Can too many drainage holes cause problems?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.While drainage holes aid in preventing waterlogging, huge holes cause an equal disaster, resulting in rapidly dry soil. Excessive draining washes out nutrients before plants can assimilate them, requiring continual drying and wetting of the roots. I have remodeled beds in which there were so many holes that daily wilting was caused, despite the watering of the plants. The plant requires food and moisture, not great variations.
Optimal Hole Spacing
- Space holes every 12-18 inches along bed perimeter
- Clay soils: closer spacing (12 inches)
- Sandy soils: wider spacing (18 inches)
- Avoid holes smaller than ½-inch diameter
Soil Protection
- Install stainless steel mesh behind every hole
- Use landscape fabric layer under soil
- Add top mulch layer to reduce evaporation
- Check screens seasonally for clogging
Moisture Monitoring
- Test soil daily at root depth with probe
- Water when top 1-inch dries but lower soil is moist
- Install simple tensiometers for accuracy
- Adjust watering based on weather patterns
To remedy over-drained beds, reduce the number of holes for a while. While they're dry, close up every other hole with waterproof epoxy. Add water-absorbing polymers to the soil to retain moisture. I maintain the balance by covering 30% of the holes in summer and dry weather, which are then reopened during the rainy seasons.
Monitor water stress in plants that physically display curled leaves or are stunted in growth, all of which will occur after 3 to 7 days of water imbalance in the soil. Place simple rain gauges to measure the amount of irrigation that nature provides. I use drip irrigation in Mediterranean climates, adjusting the timers to suit the plant needs bi-weekly. With proper management and use of regenerative receiving beds, those that are troublesome can be turned into productive gardens.
Read the full article: 10 Essential Raised Bed Drainage Fixes
