This article explains why using stones (or coarse sand) and cloth at the base of wicking beds — a common practice — often undermines their effectiveness. It argues that stones are too coarse to wick water properly, can lead to stagnant, smelly reservoirs, and reduce nutrient availability. Instead, the author recommends using biologically active soil or organic‑based “sponge bed” soils that wick water, support microbes, and nourish plants more reliably.
Why Stones and Cloth Became Popular — and Why That’s a Problem
When I first developed wicking beds, I started simple: a plastic‑lined pit filled with soil and waste organic material — and it worked well. Later I tried adding a perforated pipe to deliver water, covered with cloth to prevent soil ingress. Some others took this further, placing a layer of stones (or sand) under the soil, believing it would improve water storage and reduce maintenance. This design became very popular.
But stones are generally too coarse to provide proper capillary action — the fine, consistent moisture movement that wicking beds rely on. Water doesn’t “wick up” from coarse stones the way it does through fine soil or organic matter. There might still be some water transfer by evaporation/condensation or roots growing into the stones — but this is inconsistent and unreliable.
As a result, many people now complain of wicking beds that either never wick properly or become stagnant and foul smelling.
The Importance of Soil, Not Stones
Rather than stones and cloth, I advocate for biologically active soils — or even specially prepared “sponge soils.” These soils have fines and pore spaces finely distributed, allowing capillary water movement, good nutrient retention, and space for roots and microbes.
In soils with high porosity and good organic content, roots can reach water directly from the soil throughout the bed. This prevents stagnation (because plants naturally extract water), supports soil biology, and allows nutrients to be cycled and made available to plants.
Stones do not contribute to nutrient availability or foster soil biology — they are inert. Soil or organic-rich substrates, by contrast, host microbes, worms, fungi, and other life that help convert mineral and organic matter into plant-available nutrients.
Problems Caused by Stones & Cloth Beds
Here are some of the common issues encountered by those who use stones or coarse sand with cloth layers:
- Poor wicking action: Because the pore sizes in stones are large, capillary rise is weak or nonexistent. Water does not reliably move upward into the soil.
- Stagnant or smelly reservoirs: If roots do not reach the water and soil above cannot draw it, the water can sit stagnant — a breeding ground for anaerobic bacteria and unpleasant odours.
- Nutrient poverty: Stones contribute no minerals; organic material is not decomposed, and there is no biological activity to release nutrients. Plants may suffer even if watered regularly.
- Soil compaction and root restriction: Over time, soil may infiltrate the stone layer or compress, limiting root growth. Some builders even report soil “concrete‑like” masses forming between stones.
Why Biologically Active Soil or Sponge Soils Are Better
Using a fine-textured, porous soil mixture or organic-based “sponge soil” allows the entire bed’s volume to be used by roots — from the surface to the bottom. The key advantages:
- Reliable water wicking: Fine pores and organic matter hold and draw water via capillarity, supplying roots consistently without oversaturation.
- Active nutrient cycling: Soil biology — fungi, bacteria, worms, microfauna — breaks down organic matter and mineral amendments, making nutrients available to plants.
- Aeration and root health: Roots and soil fauna can move freely through soil voids, preventing compaction and supporting healthy growth.
- Simpler construction and maintenance: No heavy stones or geotextile layers needed; replenishment of organic matter keeps soil fertile over time.
In my own approach, I even developed “worm bed” methods: burying a compost/mineral bin within the bed, where worms break down compost and distribute nutrients throughout the soil — creating a sponge-like, biologically rich bed that wicks water effectively and nourishes plants.
Practical Advice for Building Effective Wicking Beds (Without Stones)
If you want a wicking bed that actually works and produces healthy plants, consider the following design principles:
- Use a fine-textured, organic‑rich soil or a purpose-made sponge soil instead of stones or coarse sand.
- Ensure soil has good porosity — enough voids for water retention, air, roots, and soil life. Soils designed for wicking beds often aim for high void content and good water‑holding capacity.
- Add compost, worm castings, or organic matter to feed soil biology. This helps build a living soil that releases nutrients and supports plant growth.
- If water storage is needed (e.g. in very dry climates), use a separate water reservoir or a simple buried container/pipes — but keep it independent from the root zone if possible. Ensure roots can reach into the soil layer, not just the reservoir.
- Avoid barriers like cloth or geotextile that block capillary flow — they prevent proper wicking and isolate water from soil.
Conclusion — Don’t Let Marketing Override Soil Science
The widespread use of stones and cloth in wicking beds shows how marketing and aesthetic convenience can overshadow effective design. While stone-and-cloth beds look neat and “proper,” they often fail in function: poor wicking, stagnant water, nutrient-poor plants, and high maintenance. I find it frustrating that many gardeners continue to build these systems despite such problems.
Real wicking beds — or better yet, sponge-bed soils — rely on basics: fine-textured soil, biological activity, and proper water movement. These simple elements create environments where plants, fungi, microbes and worms thrive together, cycling nutrients, preserving water, and producing healthy, nutrient-dense vegetables.
If you want to experiment or need help designing an effective wicking or sponge bed, I’m open to feedback and happy to share ideas.
Colin Austin — © Creative Commons. Reproduction allowed with source acknowledgement; commercial use requires permission.
