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Is it OK to use human waste or spent cat litter directly into the soil where you grow fruits and vegetables?

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    Related: Is it okay to locate a garden on top of a septic drain field? The answer is the same; it's not a good idea. And for the same reasons. 'With edibles, there is a risk of pathogenic contamination, so I wouldn't recommend it. It does pose a health issue, and although people do/have done it it is not a good idea.' – J. Musser Oct 2 '14 at 21:27
  • We adopted in a stray kitty that hung around the yard - she hated litter, so when we noticed her peeing in her bucket of cat nip, we started filling her box with potting soil. We scoop out and flush all the solids, then let the soil cook in full sun for a few weeks before using it in the bottom few inches of 15 gallon buckets with young fruit trees, which won't be bearing fruit for another couple seasons anyways. The soil is actually a lot cheaper than litter and does a better job of odor control. But I would never use the recycled soil on vegetables or anything you plan to eat this season. – WebChemist Oct 3 '14 at 7:46
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Not unless you particularly fancy a dose of e-coli, worms, parasites and a host of other enteric nasties you could be infected with from using it.

Generally speaking, manures from herbivores are okay, but even those must be composted prior to use, so composted animal manures are fine - but only if you're not growing root crops such as carrots or parsnips, which will fork if they're in manure enriched soil. And a word about 'fertiliser' - there are two approaches used to feeding plants in the ground, often used in combination. When you apply humus rich, composted materials (such as animal manure or leaf mould or spent mushroom compost or garden compost, anything like that) you're actually improving the soil, and the bio diversity within it, and its general mineral content, depending what you use, thus enabling your plants to access the nutrients they need themselves. You can also feed plants directly by using proprietary 'chemical' feeds such as Growmore or fish blood and bone or any of the other hundreds of proprietary fertilisers. You may, for instance, choose to use tomato food on tomatoes, even if you're growing in the ground, and the ground has been enriched with humus materials beforehand, because that tomato food supplies nutrients tomatoes particularly need.

In some parts of the world, human excrement is used as fertiliser, but not without processing first, usually using high temperatures to kill off the nasties.

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    And if you are concerned with organic gardening, processed human waste (aka Milorganite) is considered by some to be a no-no - even in organic landscaping. – That Idiot Oct 2 '14 at 17:51
  • Along the lines of organic gardening, if any of the humans (or pets, for that matter) are taking certain medications, they may get into your soil, stay there for quite a while, and could get into other living organisms (probably plants, too). Also, there's toxoplasmosis. It's a protozoan infection you don't want. It's common in cat urine (cat urine may or may not be safe for tall plants like trees and stuff, but I wouldn't put it on spinach or peas where it might get on/near the edible portions). – Shule Oct 9 '14 at 17:13
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If you are going to do what you ask, use human and pet wastes to fertilize your 'fruits and vegetables', there are a couple of things to keep in mind:

1. Processing waste material

Human wastes can and have been used to fertilize crops. The city of Milwaukee sells Milorganite to farmers, which is just processed human waste from the city.

A good minimum for home preparation of human solid wastes is layered with a substance like sawdust or ash, left 2 full years sealed off, then composted with other organic matter for another year.

2. Application types

To apply organic fertilizer to fruit trees or bushes, you can spread out the fully composted mix in a radius around, but removed from the trunk. Lightly incorporate into the soil, then cover dry organic material.

Incorporating your fertilizer into soil for vegetable crops (like roots, but even lettuces, less so vines) is where you are going to want to be careful. Human wastes contain harmful microlife, so you will want to be very confident in your process (maybe even going a bit too far). The risks are high so it really is recommended not to use this home mixture for direct application on annual vegetable crops.

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It depends on what you mean by human waste.

If solids, then these need to be composted first. A hot composting system can render these into compost in 18 days and can kill off all pathogenic microbes.

If not, then you need to leave it for longer, up to 2 years depending on the composting method.

If liquid, then it needs to be diluted before being delivered to the soil otherwise you might burn the roots. Urine has a NPK ratio of approximately 10:1:4, and needs to be supplemented with wood ash if you want to use these as a complete fertilizer.

http://permaculturenews.org/2011/11/27/urine-closing-the-npk-loop/

Note that pathogenic e-coli can be taken up into the stems of plants so don't use untreated urine if you have a urinary tract infection.

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