Oilseed Radish - Clean Water Superstar

The oilseed radish's taproot can drill up to a foot into soil decreasing compaction and improving infiltration. Photo by Kirsten Workman, UVM Extension.

Every month, Vermont's Clean Water Initiative Program highlights a "Clean Water Superstar", species that help keep waters swimmable, drinkable, and fishable. A past entry was the Raphanus sativux L, the oilseed radish. Since it's gardening season we thought we'd highlight its benefits in the excerpt below.

You don't have to be a fan of a radish's spicy crunch to reap the benefits of planting them in your garden. Although edible, oilseed, tillage, daikon, or forage radish is more commonly used as a cover crop. Cover crops are seeded before or after traditional garden or farm crops to keep soil covered when it would usually be bare. In Vermont, oilseed radish is planted in late August or September and, depending on conditions, can grow quite large before it dies in early winter as the ground freezes and the snow falls. There are numerous benefits to keeping the soil covered by a cover crop such as oilseed radish, including reduced soil erosion, increased soil structure and organic matter and increased water infiltration. Different species of cover crops have different benefits and can be used alone or in combination, depending on the soil improvement needs for a field or garden.

The benefits of using oilseed radish in particular are mostly due to its incredible taproot which can drill up to a foot into the soil. This decreases soil compaction and, after the tuberous taproot and filamentous secondary roots decompose, leaves spaces of varying size where air and water can infiltrate. Similar to a sponge, uncompacted soil has tiny pockets of air that allow water to soak in more effectively, reducing runoff and the amount of sediment and nutrients that end up in nearby lakes or streams. The taproot also reaches nutrients many conventional crops cannot and brings them to the surface as the leaf canopy grows. After the radish dies in the winter and the tap root decomposes, it provides food for beneficial bacteria and invertebrates, and the nutrients are made available to the next crop through a healthy soil ecosystem.

Oilseed radish between rows of corn. Photo by Debra Heleba, UVM Extension.

Up at the surface, the leaves are working hard to capture solar energy to produce sugars and grow the plant material that is eventually added to the soil and broken down for the next crop. Additionally, the radish's large canopy can shade out fall weeds in as few as three or four weeks. The canopy also helps to break the impact of rainwater on soil and halt the flow of water across the top of the soil, thus keeping soil and nutrients on the field or garden instead of flowing into the nearest body of water.

In the fall when fields are generally brown, hard and static until spring when the crops grow, a field or garden with cover crops is still green, alive, and producing resources valuable for the next summer growing season. Healthy soil means good crops and clean water. No matter what size your garden or farm, consider planting a cover crop such as the oilseed radish.