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Why manure is considered bad or risky for potted plants while they are considered good for plants on ground?

If they are risky or bad, why do the nursery sell them?

  • how well rotted is the manure? – black thumb Aug 3 '16 at 6:21
  • @blackthumb Its just a general question. Personally, I've never purchased any kind of manure. My neighbour got one some time ago. – 4-K Aug 3 '16 at 13:10
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It's a little bit complicated - properly composted manure can be added to potting mixes, but its the 'properly' composted bit where the problem arises. Manure should be composted with other materials for up to two years (horse manure with straw, for instance), and turned regularly so that the pile of composting manure heats up to pretty high temperatures. This ensures that the manure is, as far as possible, pathogen free, and is then safe to use, in ratio with other materials such as loam, sand, peat, etc., in potting mixes. If you're sure that any manure you have access to has been processed properly, then use it, but don't use anything that smells or looks bad.

Manuring open ground is not quite so risky because on open soil, any possible pathogens are diluted, so to speak, and will be diffused widely, which they are not when contained in a small amount of soil in a pot. Even on open ground, though, manure should be composted prior to use.

I don't know what part of the world you're in, nor what products you're referring to, so can't comment on manure based products on sale where you are.

  • But this site tells me to use manure, bat or poultry waste to feed the plant. It doesn't talk about composting the manure. Or I am misunderstanding something? wikihow.com/Feed-Plants or is it wrong? – 4-K Aug 3 '16 at 13:32
  • I've read your link; the bulk of the advice applies to plants in open ground - there is one small section that refers to potted plants, which tells you to use liquid fertiliser. That section is under a picture of a saucer with what looks like coloured water in it, above the picture of a chick. Even where it refers to using manures, its assumed the manure isn't freshly collected and used straight away - in some parts of the information to do with open growing plants outdoors (in soil) it actually mentions pelleted manure, which is processed. – Bamboo Aug 3 '16 at 13:39
  • Bamboo got it straight, it is ASSUMED that one knows about manure, organic matter and decomposed versus raw. Decomposed organic matter is super for potted plants to keep the soil from becoming a brick even it was bagged potting soil. All one needs to do is add it to the surface. But to use manure for fertilizer is for professionals who know the plants and what the plants are SHOWING that dictates what they need more or less of. – stormy Aug 6 '16 at 1:08
  • Bamboo, have you seen 'The Martian' with Matt Damon? Book is far better than the movie as always. Incredibly detailed and called Hard science fiction. The WIND at the beginning was for marketing, the author knew better but then the 'potato' farming using raw Matt Damon poop...??? It was all there was available and apparently it worked. Matt Damon is alive and well!! – stormy Aug 6 '16 at 1:13
  • Needs must when the devil drives as they say (same as I know I'd eat a rat if I was starving, as well as quite possibly even less savory items) - but even so, I assume that poop was applied to open ground, (havent' read the book nor seen the movie) not in pots. I'd rather risk the rat, less chance of e coli. – Bamboo Aug 6 '16 at 12:03
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In addition of the answer from Bamboo:

Manure is slow to decompose, so it enriches the soil on long term, but in a pot one probably change the ground more often (one or two years). Also the roots are less developed. So I would use manure for long term sustainability of soil (especially for the P and K components), but not for a pot. Additionally it needs some bacteria to decompose it, which could not be available on a pot. Note: on chemical fertilizers, one could choose the chemical components in order to have a fast or slow decomposition, on manure one has not such choice.

Acidity could cause some problems in the pot (direct or indirect, by reducing assimilation of some minerals). On ground the plants have longer roots, so they will find anyway some less acid ground. (anyway over-fertilizing causes also problems on ground)

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