How do I do a perc test before landscaping?

A perc test (percolation test) measures how quickly your soil absorbs water — it's essential information before installing irrigation, drainage systems, raised beds, or any landscaping that depends on water movement through your soil.

In New Brunswick, perc tests are most commonly associated with septic system approvals (which require a licensed professional and provincial certification), but the DIY version — sometimes called a drainage or infiltration test — is something any homeowner can do before a landscaping project. The two are different: the certified septic perc test is a legal requirement handled by a licensed engineer or soil evaluator; the DIY drainage test is a practical planning tool.

How to Do a DIY Drainage/Infiltration Test

The process is straightforward. Dig a hole 30cm wide and 30cm deep in the area you want to test — or multiple holes if you're testing a large area. Fill the hole with water and let it drain completely. This pre-soaks the soil, which gives you a more accurate reading. Then fill it again and time how long it takes to drain fully.

Interpreting your results:

• Drains in under 30 minutes — Fast drainage (sandy soil). Great for most plants, but you'll need to add organic matter to retain moisture. Common in coastal NB areas like Shediac and Miramichi.


• Drains in 30 minutes to 4 hours — Ideal drainage for most landscaping and planting.


• Takes 4–8 hours — Slow drainage. You have clay-heavy or compacted soil. Common in the Saint John River Valley and Fredericton area. Plan for raised beds, amended soil, or a French drain.


• Still standing after 8+ hours — Very poor drainage. You likely have a hardpan layer or high clay content. Significant intervention needed before planting.

NB-Specific Context

New Brunswick soils vary dramatically by region. Fredericton and the river valleys tend toward heavy clay that drains slowly and compacts easily. Coastal areas near Moncton and Shediac often have sandy, fast-draining soils. Northern NB can be rocky with shallow topsoil. Test in spring after the ground thaws (late April to May) or in fall — avoid testing during or right after heavy rain, which skews results toward slower drainage.

NB's freeze-thaw cycle also matters here. Poor drainage means water sits near plant roots and hardscape bases, freezes, and causes significant heaving. A proper drainage assessment before building a patio, walkway, or planting bed saves you from expensive repairs down the road.

Practical Tips

Test in multiple spots across your yard — drainage can vary significantly within a single property. If you're planning a patio or retaining wall, test where the base will sit. For garden beds, test at root depth (30cm). Keep notes on your results by location — this becomes useful information for any landscaper you bring in later.

If you're adding organic matter to improve drainage or retention, compost is the best amendment for NB soils in either direction — it loosens clay and adds water-holding capacity to sand.

When to Hire a Pro

The DIY test works well for general planting and garden planning. But if you're dealing with persistent standing water, basement drainage concerns, or planning a septic system, you need a licensed professional. Septic perc tests in NB must be conducted by a certified soil evaluator and approved by the Department of Environment — this is not a DIY situation.

For drainage solutions like French drains, swales, or catch basins, a landscaper with grading experience is worth the investment. Poor grading affects your foundation and your neighbours' properties — something NB municipalities take seriously.

Need help finding a landscaper who understands NB drainage conditions? New Brunswick Landscaping can match you with a local pro for free.