These Essential Soil & Water Facts Indicate How We Should Garden As the Climate Warms. Creating The Right Conditions Allow Plants to Thrive.
Table of Contents
1. The Power of Organic Matter (By Weight)
Composts and soil organic matter can hold between 10 and 20 times their own dry weight in water.
This illustrates why simply adding a 2.5 cm (one inch) layer of garden compost or well-rotted manure dramatically increases a plant’s access to water during a dry spell. The organic matter acts like a permanent sponge within the soil structure. It can be dug in though personally l prefer to add it to the soil surface and let nature pull it into the soil.
2. The Impact of Digging
Turning over the soil (digging, rotating or ploughing) increases the rate at which soil organic matter is oxidised (broken down); leading to a loss of carbon, reduced moisture retention and a reduction in soil aggregation.
Many gardeners don’t understand that when you dig, you incorporate oxygen, which “burns up” the organic matter faster. This destroys the stable soil clumps (aggregates) that earthworms and microbes create. These aggregates are critical because they form large, stable pores that allow water to infiltrate quickly rather than running off, and also smaller pores that hold water for plants. Disturbing the soil is, therefore, detrimental to long-term water management.
3. Soil Life and Water Infiltration
Fact:A healthy population of earthworms can increase the soil’s infiltration rate—the speed at which water enters the soil—by over 50%.
Earthworms are natural engineers. Their burrows create a network of macropores (large channels) that act as drainage routes for rainwater, allowing it to penetrate the soil quickly, even in heavy downpours. Without them, the water hits a compacted surface, puddles and/or runs straight off, leading to wasted water, soil erosion and surface flooding.
4. Plant Available Water
Less than 50% of the water available in the soil at its field capacity (what remains after excess water has drained away) can be used by most plants before they begin to show signs of drought stress (wilting).
Soil holds water in two ways: some is held so tightly by the clay and silt particles that roots cannot extract it and the rest is available water. This fact highlights the need to water before a plant is severely wilting, as by that point, the available water is nearly exhausted. This is why correct watering, or improving SOM (Soil Organic Matter) to increase the available water fraction, is so important.
5. The Depth of Watering
To water a plant effectively and encourage a deep, drought-resilient root system, you must apply enough water to penetrate at least 15 cm (6 inches) deep into the soil.
Shallow, frequent watering only encourages surface roots, which are the first to dry out when the weather turns warm. A deep, less frequent soaking trains the roots to grow down, where the moisture levels are more stable, making the plant much more resilient to the typical British summer dry spells.
6. The Impact of Soil Surface Shading
Crops, mulches and longer grass on lawns shade the soil, decrease the soil temperature and reduce drought conditions.
Concrete and similar materials get extremely hot if exposed to direct sunshine. Bare soil, whilst not getting quite as hot, also heats up when exposed to the sun. Short grass reduces the soil heating effect whilst longer grass, deep mulches, cover crops and established crops reduce soil temperatures even more. On lawns, setting the cutting height to the maximum level means the soil is shaded and doesn’t get so hot, the result is the grass stays green whilst short grass dies back. The same impact can be seen in cropped areas that are protected from direct sunshine.
The municipal flower bed in the following image is in the south of France where temperatures can be in the high 30s for weeks. Woodchip is used to protect the soil surface and the plants thrive.
