To build a garden drainage system, test soil, set a sloped trench with perforated pipe and gravel, then send water to a safe outlet.
Water that sits on beds or lawns starves roots of oxygen and invites rot. With a simple plan you can move excess water away from plant roots, protect paths, and keep the yard usable after rain. This guide shows the full process from quick diagnosis to a neat finish you can mow over.
Drainage Methods At A Glance
Pick the tool that matches the problem and your site. Use this table to spot the right fit before you dig.
| Method | Best Use | Notes |
|---|---|---|
| French drain (perforated pipe in gravel) | Persistent soggy strip, base of a slope, along foundations | Needs steady fall to an outlet; wrap trench, not the pipe |
| Surface channel with grates | Patios, driveways, path edges | Fast collection; link to a sump or to the pipe run |
| Grassy swale | Wide lawn area with gentle slope | Shallow, broad, mowable; guides water to a safe spot |
| Soakaway pit | Nowhere to send water, soil drains reasonably | Stone-filled pit; size to local rainfall and soil rate |
| Rain garden (bioretention) | Downspouts, driveway runoff | Planted basin that holds and filters stormwater |
| Raised beds with organic matter | Beds on slow clay soils | Lift roots above wet zone while soil improves |
Garden Drainage System: Step-By-Step Build
Most yards do best with a combo: a trench drain to move water and surface inlets where puddles form. The steps below keep things tidy and code-friendly.
1) Map Water Sources And Safe Outlets
List where water starts: roof edges, a slope above you, a compacted path, a neighbor’s over-watering. Mark low spots after a rain. You need a legal, safe place to send water: a soakaway on your land, a rain garden, or a lawful connection to a storm line. Don’t discharge onto a sidewalk or a neighbor’s lot.
Trace roof downspouts. If they dump beside a wall, plan to route them into the new line. Look for hardpan layers or old fill that holds moisture; you might see a green stripe after storms or a firm ridge a spade won’t cut. These clues help place the trench where it earns its keep.
2) Do A Simple Percolation Test
Dig a hole 12 in deep and 6–12 in wide in the area you plan to drain. Fill it with water twice to pre-soak, then refill to the top. Time the drop in inches per hour. Faster than 1 in/hr means easy infiltration. Between 0.25 and 1 in/hr calls for larger trenches or an outlet with more fall. Slower than 0.25 in/hr points to a pipe run to a ditch or a lined basin rather than a soakaway.
For design ideas on planted basins and sizing, see the EPA’s rain garden guidance. For broader drainage choices and site checks, the RHS page on installing drainage gives clear, practical notes.
3) Choose The Trench Route And Slope
Plan a straight route where you can keep a steady fall. A drop of 1–3% works well: that’s 1–3 cm for every meter of run. Aim the outlet to your chosen soakaway, rain garden, or lawful drain point. Keep at least 1 m away from tree trunks and stay clear of buried utilities.
Shorter runs clog less. If you need to snake around a patio, use sweeping curves, not tight S-bends. Where grade is flat, cut a slightly deeper outlet end or raise the inlet end with a catch basin so the line keeps falling.
4) Mark Utilities And Set Levels
Call your local utility mark-out service before any digging. Stretch string lines along the intended route. Set stakes every 2–3 m and mark the target depth on each stake so the bottom of the trench follows the planned fall.
Drop a line level on the string or use a small laser. Note the starting elevation and check each stake. A minor tweak now saves a lot of shoveling later.
5) Gather Tools And Materials
You’ll work faster with the right kit. Lay everything out before you break ground.
- Spade, trenching shovel, mattock, wheelbarrow
- Line level or laser level, measuring tape, stakes, string
- Landscape fabric or geotextile (for trench walls and top)
- Perforated 100 mm drain pipe with fittings; solid pipe for outlet
- Clean angular gravel 10–20 mm; a little sand for bedding if needed
- Catch basins or channel drains with grates (where puddles gather)
- Saw for pipe, drill for extra holes if needed, marker paint
- PPE: gloves, boots, eye protection
Pipe choices include flexible corrugated and rigid PVC. Flexible pipe lays fast around gentle arcs but crushes easier. Rigid PVC holds grade and cleans well through a cleanout. Pick based on route and load. If cars cross the line, step up pipe strength or add a sleeve.
6) Dig The Trench
Typical size for a yard drain is 200–300 mm wide and 450–600 mm deep, but match this to soil, slope, and flow. Keep side walls tidy to make lining and backfilling easier. Pile spoil on a tarp so you can reuse the best topsoil for finishing.
Watch for layers. If you hit sticky subsoil that smears, scrape it clean so water can reach the pipe zone. If groundwater seeps in, pump as you work and keep the trench safe with stepped sides where needed.
7) Line The Trench
Lay geotextile so it covers the walls and leaves enough overlap to wrap over the top at the end. Don’t wrap the pipe itself. The goal is to keep fine soil out of the gravel while letting water pass through the trench body.
Overlap seams by at least 200 mm. Where roots might seek the stone, leave enough fabric to fold snugly over the top layer before you cap with soil or mulch.
8) Add Bedding Gravel And Set The Pipe
Tip in 50–75 mm of clean gravel and level it to your slope marks. Lay perforated pipe with holes down. Join sections so the interior stays smooth. Check fall with the level as you go. Where surface water collects, set a small catch basin and connect it into the pipe run.
Keep fittings square. Make sure the outlet end sits lower than the inlet, and that no part of the line sits lower than the outlet or you’ll hold water in the pipe.
9) Backfill With Gravel And Close The Trench
Cover the pipe with gravel to within 75–100 mm of grade. Fold fabric over the top. Finish with topsoil and turf, or with decorative gravel along a bed edge. Keep the finish flush so mowers pass cleanly.
On beds, cap with mulch. On a lawn, tamp lightly and water the sod so it knits. Keep wheel traffic off the line for a week to let the fill settle.
10) Build A Soakaway Or Link To A Rain Garden
If your soil test showed moderate infiltration, add a soakaway at the end of the pipe. A common backyard pit is 600–900 mm square and deep, lined with fabric and filled with clean stone. In faster soils, a planted basin handles roof downspouts well and adds habitat. Size the basin area to the roof area you feed and your soil rate, as outlined in the EPA guide linked above.
Place the basin at least 3 m from building walls. If your site is tight, a small pre-cast dry well may suit. Keep an overflow path to turf or a swale so rare storms do not flood paths.
Planning Tips That Save Time
Good drainage starts on the surface. Before digging, check grading, compaction, and where downspouts drop water. Small fixes up top often cut the length of trench you need.
- Swap smooth PVC elbows for sweep bends to keep flow moving.
- Keep a cleanout at the high end with a removable cap.
- Add a silt trap or sump near the outlet if runoff carries grit.
- Edge the finish with brick or steel to stop turf creeping over grates.
Redirect roof leaders with solid pipe until you reach the gravel zone. That way you don’t dump concentrated water near walls or walkways. Where a patio meets a lawn, set a channel drain at the low edge so water does not jump the joint.
Soil And Slope: What The Numbers Mean
Numbers help you choose trench size and outlet style. Use the ranges below as a rule-of-thumb. Local codes and rainfall affect final choices.
| Perk Rate (in/hr) | What It Means | Action |
|---|---|---|
| > 1.0 | Water sinks fast | Smaller trench; rain garden or shallow soakaway works |
| 0.25–1.0 | Moderate infiltration | Standard trench with steady fall; larger basin volume |
| < 0.25 | Slow, heavy soil | Prioritize pipe to a ditch or lawful drain; plant raised beds |
On clay, boost soil structure over time with compost and coarse grit in beds. That helps roots find air. In a lawn, core aeration and topdressing after the install improve surface intake so less water reaches the drains in the first place.
Surface Collection: Catch Basins And Channels
Sheet flow across patios and driveways needs a slot to drop into. Set channel drains at the low edge and link to the pipe run. In lawns, a round basin with a grate at each puddle point keeps grass usable. Set the rim just below grade so water finds it naturally.
Space inlets where water actually gathers, not on a neat grid. In shady corners, leaves build up fast; pick grates that lift out easily and keep a spare on hand in case one cracks.
Swales, Beds, And Planting Choices
A shallow swale shaped with a wide base moves water quietly across the yard and doubles as a path edge. On heavy clays, raised beds filled with compost and gritty material lift roots above wet zones. Pick plants that like the conditions: moisture lovers near basins, tougher species up-slope.
Where you add a rain garden, choose deep-rooted natives that handle both wet and dry spells. Group them by height: taller clumps in the center, shorter around the rim so flow can spread without backing up.
Outlets That Don’t Cause Trouble
Good ends make good neighbors. Send water where it can spread or soak without eroding soil. A pop-up emitter works in turf for light flows. For larger volumes, discharge onto a splash pad of stone or into a planted basin. Never connect to a sanitary sewer.
If a curb tie-in is allowed, use a proper sleeve and keep edges neat. Where wildlife visits, cover outlets with a grate that keeps small animals out but still lets debris pass.
Maintenance: Keep Water Moving
Good drainage needs simple care. After big storms, lift grates and clear silt. Each spring, flush the cleanout with a hose. Keep tree roots away from the trench line. If a patch stays wet again, check for crushed pipe where vehicles crossed.
Every year or two, pull a few inches of cloggy mulch off the top of a basin and refresh it. On channels, scrub algae from grates so they don’t get slick. Where roof grit builds up, add a leaf screen at the downspout.
Common Mistakes To Avoid
- Dead-flat pipe runs. Give every run a measurable fall.
- Wrapping the pipe in fabric. Line the trench and fold over the top instead.
- Round pea gravel. Use angular stone so voids stay open.
- No outlet plan. Trench volume alone cannot solve standing water on slow soils.
- Dumping on a neighbor’s lot. Keep discharge on your land or to a legal drain.
- Tiny soakaways on slow soil. Match pit size to rain load and perk rate.
- Too few inlets. Place them where puddles appear, even if that adds fittings.
Cost And Time: What To Expect
A weekend team can install a 10–15 m line with a couple of inlets. Trenching by hand is the longest part. Budget for pipe, fittings, fabric, and a delivery of clean stone. Renting a trenching tool speeds the job on long straight runs.
Material ballpark for a small yard line: 15 m of 100 mm perforated pipe, 0.8–1.2 m³ of gravel, one or two basins, one roll of fabric, plus solid outlet pipe. Add a load of topsoil or turf if your finish needs it. Keep receipts; after the first storm you may spot a short section to extend, and matching fittings are easier when you know the brand.
Checklist: Build Sequence
Use this quick list on site to stay on track.
- Mark utilities, water paths, and safe outlets.
- Run a perk test where water collects.
- Set string lines and stake target depths.
- Dig and line the trench, leaving overlap.
- Add bedding gravel, set pipe with holes down.
- Install catch basins or channels where needed.
- Backfill with gravel, fold fabric, finish grade.
- Connect to soakaway, rain garden, or legal drain.
- Flush, check fall, and tidy grates after the first storm.
When To Call A Pro
Bring in a contractor if your lot has a steep bank, a high water table, or if local rules require permits for storm lines. Complex sites may need a survey, larger pipes, or a sump with a pump. A pro can also core-drill a curb or set a lawful tie-in where codes allow.
If you share a boundary drain or live on a hillside with many homes below, plan with neighbors. A short chat now avoids disputes later, and you might even share a trench where lines meet.
Why This Works
Plants fail in saturated ground because roots need air. A gravel trench creates open voids and a known path that water prefers. The pipe carries flows that exceed soil intake. Catch basins skim surface water before it spreads. A soakaway or planted basin gives water a place to sit briefly and then sink into the subsoil. The whole system lowers the time your soil stays saturated after rain.
Over months, beds amended with compost drain better and hold shape in storms. Pair that with clean inlets and a reliable outlet and your lawn dries faster, paths stay firm, and roots stay healthy.
Finish Ideas That Look Good
Once the trench is closed, blend the route into the garden. A narrow gravel strip along a border doubles as a path and a discrete drain line. Stepping stones set over geotextile keep mud off shoes while water finds the trench below. Use turf where you want a seamless look.
Where the outlet meets a basin, set a fan of flat stones as a splash pad. It spreads flow and looks tidy. Add a short edging of brick or steel so soil doesn’t creep and bury the exit over time.
Seasonal Care And Troubleshooting
In fall, keep leaves off grates and out of basins. In winter, watch for freeze-thaw heave that shifts channel edges. In spring, check that downspouts still feed the right points. After a cloudburst, walk the route: water should start at inlets, move through the line, and exit cleanly without eroding soil.
If a spot stays wet after your install, look for these signs. A high point in the pipe creates a belly that traps water; re-set that section with proper fall. A crushed span leaves the trench full but flow stops; replace that length and add a protective sleeve. If the outlet sits in a dip, raise it on stone or extend it so water can leave freely.
Safety And Codes
Wear PPE, brace narrow trenches, and keep kids and pets away from open pits. Check local rules on discharging stormwater, digging near property lines, and working near utilities. Many places ban connections to sanitary sewers. When unsure about a boundary or easement, ask the local office before you start.