Most complaints in the landscape gardening trade are caused by a limited set of errors: incorrect fall incomplete compaction too thin growing layer wrong plant material or poor drainage. Here are the typical errors how you discover them — and what it takes to fix them.
Introduction
Landscape gardening errors are often discovered only months or years after completion – but the causes can be traced back to decisions made during construction. Knowledge of the most common error patterns gives you a head start: you avoid them in your own work and can explain the cause if you take over a failed task.
Error 1: Voids and puddles on pavement
- 01Cause A — insufficient slope: Slope under 10 ‰ (the standard's minimum for tiles, NfA 1992) causes standing water. Industry recommendation is 15 ‰ for patios.
- 02Cause B — uneven base layer: Compression in too thick layers or with too light equipment causes local settling.
- 03Cause C — setting layer too thick and uneven: The leveling layer may vary at most ±10 mm (30 ± 10 mm standard, DS 1136). An inconsistent layer gives an uneven surface.
- 04Correction: for new installation replace the screed layer and reset the stones with correct slope and compressed base layer.
Error 2: Edge stones shift
- 01Cause: the edging stone is not set in bedding mortar, or the mortar base is too narrow and weak.
- 02Correction: remove edge stone, excavate and prepare a compressed mortar bed, reset edge stone plumb and in line and allow mortar to harden before resuming the paving.
Error 3: Paving stones settle unevenly
- 01Cause: the base layer is not compressed evenly — typically because it's laid in one too-thick layer instead of two thin layers.
- 02Cause: geotextile is missing, and raw soil material works up into the base layer (contamination).
- 03Correction: break up the surface, compress the base layer correctly (max. 15–20 cm per layer), lay geotextile and reseed.
Error 4: Plants fail and wilt
- 01Cause A — too thin soil layer: Plants in less than 25 cm soil (NfA's minimum) have difficulty setting deep roots and suffer in drought.
- 02Cause B — wrong planting depth: Container/clump plants placed too deep (top below ground surface) can choke the root collar. NfA 2023: the clump's top should be flush with the ground surface ±2 cm.
- 03Cause C — too tightly compacted soil: Dry bulk density over 1.4 g/cm³ (clayey) / 1.5 g/cm³ (sandy) for planting areas inhibits root growth (NfA 1992).
- 04Cause D — poor drainage capacity: Planting hole holds water → roots rot. Test: 10 liters of water in a 10 cm depression on 0.25 m² should drain away in 2 hours.
- 05Correction: excavate, add soil and soil amendment, replant with correct depth and drainage capacity.
Error 5: Lawn with bare patches and exposed soil
- 01Cause: too low seeding rate, poor soil contact (harrowed too loose), poor watering in germination period, or weeds taking over.
- 02Requirements (NfA 1992): minimum 1 grass plant per cm² at handover.
- 03Correction: loosen the bare soil, reseed with correct amount (1–3 kg/100 m²), water regularly for the first 3–4 weeks.
Error 6: Freeze-thaw damage and spalling
- 01Cause: stone with excessive water absorption absorbs water that freezes and expands, so the surface spalls (especially in road salt).
- 02Reason: poor drainage, so water stands in joints and under stones over the winter.
- 03Prevention: choose a frost-resistant material type documented according to DS/EN 1338 (concrete) or DS/EN 1344 (brick), and ensure fall and well-filled joints so water runs away.
Error 7: Weeds, moss and algae in joints
- 01Cause: joints filled with nutrient-rich or organic material where seeds can germinate; shade and moisture promote moss and algae.
- 02Prevention: use washed, nutrient-poor quartz joint sand according to DS 1136, or a joint material (e.g. bound grout), where weeds have difficulty growing.
- 03Correction: clean the joints, brush in new suitable grout sand, and keep the surface free of leaves and soil.
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