Describe what is meant by the pH terms: acidic, neutral and alkaline/basic.

PH SCALE he concept of pH was introduced by Danish chemist Soren Sorensen in 1909. The exact meaning of p is unknown, often referred to as “Power of Hydrogen” or some say “Potential Hydrogen”.

The pH of a solution is a measurement of its acidity or alkalinity and is defined as “The negative logarithm of the hydrogen ion concentration”.

The full scale runs from 1 to 14 and is logarithmic; 7 is considered as neutral – neither acidic nor alkaline; Below 7 is the acid range; Above 7 is the alkaline range;

SOREN SORENSEN (PERSON) The concept of pH was introduced by Danish chemist Soren Sorensen in 1909.

POWER OF HYDROGEN

POTENTIAL HYDROGEN

ACIDITY

ALKILINITY

State the pH range found in garden soils (approx 4 – 8).

SOIL PH The range of garden soils is given by the RHS as 4-8 though some books go to 8.5.

State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.

Normally: Plant growth of a great range of plants is good in the range of 6→7.5; A good pH for most gardens is 6.5 as it suits “most plants” and most plant nutrients are readily available (this alters slightly according to the soil’s texture).

Soil Structure (soil organisms, crumb formation): Worms dislike acid soils and so such soils have few worms. Worms secret alginate into the soil that acts as a soil glue creating good soil structure. Calcium products can be used to help break down clay soils chemically, so improving the structure (calcium carbonate and hydroxide will alter the soil pH, calcium sulphate will not). Soils with natural high free lime content (calcareous clay) will not respond to the application of lime products.

Nutrient Availability: See above. Nutrient availability is affected by both soil pH and soil texture.

Lime Induced Chlorosis: Where the free lime in the soil locks up iron and magnesium molecules in the soil and makes them unavailable to the plants. This causes a mineral deficiency with iron showing up as yellow young leaves and magnesium as yellow inter-venial patches on old leaves (treat plants with sequestrene of iron).

State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.

SOIL PH The range of garden soils is given by the RHS as 4-8 though some books go to 8.5.

State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.

Normally: Plant growth of a great range of plants is good in the range of 6→7.5; A good pH for most gardens is 6.5 as it suits “most plants” and most plant nutrients are readily available (this alters slightly according to the soil’s texture).

Soil Structure (soil organisms, crumb formation): Worms dislike acid soils and so such soils have few worms. Worms secret alginate into the soil that acts as a soil glue creating good soil structure. Calcium products can be used to help break down clay soils chemically, so improving the structure (calcium carbonate and hydroxide will alter the soil pH, calcium sulphate will not). Soils with natural high free lime content (calcareous clay) will not respond to the application of lime products.

Nutrient Availability: See above. Nutrient availability is affected by both soil pH and soil texture.

Lime Induced Chlorosis: Where the free lime in the soil locks up iron and magnesium molecules in the soil and makes them unavailable to the plants. This causes a mineral deficiency with iron showing up as yellow young leaves and magnesium as yellow inter-venial patches on old leaves (treat plants with sequestrene of iron).

State the effects of soil pH on soil structure (soil organisms, crumb formation) and nutrient availability (lime induced chlorosis).

CALCIFUGE acid-loving lime-hating True Acid Loving Plants (or calcifuge lime hating): Such as Rhododendrons “Pink Pearl”, Camellia “Donation”, Pieris japonica need acid soils pH range of 4.5 →6.5.

CALCICOLE lime-loving, acid-hating True Acid Haters (calcicole lime loving): Such as Clematis tangutica, Dianthus barbatus, Viburnum tinus need alkaline soil pH 7.25 and above 8.

ALGINATE

LIME INDUCED CHLOROSIS

FREE LIME

Identify materials used to influence the soil pH (lime, sulphur and organic materials). State the benefits and limitations of each (environmental, health and safety issues, timing of application, effectiveness of the material).

SOIL AMENDMENT altering soil ph etcd

LIME

CALCIUM CARBONATE see also calcium hydroxide will raise the soil pH; Fairly cheap to purchaser; Quick effect on soil.

Limitations: Careful calculation of application rate required so as not to under or over dose the soil.

Environmental: Implication of energy used in processing; Once applied, effect lasts for several years.

Health and Safety: Burning of eyes Or exposed skin, Should not breathe in dry powder.

Timing of application: Autumn – and allow to be washed into the soil; Must not come into contact with farmyard manures.

Effectiveness of the material: Very effective; You need to apply more carbonate to have the same effect as hydroxide.

CALCIUM HYDROXIDE see also calcium carbonate will raise the soil pH; Fairly cheap to purchaser; Quick effect on soil.

Limitations: Careful calculation of application rate required so as not to under or over dose the soil.

Environmental: Implication of energy used in processing; Once applied, effect lasts for several years.

Health and Safety: Burning of eyes Or exposed skin, Should not breathe in dry powder.

Timing of application: Autumn – and allow to be washed into the soil; Must not come into contact with farmyard manures.

Effectiveness of the material: Very effective; You need to apply more carbonate to have the same effect as hydroxide.

SULPHUR

FLOWERS OF SULPHUR

Benefits: Will lower the soil pH.

Limitations: Expensive as sold in small containers; Slow effect on the soil’s pH; Needs several applications.

Environmental: Implication of energy used in processing.

Health and Safety: Burning of eyes.

Timing of application: Autumn – and allow to be washed into the soil; Repeated over several years.

Effectiveness of the material: Slow.

MUSHROOM COMPOST Well-rotted house compost mixed with peat and chalk – chalk makes alkaline, therefore to be considered in how you use it; Can have live mycelium content (not always good); Little or no plant food content; Has a good physical effect on the soil.

Benefits: Will raise the soil pH as lime is used as a capping; The rest is well rotted horse manure.

Limitations: No accurate knowledge of calcium content; Can contain live mycelium and other spores.

Environmental: Cost of transport.

Health and Safety: Can contain or give off spores; Hygiene.

Timing of application: Autumn – and allow to be washed into the soil, then dig in or use as a mulch.

Effectiveness of the material: No accurate knowledge of calcium content.

WOOD ASH

Benefits: Will raise the soil pH 4% potash content.

Limitations: No accurate knowledge of calcium content; Availability.

Environmental: Cost of transport; CO2 emissions.

Health and Safety: Dust.

Timing of application: Spring as the potash content is quick acting.

Effectiveness of the material: No accurate knowledge of calcium content.

POTASH

PEAT

Benefits: Will lower the soil pH in time; Applies organic matter to the soil.

Limitations: Must be an acid peat; No plant food content; Needs several applications over time.

Environmental: No longer considered a suitable soil additive due to the environmental issues of its use.

Health and Safety:

Timing of application: Autumn dig in or use as a mulch.

Effectiveness of the material: Needs several applications.

ERICACEOUS

ERICACEOUS COMPOST

Ericaceous Compost: Benefits: Will lower the soil pH in time if dug in (best used to fill containers as acid compost).

Limitations: Cost; Slow effect on soil unless large quantities are used.

Environmental: Cost of transport; Might have high peat content.

Health and Safety: Lifting bags.

Timing of application: Autumn/any time; Dig in or use as a mulch.

Effectiveness of the material: Slow effect (best used to fill containers).

PINE NEEDLE

COMPOSTED PINE NEEDLES

Pine Needles: Benefits: Will lower the soil pH.

Limitations: Availability.

Environmental:

Health and Safety: Hygiene; Spores.

Timing of application: Autumn dig in or use as a mulch.

Effectiveness of the material: Slow.

Explain how plant selection is influenced by soil pH to include suitable named plant examples (minimum of THREE for EACH of acidic, neutral and alkaline/basic)

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