Soil and the role of dipping ponds in the garden

World Soil day, how dipping ponds can harvest water, prevent flooding and influence the microclimate, and one way that plants communicate with fungi

Wandering around my frosty garden with my camera, I noticed the water in my dipping pond was not frozen which reminded me of another benefit of this feature in my garden, but more of that later.

First, I have to mark World Soil Day which takes place tomorrow

This week, there will undoubtedly be many posts highlighting one of our most vital and undervalued resources - soil. Did you know that more than half of all species on Earth live in soil? It’s the planet’s most biodiverse habitat, yet we’ve identified only about 1% of the incredible organisms found within it. There’s still so much to discover and understand.

Soil’s role in climate change is crucial:

• It stores more carbon than the atmosphere and all the world’s forests combined, a massive10 billion tonnes of carbon in the UK alone.

• Healthy soils are natural water regulators. One hectare can hold the equivalent of 1.5 Olympic swimming pools of water, helping to prevent floods and mitigate droughts. In fact, UK soils store more water than all our lakes and rivers combined.

• Soils act as a carbon sink, removing around 25% of the world’s fossil fuel emissions every year.

• Most soil carbon is locked away in permafrost and peatlands of the Arctic and the boreal regions of the Northern Hemisphere, making these ecosystems critical for global climate stability.

To protect these benefits, we need to care for our soils by minimizing disturbance and adopting practices that enhance their health. Healthy soil isn’t just the foundation of our food systems - it’s essential for life on Earth.

To maximize its benefits we really need to disturb soil as little as possible. We need to

Preserve sequestered carbon: Prevent carbon stored in soil from oxidizing and returning to the atmosphere, where it contributes to climate change.

Protect the fungal network: Maintain the network of fungal hyphae, which play a critical role in nutrient cycling and plant health.

Enhance water retention: Trap water in the soil to reduce evaporation, especially during droughts, ensuring plants have access to moisture.

Support groundwater replenishment: Allow water to percolate through the soil, recharging the water table and improving drainage during periods of heavy rain or flooding.

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Cracking the code of plant-to-fungi communication

We know that most plants have an intimate relationship with symbiotic fungi. Recent research has found that plants release a hormone called strigolactone and this signals fungi to attach to their roots and to activates those fungal genes that are involved with phosphate metabolism, ensure the plant gets all the phosphate it needs for growth and in exchange, the plant provides the fungus with carbon products. So clever!

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Dipping ponds

This week, I’ve been reflecting on the often-overlooked dipping pond—a seemingly humble feature that brings immense benefits to any garden, homestead, or smallholding.

Dipping ponds have a long history, possibly dating back to Medieval times. A notable example is the 14m-diameter dipping pond in the Walled Garden at Croome Court, built in 1764. Croome Court, near Pershore in Worcestershire, boasts Britain’s largest Georgian walled garden (open to visitors alongside NT Croome). Land drains channel rainwater into this pond, storing it for use in the gardens, a testament to the ingenuity of historical water management before the advent of clean, piped water.

Back then, water harvesting was essential. Rainwater was collected from roofs and pumped into reservoirs, while greenhouses stored it in underground tanks for easy access. Dipping ponds were often centrally placed in kitchen gardens, either in the middle or in each of the four quarters to minimize the distance gardeners had to carry water.

In my own walled garden, the dipping pond was the very first feature we installed when we began our garden restoration project 12 years ago. It’s fed by a pipe from the nearby barn, with an overflow that drains under the wall into a swampy area, eventually joining a local stream. Unlike wildlife ponds, this one is designed purely for water harvesting. Its straight walls are made of breeze blocks with a fibreglass lining. It’s about a metre deep and holds up to 3 cubic metres (3,000 litres) when full.

The water level fluctuates throughout the year, depending on rainfall and water demand. At the moment, it’s full, but as summer progresses, the level drops, and the water turns rather green. While not the most attractive feature, it is essential to the management of the garden.

My dipping pond looking a bit gunky after the 2022 drought. You can see the inflow and overflow pipes in the top right.

Efficient watering

As I’ve shared before, the dipping pond allows me to fill up my buckets quickly, which means I can give my beds a thorough soak without the hassle of waiting around at a tap. The result is that I can water effectively and efficiently.

Slowing the flow

Beyond harvesting water, the dipping pond plays a crucial role in managing storm water. When heavy rain hits, the diversion of water from the roof to the pond, swamp and then the stream slows the flow and reduces the risk of soil erosion and flooding downstream.

Wildlife

Although the pond isn’t specifically designed for wildlife, it inevitably attracts some. Pond skaters, water beetles, and other flying insects visit regularly, and yes, midges make an appearance too. However, midges are a food source for dragonflies, and this year I recorded four different dragonfly species in the garden, from early summer right through to a few weeks ago.

Additionally, our bats seem to be thriving, hopefully helped by the midges. This year, the bats roosting in our roof space have left more piles of poo in our loft, which is a positive sign of their growing population. For those who might want to avoid midges or mosquitoes, the pond’s design could be adjusted: a deeper, covered, circular pond would deter these insects, while still gaining the benefits of water management.

Heat sink

The pond also functions as a heat sink, providing welcome benefits. During the day, the water absorbs heat, and at night, it releases warmth like a large storage heater. For example, despite temperatures dropping to -3°C overnight in the garden, the water in the pond remained unfrozen, as shown in the photo. Outside the garden walls, water in the troughs froze solid.

In summer, the evaporation from the pond not only maintains a higher humidity, but has a cooling effect, which benefits the nearby vegetable beds. This dual-purpose feature of warming in winter and cooling in summer demonstrates how the pond contributes to the garden’s microclimate all year round.

The dipping pond is truly a multi-functional asset, supporting water management, wildlife, and even temperature regulation in the garden!

Happy gardening

Sally

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