What is pH and how does it affect plants?
pH is a scale from 0 to 14 which indicates the level of acidity or alkalinity of the soil. A pH of 7 is neutral, below it is acidic, and above it is alkaline. Most agricultural plants and crops prefer neutral or slightly acidic soils., between 6 and 7. However, there are notable exceptions, and it's essential to know the optimal range for each species. To learn more about how pH affects the health of your plants, you can check out our guide on the importance of soil pH on plants.
A soil with inadequate pH can cause nutritional deficiencies, even when nutrients are present, because the roots cannot easily assimilate them. Below is a guideline table of pH ranges and their meaning:
| pH range | Classification | Description |
|---|---|---|
| <4.5 | Very acid | Severe nutrient absorption problems. |
| 4.5-5.5 | Acid | Suitable for acidophilic plants. |
| 5.6-6.5 | slightly acidic | Ideal for most crops. |
| 6.6-7.3 | Neutral Stainless - Steel | Excellent for vegetables and most plants. |
| 7.4-8.4 | Slightly alkaline | It can limit the availability of nutrients such as phosphorus. |
| 8.5-9.0 | Alkaline | Problematic soils for many crops. |
| > 9.0 | Very alkaline | Only suitable for very specific crops. |
Measure the pH of your garden
The first step to correct soil pH is measure its current valueYou can easily do this at home using:
- Distilled water
- Paddle
- Plastic container
- pH strips (available at pharmacies and specialty stores)
The test strips will give you the pH value through a color change that is compared to a manufacturer's scale. Remember that pH can vary depending on the depth and area of the garden. Therefore, the ideal is:
- Divide the land into areas of 1-2 m².
- Extract samples from each area to a depth of 45 cm; for trees, drill down to 80 cm.
- Mix all samples well.
- Mix equal parts soil and distilled water, wait for it to settle, and use the strip to measure the pH.
You can also resort to Laboratory analysis for greater precision, especially in agricultural operations.
How to lower the pH of the soil?
If your soil has a High pH (greater than 7) and you need to acidify it, you have several effective alternatives:
- Blond peat: Its pH is acidic, and when mixed with soil (a 4-5 cm layer), it helps gradually lower the pH. Repeat the measurement after a few months.
- Aluminum sulfate: Provides rapid pH reduction. Typically, 0,5 kg per square meter lowers the pH by one point. It is best applied dissolved in water.
- Agricultural sulfur: It is an economical and effective method; it slowly oxidizes to form sulfuric acid, reducing the pH over time. Use between 0,5 and 1 kg/m², checking the pH every six months.
- Iron sulphate: In addition to acidifying, it provides assimilable iron and combats iron chlorosis. Apply 2 to 4 grams per liter of water.
- Organic material: Incorporating manure, compost, or plant debris can help acidify the soil, improving its structure and fertility.
The choice of product and dosage will always depend on the soil's buffering capacity (its ability to resist pH changes), as well as its texture and amount of organic matter.
How to raise the pH of the soil?
In soils with Low pH (5 or lower), especially if you are going to plant species sensitive to acidity, such as almond or carob trees, it is necessary to raise the pH:
- Potassium carbonate: Highly soluble and effective. It can be applied through irrigation; a small teaspoon is enough to raise the pH on small surfaces.
- Agricultural lime (ground limestone): This is the most common solution. It should be incorporated into at least the top 15-20 cm of the soil. The amount varies depending on the soil's texture and cation exchange capacity; clayey and organic soils require higher doses.
- Dolomite: In addition to calcium, it provides magnesium. Recommended if the soil is also poor in this nutrient.
- Basalt flour: Suitable for dosing the pH increase and improving the structure.
- Quicklime: Only recommended for quick actions and under supervision, as it can cause sudden increases in pH.
Application should preferably be done in autumn or early spring, and sowing immediately after liming should be avoided to ensure a homogeneous reaction.
Factors influencing pH correction
La amount of amendment to be applied (lime, sulfur, etc.) depends on several factors:
- Cation exchange capacity (CEC): Soils with high CEC, such as clay or soils with a lot of organic matter, are more resistant to pH changes and require more product.
- Purity and granulometry: The finer and purer the correctors (especially lime), the more effective and faster their action.
- Application area: It is essential to mix the corrector well into the active layer of the soil where the roots develop.
Avoid correcting the pH too quickly. It is recommended to adjust one pH point per year To prevent damage to microorganisms and roots. Check the pH periodically and repeat applications if necessary.
Soils with incorrect pH present visible symptoms in plants, such as yellowing leaves (chlorosis), poor growth, poor flowering, and difficulty absorbing nutrients such as iron, phosphorus, calcium, or magnesium. Additionally, the proliferation of certain weeds can indicate excessive acidity. To learn how to detect these symptoms in your plants, visit our section on plants and soils.
Proper pH adjustment, using mechanical, organic or inorganic methods, allows:
- Better use of fertilizers
- Avoid nutritional deficiencies
- Promote the development of beneficial microorganisms
- Optimize the performance and health of all types of plants
Correcting soil pH is essential for adapting it to the needs of each crop and ensuring that plants grow strong and healthy. By implementing appropriate techniques and understanding the specific characteristics of your soil, you'll create an optimal environment for your plants, resulting in better harvests and vibrant gardens.
