Can you use rocks for a raised garden bed?

Using rocks for a raised garden bed can be a great option for creating an attractive and functional growing space. Rock gardens allow you to grow plants that require sharp drainage, help prevent soil erosion, provide insulation for plant roots and create unique landscapes. There are some key considerations when selecting and using rocks to build a raised bed, but with careful planning it can be an excellent choice.

What types of rocks work best for raised beds?

When selecting rocks for garden walls, aim for types that are sturdy, weather-resistant and non-toxic to plants. Good options include:

• Granite – Very hard stone that resists weathering. Can last for decades.
• Limestone – Relatively soft but weather-resistant sedimentary rock. Provides alkaline soil environment.
• Sandstone – Sedimentary rock that holds up well to weather. Easy to cut into shapes.
• Fieldstone – Any locally gathered stone good for wall building. Often granite, gneiss or sandstone.
• River rock – Smooth, rounded rock collected from riverbeds. Must be mortared in place.
• Ledge rock – Flat slabs harvested from rock ledges. Can stack neatly.

Avoid using rocks high in salts, sulfur or metals that can leach into the soil, like granite, slate and volcanic rock. Test any rocks with vinegar. Fizzing indicates unsuitability.

What size rocks are best?

Rock size for raised beds depends on wall construction method. Best options include:

• Small gravel or pea gravel – For filling wire frames or cages.
• Fist-sized cobbles – Drain well for mortarless dry-stack walls.
• Larger flagstones – Stacked like bricks if mortared or pinned together.
• Boulders – Used as foundation blocks for retaining wall-style beds.

A mix of rock sizes allows you to fill gaps efficiently. Flat or cubical rocks stack better than round river rock. Ensure any mortared rocks won’t wobble or shift out of place over time.

What shape should the rocks be?

Aim for rocks with relatively flat faces that stack neatly together like bricks. Rounded river rock must be mortared in place. The best rock shapes include:

• Cubes – Stack perfectly and interlock when dry laid.
• Flat slabs – Great flagstones or ledge rock. Stack like a brick wall.
• Angular chunks – Irregular shapes fit together when dry stacked.
• Flat-top cobbles – Provide a stable base layer for mortarless walls.

Avoid thin or rod-shaped stones that can shift out of place. Mixing a variety of rock shapes allows you to fill gaps and create a natural looking wall.

How deep should the rocks be buried?

Burying rocks properly distributes weight and prevents walls from shifting. Depth depends on wall height:

• Up to 2 feet high – Bury base 6 inches
• 2 to 3 feet high – Bury base 8-12 inches
• 3 to 4 feet – Bury at least 12 inches

Compact soil and gravel beneath rocks to prevent settling. For mortared walls, start by digging a trench then backfill with concrete. Wider walls require deeper footings.

Should you use mortar with rock walls?

Dry stacking rocks without mortar has benefits but lacks stability:

• Faster and simpler construction
• Good drainage between rocks
• Can dislodge more easily

Mortaring rock walls creates a stronger raised bed but is more complex:

• Stable walls up to 3 feet tall
• Prevents rock displacement
• Requires masonry expertise
• Hard to disassemble beds later

Use mortar for freestanding walls higher than 2 feet, retaining walls or sloped sites. Avoid mortar with salt-leaching rocks like limestone or sandstone.

What type of soil is ideal for rock raised beds?

Well-draining, fertile soil enriched with organic matter suits most rock garden beds. The best options include:

• A mix of compost, garden soil and sharp sand for drainage
• Potting mixes enhanced with compost or worm castings
• Lightweight blends made for container gardening
• Rich “mel’s mix” with compost, vermiculite and peat moss

When filling taller beds, put coarser gravel or rocks at the base for drainage covered by soil. Avoid heavy clay soils that compact and inhibit root growth.

What can you grow in a rock raised bed?

The rocky but well-draining environment suits a wide variety of plants, including:

• Drought-tolerant perennials like lavender, succulents and sedum
• Rock garden classics including alpine plants
• Herbs like thyme, oregano, sage and rosemary
• Shallow-rooted vegetables – Lettuce, spinach, beans, peas
• Small flowering annuals like marigolds, petunias and begonias

Avoid large vegetables and fruits or trees/shrubs, which require deeper soil. Use rock wall crevices to tuck in small potted plants.

What are the benefits of using rocks for raised garden beds?

Key advantages to using rocks for raised beds include:

• Provide excellent drainage needed by some plants
• Retain heat and radiate it to plants, extending the growing season
• Create unique landscape feature and visual interest
• Allow gardening in poor native soil by providing better grow environment
• Prevent soil erosion and retain bed shape
• Offer insulating properties to protect plant roots from temperature extremes

What are the downsides to rock garden beds?

Potential disadvantages to consider include:

• Can require more time and labor to construct
• Mortared walls are difficult to remove or alter later
• Dry-stacked walls more prone to shifting and toppling
• Require well-draining soil mix to prevent overly dry conditions
• Limit plant selection to those suited to sharp drainage
• Difficult to expand or access buried utilities if needed

Tips for constructing rock raised beds

Follow these top tips for building your own rock raised bed:

• Choose weather-resistant, non-toxic rocks suited to gardening
• Select a mix of rock sizes to fill gaps efficiently when stacking
• Dig trenches wider and deeper than wall to stabilize mortared beds
• Use larger rocks or boulders as base foundation layer
• Stack rocks with slight incline or batter inwards for freestanding walls
• Fill beds with quality, well-draining soil high in organic matter
• Leave some gaps between rocks for airflow and drainage
• Plant densely with species accustomed to excellent drainage

Example layouts for rock raised beds

Rocks can be used to form raised beds in many shapes and sizes. Here are some example layouts:

Simple rock borders:

Use medium-large cobbles or flagstones stood on edge to form borders enclosing a garden bed. Leave space between rocks for drainage and plant densely.

Dry-stacked rock walls:

Use larger, flatter fieldstones, ledgerock or pavers stacked like bricks leave small gaps between. No need for mortar if less than 2 feet high.

Mortared rock walls:

For permanent freestanding walls above 2 feet, use mortared stone or urbanite blocks. Bury lower edge below frost line.

Terraced rock beds:

On slopes, make stair-stepped beds contained by mortared rock retaining walls. Allows more planting space.

Decorative rock beds:

Use shaped, ornamental rocks and boulders to form creative patterns. Combine with gravel and low-growing plants.

Rock and timber raised beds:

Line beds with rocks then use rot-resistant wood planks secured with rebar pins for the upper portion. Efficient use of materials.

Conclusion

Rocks can make an excellent building material for raised garden beds of all types. Select your rocks carefully, use proper construction techniques for stability and pair them with suitable soil and plants. With some planning, a rock raised bed can become a unique and functional focal point in your landscape that will offer years of gardening enjoyment.