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Organic Gardening:

How to use organic fertilisers and manures


There are lots of organic fertilisers in use, but many of them come with no instructions. So how do you know what to do with them? Not every fertiliser is suitable for every situation, and it can be confusing for a beginner just starting out.

Your basic fertilising toolkit should really contain a good broad fertiliser such as blood, fish and bone, a bottle of liquid seaweed fertiliser to give a quick boost and for use as a foliar feed at half strength, plus comfrey liquid if you will be growing fruiting crops like tomatoes, courgettes (zucchini) or, indeed, fruit.

But if someone offers you something you've never used before, it helps to know what you can do with it. This table puts the when, where and how much of various organic fertilisers at your fingertips.

Important Note: Figures for NPK given in the table do not reflect the percentage of each nutrient, but the proportion of each in comparison with the other two.


Material Notes N P K per sq. m/sq. yd
Animal hair Slow to break down, a good slow-release source of nitrogen 3.8     250g/8 oz
Bark, composted Contains little nutrient value, but high in humus. Particularly good as mulch.
Bone meal Sometimes available as bone flour and crushed bones Good for light soils. 4 12 - 85g/3 oz. 112g/4 oz for fruit bushes
Bracken Burn when green in a slow bonfire.     2 450g/1 lb
Calcified seaweed Every 3 years   1 1 6 oz (trees 10 oz)
Chicken manure Very strong manure that should be stored for several months before use. Useful as a compost activator. 3 2 2 25-50g
Compost Can be used as a mulch 3-4" deep. 0.5 0.27 0.81 1 barrowload per 4.5m (15') row
Dolomite (magnesium limestone)* Neutralising agent and to prevent magnesium deficiency.       113g/4 oz
Dolomite & gypsum* Lightens heavy clay: Apply in spring and October/November at 340g/12 oz and then 85g/3 oz in following years.       250g/8 oz
Dried blood Dissolve in 1 litre of water, standing for three days and stirring occasionally, or sprinkle round the plants and then with water with a fine rose and tease into the surface. 12     56g/2 oz
Farmyard/cow manure (Well-rotted) Excellent soil conditioner. High in nutrients and humus (from straw). Not for mulching. 0.6 0.4 0.5 140g/5 oz
FeathersNot for use on clay. Dig in during autumn and winter. 2     140g/5 oz
Fish, blood and bone Apply in early spring and repeat when crops are about half grown. 6 6 6 56g/2 oz
Fish meal Very expensive. 2 3 1 85g/3 oz
Goat manure Compost with straw. 2 2 2 50 kg/1 cwt
Grass clippings, fresh Good addition to the compost heap, in thin layers only. Can also be used as a mulch. 0.66 0.19 1.55 -
Grass clippings, dried Good addition to the compost heap, in thin layers only. Can also be used as a mulch, but may blow away. 1.2 0.4 0.71 -
Green manures See >separate table..
Hoof and horn Add about 56g/2 oz to each bucketful of potting soil. Do not use on spring cabbage, spinach, Swiss chard or sprouting broccoli. 12     112 kg/4 oz
Spent hops Soil improver. Little nutrient value but useful as humus source or mulch.       1-1.5 kg/2-3 lb
Horse manure Only if mixed with straw, rather than wood shavings. Compost well first. 0.7 0.3 0.6 1 barrowload per 4.5m (15') row
Leaf mould Soil conditioner. Beech and oak are best. Avoid evergreens. Can also be used as a mulch. Always rake aside in winter, to allow birds to find and eat pupating pests. 0.5-1   0.25-0.75 2.25 kg/5 lb
Leaves A new garden full of raw subsoil can have up to 6 inches of raw, dead leaves spread on the surface and rotavated through the top 8 inches or so, which chops them and distributes them through the surface layer. Give two cultivations, and before the second one spread up to 450g (1 lb) a square yard of lime to correct acidity.
Do not mix with manure
Neutralising agent
Quicklime must be slaked before use: 750 g/1.5 lb max.
Hydrated lime: 112g/4 oz, 250 g/½ lb on heavy soil.
Dolomited limestone: 500g/1 lb max
Carbonated lime for light soils: 168-250 g/6-8 oz.
- - - Depends on pH of soil
Manure with peat Not suitable for organic gardening.
Municipal compost May contain heavy metals and fragments of glass and plastic. Do not handle with bare hands. Not really suitable for organic gardening unless certified organic (which some are nowadays).   1 1 1.35 kg/3 lb
Spent mushroom compost Avoid compost made entirely from straw composted with chemical activators and no horse manure. Best composted first. Contains chalk, so not for use on alkaline soils or lime hating plants. 1 1 1 1.35 kg/3 lb
Peat Not suitable for organic gardening
Pig manure, rotted Contains copper. Must be composted for at least 8 months before use, preferably with plenty of vegetable matter. 0.8 0.7 0.5 38 kg/0.75 cwt per 4.5m (15' row
Pigeon manure Can be used moist as a compost activator. 11-16 8-12 2-3 250g/8 oz dried
Plant ash   - 1 6 500g/1 lb
Rabbit droppings Nutrient value improves when composted. 2.4 1.4 0.6 500g/1 lb dried
Rock phosphate A slow-release source of phosphorus. One dressing will last at least 3 years. - 3-8 - 8oz
Rock potash Particularly useful for tomatoes, potatoes and gooseberries. Remains in the soil for about 3 years. - - 60 250g/8 oz
Sawdust Used as a mulch around gooseberries and currants. Sprinkle a general fertilizer underneath to avoid leaching the soil as it rots.
Seaweed Very good soil conditioner containing valuable trace elements. Best dug in, as once it dries out, it becomes light enough to be blown away. Since it contains salt, it is best to stack it (with a porous cover, such as sacking, to prevent wind loss) and either wait for a good rainstorm, or soak it really thoroughly with a hosepipe before use (or use sparingly). 1.68 0.75 4.93  
Seaweed meal Use as a spring lawn tonic at 112g/4 oz. An excellent compost activator. 2 2 2 56g/2 oz
Sewage sludge Use only digested sludge. Contains heavy metals - best used for ornamentals only. Use in early spring and again when crop is about half-grown. Can also be used at 3 parts to 1 part seaweed meal as an excellent compost activator. Can also be used on the lawn before the first spring mowing at 224 g/8 oz. 2 2 2 168 g/6 oz
Shoddy Waste material from wool and cotton manufacturing. An excellent slow-release source of nitrogen and humus. 3.8 - - 500g/1 lb
Soot Use only on neutral or alkaline soils. Old gardeners used to use this to 'darken' lighter soils to aid heat retention. 1      
Wood ash Must be stored very dry. The best ash comes from tree thinnings and fruit tree prunings, used as soon as it cools. - 1 6 4 oz maximum
Wood chips, composted Contain little nutrient value, but high in humus. Particularly good as mulch. As it robs nitrogen, it is wise to sprinkle some Fish, Blood & Bone on the surface before applying.
Worm compost Use in potting compost and as a mulch. 2 2 2  
* Do not mix any type of lime with manure; ammonia will be released and nitrogen lost.

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Article ©2004 Frann Leach. All rights reserved.

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