FERTILISERS

Photo: Senettia respond well to organic feeding.

The world of fertilisers can be a bit of a daunting one as there are so many different types to choose from, both natural and chemical. Like a lot of work in the garden, a bit of trial and error will be needed until the balance is right.

NOT TOO MUCH
Many gardeners apply fertiliser routinely rather than when the plants in their garden actually need it. This leads to a build-up of excess nutrients in the soil that are eventually washed out by the winter rains, causing pollution to groundwater and rivers. This is especially the case with inorganic or 'chemical' fertilisers, which is why it can be better to use organic feeds such as comfrey juice or well-rotted manure, where the risk to the environment is very much reduced. If you do apply chemical fertiliser routinely, do so only to those areas of the garden where demand for nutrients is high, such as the heavily cropped fruit and vegetable areas, flower beds and borders and plants that are cut back a lot, such as the lawn, rose beds or alongside a trimmed hedge. The amount you apply should also depend on the fertility of your soil. Sometimes isolated plants or whole areas of the garden can show symptoms of deficiency, especially on light sandy soils, and these need to be treated on a case-by-case basis.

A NEED TO FEED
Plants need a balanced diet of essential nutrients to grow well. There are three main plant nutrients - nitrogen (N), phosphorus (P) and potassium (K). Alan Titchmarsh used a simple method to remember what N P and K is used for. He thinks of these as a three-course meal: phosphorus is the starter, promoting root growth and general health; nitrogen, the main course, that's mainly needed for leafy growth; and potassium, the pudding, encouraging fruit and flower production. As a side dish, plants also need calcium, magnesium, and sulphur in smaller amounts as well a range other nutrients. The other nutrients Alan looks to as the vitamins, which the plants need in tiny quantities. These include iron, copper and manganese. Nutrients such as these are known as trace elements. Most soils contain all these essential nutrients.

IDENTYFYING NUTRIENT DEFICIENCIES
If a plant suffers from a shortage of just one nutrient this often can be identified by the unusual type of growth it produces. This can be tricky to diagnose in practice because symptoms vary with the severity of the deficiency and from plant to plant, but use the following as a guide:

Distorted leaves
Slightly distorted leaves, elongated in shape, reduced vigour…molybdenum (Mo) deficiency.
Shrivelled leaves, turning brown, fall prematurely…drought
Very distorted growth, pale white or yellow streaks…weed killer damage
Flattened and distorted growth on or near the growing tip…fasciation (leaning) disorder

Small leaves
Unusually small leaves, older leaves turn purplish colour…phosphorus (P) deficiency

Stunted growth
Stunted growth, yellowing leaves, older leaves die and fall…nitrogen (N) deficiency
Stunted growth, bluish-green leaves, older leaves have scorched edges…potassium (K) deficiency.
Stunted growth, pale green between veins, reddening with age…manganese (Mn) deficiency

Yellow leaves
Yellowing leaves, stunted growth, older leaves die and fall…nitrogen (N) deficiency
Young leaves yellow, paler at the margins…. calcium (C) deficiency
Young leaves yellow, bright green veins…iron (Fe) deficiency
Yellowish margin to older leaves, pale green between veins…magnesium (Mg) deficiency


How to treat nutrient deficiencies
Before you apply additional fertiliser, it is important to check that other factors are not the cause of your plant's distress. For example, iron (Fe) and manganese (Mg) can become chemically 'locked up' and unavailable to plants if the pH is too alkaline (eg on chalky soils) and applying more fertiliser will not help. Drought can also result in a temporary shortage of available nutrients.

Nitrogen (N) Apply a high-nitrogen fertiliser such as dried blood (organic), sulphate of ammonia (inorganic).
Phosphate (P) Apply a high-phosphate fertiliser such as bonemeal (organic), superphosphate (inorganic).
Potassium (K) Apply a high potassium fertiliser such as rock potash (organic) sulphate of potash (inorganic).
Magnesium (Mg) Apply Epsom salts to the soil or as a foliar feed.
Calcium (C) Apply garden lime such as ground chalk or calcium carbonate.
Iron (Fe), Manganese (Mn) or Molybdenum (Mo) Apply a fertiliser containing these trace elements or add seaweed to the soil or as a foliar feed.

Horticultural,environmental.