Allotment Growing

Fertiliser Use for Best Vegetable Results

When you look at a farmer's field full of cauliflowers, all fat and looking wonderful and then look around the average allotment site's offering you have to wonder what the farmer knows that we don't.

The fact is that the farmer makes his living from his crops and invests in getting the best possible yield. First of all the farmer needs to know what the optimum nutrient supply for the crop should be, so he has the soil analysed to find out what is already there in his ground. From this starting point he calculates what he is going to need to add and decides how to add it.

The average gardener or vegetable grower isn't going to spend out for a laboratory soil analysis and there is an argument that providing the optimum nutrition for growth doesn't provide necessarily produce the best flavour either. High nitrogen supplies also tend to produce lush growth, beloved by aphids, so our pest problems can be made worse by too much fertiliser use.

Over-use of fertilisers is, from the farmer's point of view, a waste of money as there is no benefit to it. It can also cause environmental problems, causing algal blooms in streams and rivers.

Having said all of that, starving our plants is not going to produce good results and it's worth looking at what the nutritional requirements of our plants are and how we can supply them. Before we do that, it's important to understand what the components of fertilisers are and what they do - see What the NPK Means in Plant Fertiliser

Different fertilisers will provide different percentages of various nutrients so the quantity added will depend on the content. For example, if you want to add 10g of nitrogen per square metre you would need to add 83g of dried blood (12% nitrogen) or 50g of sulphate of ammonia (20% nitrogen) but if you wanted to supply that nitrogen from cow manure you would need 1,660g at its average 0.6% supply.

Of course, your cow manure will supply valuable humus that the fertilisers will not.

NPK Values of Common Farmyard Manures

Let's take a look at the N-P-K values of the most common farmyard manures. These are pretty variable according to the diet the animals have had, how long it has been rotted for etc but it gives a reasonable idea.

More information on farmyard manures

NPK Value of Home Made Compost

Your own home made compost has NPK values quite similar to those of animal manure:

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:

Although the percentage NPK values are relatively low in comparison with manures, being in liquid form, nutrients are immediately available to the plants.

More information on growing comfrey and comfrey tea or liquid fertiliser

In organic systems there is qualified acceptance of using 'natural' fertilisers to supplement nutrient levels achieved by composts and manures. These are

Unlike artificial fertilisers, the 'natural' fertilisers tend to dissolve slowly and thereby release their nutrients more slowly. More information on natural fertilisers.

Artificial Fertilisers

These are manufactured chemicals or sometimes mined and processed minerals. They are not usually approved for use in organic systems but they do not have any potential risks like pesticides to humans. More information on artificial fertilisers.

Straight fertilisers are those that purely supply one element, like bloodmeal or hoof & horn.

Straight Artificial Fertilisers:

Compound Artificial Fertilisers

Compound artificial fertilisers are produced by combining straight fertilisers in various proportions to form balances suitable for general growing or for specific crop requirements.

Many more compound fertilisers are available, often balanced to provide the NPK ratios favoured by specific crops such as tomato foods and incorporating various trace elements.

Trace Elements & Micro-Nutrients

Just as people need vitamins and minerals in their diet for long term health, plants require other elements in their diet to thrive. Many of the compound fertilisers add these trace elements just as vitamins are added to some of our foods. These other elements are covered in Additional Elements of Plant Nutrition and in Trace Elements or Micro-Nutrients of Plant Nutrition

Having covered the range and types of fertilisers available let's take a look at some specific plant requirements and how we can meet them The main element for growth is nitrogen. Nitrogen is vital to the production of the leaves, which in turn power the plant's growth and the more leafy growth a plant produces the more nitrogen it will require.

Because nitrogen has the shortest life in the soil, being easily washed out by heavy rain for example, it is the one element to concentrate on and with crops that are in the ground for a long time worth applying in stages rather than one go.

Nitrogen Requirements of Various Crops

Very High Nitrogen Requirement

• Brussels Sprouts
• Cabbages
• Rhubarb

High Nitrogen

• Beetroot
• Celery
• Leeks
• Spinach

Medium Nitrogen

• Broccoli
• Calabrese
• Cauliflower
• Lettuce

Low Nitrogen

• Asparagus
• Runner Beans
• Parsnip
• Swede
• Onion

Very Low Nitrogen

• Carrots
• Radish

No Nitrogen

• Peas
• Broad Beans

Remember that legumes produce their own nitrogen due to a symbiotic relationship with bacteria that fix nitrogen from the air for the plant, which is why peas and broad beans need no nitrogen and runner beans with all their foliage need just low levels to supplement their own produced nitrogen.

Specific fertiliser requirements and feeding plans for various vegetables are listed below under resources along with other articles in this section.

Resources

• NPK Basic Components of Fertilisers
• Natural Fertilisers
• Artificial Fertilisers
• Additional Elements in Plant Nutrition
• Trace Elements or Micro-Nutrients of Plant Nutrition
• Farmyard Manures - Improve Soil Fertility
• Fertiliser Tips
• Garden Lime, Why Lime, When to Lime & How Much to Lime
• Green Manures

See Also: Comfrey - Growing and Using

Test ph, NPK with this easy to use soil testing kit from Harrod Horticultural

Allotment Information