How to Raise Your Soil pH With Garden Lime

Soil pH is a significant part of the delicate, all-important relationship between plants and their root environment. The proper pH makes all the difference in nutrient absorption; even the most fertile gardens will only do so much for the plant without the right acidity or alkalinity. Thankfully, amendments like lime can help raise the soil pH in your garden.

Most ornamental and edibles grow best in slightly acidic to neutral soil, with a pH between 6.2 and 6.8. A balance of texture and nutrients achieves this sweet spot. Some plants grow well in acidic or alkaline conditions, depending on their native range.

You can improve soils with an excessively low pH by adding this organic amendment. Maintaining the ideal pH is as essential for thriving plants as adding other nutrients and organic material. With easy testing and amendments, benefits are within reach.

What is Soil pH?

Soil pH, or “potential hydrogen,” relates to acidity and alkalinity. Specifically, it’s a measure of hydrogen and aluminum ions. When hydrogen levels become too high, soils become acidic. The higher the amount of hydrogen, the lower the pH.

So, what does this mean for our gardens? Most plants grow best in ground with a pH between 6.0 and 7.0. These slightly acidic to neutral conditions provide optimal access to nutrients and other benefits. 

pH runs on a scale from 0 to 14. Acidic (sour) soils are those between 4 and 6.5. Alkaline (sweet or basic soils) are between 7.5 and 9. A balanced 6.5 to 7.0 measure is a more neutral setting supporting roots and nutrition.

In highly acidic ground (low pH), particles block access to essential nutrients. Nutrients are less soluble in overly alkaline compositions, making it more difficult for roots to uptake them.

The best way to determine your garden’s pH is with a soil test. At-home kits with interpreted results and recommendations do an excellent job assessing the conditions. Your local university extension office is another resource for tests and recommendations.

The key to success is following the recommendations by knowing exactly what levels of amendments are necessary for plant health. Testing every three to five years is a reasonable timeframe.

Factors That Affect pH

Even without being a chemist, the factors that affect pH are intriguing. The main factors are climate, soil type, and organic matter.

Researchers created a map of worldwide pH levels that shows the role of climate. Western parts of the United States, where it’s drier with high temperatures, have more naturally occurring limestone. Soils are alkaline. 

Eastern areas receive more rainfall, and tend to be more acidic. Rainfall passes through the ground profile and leaches nutrients like magnesium, potassium, and calcium. Acidic ions like hydrogen and aluminum remain.

Soil texture also affects pH. The parent rocks may have been more acidic or basic, resulting in a higher pH.

The three main belowground particle sizes are sand, clay, and silt. Their quantities and structure impact how lime holds or passes through. It also affects how much air and water the root zone has. The bulk of the particles determines the overall texture (i.e., more clay particles mean clay texture). Loams are ideal for many crops and ornamental plants, blending equal parts sand, clay, and silt with organic matter.

Accumulated organic matter is another primary factor in pH. Leaves and pine needles breaking down may lower the pH. Acid-loving plants like pine trees and oaks thrive in lower pH levels, and their organic matter fosters the conditions.

Acidic Soils

Acidic soils have a pH lower than 6.5. Many plants cannot access nutrients with a low pH, like 4.5, and may experience toxicity. Fewer plants thrive as acidity increases.

In low-pH conditions, nutrients like calcium, phosphorus, and magnesium become less available. Aluminum becomes more available and can be toxic to the plant at high levels. 

If your ground is naturally acidic, grow trees, shrubs, and perennials well-suited to those conditions. You can also amend garden areas with garden lime to raise the soil pH and increase alkalinity. For the most widespread growing preferences, move the pH toward slightly acidic (around 6.8).

Basics of Garden Lime

Garden lime is ground limestone. Adding lime your garden helps raise the soil pH level and makes it less acidic. This is an organic amendment.

Limestone is ground into an ultra-fine powder and often pelletized for easy spreading. The finer the powder, the more quickly the ground absorbs it.

There are two primary types for the home landscape: agricultural (garden) and dolomitic. Garden lime is calcitic, meaning it contains calcium, while dolomitic lime contains calcium and magnesium. The soil test will indicate which is better for your site.

Consider your soil texture, organic matter, and plant selection before adjusting the pH level. Again, a soil test helps determine the best amendment and quantities. Different beds require varying amounts to raise or lower the pH.

Benefits of Liming

Raising the pH of acid soils creates better conditions for most plants to thrive. Nutrients become more available in the root zone. While some ground may be very fertile, it won’t help with nutrient absorption if the pH is too low. The nutrient is present but not available for uptake.

Garden lime has the additional benefit of calcium, which is essential for healthy crops. Tomatoes rely on it for mature fruits, and without access to calcium, blossom end rot occurs. The perfect tomato suddenly rots on the stem. With added calcium, future tomatoes can flourish. Tree fruits also depend on the nutrient to develop.

Beneficial microorganisms do their best work in slightly acidic to neutral soils. In highly acidic ground, they cannot break down organic matter efficiently, and nitrogen becomes unavailable to roots. Lime increases nitrogen availability by speeding up decomposition through active microbes.

This amendment can also improve soil structure. Neutral pH leads to a balanced texture that promotes good aeration and moisture retention for healthy root development. 

Application

Garden lime is easy to spread and relatively inexpensive. Its benefits are numerous. Apply in the spring or fall. It takes two to three months to adjust, and fall is optimal for absorbing the material before spring planting.

Applying an excess can raise the pH too much. It may result in weaker plants and fruits, making them unable to absorb nutrients on the opposite end of the sale—a high pH. Chlorosis (a yellowing of leaves) is common in alkaline soils. An overapplication leads to iron deficiency in soils above 7.0.

So, while garden lime is an organic material, applying too much has ramifications. It’s also important to consider site specifics. Raising the pH with garden lime will hinder their growth if you grow acid-loving plants like camellias, azaleas, rhododendrons, and blueberries. Limit it to other planting zones.

To apply the amendment, distribute it across the bed surface. Spread it by hand or use a mechanized spreader. Depending on your spreader, look for pelletized or pulverized (a finely ground powder). Follow application guidelines, and spread half working in one direction. Apply the other half in the opposite direction for uniform coverage. Lightly turn into the upper layers for best incorporation.

Amending different soil types varies. Clays differ from loams; clay requires more lime and added organic matter to raise the pH. Sandy ground has more particulates and need less material to increase levels. Follow pH testing and application guidelines for your site.

Frequently Asked Questions