What To Put Under Artificial Grass For Drainage
We have all been there—staring at a patchy, waterlogged lawn after a heavy rainstorm. It is incredibly frustrating when your outdoor sanctuary turns into a muddy swamp that stays wet for days on end.
The secret to a lush, evergreen look that stays bone-dry is knowing exactly what to put under artificial grass for drainage before the first roll is ever laid. Getting the foundation right is the difference between a dream lawn and a soggy nightmare.
In this guide, I will walk you through the essential layers, from crushed stone to permeable membranes. You will learn how to build a professional-grade base that ensures your new lawn remains puddle-free and smells fresh for years to come.
What's On the Page
- 1 What to Put Under Artificial Grass for Drainage: The Essential Layers
- 2 Choosing the Right Permeable Membrane
- 3 Solving Drainage Issues in Clay Soil
- 4 What to Put Under Artificial Grass for Drainage for Pet Owners
- 5 The Tools You Need for a Perfect Base
- 6 Common Pitfalls to Avoid
- 7 Frequently Asked Questions About What to Put Under Artificial Grass for Drainage
- 8 Conclusion: Build It Right, Enjoy It Forever
What to Put Under Artificial Grass for Drainage: The Essential Layers
When you are planning your installation, think of your lawn like a high-performance filter. Every layer must allow water to pass through quickly while remaining structurally sound. If you get the sub-base wrong, the water has nowhere to go.
The first and most critical layer is the sub-base, typically made of crushed stone or aggregates. Most DIYers make the mistake of using dirt or soil, but these hold onto moisture and will eventually cause the ground to dip and sag.
For most residential gardens, I recommend a 50mm to 100mm layer of MOT Type 3. Unlike the standard Type 1, Type 3 is “reduced fines,” meaning it has fewer tiny dust particles. This allows water to flow through the gaps between the stones much faster.
The Role of the Laying Course
Once your heavy sub-base is compacted, you need a smoother “laying course” on top. This layer provides the final level for your turf while still contributing to the overall drainage capacity of the system.
Many people reach for sharp sand, but I prefer grano dust (crushed granite). Grano dust is far superior because it creates a firm, permeable surface that does not shift or wash away as easily as sand does during heavy downpours.
When deciding what to put under artificial grass for drainage, choosing grano over sand is a pro move. It provides a more stable footing and ensures that your lawn stays flat and functional even if your kids or pets are constantly running across it.
Choosing the Right Permeable Membrane
A common question I get is whether to put a weed membrane above or below the stone base. To keep your drainage working perfectly, the placement of this geotextile layer is absolutely vital for long-term success.
I always suggest placing a non-woven geotextile membrane directly beneath the sub-base. This prevents the heavy stones from sinking into the soft soil over time, which is a process known as “soil migration.”
If you place a cheap, plastic-style membrane directly under the grass, it can actually trap water and pet urine. This leads to that dreaded “sour” smell. Always opt for a high-quality, felt-like fabric that is specifically designed for high permeability.
Why Breathability Matters
Your lawn needs to breathe from the bottom up. A high-quality membrane allows air and water to move freely, which prevents the growth of mold or mildew in the backing of your artificial turf.
If you live in an area with heavy rainfall, consider a “heavy-duty” membrane. These are slightly thicker but are engineered to handle high volumes of water without clogging up with silt or fine dirt particles from the ground below.
Solving Drainage Issues in Clay Soil
If your garden sits on heavy clay, you have a unique challenge. Clay acts like a bathtub; it holds water and drains very slowly, which can cause your artificial grass base to become saturated and unstable.
For clay-heavy areas, you should dig slightly deeper—around 150mm. Fill the bottom 50mm with clean, 20mm shingle or pea shingle. This creates a “void space” where water can sit and slowly soak into the clay without backing up into your lawn.
I often tell my friends that dealing with clay is all about patience. You cannot force the water into the ground, so you must give it a place to wait. Adding a French drain at the lowest point of the garden is also a fantastic “insurance policy” for these scenarios.
The Importance of Grading
Never lay your base perfectly flat. Even with the best drainage materials, you want gravity to be on your side. Aim for a very slight fall or slope (about 1 in 100) away from your house or patio.
This subtle grade ensures that during extreme weather, excess water is directed toward flower beds or soakaways. It is a small detail that makes a massive difference in how your garden handles a sudden summer thunderstorm.
What to Put Under Artificial Grass for Drainage for Pet Owners
If you have dogs, drainage isn’t just about rainwater; it is about managing pet waste. Urine can get trapped in the base layers, leading to unpleasant odors that are hard to get rid of once the grass is installed.
For pet owners, I highly recommend adding a layer of Zeolite or an antimicrobial infill. These volcanic minerals are porous and help neutralize the ammonia in pet urine before it reaches the sub-base layers.
When homeowners ask me what to put under artificial grass for drainage to keep things smelling fresh, I suggest avoiding standard weed membranes directly under the grass. Instead, use a “pet-friendly” turf with a fully permeable polyurethane backing rather than a hole-punched latex backing.
Flushing the System
Even with the best base, you should occasionally “flush” your lawn with a hose. This helps move any crystallized salts from pet urine down through the grano dust and into the sub-base, where they can be naturally filtered away.
Think of your base as a living system. By keeping it clean and clear of debris, you ensure the drainage channels remain open. A quick rinse once a week in the summer is usually all it takes to keep everything pristine.
The Tools You Need for a Perfect Base
You can have the best materials in the world, but if they aren’t installed correctly, your drainage will suffer. You need to ensure every layer is compacted properly to avoid future “pooling” in low spots.
Do not try to tamp down the stone with a hand tool or your feet. Rent a vibrating plate compactor (often called a wacker plate). Run it over the sub-base in multiple directions until the surface is rock-solid and does not show footprints.
- Spirit Level: Use a long level to check your grade and ensure there are no “dips” where water could collect.
- Screed Bar: This helps you smooth out the grano dust layer perfectly before the grass goes down.
- Turf Cutter: Essential for removing existing sod cleanly to make room for your new drainage layers.
Taking the time to prep the ground properly might feel like a lot of work, but it is the secret to a lawn that lasts 15 to 20 years. Trust me, you do not want to be lifting up your grass in two years to fix a sinkhole!
Common Pitfalls to Avoid
One of the biggest mistakes I see is people using recycled aggregates that contain bits of brick or wood. These materials can decompose or shift, creating uneven drainage and potentially damaging the underside of your turf.
Another “no-no” is using a solid concrete slab as a base without proper modification. If you are laying artificial grass over concrete, you must ensure the concrete itself has a slope and that you use a drainage cell or mat between the concrete and the grass.
Without that air gap, water will simply sit between the grass and the concrete, leading to a squelching sound when you walk on it. It can also cause the backing of the grass to rot prematurely, which is a very expensive mistake to fix.
Don’t Skip the Edging
Your drainage layers need to stay contained. Use pressure-treated timber, composite battens, or steel edging to create a firm perimeter. This prevents the grano dust from washing out into your flower beds during heavy rain.
A secure edge also allows you to “tuck” the grass in, creating a neat finish that looks professional. It keeps the entire drainage system “locked in” so that it can do its job effectively for the long haul.
Frequently Asked Questions About What to Put Under Artificial Grass for Drainage
Can I just put artificial grass directly on top of dirt?
I strongly advise against this. Dirt holds moisture, expands when frozen, and turns into mud when wet. Without a proper stone sub-base, your grass will quickly become uneven, and you will deal with constant drainage issues and weeds.
Is sharp sand okay to use for the top layer?
While sharp sand was the industry standard for years, grano dust is now the preferred choice for experts. Sand can shift over time and can hold more moisture than crushed granite, which may lead to slower drainage in high-traffic areas.
How do I know if my garden has poor drainage already?
Perform a simple “perc test.” Dig a hole about 30cm deep, fill it with water, and see how long it takes to empty. If it takes more than a few hours, you have slow-draining soil and should definitely use a thicker MOT Type 3 base layer.
What to put under artificial grass for drainage if I have a very small balcony?
For balconies or roof terraces, you should use a drainage tile or a “shock pad” with built-in drainage channels. This allows water to flow underneath the grass and toward the balcony’s existing drainage outlets or scuppers.
Conclusion: Build It Right, Enjoy It Forever
Creating a beautiful, low-maintenance lawn is a rewarding project, but the magic really happens beneath the surface. By carefully choosing what to put under artificial grass for drainage, you are protecting your investment and ensuring your garden remains a functional, dry space for your family.
Remember to prioritize permeability at every step. Use MOT Type 3 for your foundation, grano dust for your leveling layer, and a high-quality geotextile membrane to keep everything in its place. These steps might take a bit more effort upfront, but the result is a professional-grade lawn that can handle whatever the weather throws at it.
If you are ever in doubt, especially with complex slopes or heavy clay, don’t hesitate to reach out to a local landscaping professional for a quick consultation. But for most of us, following these steps will lead to a stunning, puddle-free garden. Now, grab those tools and get started—your perfect lawn is just a few layers away!
