Re: Potting mixes
susannah@gladstone.uoregon.edu wrote:
>
> One or 2 people have mentioned fertilizer crashes in commercial potting
> mixes. I'm wondering if this could explain a problem I've had with several
> different brands. Before reading the posts, I had narrowed down my
> theories to two main ones: too much fertilizer, or too little!
>
> The symptoms are lack of growth (especially in seedlings), and eventually
> leaves turning a bright red and the plant dying. This can take up to 6
> months. The stunted growth and slow decline would lead me to think there
> was a crash... if the immediate problems with seedlings when the soil is
> fresh weren't making me think there was too much fertilizer to start with.
> Maybe too much and too short-lived?
>
> I don't think it's an acid/base problem, because it affects such a wide
> range of species. I sure would appreciate any suggestions or theories.
>
Susannah
Nobody else seems to have attempted to tackle this one, so I will try. I
have long given up commercial mixes myself partly because of their
variability and mainly because of my attempt to be strictly organic, but
tests done by my local Consumer organization on commercial mixes
available here do indicate that, even though a few performed very well,
how many are unsatisfactory. One of their major problems in my opinion
is the preponderence in the majority of peat, ground bark or other
materials with little or no actual food content, so thay are almost
wholly dependent on added fertilizers. Too often, I suspect, these are
largely in the soluble, instant-use form and not enough emphasis is put
on the more long-term slow release variety. The main advantage of using
natural materials like soil or compost is that virtually all their
contained nutrient is slow release, so there is a regular supply of food
availble at a safe rate rather than the boom and bust of many synthetic
mixes.
>From your description I do wonder if your problem might be too much,
rather than too little fertilizer plus possibly the form it is offered
in (instantly available, rather than slow-release). To strong a feed
could result in the initial stunting because the roots are compromised.
At the same time, if the nutrient _is_ in highly soluble form it would
be rapidly washed out of the pot by regular watering, so if and when the
damaged roots recovered they can no longer find food.
Another possibility is that the bad mixes contain some product which
interfers with the uptake of fertilizers. I and several other
correspondents on this and other lists have, for instance, had very
unsatisfactory results with mixes containing cocopeat (what its problem
is we have been unable to resolve and I have myself stopped using it).
In this case plants have simply not grown and seeds failed to germinate.
If you wish to continue with purchased mixes, I can only suggest you
make careful note of what you buy and how it performs until you find a
product which is consistantly satisfactory (and then hope the firm
continues to stick to the same formula!!) If you strike one of those
lemons, in which the growth is obviously unsatisfactory, I am sure it is
not worth continuing to torture your plants and waste a growing season,
but you really need to go to the trouble of repotting in a different mix
before thay become totally debilitated.
Moira
--
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata,
New Zealand (astride the "Ring of Fire" in the SW Pacific).
