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I have many small shrubs, mostly flowers, ginger, onions and chili etc. I want to add some natural fertilizers to make them grow more. What is an efficient natural fertilizer?

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There are some differences between fertilizing shrubs and other plants, generally, and between different individual shrubs. But one thing I've noticed is that in your question, the plants you listed were:

  • Flowers
  • Ginger
  • Onions
  • Chili

Which are, for the most part, annuals or herbaceous perennials, not so much shrubs, although there are some shrubs in the flowers category. Anyway, I'll take the listed plants one by one and give my recommendations for organic/natural fertilizers.

Flowers

This is very general, but I'm going to assume that most of yours are annuals. It is good to know what the biggest nutrients (by volume uptake) that plants use are: Nitrogen (N), phosphorus (P), and potassium (K). This is called the NPK ratio in fertilizers, even processed organic fertilizers. But in my opinion, the best thing for soil is decomposed organic matter (eg compost).

Flowering uses lots of the nutrient potassium, so whatever you use, make sure plenty of this is supplied. Nitrogen stimulates top growth, so too much of this (ie, straight poultry manure or blood meal) will cause good, green growth, but will decrease flowering. Phosphorus is needed for the root growth, and for building up storage areas. Don't use huge amounts on most flowers, but it is necessary to use at least some.

Here are some fertilizers you can use:

  • Homemade compost

    enter image description here

    This is mostly for an increase in microbial soil life, and the organic matter (humus) content of your soil. The nutrient and mineral levels are extremely variable, and depend on what was put into the compost, but a good compost is usually a great micronutrient complex. It does not usually contain high levels of npk.

  • Bone meal

    enter image description here

    The npk is 3-15-0, on average, so it's a great root-feeder. You only need to apply once a year, as it breaks down and feeds slowly. It may attract neighborhood dogs, so keep that in mind.

  • Hoof and horn meal

    enter image description here

    This has an npk of 12-0-0, so it promotes strong green growth, but should be used in reasonable amounts. This stuff is awesome, because it is slow-release, and adds nitrogen to the soil over a long period of time.

  • Fish emulshion

    enter image description here

    Sustainability

    Sustainability is a real concern for anything made from living ocean organisms these days.

    The world’s oceans are in a state of near-collapse due to overfishing, destructive harvesting practices, and changing environmental conditions.

    This doesn’t mean everything that’s harvested from the sea is necessarily causing further environmental damage.

    Some fish products are more sustainable than others, so it’s worth checking out the specifics of the one you’re thinking about buying. If the seller can’t tell you where it comes from, I’d think twice about buying it.

    It’s also worth checking whether fish is the only ingredient in a product you’re considering using, since not only beneficial organic additions like seaweed and crab shells, but also non-organic materials are sometimes added to boost NPK.

    The npk is usually about 5-1-1, but very fast acting, so use moderately.

  • Wood ashes

    enter image description here

    They have an npk ratio of 0-1-3, so it is a great flower-booster, but should be used carefully, noting that wood ashes are extremely alkaline, and will raise the pH of soil.

Ginger

As a root (storage function) plant, these need a good bit of phosphorus, with lower amounts of potassium and nitrogen as compared with flowers.

Here are some fertilizers that will be good for ginger:

  • Homemade compost

    enter image description here

    This is mostly for an increase in microbial soil life, and the organic matter (humus) content of your soil. The nutrient and mineral levels are extremely variable, and depend on what was put into the compost, but a good compost is usually a great micronutrient complex. It does not usually contain high levels of npk.

  • Cottonseed meal

    enter image description here

    npk: 6-1-1.5. This is a good, neutral, balanced, general fertilizer that suits ginger. It is a byproduct of the textile industry, and be aware that depending where you source, it may be genetically altered, or contain trace amounts of sprayed pesticides.

  • Alfalfa meal

    enter image description here

    It has an npk ratio of 2-1-2, and is a super soil builder. You can even use it as a mulch, with amazing results. Be aware that it can be expensive, because of high production costs.

  • Bone meal

    enter image description here

    The npk is 3-15-0, on average, so it's a great root-feeder. You only need to apply once a year, as it breaks down and feeds slowly. It may attract neighborhood dogs, so keep that in mind.

Onions

These are also root crops, and require similar fertilization that ginger does.

Here are some important fertilizers you might be able to use for onions.

  • Homemade compost

    enter image description here

    This is mostly for an increase in microbial soil life, and the organic matter (humus) content of your soil. The nutrient and mineral levels are extremely variable, and depend on what was put into the compost, but a good compost is usually a great micronutrient complex. It does not usually contain high levels of npk.

  • Alfalfa meal

    enter image description here

    It has an npk ratio of 2-1-2, and is a super soil builder. You can even use it as a mulch, with amazing results. Be aware that it can be expensive, because of high production costs.

  • Bone meal

    enter image description here

    The npk is 3-15-0, on average, so it's a great root-feeder. You only need to apply once a year, as it breaks down and feeds slowly. It may attract neighborhood dogs, so keep that in mind.

  • Wood ashes

    enter image description here

    They have an npk ratio of 0-1-3, so it is a great flower-booster, but should be used carefully, noting that wood ashes are extremely alkaline, and will raise the pH of soil.

Chili peppers

These are fruit crops, and as such, require a good bit of potassium.

My fertilizer recommendations below:

  • Homemade compost

    enter image description here

    This is mostly for an increase in microbial soil life, and the organic matter (humus) content of your soil. The nutrient and mineral levels are extremely variable, and depend on what was put into the compost, but a good compost is usually a great micronutrient complex. It does not usually contain high levels of npk.

  • Bone meal

    enter image description here

    The npk is 3-15-0, on average, so it's a great root-feeder. You only need to apply once a year, as it breaks down and feeds slowly. It may attract neighborhood dogs, so keep that in mind.

  • Hoof and horn meal

    enter image description here

    This has an npk of 12-0-0, so it promotes strong green growth, but should be used in reasonable amounts. This stuff is awesome, because it is slow-release, and adds nitrogen to the soil over a long period of time.

  • Wood ashes

    enter image description here

    They have an npk ratio of 0-1-3, so it is a great flower-booster, but should be used carefully, noting that wood ashes are extremely alkaline, and will raise the pH of soil.

  • Animal manure

    enter image description here

    This shouldn't be used on root crops unless thoroughly broken down, but it makes a great fertilizer for peppers. The npk is usually high, but extremely variable, depending on species, gender, age of the manure, the animals diet, etc. Side dress the plants at any time for great results.

7

As with virtually anything in Permaculture the answer is going to be, "It depends." What resources do you have on hand? What are you willing to do? Are you wanting a fix for "right now" or are you wanting something more long term?

The answer, in general, is going to be compost. Depending upon how it's made, what is in it and where it's from that's potentially the "best" fertilizer for the plants you are wanting to grow. Leaf mold comes in a close second in my book though I generally use that for the more woody/perennial plants and only occasionally on my annuals.

Another option is worm castings from worm farms. Once you get a worm farm or two going they are fairly easy to maintain and produce 2 kinds of fertilizer; Worm juice, the runoff (leachate) from the maintenance of the moisture levels of the casting substrate (see addendum below) and the finished worm castings. Both are fantastic for upping fertility of virtually any growing area, indoors or out.

If you would like other alternatives or ideas then you're going to need to give some more details about your particular setup and needs.

EDIT: Addendum - After some research thanks to the comments by THelper I'm now in agreement that the so-called Worm Juice (lechate) that comes from maintaining the moisture levels is not a good fertilizer. That said, it still can be used to boost fertility, just a bit more indirectly than dumping it straight on soil around your plants. Apparently one needs to pour the lechate over a highly carbonaceous material like sawdust or shredded cardboard/newspapers and allow it to break down for a period of time. Another method is to just dump it on your compost piles. Once that breaks down you can then use the resulting compost to fertilize your plants. Basically you just add an extra step and a bit of time and you get the second fertility booster of vermicomposting, just in a safe and healthy way. Also, one can utilize worm castings in the production of Worm Tea, which is not the same thing as the runoff that comes from maintaining your worm farms. Hope that clears things up.

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    Welcome to Sustainable Living! Good answer! There is however one thing I disagree with and that is the leachate. Many people believe that leachate is a wonderful fertilizer. It can be, but the problem is that leachate can also be full of toxins so a word of warning there. More info here – THelper Apr 22 '14 at 11:59
  • Hey there. Thanks for the welcome! It's a fair point though I would add that many composts created with "toxic" ingredients would suffer from much the same issue depending upon what the toxin is and if it can be broken down via the composting process. For example if you throw plant matter that has been used in bioremediation of heavy metal concentrations on your pile, your compost is going to have high amounts of the heavy metal. All this means is that Worm farms and their leachate suffer the same limitations that composting does, plus a little bit extra. – m.w.jacobsen Apr 22 '14 at 14:04
  • Of course everything can be polluted with toxins, but the reason I'm mentioning leachate is because a few years ago most people thought it was a great fertilizer, whereas nowadays more and more people are warning against it. Leachate might be a much bigger risk than (vermi)compost. – THelper Apr 23 '14 at 7:22
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    I've never heard the issues with leachate. Could you share sources? – michelle Apr 23 '14 at 13:20
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    @Michelle, Wikipedia or this page and this page all explain it nicely – THelper Apr 29 '14 at 7:21
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Humic acid is the ultimate organic fertilizer. Google it also under Humates. It's not actually fertilizer but it is that which makes rich black earth black and rich. All plants love it. It is what they have been using for hundreds of million years to transport nutrients from the soil and into their roots. Most of the humic acid used here in Vancouver comes from a 20 million year old deposit on the Canadian great plains ( Saskatchewan Province )

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