By Sue Lavallee
As the weather warms and my thoughts turn to starting up the vegetable gardens again, I know that the garden task that’s always on the top of my list needs to be done soon. Topdressing the garden beds with compost! This crucial step replaces the much-needed organic matter that is depleted every year and if it’s not done, the soil will become sandy, lacking nutrition and lifeless. Who can forget the Dust Bowl during the Great Depression?
Years ago I used to topdress the garden beds with an inch of compost and then till it in. This is no longer the case for me since I have learned that tilling the soil disrupts the delicate balance of the Soil Food Web.
Even though you can’t see most of it with the naked eye, a complex Soil Food Web lives in the top 3 – 5 inches of your garden soil and it’s teeming with earthworms, mites, insects, and a large amount of microscopic organisms. In fact, a mere teaspoon of rich composty soil can contain millions of invisible bacteria, fungi, protozoa and nematodes. These micro-organisms are interdependent and not only need each other to survive, they also need the presence of living plants, organic matter, water and air.
Let’s take a look at how this is all connected. It starts with the plants in your garden that are able to make some of their own food through the process of photosynthesis. A simplistic definition of photosynthesis is the process by which green plants capture the energy from sunlight and, in combination with water and CO2, make glucose and carbohydrates that they then use for energy. It’s also widely known that plants take up nutrients through their root system. But what many of us don’t realize is that plants also act as little solar-powered engines that pump a steady flow of carbohydrates out through their root hairs. Between 20 and 40 percent of a plant’s total carbohydrate production is released into the soil through its roots! In the nutrient-rich area around the root hairs, microscopic bacteria and fungi feed and multiply. Nematodes (tiny worms) and other critters move in to feed on the bacteria; in turn, the root hairs absorb nutrients released by the population of these microbes. This is how the Soil Food Web works….well, in a nutshell at least.
So what does all this have to do with tilling the soil? Every time the soil is tilled, organisms that make up the Soil Food Web are buried, threads of beneficial fungi are broken and earthworm tunnels are destroyed. Tilling can bury the compost topdress up to a foot deep where oxygen levels are too low for decomposition and to support microbial life. The buried debris then acts as a physical barrier to the movement of water upward and downward. Even if you till only a few inches deep, more damage is done than good. Worm tunnels and root paths that facilitate water absorption are destroyed, and soil clumps or aggregates are broken up, leaving little air space in the top layer. Then when it rains on the freshly turned soil, it compacts easily leaving even less air needed for the microbes and newly planted crops. Of course, if you are starting a new garden bed, tilling the soil that first year can save a lot of time and energy but its best just to apply a topdress thereafter.
The best way of conditioning your garden beds is to topdress them with an inch of compost each spring. If you have mulch around your existing garden beds, simply scrape it away, apply compost to the soil surface and rake the mulch back into place. The earthworms will gladly pull the organic matter into the soil where it is broken down by beetles and the larvae of other insects, opening it up for fungal and bacterial decay. This method is far easier (and less exhausting) than tilling. It might be time to put your tiller to bed…. for good! Lastly, here are some benefits that you’ll reap by topdressing your garden beds with organic compost every year:
- Attracts earthworms which are the earth’s best composters.
- Improves sandy and clay soil and by increasing fertility and porosity.
- Results in higher crop yields, improved flavor of your harvest and a higher nutritional content
- Encourages rigorous plant growth.
- Increases plant health and disease resistance.
- Increases soil fertility naturally.
- Helps to balance the pH of the soil.