To Till or Not to Till
Jennie Johnson, Anoka County Extension Master Gardener
That is the question, and the answer is: it depends. Tillage, or tilling, is the agitation of soil by digging, stirring, and turning over the soil in preparation for growing crops. Garden tilling can be accomplished with hand tools, including shovels or hoes, or with mechanical devices such as rototillers. Commercial farmers recommend cultivation twice a year, in the spring and fall, but home gardeners have mixed opinions.
Advantages of Tilling
Tilling changes the structure of the soil, loosening the particles and incorporating organic matter needed for plant growth. In the spring, tilling allows the soil to warm more quickly by increasing the air in the soil. Loosening the soil particles makes it easier for plants to send down roots. The additional air in the soil also stimulates aerobic bacteria, which helps break down organic matter more quickly. The increased organic matter, together with the physical mixing of the tilling process, makes the nutrients in the organic matter and water more available to new plant growth. However, this also makes the nutrients more available to weeds, which tend to grow faster than vegetables and flowers. In the fall, tilling mixes organic matter from dying garden plants, grass clippings, and leaves into the topsoil. This mixture will compost over the winter and increase organic matter for the next growing season.
Disadvantages of Tilling
The surface soil helps retain moisture and nutrients, and that process is disrupted with tilling. In addition, tilling increases the likelihood of soil erosion through the action of wind and water on the overturned and loosened soil. Essential nutrients can be lost due to water runoff, which creates the potential for water pollution depending on how much water runs off and where it goes. Also, soil type matters when deciding whether to till. For example, sandy soil with its larger, loose particles might be more susceptible to erosion from cultivation than loam, which has a higher percentage of smaller, more densely packed particles.
Additionally, tilling can expose the soil’s nitrogen-producing microorganisms to the sun, which kills them and eliminates a source of this essential element for plant growth. Tilling can increase the need to fertilize. It can even promote compaction when done too often; over time, tilling allows smaller particles to work their way down into the soil and form hardpan (also called tillage pan), which blocks water and nutrient absorption. Finally, tilling is time consuming and hard work whether it is done by hand or mechanically.
For home gardeners, whether to till or not is a personal choice to be made after considering all the pros and cons. You should factor in your soil type, the size and location of your garden, your goals for production, and the time, energy, and money you are willing and able to devote to site preparation. You could also decide to till but do so only once a year instead of twice.
For information about tilling alternatives, check out this Extension article: https://extension.umn.edu/managing-soil-and-nutrients/reducing-tillage-your-garden