Slow release fertilizers

Hamish Sloan
Sat, 21 Feb 2004 13:38:49 PST
Hello Mary Sue,

It may be that the coating in Nutricote is a polymer or resin which either
1.    does not break down under your soil/temperature/water/etc conditions -
hence the unchanged physical appearance; the fertilizer is leacheed out by
water going into the pellet through the pores in the polymer coat and
solution comes out again. I would still expect some temperature effects on
usage rate.
2.    does break down but very slowly. Thus your fertilizer is a very long
lasting source that just happens to be much longer than a season.

Possibly, too, the pellets are a mix of stabilities to give a proportion
releasing fertilizer at any one time over a long period.

My info on the latest version of Osmocote mentions a resin coating that
"protects young roots from scorching" and claims that release rates are not
affected by water availability. Another source says Osmocote has an organic
resin coating and fertilizer is released by water diffusing through the
coating, dissolving fertilizer and solution diffusing out. Soil temperature
is indicated as affecting the release rate - scientifically, one would
expect faster diffusion and faster solution at higher temperatures.

This info is from two very recent trade catalogues and they both emphasise
"new formulation" of the Osmocote as if the coating has been changed

I have not used such long life fertilizers. When fertilizing bulbs coming
into flower with straight soluble fertilizer, I have noted effects adversely
affecting completion of the flowering stage, e.g. collapse of the scape in
Nerine. Lower concentrations give fewer affected scapes. However, this
collapse may be due to other reasons. My observations so far are very
limited and this is just my current hypothesis.

It seems to be a matter of not too much and not too little as well as
proportions. I prefer Phostrogen, with its higher ratio of K to N, rather
than Miracle Gro.

Sorry about all the big technical words!!

Jim S mentioned excessive phosphate build up in clay soils binding the iron.
This reminds me of the old chrysanthemum growers' trick that I used to use
of throwing a handful of iron filings into the compost mix. Any old iron
will do! If you have a model engineering society near you, its members will
probably be delighted to help. It's called re-cycling!

Regards Hamish
Wettish zone 9 Central south of England

----- Original Message ----- 
From: "Mary Sue Ittner" <>
To: "Pacific Bulb Society" <>
Sent: Thursday, February 19, 2004 3:23 PM
Subject: RE: [pbs] Slow release fertilizers

> Dear Kathy,
> A number of people in the past have reported losing their bulbs from
> Osmocote dumping too much at once. Uli had some horror stories about his
> Hippeastrums and I think Diana Chapman reported some sad results too, but
> she can report that herself. Uli is currently off line. There is a time
> release fertilizer called nutricote that isn't supposed to be temperature
> sensitive. I've tried that since I live in an area with excessive rainfall

I know a number of people who swear by dilute miracle gro with every
> watering. Will Ashburner who was a participant in the IBS forum in the
> said something that has stuck in my brain. He suspected getting your
> correct was more important than what kind of fertilizer you used. He
> stressed a medium with the correct air filled porosity.
> I hope this helps.
> Mary Sue

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