Horfield and District Allotments Association

Manuring our Allotments


Manuring Our Allotments

This is a complex subject and doubtless large portions of degrees on agriculture and horticulture are set around this subject.  If you can get hold of a copy of a book, now out of print – Know and Grow Vegetables –P.J.Salter;J.K.A. Bleasdale; and others – from The National Vegetable Research Station, it is a unique, interesting and  comprehensive study of many aspects of vegetable growing.

However, most plot holders just want to know which of the manures available will give the best results on their plots.

It must be remembered that adding any organic manure will contribute to the acidity of the soil due to the breakdown process of the compost. But, for most plotholders on our heavy clay ground, adding organic matter, no matter how poor in essential nutrients, helps to break down the heavy structure of the soil and allows for freer drainage and greater nutrient uptake – of course, it is more complicated than that.

As a simplification of the needs of plants – Nitrogen[N] is used for leaf growth, Phosphorus[P] is for seed germination and root growth and Potassium [K]  for flowers and fruit.

Not all of our members are dedicated organic growers and their choices must be respected though, continued addition of non-organic fertilisers brings its own problems and there is an argument to suggest it is not sustainable.

I have gained the following information from:




NPK Values of Animal Manures

                             N Nitrogen %   P Phosphorus %     K Potassium % [potash]

Cow Manure                 0.6                       0.4                        0.5

Horse Manure                 0.7                       0.3                        0.6

Pig Manure                 0.8                       0.7                        0.5

Chicken Manure        1.1                       0.8                        0.5

Sheep Manure                 0.7                       0.3                             0.9

Rabbit Manure                2.4                       1.4                        0.6



Growers usually have a preference for either cow of horse manure but, for the most part it does depend on what is available and how much straw [or even hay] is mixed in. Of course, the addition of the straw is very useful for improving the quality of your soil, particularly in heavy clay. Resist the temptation to add fresh manure to your ground – it too strong. At least pile it up, cover it with a plastic sheet, a tarpaulin or an old carpet and leave it for a couple of months – longer is preferable.

With all poultry manure it is generally too strong to use directly on the garden but it does make an excellent activator for a compost heap. There is little bulk in poultry manure so using it as an activator makes most sense. The only plant that you can apply it to directly is comfrey.


NPK Value of Home Made Compost


                                            N Nitrogen % P Phosphorus % K Potassium%

Average Home Made Compost       0.5                        0.27               0.81


NPK of Natural Fertilisers


                                          N Nitrogen %               P Phosporus %                K Potassium %

Bloodmeal                                  12                                  0                                       0

Bonemeal                         3.5          18                 0

Hoof & Horn                 12            0                          0

Fish, Blood & Bone      6        6                                      6        

Chicken Manure Pellets           4          2.5                2.3




NPK - Liquid Comfrey – although low, it is immediately available to plants


Having covered manures and compost, the next thing to look at is a fertiliser you make yourself, comfrey tea. Following the recipe of 6 Kg (14lbs) of wilted comfrey in 90 litres (20 gallons) of water in a barrel, produces a liquid feed with these values

N Nitrogen % P Phosporus % K Potassium %

Comfrey   0.014          0.0059    0.03440




That said, none of these tables shows the availability of or the importance of the trace elements. And, how do we ensure our plants have enough of these to assure excellent growth and crops. Have a look at the page on adding lime where a table of the 12 essential nutrients, which includes the trace elements, is available.


MMcC  -November 2012