River rock can make for an attractive and natural looking ground cover for landscaping projects. However, proper installation is key to creating a finished look that is stable, weed-resistant and permeable. An important part of river rock installation is selecting and preparing the correct base material to go under the rocks. This provides a foundation for the river rock to rest on and prevents the rocks from sinking into the soil. There are a few good options for base materials that work well under river rock in landscaping applications.
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Reasons for Using a Base Under River Rock
There are several important reasons why some type of base material should be installed under river rock for landscaping:
- Provides a stable foundation – River rocks need a solid base underneath in order to stay in place. Without a base, the rocks can shift around and scatter.
- Prevents sinking – Uncompacted soil has a tendency to erode and sink under the weight of rocks. A sturdy base prevents the rocks from sinking into the dirt.
- Inhibits weed growth – A compacted base acts as a weed barrier, preventing seeds below from germinating and poking through the rocks.
- Allows for drainage – Bases made from porous materials like gravel allow for drainage and permeability.
- Makes installation easier – It’s much simpler to place and level river rocks on top of an even, flat surface.
- Extends longevity – A proper base prevents erosion and keeps the river rocks in place longer.
Installing some type of clean, compacted base material under river rock is highly recommended for successful landscaping.
Sand
One option for a base under river rocks is sand. A layer of coarse sand needs to be at least 2-3 inches deep in order to provide adequate support. Sand offers these advantages:
- Readily available and inexpensive.
- Naturally permeable, allows drainage.
- Easy to smooth and level.
- Prevents rock sinkage in soft or muddy soils.
There are also some disadvantages to using sand under river rock:
- Can erode or shift over time.
- May need occasional re-leveling.
- Provides less stability than gravel or crushed rock.
- May compact down over time.
Sand is best used as a base for river rock in well-drained areas and smaller landscaping applications. For larger spaces or areas prone to erosion, gravel or crushed rock are better options.
Gravel
Gravel makes an excellent base under river rock landscaping. A 2-4 inch layer of gravel should be compacted down before adding river rocks. Gravel offers these benefits:
- Excellent drainage properties.
- Very stable, does not erode easily.
- Natural weed barrier.
- Heavy enough to keep rocks in place.
- Relatively inexpensive.
- Easy to grade smooth and level.
The minor drawbacks to using gravel as a base include:
- Can settle a bit over time.
- May need occasional topping off.
- Takes more effort to excavate and remove, if needed.
For most situations, a compacted gravel base under river rock is an ideal choice. The crushed stone offers durability, excellent drainage and stability.
Crushed Rock
Crushed rock makes an extremely solid base under river rock in landscaping applications. Materials like 3/4-inch minus crushed granite or crushed limestone are excellent choices. A 4-6 inch layer should be compacted down. Advantages of crushed rock include:
- Very stable, does not erode.
- Natural weed barrier properties.
- Allows excellent drainage.
- Angular shape locks rocks together.
- Heavy weight keeps rocks from shifting.
- Withstands freeze/thaw cycles.
Disadvantages of crushed rock are:
- Typically more expensive than sand or gravel.
- Requires heavy equipment to excavate, if needed.
- Angular sharp edges may puncture landscape fabrics.
In summary, a crushed rock base provides maximum stability and longevity for river rock landscaping, but is more expensive and difficult to install compared to sand or gravel options.
Paver Base
For patios or walkways using river rock, you can use the same materials that are used under pavers or flagstones. This might consist of a compacted sub-base of crushed gravel topped with a 1-2 inch layer of paver sand or chip stone dust. The paver base provides these advantages:
- Very smooth and level surface for achieving a flat finish.
- Stays in place, does not erode easily.
- Prevents vegetation growth.
- Excellent drainage.
- Specialty materials may provide optimum performance.
Possible disadvantages of using paver base include:
- More expensive than plain gravel or sand.
- May require professional installation for best results.
- Sub-base excavation can be challenging.
Paver bases are ideal for river rock used in patios, walkways and paths where a very smooth, level surface is desired.
Landscape Fabric
Using a landscape fabric under river rock can provide added stability and also helps block weed growth. The fabric provides these benefits:
- Prevents vegetation from sprouting up.
- Keeps rocks from sinking into soft soil.
- Allows drainage while filtering sediment.
- Can prolong the life of the base below.
- Comes in lightweight poly or heavier duty woven options.
Some things to keep in mind when using landscape fabric under river rock:
- Do not use plastic sheeting, it blocks drainage.
- Fabric may need to be secured with spikes or staples.
- Overlap seams 6-12 inches to prevent weeds.
- Can tear during installation or use.
- May need occasional maintenance for best results.
In summary, landscape fabric can provide added stability but an appropriate gravel or crushed stone base is still required under river rock installations.
Sand vs. Gravel vs. Crushed Rock
When selecting a base for river rock landscaping, there are some key comparisons between sand, gravel and crushed rock:
| Base Material | Sand | Gravel | Crushed Rock |
|---|---|---|---|
| Cost | Low | Medium | High |
| Permeability | High | High | High |
| Stability | Low-Medium | Medium-High | Very High |
| Weed Prevention | Low | Medium | High |
| Leveling Difficulty | Easy | Medium | Hard |
As this comparison shows, sand provides the most affordable and easiest to install option, gravel offers a good balance, while crushed rock is the most rigid, stable, weed-free choice.
Installation Tips
Here are some important installation tips to ensure proper preparation of a base under river rocks:
- Excavate area to necessary depth, removing all vegetation and organic matter.
- Install landscape fabric if desired, securing edges with spikes.
- Spread base material to needed thickness; maintain proper slope for drainage.
- Compact base using equipment like a plate compactor or hand tamp.
- Level and smooth base, being sure it is even and stable.
- Moisten base and do final compacting to firm it up.
- Place river rocks onto the prepared base, filling in gaps as needed.
- If needed, use polymeric sand to fill small spaces between rocks.
Properly installing an appropriate compacted base under river rocks results in an attractive, durable finished landscape.
Maintenance
River rock landscaping installed over a proper base requires minimal long-term maintenance but here are some recommendations:
- Inspect area after major storms and refill any washouts.
- Pull any weeds that grow up through the rocks.
- Rake to smooth out rocks that have shifted.
- Add new rocks periodically to replace any that have sunk or scattered.
- Control ant/insect mounds which can displace rocks.
- Re-compact base if any soft or low spots appear.
- Prevent soil or mulch buildup which holds moisture.
- Power wash to maintain appearance (no chemicals).
With proper installation and occasional maintenance, a river rock landscaped area can provide years of beauty and enjoyment.
Costs
Costs for materials to install a base under river rock can vary based on type of materials, hauling fees and local availability. Some typical price ranges are:
- Washed masonry sand – $15 to $50 per ton
- Gravel (3/4-inch) – $30 to $60 per ton
- Crushed granite – $60 to $120 per ton
- Landscape fabric – $0.15 to $0.30 per square ft
Professional installation costs are additional, typically ranging from $5 to $12 per square foot depending on the site accessibility and complexity.
With proper base preparation and installation, a river rock landscaped area can provide an attractive, maintenance-free ground cover solution for years to come. The beauty and durability of river rock can be enhanced by selecting the right base materials and construction methods suited to your specific site conditions and project goals.