Retaining Wall with Trees: Build Guide & Planting

A retaining wall provides crucial soil stabilization on sloped properties, and integrating trees into this structure offers both aesthetic beauty and environmental benefits. Proper drainage systems are vital for the longevity of any retaining wall, especially one supporting the added weight and water needs of trees. Allan Block, a leading manufacturer of retaining wall systems, offers guidelines for constructing durable walls capable of withstanding the pressures of soil and root systems. Landscape architects often specify particular tree species, considering factors such as mature size and root structure to ensure the long-term stability of the retaining wall with trees and the surrounding landscape.

Building a Lasting Landscape: Your Guide to Retaining Walls with Trees

A retaining wall combined with carefully chosen trees isn’t just a structure; it’s a living, breathing part of your landscape. It can prevent soil erosion, create usable space on sloped properties, and add significant visual appeal. But getting it right requires careful planning and execution. This guide provides a comprehensive approach to building a retaining wall and integrating trees for a beautiful and functional result.

Part 1: Planning is Paramount

Before you even think about digging, meticulous planning is crucial. This phase sets the stage for a successful and long-lasting project.

1. Assess Your Site & Define the Purpose: Understanding your soil type, the slope of the land, and the amount of weight the wall will need to hold back (soil, water, and tree root systems) is the first step. What problem are you solving with the retaining wall? Are you creating a level patio, preventing erosion, or just adding visual interest? Also consider the location of existing underground utilities. Call before you dig.

2. Wall Design & Material Selection: The height of the wall significantly impacts the design and material choices. For taller walls (generally above 4 feet), you’ll likely need engineering plans and permits. Common materials include:

   • Treated Timber: Affordable and relatively easy to work with, but has a shorter lifespan than other options.
   • Concrete Blocks: Durable and versatile, offering a range of styles and colors.
   • Natural Stone: Provides a beautiful, natural look but can be more challenging to install.
   • Poured Concrete: Extremely strong and durable, but requires specialized equipment and expertise.

   Your local climate should also influence your material choices. In areas with freeze-thaw cycles, materials resistant to cracking and expansion are essential.

3. Drainage Considerations: Proper drainage is non-negotiable. Without it, water pressure builds up behind the wall, leading to eventual failure. A well-designed drainage system includes:

   • Gravel Backfill: A layer of gravel behind the wall allows water to drain freely.
   • Perforated Drain Pipe: Placed at the base of the wall, this pipe collects water and directs it away from the structure.
   • Weep Holes: Small openings in the wall that allow water to escape.

4. Permits and Regulations: Check with your local building department about required permits for retaining walls. They will also have information on required setbacks from property lines and underground utilities.

Part 2: Building the Retaining Wall

Now that you’ve planned, it’s time to get your hands dirty! Building a retaining wall requires patience, precision, and attention to detail.

1. Excavation: Dig a trench along the planned wall alignment, wider than the wall’s base. The depth depends on the height of the wall and the soil conditions. Remember to account for the base material (usually gravel).

2. Base Preparation: A solid, level base is critical. Compact the soil at the bottom of the trench and then add a layer of compacted gravel. This provides a stable foundation for the wall.

3. Laying the First Course: This is the most important step. Ensure the first course of blocks or stones is perfectly level, both horizontally and vertically. Use a level and shims as needed.

4. Building the Wall: Continue laying courses, overlapping the joints for strength. Add drainage material (gravel backfill and perforated pipe) behind the wall as you build.

5. Backfilling: Once the wall is complete, backfill behind it with gravel and then topsoil. Compact the soil in layers to prevent settling.

Part 3: Selecting the Right Trees

Choosing trees that thrive near retaining walls involves considering their size, root system, and water needs.

1. Root System Considerations: Avoid trees with aggressive, shallow root systems that can damage the wall. Opt for trees with deep, non-invasive roots. Consider these examples:

   Tree Type	Root System Characteristics	Suitability for Retaining Walls
   Japanese Maple	Relatively shallow, but not aggressive; well-suited for containers.	Good
   Eastern Redbud	Deep taproot; less likely to interfere with the wall.	Excellent
   Serviceberry	Non-aggressive, fibrous root system.	Excellent
   Dwarf Conifers	Compact root systems.	Good
   Willow Trees	Highly Aggressive root system; Avoid planting near wall.	Poor

2. Mature Size: Choose trees that won’t outgrow their space. Consider the mature height and width of the tree to ensure it won’t overhang walkways or obstruct views. Also, a too large tree could cause damage to the retaining wall.

3. Water Needs: Select trees that tolerate the drainage conditions near the wall. The area behind the wall may be drier than other parts of your landscape. Drought-tolerant species are often a good choice.

4. Sun Exposure: Match the tree’s sun requirements to the amount of sunlight the area receives.

Part 4: Planting Trees Near the Retaining Wall

Planting trees near a retaining wall requires careful placement and proper soil preparation.

1. Planting Distance: Maintain a safe distance between the tree and the wall, especially for larger species. Consult with a landscape architect or arborist for specific recommendations. As a general rule, the tree should be planted at least half the distance of its maximum mature height.

2. Soil Preparation: Amend the soil with compost or other organic matter to improve drainage and fertility.

3. Planting Technique: Dig a hole twice as wide as the root ball and just as deep. Gently remove the tree from its container and loosen any circling roots. Place the tree in the hole, ensuring the top of the root ball is level with the surrounding soil. Backfill with amended soil and water thoroughly.

4. Mulching: Apply a layer of mulch around the base of the tree to help retain moisture and suppress weeds. Keep the mulch a few inches away from the trunk to prevent rot.

5. Watering: After planting, trees should be watered well and consistently for the first few months. It is important for new trees to become established. Also, consider setting up a watering plan for the summer months.

So, there you have it! Building a retaining wall with trees might seem like a big project, but with a little planning and elbow grease, you can create a stunning and functional landscape feature. Just remember to take your time, choose the right materials and plants for your climate, and enjoy the process. Happy gardening, and here’s to many years of enjoying your beautiful retaining wall with trees!