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Organic fertilisers: how manure and other goodies can help your vegetable garden

The most important difference between organic and chemical fertilisers is easy to remember: organic feeds the soil through slow release, chemicals feed the plants directly with an immediate injection. In our first feature we already cover why organic is better. Organic growing improves the soil, encourages earthworms and good bacteria, which give your plants a natural boost. Chemicals can kill these earthworms and good bacteria.

Now Please tell me what I need to Know

So instead of grabbing chemical fertilisers in a box why not follow the ways of many successful gardeners and go organic. Fertilisers are normally expressed by their NPK rating. This is the ratio of nitrogen (N), phosphorus (P) and potassium (K) - all vital ingredients in a rich soil.

Put simply nitrogen makes all the green stuff grow like crazy. Phosphorus makes the roots strong and gives flowering a boost. And potassium keeps the juice pumping through the plant, helps your plants during difficult times (very low or high temperatures, lack of water and during disease) and gives fruit and seed production a push along. They're all critical to healthy plants.

Also of importance is calcium which prevents new growth from dying and a swag of problems. Sulfur is also important in keeping growth going. Then there are the micronutrients. All those small quantities of other nutrients which maintains plant health. Fortunately mother nature (sometimes with a little processing help by mankind) has all these elements in abundance so you can give your soil a boost.

One thing to always remember when handling manures, soil or any organic matter is to always wear tough gloves to protect you from bacteria getting into any cuts.

Manures

Matured animal manure is one of the most important things an organic gardener can get their hands on (while wearing gloves of course!) Manures are generally good all rounders having a fair amount of nitrogen and a little bit of everything else, including very small amounts of micronutrients. You should be able to easily buy bags of aged manure from your local nursery. Mature manure has had time to rot down a little, losing its volatility which can "burn" plants. If you have access to fresh manure make sure it "cools" down. Pile it up and let it rot down for 6-8 weeks, making sure it's covered to keep flies away and to stop rain leaching the nutrients out. You can also add it to your compost heap.

The next big question is what manures are better for your garden? This varies depending on what you want to achieve. Chicken manure (fresh or in processed pellets) is very high in nitrogen. Plants boom with chook manure (maybe they're trying to grow away from the smell?) But chicken manure is lacking in almost all other nutrients. The rest of the stable (literally) is more balanced. Sheep, cow and horse manure are well rounded fertilisers which will help boost the organic content of your soil.

Compost

Compost is fantastic. Rich in NPK and packed with micronutrients and micro-organisms it is a must. Problem is you can rarely buy it in a bag from the nursery although this is changing. You generally have to make your own. Making compost is an important enough topic to have its own feature. We'll aim to write it over the next month.

Mushroom compost

This you can easily buy in a bag. It's a bit of a mix between compost and manure. Afterall, it's just horse manure which has rotted down and had mushrooms grown in it. It doesn't have as many nutrients though as most organic fertilisers. But it's great for bulking up the organic content of the soil. A good use for mushroom compost is when you start making your vegetable patch. The root crop and onion bed doesn't like a lot of nitrogen, but needs organic matter. For this bed mushroom compost is very handy.

Blood meal

This is packed with nitrogen. Every wonder where the cows go after they've made the steaks? Now you know. It's fantastic for promoting green growth and micro-organisms in the soil love it. In Australia you won't find blood meal as a distinct product. It's usually packaged with bone meal and marketed as blood and bone - and it's the best stuff you can get!

Fish meal

Now take the cow analogy and apply it to fish. Fish meal is a great nitrogen-phosphorus all rounder with a lot more N and P than manures. It's higher in phosphorus than blood meal as it includes crushed and processed fish bones.

Fish liquid fertilisers

Just like fish meal but in a liquid rather than a powdered form.

Bone meal

Blood meal's brother but packed with phosphorus instead of nitrogen. The good part about bone meal is it breaks down quickly for faster use by the plants.

Rock phosphate

This is nothing more than crushed rock high in phosphorus. Sprinkle it around for a slow up take of phosphorus.

Sulphate of potash (or Sul-po-mag)

Sounds like a chemical fertiliser but it's not. This mineral product has an incredible amount of potassium which is good news for fruiting vegetables (eg tomatoes, peppers (capsicums and chillies) etc) and your fruits (including melons and all fruit trees). Because it's so packed with potassium you don't need huge qualities, just a nice sprinkle around your plants (1 part to 10 parts of blood and bone meal will give you a great all round fertiliser). It's also readily available which is very handy when your fruits are forming. Sulphate of potash is also very high in sulfur which keeps your plants healthy. In Australia, you can only get suplhate of potash, not sul-po-mag so you'll miss out the magnesium side of things (which you can get in dolomite...)

Lime

Normally when you think lime you think about increasing the pH level of your soil. But it is also a handy source of calcium. If you can get your hands on dolomite lime you'll also get an added boost of magnesium.

Gypsum

If you've already got a very alkaline soil and don't want to risk adding lime try gypsum. It's not only a clay breaker it's also rich in calcium and sulfur.

Liquid seaweed fertiliser

This is one of the best organic fertilisers you can get. It's made up of lovely seaweed found in colder seaside climates, not the grassy trash around here. It's fantastic not so much for NPK, but for the micronutrients and trace elements not often found in most of the fertilisers above. We use a capful of concentrated seaweed fertiliser with a litre of water to dilute it. Sprayed onto the leaves early in the morning it is absorbed to give a real boost. You can also give a bit of a spray at ground level onto the mulch where it will eventually seep down to the roots. One fertiliser you've got to have.

Liquid manure (compost tea)

This is a real make your own organic fertiliser without much science involved. Get a nappy bucket or small rubbish bin and fill it with water (We find the nappy bucket is a lot more manageable). Then either mix in, or put into a hession bag, all your organic goodies. We usually toss in manure, a little compost, blood and bone meal, a capful of concentrated seaweed fertiliser, add a few comfrey leaves and give it a good stir. Put a lid on it to keep the smell in (because it does smell) and the flies and mosquitos out. Around a week later we put 2 litres of the mix into a 10 litre watering can and then add 8 litres of fresh water (1:4 ratio). This dilutes the mix otherwise it's too strong. The ratio can sometimes blow out to 1:6 as it is very potent at the bottom of the bucket. Then we start pouring it into the soil around our vegetables and fruit trees. Done every 2-3 weeks this helps keep your plants healthy.

Green manure
Two green manure crops: the background crop has just been dug in, while the younger crop in the foreground is just getting started

Green manure

During slow growing seasons you can boost the organic nature of your soil by growing green manure. Sounds odd but green manure is just plants that are dug into the soil to add organic matter and improve its quality. One of the key ingredients in green manure are legumes which fix nitrogen into the soil. To get the best nitrogen boost though you need to make sure the seeds are inoculated with a special bacteria.

You normally sow green manure into a bed which has had its nutrients sapped by a hungry earlier crop, like sweet corn, pumpkins, cucumbers and melons. Till the soil before hand and toss around a mix of green manure seeds. This is done early in winter in cold climates and early in summer for very hot and humid climates. Then with a rake cover them a bit, water and walk away. Around 2-3 months later you should have a lush knee high mat covering the bed. Then all you have to do is dig it into the soil where it breaks down over 1-2 months. Once you've done this the bed is ready for the next crop and the soil is even better than when you started.

For cold climate winter green manure go for:

  • Lupins

  • Tic beans

  • Oats

  • Subclover

  • Fenugreek

  • Barley

  • Woolly pod vetch

For humid and hot summer green manure go for:

  • Cowpea

  • Japanese millet

  • Grey sun flower

  • Buckwheat

  • Lablab

Last updated 23 October, 2008

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