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PH Soil Meters

pH Soil Meter Technical

What is soil pH?

Soil can exhibit either alkaline or acidic properties (sometimes called basicity). The pH of soil serves as a measure of its acidic or alkaline levels. Typically displayed on a colour chart, red indicates acidity and blue represents alkaline.

The pH value indicates the concentration of hydrogen ions within the soil. The pH scale is logarithmic, meaning lower pH values signify higher hydrogen ion concentrations, showing strong acidity. Garden soil generally falls within a pH range of 3.5 to 10.

The three primary classifications for soil pH are as follows:

  • - pH 0 to 6.5: Acidic
  • - Neutral.
  • - pH 7.5 to 14: Alkaline

The content of the soil determines the soil pH. Other factors that can affect the acidity of soils include:

  • - Weather processes
  • - Root respiration
  • - Plant growth
  • - Fertiliser
  • - Acid rain
  • - Addition of minerals to the soil
  • - Water flow

Why is soil acidity important?

Gardeners must be attentive to their soil's acidity. The pH level significantly impacts plants' solubility and absorption of nutrients and chemicals. The ability of plants to absorb nutrients depends on the soil acidity.

The ideal range for plant growth is around a neutral pH level, which falls between 5.5 and 7.5. Most of the seventeen essential nutrients required for plants are readily available in the soil within this range.

Moreover, the pH level also influences the activity of microorganisms responsible for decomposing organic matter in the soil. Strong acidity can hinder the bacteria responsible for decomposition, reducing available nutrients in the soil.

Consequently, inadequate blooms or crops may result from imbalanced soil pH levels due to nutrient deficiency. As previously mentioned, soil acidity can even affect the colour of certain plants. For instance, acidic or alkaline soil affects the growth of colours of hydrangea flowers.

The following table illustrates the availability of minerals to plants based on the soil's acidity. Green indicates a strong mineral balance, while amber indicates a less robust balance.

How does soil acidity affect plants?

Acidic soil

Ericaceous and calcifuge plants thrive in acidic soil conditions. These plants have adapted to flourish in such environments and must be better suited to alkaline soils.

If grown in alkaline-heavy soil, these plants may display yellow leaves, a condition known as lime-induced chlorosis.

This occurs because alkaline soil lacks essential nutrients like iron, which are crucial for their growth. As a result, plants suffering from this condition will struggle to develop and may eventually perish.

Examples of ericaceous and calcifuge plants that are ideal for planting in acidic soil include:

  • - Rhododendrans
  • - Azaleas
  • - Heathers
  • - Blueberry
  • - Camellia
  • - Lily
  • - Pieris
  • - Magnolia

Alkaline soil

Calcicole plants are well-adapted to thrive in alkaline or lime-rich soil. Calcicole plants grown in acidic soil exhibit comparable effects, such as chlorosis, stunted growth, and curling leaves. These effects stem from the availability of nutrients in the soil.

Alkaline soil contains elevated levels of calcium when compared to acidic soil. Due to the presence of chalk and limestone in Britain, many commonly find soil rich in calcium, resulting in chalky soils.

Examples of calcicole plants that are ideal for planting in alkaline soil include:

  • - Ash trees
  • - Honeysuckle
  • - Lilacs
  • - Clematis
  • - Syringa
  • - Phacelia
  • - Polemoniums
  • - Lavender

How does the soil pH meter work?

The EL-SM-METER3IN1 is an electronic soil pH tester instrument which requires no batteries or external power. So, let’s explain that apparent contradiction first. Both batteries and solar power provide electricity.

This Monitor incorporates a light sensor to give a measurement of sunlight. This sensor works by generating a voltage that depends on the strength of the light. Although it is small for a solar cell, there is enough power to operate the Monitor.

But other power sources are available. Every time the probes are inserted into moist soil, this monitor makes a battery. The probes are made of different metals (there are four separate contacts on its two probes, using three types of metal).

When placed in an electrically conducting environment like moist soil, all the components of an electric cell (battery) are in place. The Monitor will still work even in the dark.

The light meter displays the voltage generated by the light sensor. The pH meter displays the voltage generated by its probe/soil battery. The measure moisture meter displays the current passing through the soil, which depends on its soil moisture level.

The indicating meter is a spring-loaded, electric motor that rotates the indicating needle if more electrical voltage is generated.

A clearly labelled 3-position switch gives the choice to select the meter function. Insert the probes into the soil and turn the meter on. The device accurately measures the soil acidity level and provides a much more accurate reading than other testers on the market.

The pH function measures the pH. A lower value below seven increases acidity, whereas a higher number above seven increases alkaline levels. A pH measurement of 7 is a perfect balance being neither acidic nor alkaline. Note that different plants prefer different pH, and not necessarily 7.

Avoid leaving the meter and probes in the soil. Ensure the probes are cleaned after each use for more accurate results and reduce damage to the probes.

Changing your soil pH

There are several ways you can alter the pH of your soil, including:

  • - Nitrate-based Fertilisers for acidic soil to raise the pH level.
  • - Mineral fertiliser and sulphur to lower the pH level.
  • - Lime for acidic soil to raise the pH level.
  • - Wood ash for acidic soil to raise the pH level.
  • - Aluminium for alkaline soil to lower the pH level.

Vegetables             Ideal pH Reading                                     Ideal pH Reading
Bean                        6.0 - 7.5                         Lettuce                   6.0 - 7.0
Broccoli                     6.0 - 7.5                        Onion                     6.0 - 7.0
Brussels                    6.0 - 7.5                        Pea                        6.0 - 7.5
Cabbage                   6.0 - 7.5                         Pepper                    5.5 - 7.0
Carrot                       5.5 - 7.0                         Potato                     4.5 - 6.0
Cauliflower                 5.5 - 7.5                        Radish                     6.0 - 7.0
Cress                        6.0 - 7.0                        Spinach                    6.0 - 7.5
Cucumber                  5.5 - 7.5                        Swede                      5.5 - 7.0
Leek                         6.0 - 8.0                         Tomato                    5.5 - 7.5
Fruit                        Ideal pH Reading                                       Ideal pH Reading
Blackberry                 5.0 - 6.0                           Melon                      5.5 - 6.5
Cherry                      6.0 - 7.5                           Peach                      6.0 - 7.5
Currant Black             6.0 - 8.0                           Raspberry                5.0 - 6.5
Currant Red               5.5 - 7.0                           Rhubarb                  5.5 - 7.0
Gooseberry                5.0 - 6.5                           Strawberry               5.0 - 7.5
Grapevine                  6.0 - 7.0                           Lawns                     6.0 - 7.5
Flowers/Shrubs          Ideal pH Reading                                     Ideal pH Reading
Alyssum                    6.0 - 7.5                          Gladiolus                  6.0 - 7.0
Azalea                      4.5 - 6.0                          Hydrangea Blue         4.0 - 5.0
Carnation                  6.0 - 7.5                          Hydrangea Pink         6.0 - 7.0
Chrysanthemum        6.0 - 7.0                           Hydrangea White       6.5 - 8.0
Clematis                   5.5 - 7.0                           Marigold                   5.5 - 7.0
Daffodil                     6.0 - 6.5                           Rhododendron          4.5 - 6.0
Dahlia                       6.0 - 7.5                           Rose                        6.0 - 7.0
Fuchsia                      5.5 - 6.5   

Red Zone
             Green Zone         Green Zone          Green Zone           Green Zone
Plants 1-3            Plants 4 - 5         Plants 5 - 6          Plants 6-7             Plants 6-7
Aloe                       Parachute Plant     Action Plant           Amazon Lily            Moon Flower
Anchor Plant           Pen Wiper             African Violet         Angel Wings            Mosaic Plant
Asparagus Fern       Pink Buttons          Angle Tears           Apostle Plant     Mother-In-Law Plant
Baby Jane              Pocket Book          Plant Aralia            False Azalea           Mouse Plant
Baby pine of China  Poinsettia               Bachelor Button     Brazilian Firecracker  Nut Orchid
Baby’s Breath         Queens Tears         Boxwood               Bridal Wreath          Oleander
Beaver Tail             Roman Candle       Burn Plant              Burro's Tail               Peacock Plant
Bishops Cap            Sand Dollar           Cape/Crape Myrtle Butterfly Gardenia   Peperomia
Bloodleaf                Sedum                  Chile Bells             Caladium               Periwinkle
Cactus                    Shrimp Plant         Cloth of God          Calla Lily                Petticoat Palm
Chicken Gizzard      Tiger Jaws             Corn Plant             Camellia                  Pitcher Plant
Christ Plant             Umbrella Tree       Crimson Flag          Chenille Plant      Polynesian Ti Plant
Crassula                 Wall Fern               Devils Ivy             Cobra Plant           Pothos
Crown of Thorns     White Jewel            Dieffenbachia         Coleus                   Prayer Plant
Dumb Cane              Green Zone          Euonymus             Columnea             Quaker Ladies
Easter Orchid          Plants 4-5            Finger of God         Copper Leaf          Sansevieria
Euphorbia               Airplane Plant         Firethorn                Croton                  Saxifraga
Fig, Fiddle Leaf        Begonia                 Flamingo plant        Darlingtonia         Scindapsus
Firecracker Plant     Bird of Paradise      Fleur D’Amour         Dawn Flower        Sea Grape
Flaming Sword        Blushing Bride         Flower of Heaven    Dracaena Palm     Spider Plant
Floral Firecracker     Bonsai Tree           Glory Lily                Easter Lily            Temple Bells
Foolproof Plant        Bromeliad              Gold Dust Plant          Echeveria             Turk’s Cap
Gas Plant                Candle Plant          Hoya                      Egyptian Star Cluster  Velvet Plant
Geranium               Century Plant         Impatiens               Explosion Plant      Verbena
Ghost Plant             Ceropegia              Kashmir Bouquet     False Holly            Violet Flame
Glory of Texas        Chain Cactus          Kiss-Me-Today        Fan Iris                 Wandering Jew
Golden Dew Drop    Daphne                  Lady of the Night     Fan Ivy                 Wax Plant
Good Luck Plant      Earth Star               Lantern Plant          Farewell to Spring   Zebra Plant
Hibiscus                  Echeveria               Medicine Plant         Ferns 
Honey-Bunny          Hairy Toad Plant      Naked Lady Lily      Fiery Love Flower   Blue Zone          
Ice Plant                 Hearts on a String   Pussy Foot              Fig, Creeping         Plants 8-10 
Ivy                         Hen and Chicken    Queens Jewels         Finger Aralia         Watering is not
Jade Plant               Inch Plant               Rouge Plant            Fingernail Plant       necessary 
Jasmine Star           Little Stars              Rubber Plant           Fire Dragon 
Jelly Beans              Mock Orange          Shooting Star          Five Fingers 
Lantana                   Norfolk Island Blue Solomon's seal         Fuchsia 
Little Candles           Patience Plant        Star of Bethlehem    Gardenia 
Little Owl Eyes         Pearl Plant              Victoria Aralia         Honey Bells 
Living Vase              Philodendron          Water Melon            Jasmine 
Lobster Plant            Ponytail                                               Jungle Flame 
Marguerite Blue        Radiator Plant                                      Kalanchoe 
Mimicry Plant           Sea Urchin                                           Ladies Tresses 
Moonstones              Stoneface                                            Leopard Plant 
Mother of Pearl         String of Pearls                                    Magic Flower 
Musk Plant                Vitamin C Plant                                   Man in a Boat 
Panda Plant               Youth and Old Age                              Match me if you Can