By Marianne Lepa, Simcoe County Master Gardener (in training)
This article is adapted from a talk I gave at the Innisfil Seedy Saturday in March.
Many years ago, when I was much younger and had a lot more energy, I ran a two and a half acre market garden. I used to love getting out there in spring and tilling the soil to get it ready for planting. That garden had clay soil that I had been amending, turning it into a lovely clay loam. Tilling made it soft and fluffy and it looked like chocolate cake when I was done. What I didn’t know then is that my spring tilling was actually disrupting the natural organisms that have been helping plants grow since plants evolved on earth.
Tilling means using a mechanical device that turns over the soil several inches deep. Gardeners use tillers to incorporate organic matter and air into the soil. It breaks up weeds and opens up dense compacted ground. In a no-till garden, compost and mulch is laid on top of the beds and the soil is disturbed only enough to plant. Incorporating the organic matter and air is left up to earthworms and other soil dwelling insects.
Some advantages of tilling:
*Organic matter is easily transferred deep into the soil where the roots are
*It helps to keep down weeds, (though some argue tilling turns up seeds and makes the weeds worse)
*Tilling also has the advantage of getting garden beds warm and dry quicker in spring.
Some advantages of the no-till method:
*It’s less work, you lay the mulch and leave it
*Preserves soil structure and the microorganisms that ultimately feed your plants
*Keeps carbon locked into the soil. Plants absorb carbon from the air and transfer it into the soil where it remains as long as the soil is undisturbed.
Disadvantages of tilling
*There is a cost. To buy a tillers you’ll pay between $200 to $600 or more. Plus, like any device with an engine, there is also gas and maintenance costs along with that.
*Regular disruption of the soil structure can cause it to break down over time making it less and less fertile
*Tilling releases stored carbon back into the atmosphere
Disadvantages of no-till
*It takes longer for your soil improvements to have an effect.
*Soils may not warm up as quickly in spring
*Weeds will have to be hand pulled or hoed down
The image below gives you an idea of what’s going on down in that dirt.
Plant roots have two functions: The thick part of the root holds the plant in place while the fine root hairs have the job of seeking out water and nutrients. They do this through a relationship with fungi in the soil. Fungi (the light coloured webs in the image,) attach themselves to the root and the roots feed them with carbohydrates and sugars that the plant made through photosynthesis, (represented by the yellow arrow from the plant leaves). At the same time the fungi feed minerals and water to the roots that they have taken from the soil.
You may have seen the word mycorrhizae a lot lately. Mycorrhizae describes this relationship between roots and fungi. The fungi are like strings or webbing that spreads through the air pockets in the soil and connect with other plants. Mycorrhizal fungi exist in any soil that has organic matter — even bad soil.
In the image, we can see that the fungi find food from a number of sources and that all feeds back into the web established in the soil. That’s how plants help each other survive. But, when you till, those strands are broken and can take months to recover and possibly years to fully re-establish. Tilling again and again prevents theses mycorrhizal colonies from establishing and keeping your plants healthy.
While the immediate results from tilling seem to make it worthwhile, over time, the soil will lose it’s ability to hold the air and water that are necessary to plant growth and will require more and more help with nutrients to keep plants growing. The no-till method may take some time to show a benefit but we are giving our earth the chance to recover and grow resilient once again.
Is there ever a time that tilling is appropriate?
Some of you may be familiar with Robert Pavlis. He’s a microbiologist and an Ontario Master Gardener. Robert has written a number of books on Garden Myths and one on Soil Science. He has a blog called Garden Myths and a Facebook group called Garden Fundamentals. He recently gave a webinar on soil science that I attended. He discussed the role of mycorrhizae in plant health and how tilling disrupted that ecosystem.
I had the chance to ask him if there was ever a time when tilling is necessary. He said “no” very firmly. But then said the only possible exception was if you were establishing a new garden in very bad soil. In that case, tilling in organic matter would help get the soil into good shape quicker than waiting. But only till once, he said. After that, let nature take over.
As we learn more about how the intricate relationships in nature have evolved over time and along with humans, we are coming to understand that our ecosystem does provide us with all that is necessary and without too much interference from us. We are learning to appreciate that under our feet is a whole universe of fungi and organisms that are living their lives helping our plants grow.