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Knowing and regulating soil pH is essential for a successful crop. Each type of plant has different requirements regarding alkalinity and acidity, so it’s important to understand how to raise or lower the pH to provide plants with exactly what they need. Does that sound more complicated than an advanced chemistry class? In reality, it’s quite simple. Keep reading, and everything will become much clearer.
What Is pH?
Before learning how to adjust the pH of your soil, it’s important to understand what pH is. It’s a value used to measure the acidity or alkalinity of soil. A pH of 7 is neutral, while values below 7 (down to 0) indicate acidity and values above 7 (up to 14) indicate alkalinity. This table provides a clearer understanding of each range.
| pH Range | Classification | Description |
|---|---|---|
| < 4.5 | Very Acidic | Extremely acidic soil; can inhibit plant growth. |
| 4.5 – 5.5 | Acidic | Suitable for acid-loving crops like blueberries and potatoes. |
| 5.6 – 6.5 | Slightly Acidic | Ideal for most agricultural crops. |
| 6.6 – 7.3 | Neutral | Excellent for most crops, especially vegetables. |
| 7.4 – 8.4 | Slightly Alkaline | Tolerated by adapted plants; may limit nutrients like phosphorus. |
| 8.5 – 9.0 | Alkaline | May pose challenges for many plants; requires soil adjustments. |
| > 9.0 | Very Alkaline | Highly saline-sodic soil; difficult for agriculture without intensive treatment. |
In general, plants and vegetables thrive in neutral to slightly acidic soil. In contrast, very acidic or alkaline soils tend to block essential nutrients, preventing plants from developing properly.
For cannabis cultivation, the ideal pH range is between 5.5 and 6.5, depending on the growth phase. Cannabis prefers slightly acidic soil during early growth stages and more neutral soil during the flowering phase.
How to measure pH
To regulate soil pH, the first step is learning how to measure it. There are several ways to do this.
Using pH test strips
You can purchase pH test strips at supermarkets and hardware stores. They are affordable and easy to use. You’ll also need distilled water, which has a neutral pH of 7. Start by taking a soil sample. Avoid sampling from the surface; it’s better to take samples at a depth of 10 to 45 cm. Collect samples from different areas to ensure accuracy.
Mix the soil with distilled water in equal proportions, stir, and let it sit for a couple of hours. Then dip the test strip into the mixture, and it will indicate the soil’s pH.
Using vinegar and baking soda
You can also use a homemade method to measure pH with vinegar and baking soda as reactants. The process is similar: mix soil with distilled water in two separate containers. Add a pinch of vinegar to one container—if it bubbles, the soil is alkaline. In the other container, add baking soda—if it bubbles, the soil is acidic. If there’s no reaction, the soil is neutral. This method provides an approximate pH value but not precise data.
How to lower pH naturally
Once you know your soil’s pH, you can determine if adjustments are necessary. A common issue is that the soil is too alkaline for crops and needs to be lowered. Here are natural methods to achieve this:
With irrigation water
To acidify irrigation water, you have several options:
- With vinegar. Vinegar contains acetic acid, which can lower soil pH. Mix one tablespoon of vinegar in a liter of water and use this solution to irrigate.
- With rainwater. Rainwater is naturally acidic due to atmospheric carbon dioxide. It’s a good idea to collect and store it for future irrigation.
- Lower the soil pH with lemon. Citric acid can also help reduce pH in highly alkaline soil. Mix it with irrigation water.
With acidic amendments
Soil amendments are additives used to improve soil properties. Common acidic amendments include elemental sulfur, iron sulfate, and aluminum sulfate. Be cautious and follow manufacturer guidelines to avoid harming plants and soil.
With organic matter
A natural way to lower soil pH is by using compost, manure, or peat moss. These products also provide nutrients, protect roots, and stimulate plant growth.
With acidifying plants
Certain plants, such as azaleas and blueberries, naturally lower soil pH.
With commercial products
There are nitrogen-rich fertilizers on the market that contain a compound called ammonium, which can be used to acidify the soil. It’s crucial to follow the instructions and dosage carefully to avoid damaging crops.
How long does it take to lower the pH?
While you can adjust soil pH according to crop needs, this is not an instant process. Generally, you’ll need to wait for the soil to absorb the chemicals and change its pH. The time required varies depending on factors like soil type and environment.
- Soil type. Clay soil retains alkalinity longer and takes more time to become acidic. Sandy soils, on the other hand, are easier and faster to acidify.
- Moisture. Soil moisture levels also affect acidification. If the soil is too dry or too wet, the process will take longer.
- Nutrients. Fertile, nutrient-rich soil resists pH changes, requiring more time and patience to acidify.
- Temperature. Temperature influences microbial activity, which affects pH. Warmer climates make it easier to acidify soil compared to colder climates.
- Organic matter. Organic matter naturally acidifies soil, so soils rich in organic matter will adjust their pH more quickly.
How to raise soil pH
In some cases, it may be necessary to raise soil pH. Some plants, like artichokes, melons, olives, and barley, prefer alkaline soil. Common ingredients used to alkalinize soil include the following:
- Ground limestone. This involves mixing finely ground limestone with the soil.
- Quicklime. Another option is to use hard or calcium-rich water for irrigation.
- Acidic organic matter, such as eggshells or light peat.
As you can see, knowing how to adjust soil pH is crucial for achieving the right acidity level that crops need, especially when planting directly in the ground.
