The following is an excerpt from the in progress guide to raising food in a changing climate and uncertain future.
Two of the techniques that most aid in maintaining rich soil in gardens are extremely simple and also probably the most important for microbial life: hugelkultur/core gardening, and deep mulching a la Ruth Stout or the “Back to Eden” method.
Hugelkultur is a term popularized by Austrian farmer Sepp Holzer, whose technique for incorporating woody biomass into garden beds has become popular with American permaculturists in the last decade or two. It’s supposed to have been a practice used fairly regularly in that region, likely as much as a way to dispose of excess debris after clearing a wooded area as it is specifically for gardening. The principle is simple: bury wood, which as it decomposes enriches the soil and holds on to water like a sponge, reducing irrigation needs. The main drawback is that wood tends to initially lock up some of the nitrogen in the soil as part of the decomposition process, so if you’re using a lot of smaller sized pieces of wood particularly, you may need to add more nitrogen while doing this. Because of this, some folks will “charge” the wood by adding nitrogen rich material and/or liquid fertilizer to the wood before burying it.
As the wood decays and eventually breaks down into soil, it also harbors a lot of life. In addition to the microbes, particularly fungal life that enjoys woody material, a woody core in a garden bed is ideal for a lot of bugs and other non-microbe critters. Occasionally even larger animals.
Along the same lines but more broad in application is “core gardening”. This is more of a catch all term for putting coarser biomass into the middle of a garden bed. Leaves, hay, and straw are commonly used for this, especially when gardeners have access to spoiled bales of hay or straw. It may no longer be useful for animal feed or bedding, but it can still enrich the soil. The main difference between this and hugelkultur in a functional sense is the time period in which the materials break down. Because of this, I’ve tended to incorporate some leafy matter when I pile wood into new beds. Many of my sources for leafy material also have relatively high nitrogen, like comfrey. But even tree leaves tend to have enough to be useful in feeding the soil and offsetting and nitrogen lock up the wood might cause.
Also along the same lines is a soil amendment that’s been gaining popularity in recent years, biochar. Biochar isn’t anything particularly special, even though it sounds it; essentially it’s just (usually hardwood) charcoal broken into small pieces and maybe had some fertilizer added. You can even make some from store bought charcoal, you just need to be sure to use lump charcoal and not briquettes, which are formed into shape and bound together using materials that may not be particularly healthy for the soil or us. You can also turn wood debris into charcoal by smothering it after it’s been burning hot for a little while but hasn’t yet burned down to ash. At home scale and without specialized equipment you’re likely to get bits that aren’t totally charred, but it’s still good woody mass. Then break it up as small as possible and add it into your soil. I made several small batches in a charcoal grill by just building up a big fire of fallen oak branches, and then smothering it when it was good and hot.
Deep mulching is probably the most important thing you can do for your garden. If you take away only one bit of information about gardening from this piece, let this be it. The soil needs to be covered. So many gardeners open their soil up to erosion, evaporation, and UV damage to microbial life and generally for no purpose other than that’s how they learned to garden. Healthy terrestrial ecosystems don’t typically have exposed soil, but rather nourish and enrich the soil with layers of decomposing plant material that are added to each year. It’s definitely how forests function.
Utilizing deep mulching can be as simple as piling up old hay several inches thick in your growing space, as Ruth Stout did in her garden, or as complicated as the popular “lasagna gardening” method in which layers of different materials are laid down to decompose and enrich the soil. Whichever method or materials you might end up utilizing, the thickness of the mulch layer not only protects the soil and allows the lower mulch to better be broken down into soil, but it also smothers weeds. This is not to say that it completely negates the weeding, but it does greatly reduce it. I find that with my beds the weeds mostly pop up around the edges. Otherwise, the mulch layer is too thick for most of them to grow through.
Focusing as I do on growing in a forested ecosystem and being able to take advantage of less horticulturally minded people’s habit of removing leaves from their yards in the fall, I’ve become quite a fan of tree leaves as a mulch. Shredded up, layered a few inches thick, and moistened, they make a great mulch and add minerals to the soil that are often lacking and aren’t as present in hay and straw. Mineral and other nutrient content vary by species of course; I’ve tended to prefer using a combination of mostly maple and oak leaves, in part because that’s why I have available and in part because the lignin heavy oak leaves create a sort of fluffiness while maple leaves seem to break down faster and add more nitrogen. I think they have more cellulose.
Just as with the hugelkultur/core method described above, and perhaps even more so, having a thick layer of mulch on top of the garden soil reduces the need for irrigation. Depending on where your garden is situated, your climate, and how much organic matter is in your soil already, it may even eliminate the need entirely and facilitate dry gardening without sacrificing the productivity of your crops.
What you’ll often see in deep mulched gardens is a lot of worms and pill bugs when you pull back the layers to plant. These decomposers will be attracted to the plentiful coarse organic matter and regular moisture, especially if there is a healthy amount of fungal mycelium growing in that layer (and also aiding in the decomposition).
And that brings us to an important aspect of building healthy soil in the garden (and elsewhere): soil life. Good soil is living soil and is home to an extremely diverse collection of lifeforms. In most situations, if you’ve followed the advice for building your growing areas in the ways I mention above and especially if you’re using homegrown compost, you don’t necessarily need to do anything else to make sure your garden soil is full of life. Providing the habitat and lots of organic matter is often adequate for fostering the naturally occurring flora, fauna, and fungi to move in and thrive. But sometimes it’s not, and sometimes we want to add to it. This is particularly a good idea if the soil where you’re growing has been depleted for a long time.
If you want to make sure you get some extra biodiversity from around your area to exist in your garden space, you can go to a few places nearby like forests and riparian zones to take bits of soil, rotting wood and leaves, etc. to add to your garden beds. Don’t necessarily take a lot. A few chunks of rotting wood here and there, some nicely decomposed leaf duff from the forest, maybe some soil from a healthy looking field. Put these under your mulch layer and maybe don’t think about it again.
A bit of a more involved way to cultivate diverse soil biome is commonly practiced in Korean Natural Farming, which involves using steamed rice as a medium to grow indigenous microbes and then ferment and compost them in prescribed preparations, which can then be used to introduce those microbes into your soil. I’m only passingly familiar with the process, but for those interested in actively cultivating local microbial life, it sounds like a good method.
There are also commercial available microbe innoculants you can use that often suggest using with specific crops. In the past I’ve shelled out the money to make sure that our soil has the microbes that work along with legumes to help fix nitrogen from the air. I’ve also bought some stuff that supposedly helped introduce fungal species that form mycorhizal relationships with plants, but I suspect that was less useful than my newest favorite crop: growing gourmet mushrooms right in the garden.
Growing mushrooms isn’t something most gardeners think to do, and perhaps it goes back to the prevalence of stripped, barren garden soil I mentioned above. Gardens aren’t the habitat most people associate with mushroom growing, but some species of mushrooms grow quite well in garden mulch. Two of the most popular are wine cap mushrooms and oyster mushrooms. Both are rapid decomposers of coarse organic material, and so enrich your soil faster than just deep mulching without them present. They both also may aid in pest control by way of consuming soil dwelling pests like nematodes. Fungi will often facilitate the exchange of nutrients between plants in polycrops. Some have a documented effect of improving yields of certain crops, such as elm oysters boosting the growth of plants in the brassica family or wine caps having a long history of cultivation along with maize. These companion relationships haven’t been well enough documented yet, so we may well discover other combinations that work well together. So even if you’re not a mushroom lover like I am, we can see a clear advantage to cultivating certain fungi along with our plant crops.
Given all that, it makes sense to get them started in your growing space now while we have the ability to order mushroom spawn if you don’t already have them locally to get samples of.
This fall I layered most of my garden beds as follows: a bit of biochar, some compost and/or manure, an inch or two of shredded leaves, some mushroom spawn, and about six inches of straw. This was place on top of last year’s mulch layer, too. We’ll see how it does.
When it’s time to plant, we usually move aside the top layer of mulch in a line or just a whole for a single plant, and if we have compost available we put some of that in the gap we’ve just made. Then we seed or transplant into that. If no compost is available, we just plant into the soil underneath.
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Inspired
Great information, thanks for all your work.