Feeding Plants: Manures & Fertilizers

By Alex N

Just like people, plants need a regular supply of food if they are to flourish. The main ways of feeding your plants are by applying fertilizers and bulky organic matter (like manure) to the soil.

Manure supplies some nutrients, but its most important function is to improve the soil structure by adding organic material. This turns the soil into a healthy medium in which plants can thrive. Chemical fertilizers artificially provide some, or all, of the basic plant foods.

When digging, particularly in late autumn or early winter, it is wise to incorporate in each trench well-rotted farmyard manure, garden compost, sea­weed or mushroom compost. These materials will supply bulky organic matter and a variable amount of plant food. None of them, however, supplies adequate nut­rients for the plants to make optimum growth; therefore fertilizers will have to be added at planting time to ensure that the plants have sufficient food.

The organic matter is digested by bacteria in the soil and turned into humus. This humus is like a sponge; it holds water and prevents rapid drying- out of light soils. It also helps to break up sticky clay soils by improving drainage. Organic material is, therefore, essential because it improves the soil’s structure.


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Never apply manure at the same time as lime (calcium). This is because the lime can liberate any available nitrogen in the form of ammonia, which may then be lost through evaporation. Also, never grow root crops on ground where fresh manure has been used, for your vegetables may well produce deformed roots.

Always ensure the manure is well rotted. It should be dark in color, have a light crumbly texture when dry and a sweet smell. If it’s green and slimy and smells of ammonia then it is too fresh to add to your garden and can kill young plants by burning the leaves shoots and roots.

Seaweed as manure

If your garden is near the coast, use seaweed as a manure. It is excellent for digging - wet or dried - into the soil in the autumn. Seaweed is one of the oldest manures known and contains many plant foods. It is now possible to obtain specially refined seaweed manures from gardening shops.

Manure for mulching

Well rotted manure or garden compost makes a good mulch for established plants such as trees, shrubs, top and soft fruit, vegetables, and established flower borders. Place a layer of mulch, 5-8cm (2-3 in) thick, around the plants in spring. It will then provide some food and humus and help prevent evaporation of moisture from the surface soil.


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Bulky organic matter is not capable, by itself, of supplying all the foods the plants will require, so fertilizers must also be added to the soil.

As a general rule, dry fertilizers should be applied to moist soil, or else well watered in after application if the ground is dry. Always apply them evenly, and discard or break up any lumps; these can ‘burn’ roots. Apply all fertilizers carefully and according to maker’s instructions. If you exceed the recommended rate of application you may seriously injure or even kill your plants.

Before sowing or planting, the usual procedure is to rake in a dry fertilizer which contains the major plants foods (nitrogen, phosphates and potash). There are many of these ‘general-purpose’ or compound fertilizers on the market. Probably the best known is National Growmore, which is available under numerous brand names. This is suitable for all vegetables, fruit and flowers. You can also apply it as a top dressing in spring or summer by lightly raking it into the soil surface around any of your established plants.

Special dry fertilizers for specific crops (such as roses and tomatoes) are avail­able. These contain the correct balance of nitrogen, phosphates and potash suited to the particular plant.

Lawn fertilizers

There are several proprietary lawn ferti­lizers which make the lawn ‘green up’ quickly and grow well due to the high proportion of nitrogen they contain. Feed your lawn once or twice during spring and summer to ensure a lush, deep-green sward. Autumn lawn fertilizer, which is applied in mid autumn (September), contains more potash; this helps to ‘ripen’ the grass and make it more resistant to hard winter weather.

‘Straight’ fertilizers

You can also apply ‘straight’ fertilizers to plants, especially as a supplement to the ready-mixed, general-purpose kinds ap­plied earlier in the growing season; but you must be aware of specific food requirements of individual plants before trying out these fertilizers. Be sure to handle them carefully and accurately.

Sulphate of ammonia and nitro-chalk supply nitrogen which encourages plants to make lush, leafy growth. They are quick-acting fertilizers and should be used very sparingly. They can be used on lawns and also on green vegetables such as cabbage, kale, broccoli and spinach. Apply them in spring and summer only.

Sulphate of potash and muriate of pot­ash both supply the potash (potassium) essential for the production of fruit and flowers. It also helps to ripen the stems, which is necessary for the successful overwintering of all hardy plants. Potash can be applied in summer or early autumn. Wood ashes contain potassium and, once they have weathered for 3-6 months, can be dug into the soil during autumn digging or raked into the surface.

Superphosphate of lime supplies phos­phate (phosphorus). This is also essential for good root production and all-round growth. It is usually applied in spring and summer at the rate of 3g per litre 1/2 oz per gal.) of water and applied to the soil around plants about once a week.  Avoid getting it on the foliage.

Liquid fertilizers

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Use liquid fertilizers in conjunction with powdered or granulated fertilizers - not as a substitute. They should be considered supplementary feeds to boost the growth of plants. They are generally used in the summer when plants are in full growth. Being liquid, they are quickly absorbed by plants and rapidly stimulate growth.

Dilute liquid fertilizers according to the manufacturers instructions, and apply them to moist soil. Use them as frequently as once a week and on all kinds of plants in the house, greenhouse and garden. You can apply them most easily with a ‘rosed’ watering can.

There are many brands of liquid fertilizer on the market, some of which are formulated for specific crops.

Foliar feeding

Foliar feeding is a comparatively recent technique of applying liquid fertilizers to plants. The fertilizer is sprayed or watered onto the leaves where it is quickly absorbed by the plants and circulated in the sap stream. The nutrients are made im­mediately available to plants. This makes them particularly useful to transplanted plants before their new roots have become established.

You can buy special foliar feeds from gardening shops. Alternatively you can apply any liquid fertilizer to the foliage and it will be quickly absorbed.

Sulphate of ammonia can be dissolved at the rate of 3g per litre (| oz per gal) of water and applied to leaves to promote growth of foliage. Likewise sulphate of potash will encourage fruiting and ripen­ing of growth.


Lime is another plant food and this is applied on its own, generally in the winter after autumn digging, in the form of dehydrated lime. It is mainly the veget­able plot that will require lime and an application every two or three years will be adequate.

Lime lowers the acidity of the soil, and as many plants (especially vegetables such as brassicas) do not thrive in an acid soil, liming enables you to grow a wider range of plants. But do not lime if you have a naturally alkaline or limy soil with a pH of 7 or above. Hydrated lime is the type generally used.

If you would like to learn more about gardening why not consider taking one of MyGardenSchool’s 4 week online gardening courses click here for details

Alex N

I'm passionate about online learning, and lucky enough to work for Learning with Experts. Most recent course: The Pie Shop with River Cottage's Tom Morrell. Next course: Container Gardening with Chris Beardshaw.

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