Soil and Water: A Complicated Relationship
- Bob Dahm
- Jun 25
- 3 min read
Every gardener knows that you need water for healthy plants in your garden. Did you know soil needs water to be healthy, too? But it’s a complicated realtionship and there needs to be some helpers to make sure they get along.
Protect Soil from Run Off
Rain can be friend or foe. Rain on bare soil compacts it and forms a crust that is hard for seeds to push through. The soil that isn’t compacted will erode and wash away and it forms channels and gullies that focus runoff, creating more erosion. Just a little bit of organic matter on the surface, like leaves, debris, plant stems or mulch will protect the soil and slow down the water so it can soak in instead of run off.
Help Soil Microbes Grow!
When water soaks into soil, it does so along roots and open pores which are usually created by the living organisms in the soil. Think earthworm holes and smaller. These organisms create little holes and tunnels all throughout the soil. This structure is usually lined with glomalin, a carbon rich secretion similar to earthworm slime. This substance holds soil together and creates voids that hold water. The more diverse and active your microbes, the deeper the voids and structure. This microbial action is what de-compacts soil. Water flows in and roots follow. Root mass increases by spreading down and across the soil profile. As root mass increases, so do the beneficial microbes, and the more water is stored. This creates a soil aquifer that plants can tap when it gets dry or a drought occurs.
When healthy soil heats up, microbes plug up the surface holes so no water evaporates. This is why soil sometimes beads water on it’s surface for awhile before it infiltrates. These plugged holes don’t let water out or in, until the plugs dissolve and allow the water to enter the pores. This process of infiltration is called capillary action, because it draws in the moisture. Soil coverings like leaf canopy, debris or mulch slow water down and keep the soil from excessively drying.
Don’t Over Water
Even healthy soil has its limits on how much water it can hold. It has an amazing capacity to move water downward, eventually recharging groundwater and our aquifers, but it can only handle so much before it fills up and says “no more”! The excess runoff into our wetlands.
Healthy Soil Protects Wetlands
Wetlands have an amazing ability to hold water and clean it up before sending it on to our lakes and streams. Wetland plants have this super power where they can take water in through their roots and pump it through their leaves into the atmosphere.
Healthy soil manages our water by deciding where it goes. It holds some for itself, sends some deeper to the aquifer, removes dirty runoff to a wetland to be cleaned up before it either goes up into the atmosphere or continues into the watershed. It needs the help of healthy soil and wetland biology, plants and their leaves and roots, and organic matter to protect the soil and feed the microbes. Soil health controls our water, nutrition, health and resilience and it does the same for pollinators, wildlife and our climate.
Contact Bob today to see how you can get your soil healthy.
Resources
U of M Extension
NRCS-USDA
Gardening in Urban Soil https://www.health.state.mn.us/communities/environment/hazardous/topics/gardurbsoil.html
Soil Health, Water Quality and Climate Change