Part 2: The Ground Up Method

Gardening starts with the soil we dig into, but what lies beneath it? As part of the Ground Up Method, understanding the bedrock layer is essential for creating a healthy and thriving garden ecosystem. Often overlooked and misunderstood, bedrock forms the stable foundation of your garden’s ecosystem, influencing soil structure, drainage, and even the types of plants that will thrive. By examining this critical layer, we gain deeper insight into how the Ground Up Method emphasizes working with nature from the ground—literally—up.

What Is the Bedrock Layer?

The bedrock layer is the solid layer of rock that lies beneath the soil and subsoil in your garden. Within the Ground Up Method, it’s considered the starting point for nutrient cycling and structural stability. Over time, this rock gradually weathers, releasing minerals into the soil—a key process that contributes to soil fertility and affects the soil’s pH and nutrient profile.

Why the Bedrock Layer Matters

In the Ground Up Method, the bedrock layer serves as the foundation for all other layers in the garden. While it’s hidden from view, its influence on soil fertility, drainage, and pH is pivotal. By understanding the role of bedrock within this method, you can work with nature to create a healthier, more resilient garden.

How the Bedrock Layer Fits into the Ground Up Method

1. Mineral Supply
   As bedrock weathers, it releases essential minerals like calcium, magnesium, and potassium into the soil. These nutrients help plants grow strong and healthy.
2. Soil pH Influence
   The type of bedrock beneath your garden affects the pH of the soil. For example:
   • Limestone bedrock tends to create alkaline soils.
   • Granite bedrock often leads to more acidic soils. Knowing your soil’s pH can help you choose the right plants or amendments.
3. Drainage and Water Retention
   Bedrock depth and type influence how well your garden drains. Shallow bedrock can lead to water pooling, while porous rock like sandstone may improve drainage.
4. Microbial Interactions
   Even microbes interact with bedrock, breaking it down into smaller particles and enriching the soil with minerals. This is part of the natural process that supports your garden’s bioactivity.

A Master Gardener’s Story: Challenges with Decomposed Granite

My property sits on decomposed granite bedrock. There’s about two or 2 1/2 feet of topsoil then you hit granite hardpan, which is extremely hard today through. While beautiful and rich in minerals, it presented several challenges for gardening:

1. Shallow Soil Depth
   Decomposed granite often leaves only a thin layer of soil above it. This made it difficult for plants to establish deep roots, limiting their access to water and nutrients.
2. Water Saturation and Runoff
   The compact nature of decomposed granite caused water to pool during heavy rains, leading to saturation in some areas and excessive runoff in others. Managing drainage became a critical part of the garden’s design.
3. Nutrient Availability
   While decomposed granite is mineral-rich, the nutrients aren’t always immediately available to plants. I have found that adding organic matter and microbial tea was necessary to enhance soil fertility, and to provide optimal plant growth.
4. Plant Selection
   Choosing drought-tolerant plants with shallow root systems has helped overcome the limitations of the shallow soil and inconsistent water retention. D and in areas where I want to grow specialty plants, raised beds, and using the No-Till/No-Dig method has been important.

This experience taught me the importance of understanding your bedrock layer before planting. By addressing these challenges with thoughtful planning and soil amendments, we created a thriving, resilient garden that adapted to its unique foundation.

How to Work With the Bedrock Layer

Although you can’t change the bedrock itself, understanding its role can help you make better gardening decisions.

1. Test Your Soil
   A soil test can reveal the pH and mineral composition of your soil, giving you clues about the underlying bedrock. Most gardening centers or extension services offer affordable testing kits.
2. Choose the Right Plants
   Select plants that thrive in your soil’s natural conditions. For example:
   • Acid-loving plants like blueberries or azaleas may do well over granite bedrock.
   • Alkaline-tolerant plants like lavender or lilacs may thrive over limestone.
3. Amend Soil as Needed
   If your soil lacks nutrients or has an unsuitable pH, you can amend it with organic matter, lime, or sulfur to create a better growing environment.
4. Improve Drainage
   If shallow bedrock causes poor drainage, consider raised beds or planting species adapted to wetter conditions.

Bioactivity and the Bedrock Layer in the Ground Up Method

Bioactivity—the life and processes driven by microorganisms, plants, and animals—plays a surprising role in breaking down bedrock and shaping soil formation.

• Microbial Activity: Microbes release acids and enzymes that chemically weather bedrock, dissolving minerals and making nutrients available to plants.
• Plant Roots: Deep-rooted plants exert pressure on bedrock, causing cracks. Roots also release organic compounds that attract microbes and further aid in mineral breakdown.
• Natural Ecosystem Engineers: Worms, insects, and burrowing animals aerate the soil and allow water and organic matter to reach the bedrock, enhancing weathering processes.
• The Feedback Loop: As bioactivity breaks down bedrock, the resulting minerals enrich the soil, fostering even more life above.

Fascinating Facts About Bedrock and Gardening

• Glacial History: In many regions, glaciers scoured the landscape, exposing or depositing different types of bedrock. This history influences modern soil characteristics.
• Deep Roots: Certain plants, like trees, can send roots deep enough to interact directly with fractured bedrock, accessing water and nutrients.
• Human Impact: Quarrying and urban development can alter the natural bedrock layer, sometimes disrupting local ecosystems.
• Ancient Bedrock: Some bedrock formations are billions of years old, serving as a window into Earth’s geological history.
• Natural Filtering: Bedrock can act as a natural filter for groundwater, influencing the purity of water sources in your area.
• Plant Adaptation: Plants native to a region often evolve to thrive with the specific minerals and conditions provided by the local bedrock.

Next Steps with the Ground Up Method

Curious about how the bedrock layer interacts with other layers in your garden? Stay tuned for the next post in our Ground Up Method series, where we’ll explore the soil layer and how to build healthy, nutrient-rich earth for your plants.

Additional Resources

Here are some excellent resources and links to help gardeners understand the role of bedrock in their gardening ecosystem:

1. Bedrock and Geology
2. Vegetation, Growth and Bedrock