What Does Lime Do to Soil in the Garden?
Lime, most commonly in the form of agricultural lime, primarily increases the soil pH, making it more alkaline. This improves nutrient availability for many plants, reduces the toxicity of certain elements, and fosters a healthier soil environment.
Understanding Soil Acidity and Alkalinity
Soil pH is a measure of its acidity or alkalinity, ranging from 0 to 14, with 7 being neutral. Soils with a pH below 7 are considered acidic, while those above 7 are alkaline. Many plants thrive within a narrow pH range, typically between 6.0 and 7.0. Factors like rainfall, decaying organic matter, and fertilizer use can contribute to soil acidity. Amending soil with lime counteracts these acidic influences. Without proper pH, even if the soil is rich in nutrients, the plants may not be able to access them.
Benefits of Applying Lime to Soil
Liming offers a multitude of benefits for garden soil, directly impacting plant health and yield.
- Increases Nutrient Availability: Acidity can lock up essential nutrients, making them unavailable to plant roots. Lime helps to release these nutrients, ensuring plants have access to the building blocks they need.
- Reduces Aluminum and Manganese Toxicity: In acidic soils, aluminum and manganese can become soluble and reach toxic levels, inhibiting root growth and causing nutrient deficiencies. Lime precipitates these elements, rendering them harmless.
- Improves Soil Structure: Lime can improve soil structure by promoting flocculation, which causes soil particles to clump together. This enhances drainage, aeration, and root penetration.
- Enhances Microbial Activity: Beneficial soil microorganisms thrive in a neutral to slightly alkaline environment. Liming provides an optimal pH for their activity, which aids in nutrient cycling and disease suppression.
- Improves Fertilizer Efficiency: When soil pH is optimal, plants are better able to utilize fertilizers, leading to improved growth and reduced fertilizer waste.
- Reduces Clubroot Disease: In brassica crops (cabbage, broccoli, etc.), lime can help to reduce the incidence and severity of clubroot disease.
Types of Lime and How They Work
Several types of lime are available, each with slightly different properties and application rates:
- Agricultural Limestone (Calcium Carbonate – CaCO3): The most common and readily available type. It’s relatively slow-acting but provides a sustained pH increase.
- Dolomitic Limestone (Calcium Magnesium Carbonate – CaMg(CO3)2): Contains both calcium and magnesium, making it ideal for soils deficient in magnesium.
- Hydrated Lime (Calcium Hydroxide – Ca(OH)2): A faster-acting but more caustic form of lime. Requires careful handling to avoid burning plants.
- Quicklime (Calcium Oxide – CaO): The most caustic form of lime. Requires extreme care when handling and is rarely used in home gardens due to its potential to damage soil and plants.
The active component in lime is the carbonate ion (CO3^2-), which reacts with hydrogen ions (H+) in the soil to raise the pH. This process essentially neutralizes the acidity.
Application and Timing
Applying lime is best done before planting or during the fall to allow it to react with the soil over the winter. The amount of lime needed depends on the soil type, its initial pH, and the type of lime being used.
| Soil Type | Texture | Typical pH | Example Crops That Thrive |
|---|---|---|---|
| Acidic | Sandy | 4.5 – 6.0 | Blueberries, Azaleas |
| Neutral | Loamy | 6.0 – 7.0 | Tomatoes, Peppers |
| Alkaline | Clay | 7.0 – 8.5 | Lavender, Salvia |
General Application Steps:
- Soil Testing: Always test your soil pH before applying lime. This will tell you how much lime is needed to reach the desired pH.
- Calculate Lime Requirements: Use a lime requirement chart or consult your local agricultural extension office to determine the appropriate application rate based on your soil test results.
- Spread Lime Evenly: Distribute the lime evenly over the soil surface.
- Incorporate into Soil: Mix the lime into the top 6-8 inches of soil using a tiller, shovel, or garden fork.
- Water Thoroughly: Water the soil to help the lime react with the soil particles.
Potential Issues and Common Mistakes
While liming offers numerous benefits, incorrect application can lead to problems:
- Over-liming: Applying too much lime can raise the soil pH too high, leading to nutrient deficiencies and stunted growth.
- Incorrect Lime Type: Using the wrong type of lime for your soil conditions (e.g., hydrated lime on a sandy soil) can lead to imbalances.
- Insufficient Incorporation: Failing to properly mix the lime into the soil can result in uneven pH distribution and reduced effectiveness.
- Ignoring Soil Testing: Applying lime without a soil test is like guessing – you might get lucky, but you’re more likely to make a mistake.
- Applying Lime with Certain Fertilizers: Avoid applying lime at the same time as fertilizers containing ammonium, as it can cause nitrogen loss.
Plants That Prefer Acidic Soil
It’s important to remember that not all plants thrive in alkaline soil. Some plants, such as blueberries, azaleas, rhododendrons, and camellias, prefer acidic conditions. Applying lime to soil where these plants are grown can be detrimental. Know your plants and their pH preferences before making any soil amendments.
Frequently Asked Questions (FAQs)
1. How do I know if my soil needs lime?
The most reliable way is to conduct a soil test. Soil test kits are available at garden centers or through your local agricultural extension office. The test will provide you with information on your soil’s pH, nutrient levels, and recommendations for amendments. You might suspect an acidic soil if plants are struggling even with proper watering and fertilization, or if you see signs of aluminum or manganese toxicity (e.g., stunted growth, leaf discoloration).
2. What is the best time of year to apply lime?
Fall is generally considered the best time, as it allows the lime to react with the soil over the winter months. However, lime can be applied in the spring as well, ideally several weeks before planting. Avoid applying lime during periods of heavy rain, as it can wash away before it has a chance to react.
3. Can I use wood ash as a substitute for lime?
Wood ash can act as a liming agent because it contains calcium carbonate and other alkaline compounds. However, its effectiveness varies depending on the wood type and burning conditions. It’s also more variable in composition than commercially available lime. A soil test after application is crucial.
4. How long does it take for lime to work?
The speed at which lime works depends on several factors, including the type of lime, the soil type, and the amount of moisture. Hydrated lime will raise the pH faster than agricultural limestone. Sandy soils will react more quickly than clay soils. Generally, it takes several months to a year for lime to fully correct the soil pH.
5. Can I apply lime to potted plants?
Applying lime to potted plants is generally not recommended unless a soil test indicates a specific need. Container soils are often formulated to be slightly acidic, and excessive liming can disrupt the delicate balance. If needed, use dolomitic lime sparingly and mix it thoroughly into the potting mix before planting.
6. What are the symptoms of over-liming?
Symptoms of over-liming include nutrient deficiencies, particularly of iron, manganese, and zinc. Leaves may turn yellow (chlorosis), especially between the veins. Plant growth may be stunted, and yields may be reduced. In severe cases, plants may die.
7. Will lime kill earthworms?
No, lime generally does not kill earthworms. In fact, lime can benefit earthworms by creating a more favorable soil environment. Earthworms prefer a neutral to slightly alkaline pH, and lime can help to create these conditions in acidic soils.
8. Can I use lime on my lawn?
Yes, lime can be beneficial for lawns that are growing in acidic soil. It helps to improve nutrient availability, reduce weed growth, and promote a healthy, green lawn. Perform a soil test to determine if your lawn needs lime.
9. What is the difference between agricultural lime and garden lime?
Agricultural lime is usually in granular or powdered form to improve its ability to mix with the soil. Garden lime is a general term that typically refers to agricultural lime sold in smaller quantities for home garden use. Both products work similarly to raise the pH of soil.
10. How often should I lime my soil?
The frequency of liming depends on the soil type, rainfall, and the types of plants being grown. Sandy soils require more frequent liming than clay soils. High rainfall can leach lime from the soil more quickly. A soil test every 2-3 years will help you determine when to reapply lime.
11. Can I use lime with compost?
Yes, lime can be used with compost. Applying lime with compost can help to balance the pH of the compost and improve its nutrient content. However, it’s important to avoid over-liming, as this can inhibit the decomposition process.
12. Is lime harmful to humans or pets?
Agricultural lime is generally considered safe for humans and pets when handled properly. However, hydrated lime and quicklime are caustic and can cause skin and eye irritation. Always wear gloves and eye protection when handling lime, and keep it out of reach of children and pets. Wash thoroughly after handling lime.