 2004 12:41 AM
Subject: [pbs] Slow release fertilizers

Hello, all

Some time ago someone referred to a previous discussion years ago (possibly through IBS?)concerning Osmocote and similar slow release fertilizers.  I have been unable to find it in the archives.  Can anyone recall the date or answer the question that the brief mention tantalized me with:  what did the research indicate about heat and it's effect on this type of fertilizer?  If this rather garbled message rings a bell for anyone, please let me know.  I need to fertilize some bulbs.

Kathy S.

It's rained 9 inches here since Sunday.  Daffodils are starting to bloom as are Iris reticulata.  Zone 8/9, Sierra foothills, Northern California, wet in winter, very dry and hot in summer.
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