Dateline: 11 March 2017

Amazing beauty, on a microscopic level

My new Minibeds-on-Plastic experimental garden is designed as a no-till system for growing vegetables. While there will be no soil disturbance under the plastic covering most of the garden, the “island” minibeds themselves will also remain mostly undisturbed. This minimal-till approach is central to the Minibeds-on-Plastic method, and I’ll explain why.

Contrary to common belief, tilling the soil does not enhance its structure. It doesn’t improve aeration or create the porous texture crucial for a thriving garden.

I used to rototill my entire garden every spring, believing it was the correct way to prepare for planting. However, I’ve since realized that extensive tilling is detrimental to both the soil and the plants. Since I stopped this practice, my gardens have become more productive.

My shift to no-till gardening stems from learning about the vital role of soil structure and, more specifically, mycorrhizal fungi.

The Mycorrhizal Factor

The image at the beginning of this post displays a mycorrhizal arbuscle within a plant root cell. This isn’t a harmful invasion but a mutually beneficial relationship crucial for gardeners to grasp. Mycorrhizal fungi offer numerous advantages to plants.

Essentially, plants provide nourishment to these fungi. Through photosynthesis, plant leaves use sunlight and carbon dioxide to produce sugars (carbohydrates). While some of these sugars fuel plant growth, a significant portion is released into the soil.

Plants “leak” or “pump” a surprising amount of these sugars to support soil microbes, with mycorrhizal fungi being major beneficiaries. In the image, the arbuscle, resembling a tree, absorbs these sugars for its growth.

As the mycorrhizal fungi grow, they extend a vast network of thread-like hyphae far beyond the plant’s root system. These hyphae act as extensions of the roots, accessing water and nutrients that the roots cannot reach.

The famous illustrations of root systems by Professor John Weaver do not depict the vast network of mycorrhizal hyphae that likely coexist and collaborate with these roots. Imagine those root systems intertwined with an equally extensive, if not larger, network of hyphae.

Plants colonized by mycorrhizal fungi exhibit increased nutrient and water uptake, resulting in visible improvements above ground.

These fungi also enhance plant resilience against diseases and, remarkably, participate in a complex underground communication network between plants and the soil ecosystem.

Beyond benefiting plant growth and health, mycorrhizal fungi significantly improve the soil structure surrounding them.

The Glomalin Factor

Mycorrhizal hyphae release a substance called glomalin as they spread through the soil. This newly discovered (1996) “biological glue” binds soil particles together, improving soil aggregation and tilth.

Aggregation results in both large and small pores within the soil. Well-aggregated soil allows water to be absorbed and drained efficiently, promoting aeration and a thriving environment for beneficial soil microbes. This is clearly demonstrated in the video at the end of this post.

Unfortunately, common gardening practices, such as tilling, disrupt the mycorrhizal network and destroy glomalin.

No-till gardening preserves glomalin, enhances soil structure, and allows plants to reap the full benefits of naturally occurring mycorrhizal fungi.

No-Till With Minibeds-on-Plastic

Mycorrhizal fungi and glomalin are most effective in the presence of living roots. In my Minibeds-on-Plastic system, a significant portion of the garden is covered with black plastic mulch. This creates a no-till environment under the plastic, but without plants or roots.

While this might seem like a drawback, I see it as a necessary trade-off. I’m accepting a reduction in the overall benefits of a fully no-till system in exchange for increased manageability and productivity within the focused area of the minibeds.

Without the plastic mulch, weeds would quickly take over my garden. This has been a recurring challenge, making the garden less productive and requiring constant effort to control weeds. The Minibeds-on-Plastic system will prevent this and eliminate the need for disruptive tilling.

Because I won’t be digging the minibeds, the existing roots, mycorrhizal hyphae, and glomalin will remain undisturbed, allowing them to extend their benefits beyond the minibed boundaries.

Furthermore, my no-till approach includes rotating root-dense cover crops, particularly rye, in the minibeds during the fall and spring. These cover crops will not be tilled in as green manure; instead, their above-ground growth will be harvested, chopped, and used as mulch or added to compost.

This is my vision of no-till gardening within the Minibeds-on-Plastic system.

Dan Grubbs has raised concerns about potential heat buildup under the black plastic and its impact on beneficial soil organisms. This is a valid point, particularly in specific growing regions, as I addressed in Minibeds-on-Plastic Report #1 (see Question 15 on page 25). If this becomes an issue, I plan to add a layer of wood chips over the black plastic.

Some Fungal Loose Ends

It’s important to note that mycorrhizal fungi are just one type of fungi found in soil. Some break down organic matter, others are harmful, but most are beneficial.

While mycorrhizal fungi form symbiotic relationships with most plants, they do not cooperate with brassicas.

These fungi are naturally present in most garden soils and will thrive under the right conditions, such as no-till practices.

Commercially available mycorrhizal inoculants exist, but their efficacy is debatable.

Additionally, some bacteria contribute to soil aggregation on a smaller scale by producing bio-glues.

Evidence Of Good Soil Structure

This video featuring Ray Archuleta offers a compelling look at the advantages of no-till gardening and farming. It is a must-watch!