More Silica, More Success: Increase Silica Levels for Stronger, More Productive Crops

Introduction

Silica sand is composed of granules of quartz and other minerals that are rich in the element silicon. Silicon exists in nature as silica and silicates, which make up about 75% of the earth’s crust. In soil, silica plays a key role in plant health and growth.

Adding silica sand and other forms of silica can provide multiple benefits for soil fertility and plant development. Silica helps strengthen plant cell walls, which improves overall plant stability and health. It also helps plants develop resistance to insects, disease, and environmental stress. Additionally, silica aids water, nutrient, and oxygen absorption in plants.

For these reasons, gardeners and farmers often aim to increase levels of plant-available silica in soils that are deficient. There are several methods for doing this, ranging from top dressings of silica sand to soil amendments and foliar applications. The best approach depends on factors like soil composition, pH, and crop needs. This guide will provide an overview of techniques to improve silica levels and promote optimal plant growth.

Test Soil to Determine Current Silica Levels

Knowing your soil’s current silica levels is crucial before attempting to increase them. A soil test will reveal the exact concentration of plant-available silica, measured in parts per million (ppm).

There are a few methods for testing soil silica:

– Lab extraction using acetic acid or calcium chloride solution

– Field testing with portable meters

– At-home soil test kits

Professional lab tests provide the most accurate results. Look for a lab that offers ‘plant-available silica’ testing, not just total silica. Reputable labs include A&L Great Lakes Laboratories and Logan Labs.

When you receive the test results, look for the soluble silica level. Adequate silica for healthy plant growth is 50-100 ppm. Below 30 ppm is considered deficient and above 150 ppm is excessive.

Ideal silica levels vary by plant:

– Vegetables and herbs: 50-100 ppm

– Flowers and ornamentals: 100-150 ppm

– Silica-loving plants like rice, wheat, oats, and horsetail: 150-300 ppm

Use your soil test silica level to determine how much needs to be added. Then you can choose amendments and fertilizers to boost your soil’s silica content.

Add Silica Sand Top Dressings

Silica sand can be added as a top dressing to increase the silica levels in soil. When selecting a silica sand, opt for a coarse sand with grain sizes between 0.5-2mm. Avoid fine sands like builders sand as these can compact and prevent water and air penetration.

To determine how much silica sand to apply, first test your soil’s current silica levels. As a general guideline, apply 1-2 cups of silica sand per square foot of soil, and mix into the top 2-3 inches. The sand particles will gradually work their way down into the soil over time. Reapply 1-2 times per year as needed based on soil test results.

When incorporating silica sand, lightly rake it into the top layer of soil. Take care not to disturb plant roots or soil structure. Water thoroughly after application to wash some of the silica down into lower layers. The sand will release plant-available silica into the soil over the growing season. Monitor soil tests to ensure the silica levels remain in the optimal range for your plants.

Amend Soil with Silica Supplements

Silica supplements are concentrated sources of soluble silica that can be worked into the soil to increase its silica content. Some common silica supplements include:

1. Diatomaceous Earth

Diatomaceous earth is a powder produced from fossilized diatoms. It contains about 90% silica and can raise soil silica levels significantly when added. Mix in 1-2 cups per square foot of soil, or follow package instructions. Diatomaceous earth has a very fine texture that can help improve soil structure. However, it is slower acting than liquid silicates.

2. Rice Hulls

Rice hulls contain 20% silica and make an excellent organic soil amendment. Mix rice hulls into soil at a ratio of 1 part hulls to 4 parts soil. Rice hulls improve drainage and aeration in heavy soils. They break down steadily over 1-2 years to release silica. Compared to sand, rice hulls provide organic matter and nutrients.

3. Silica Gel

Silica gel is synthetically produced, nearly 100% silica. It rapidly releases soluble silica when worked into soil. Use 1-2 tablespoons per gallon of soil. Silica gel is more concentrated than sand or rice hulls, but provides no organic matter. It must be thoroughly mixed in to prevent concentrated pockets.

While silica supplements deliver a concentrated dose of silica, they must be mixed in thoroughly and reapplied to have a lasting impact. Sand has the benefit of providing a permanent silica reserve in the soil that gets released gradually over time. However, supplements can amend soil more quickly for plants with high silica needs.

Use Silica-Rich Organic Amendments

One organic approach to increasing the silica content in soil is to add natural silica-rich amendments. Rice hulls contain high levels of silica and make an excellent soil addition. Simply mix some rice hulls into the top few inches of soil to provide a slow-release silica source.

Horsetail is another organic material naturally high in silica. Dry and grind up horsetail stems and leaves, then mix into soil. The ground horsetail will break down over time and release silica.

Making and using compost teas is another organic method. Steep horsetail, nettles, oat straw, or other silica-rich plants in water to extract soluble silica. Use this silica tea as a foliar spray or soil drench to deliver silica directly to plants and soil.

Adding organic materials like rice hulls, horsetail, nettles, oat straw, and compost teas provides a natural way to increase the silica content in soil without synthetic chemicals. Over time, the silica in these organic amendments will become plant-available through decomposition and will help strengthen plant tissues.

Apply Liquid Silicates

One way to increase the silica content in soil is by applying liquid silicate products. The most common types are potassium silicate and sodium silicate. These can be applied either as a foliar spray on plant leaves or as a soil drench.

Foliar sprays with liquid silicates allow the silica to be directly absorbed by the plant leaves and transported to where it is needed. Dilute the silicate product in water according to the label instructions and spray it on the plant leaves. Ensure full coverage of the leaves, including the undersides. Repeat applications may be needed every 1-2 weeks during the growing season. Foliar sprays are useful for crops that rapidly take up and utilize silica like cucumbers, melons, rice, and some flowers.

Soil drenches with liquid silicates work by increasing the level of soluble silica in the soil that plant roots can access. Dilute the silicate product and water it into the soil around the base of the plants. For best results, avoid foliar contact as the product may cause leaf burn. Repeat applications every 2-4 weeks to maintain adequate soil silica levels. Soil drenches allow slower uptake for crops like fruit trees, grapes, and tomatoes.

Both foliar sprays and soil drenches with liquid silicates provide a readily available silica source to increase concentrations in plant tissues and improve crop yield and quality. Proper dosage and application timing is important to get the benefits without risk of toxicity.

Mulch with Silica-Rich Materials

Mulching the soil surface with silica-rich organic materials is an easy way to increase the amount of plant-available silica over time. Good silica-rich mulching sources include rice hulls, straw, bamboo leaves, peanut shells, and coconut coir. These materials will slowly break down and release silica into the soil as they decompose.

When applying a silica mulch, it’s important to distribute it evenly in a 2-4 inch layer across the entire garden bed or around individual plants. Avoid piling mulch up around the base of plants. The mulch layer should be refreshed annually as the materials break down. Thinner layers may need to be topped off more frequently. Silica mulches improve moisture retention in the soil, moderate soil temperatures, prevent weeds, and feed beneficial soil microbes as they decompose. Over time, the silica released from the mulch will accumulate in the soil, increasing the available silica levels.

Grow Silica Accumulator Plants

Certain plants are able to absorb higher levels of silica from the soil than others. These plants are known as silica accumulators. By growing these types of plants, you can gradually increase the silica levels in your garden soil over time.

Some examples of high silica accumulator plants include:

– Strawberries

– Cucumbers

– Onions

– Lettuce

– Wheat

– Oats

– Bamboo

– Horsetails

You can rotate these types of crops into your garden beds on a regular basis. After harvesting them, the silica rich plant matter will breakdown and release silica back into the soil.

Cover crops can also help boost silica levels. Plant cover crops like oats, wheat and horsetails. Once they reach maturity, turn them back into the soil. As they decompose, the silica within the plants will become plant-available.

By making use of silica accumulator plants, you can steadily improve the silica content in your garden soil. Over time, this will create better soil structure and plant health.

Adjust pH Levels

Silica is more readily available to plants in neutral to acidic soil conditions. When soil pH becomes too alkaline (above 7), silica gets locked up in the soil and becomes less accessible to plant roots.

To optimize silica availability, test your soil’s pH and amend as needed to reach the ideal range for your plants. Most vegetables, fruits and flowers prefer a pH between 6.0-7.0.

If your soil tests above 7.5, you can lower the pH by adding elemental sulfur, aluminum sulfate or iron sulfate. Aim to lower the pH slowly over time, by 0.5 points every 6 months. Going too acidic too fast can shock plant roots.

Adding organic matter like compost, leaf mold or peat moss will also help lower pH in alkaline soils. The organic acids help neutralize the alkalinity.

Getting the soil pH in the optimal zone will ensure silica and other nutrients are readily available to your plants. This helps produce healthy, vigorous growth and disease resistance.

Conclusion

Improving the silica content in soil is an important part of maintaining healthy, productive soil. Silica helps strengthen cell walls in plants, improve drought and pest resistance, and enhance overall plant vigor. There are several methods that can be used to increase silica levels in soil:

– Adding silica sand top dressings directly on top of the soil is a straightforward way to quickly boost silica percentages. Focus on areas where silica-loving plants will grow.

– Amending soil with soluble silica supplements, such as potassium silicate, sodium silicate or magnesium silicate provides an immediately bioavailable form of silica that plants can uptake. Mix thoroughly into soil before planting.

– Using organic mulches and amendments made from silica-rich materials like rice hulls, horsetails, or diatomaceous earth will break down slowly and release silica over time.

– Liquid silicate sprays can be foliar applied directly on plants to supply silica quickly. Target applications when plants are rapidly growing.

– Growing silica accumulator plants like horsetails, bamboo and rice will pull silica from the soil and concentrate it in their tissues. Rotate these crops to avoid depleting silica reserves.

– Adjusting pH into the slightly acidic range can help make silica in the soil more plant-available. Test soil pH annually and amend as needed.

Ongoing soil tests are important to monitor silica levels and make adjustments. Aim for silica levels above 100 ppm, with 150-300 ppm being ideal for most plants. Incorporating multiple silica enrichment techniques leads to sustainable, long-term improvements in soil silica status for improved plant health and productivity.