Soil pH It is an essential factor in gardening, agriculture and landscaping, as it determines the acidity or alkalinity of the substrate where the plants grow. This property influences the availability of essential nutrients and, therefore, the vigor and health of crops, orchards, and gardens. Understanding how to measure, adjust, and maintain pH within the proper range is key to maximizing yield and avoiding deficiencies or toxicities in plants.
What is soil pH and why is it so important?
Soil pH It is a measure of its acidity or alkalinity, on a scale ranging from 0 (very acidic) to 14 (very alkaline), with 7 being a neutral value. A pH below 7 indicates an acidic substrate, while values above 7 indicate alkalinity.
pH directly affects nutrient availability such as nitrogen, phosphorus, potassium, calcium, magnesium, and other micronutrients. If the soil is too acidic or alkaline, plants can suffer from nutritional deficiencies or toxicity, resulting in poor growth, chlorosis, and lower production.
For instance, crops such as azaleas, blueberries, rhododendrons and conifers They prefer acidic soils (pH 5.0 to 5.5), while most vegetables, lawns and ornamental plants grow optimally in moderately acidic or neutral soils (pH 5.8 to 6.5). Correct soil pH It is essential to achieve the ideal conditions for each species.
pH ranges and their effect on plants
| pH range | Classification | Description |
|---|---|---|
| <4.5 | Very acid | It hinders growth, blocks nutrients. |
| 4.5-5.5 | Acid | Suitable for acidophilic plants such as blueberries, potatoes, azaleas. |
| 5.6-6.5 | slightly acidic | Optimal for most agricultural and ornamental crops. |
| 6.6-7.3 | Neutral Stainless - Steel | Ideal for vegetables and many flowers. |
| 7.4-8.4 | Slightly alkaline | Phosphorus and micronutrient deficiencies may occur. |
| 8.5-9.0 | Alkaline | Problematic soils; many crops fail to thrive. |
| > 9.0 | Very alkaline | Salinity risk; requires intensive correction. |
Some plants like hydrangea, camellia, gardenia, heather and fuchsia are acidophilic and require acidic soils, while others such as grasses, rice, and some vegetables tolerate or prefer alkaline soils. If you want to expand your knowledge, you can visit How to care for a phalaenopsis orchid to learn more about pH care in different plants.
Factors that influence soil pH
Soil pH is influenced by:
- The parent material from which the soil originated (basic rocks contribute high pH, acidic rocks produce acidic soils).
- The amount of rainfall and drainage, which leaches bases such as calcium and magnesium and replaces them with acidic elements (aluminum and iron).
- The use of fertilizers (especially those containing ammonium or urea, which acidify the soil).
- The decomposition of organic matter and microbial activity.
Humid and temperate regions tend to have more acidic soils, while dry or low-rainfall areas have more alkaline soils. To better understand how this affects your plants, we recommend how to measure soil pH.
How to measure soil pH
Before making any corrections, it is essential measure pH with a digital meter, test strips, or laboratory analysis to determine the exact value and decide on the appropriate treatment. You can take small samples from different points in the field, mix them, and analyze them to obtain a representative value.
There is also a homemade method: Place some soil in a container and add vinegar; if it bubbles, it's probably calcareous (alkaline) soil.
Methods to increase soil pH (correct acidic soils)
Correcting an acidic pH is known as “liming”There are different materials and techniques:
- Crushed limestone: This is the most commonly used material. Its effectiveness increases with finer grinding. For sandy soils, less is required than for clay soils.
- Types of limestone to choose from:
- Spray: Fast acting, but may form dust.
- Granulated or pelletized: easier to apply and less likely to clog irrigation equipment.
- Hydrated: Powerful, should be used with caution.
- Wood ash: They provide potassium and calcium, especially useful in sandy soils. Avoid direct contact with roots or seedlings. Do not use charcoal ash, as it can increase acidity.
- Agricultural plaster y basalt flour: Useful for clayey soils or soils with sodium problems.
La Application should be made months before plantingIdeally, this should be done in autumn or winter to allow time for the chemical reaction. Soil moisture favors the reaction of the liming materials.
Methods to lower soil pH (correct alkaline soils)
Some plants require acidic or slightly acidic soils. Lowering the pH of an alkaline soil is more difficult than raising the pH of an acidic one., but there are effective techniques:
- Powdered sulfurIts effect is slow (it can take months) but effective, as it is transformed into sulfuric acid by bacteria in the soil. It must be incorporated and the soil kept moist to promote the reaction.
- Aluminum sulfate: Its action is rapid and is primarily used for species such as hydrangeas. Do not exceed the recommended dose to avoid toxicity.
- Iron sulphate: Corrects pH and provides iron, useful for combating iron chlorosis.
- Blond peat: It has a very acidic pH and is used mixed in the substrate of pots or flowerbeds.
- Organic material: Compost, manure or plant remains help to progressively acidify the soil and provide nutrients.
- Iron chelates: Essential for acidophilic plants in calcareous soils, they quickly correct chlorosis.
In very alkaline soils, it may be necessary to repeat applications each season, as the effect tends to neutralize over time. Irrigation with calcareous water It also raises the pH, so it is recommended to acidify irrigation water with citric acid for plants that require it.
Recommendations according to the type of crop
- Acidophilus: Azalea, rhododendron, camellia, gardenia, heather, hydrangea, fuchsia, blueberry. Use acidic substrates and amendments.
- Grasses and rice: Alkaline soils may be acceptable. Improve structure with organic matter.
- Vegetables, fruit trees and grass: They prefer a slightly acidic or neutral pH. Regular checks and slight corrections are required if necessary.
Amount and frequency of application of concealers
- limestone: Between 150-250 g/m² depending on the type of soil and the initial pH value.
- Sulfur: Between 30 and 50 g/m², incorporating well into the surface layer.
- Chelates and sulfates: Follow the product instructions, avoiding excesses that may cause toxicity.
- Annual sampling and analysis: It is important to repeat tests every year, especially if corrections are applied.
Proper soil pH management is the basis for healthy and productive crops. Knowledge and application of correction techniques allow the substrate to be adapted to the specific needs of each plantThis way, you can enjoy a lush garden or orchard, avoid nutritional deficiencies, and obtain more abundant and healthy harvests, all while maintaining the soil's chemical balance over the long term.
