The soil food web is what makes it possible for plants to grow.
‘Paramecium Bursaria’, a protozoa which farms algae (Bob Blaylock) CC BY-SA 3.0 https://en.wikipedia.org/wiki/Paramecium_bursaria#/media/File:20090719_062218_ParameciumBursaria.jpg
Alligator lizard (Kate Russell)
Soil is not simply ground up minerals. We now know that there are gazillions of living things breathing, growing, moving, and reproducing beneath our feet.
The living things found in soil are mostly smaller than you can see, with only a few exceptions. As these tiny life forms move through the soil, they reduce erosion, impact water and nutrient availability, and aid in decomposition of manure, plants, and pesticides.
Algae are single-celled organisms that can form substantial chains. Algae are classified by color. [Did you know that kelp is a type of algae? I didn’t either.] Algae convert sunlight into energy through photosynthesis. They can also fix atmospheric nitrogen. There may be 10,000 to 100,000 algae in a teaspoon of soil. Algae aid in nutrient cycling and help prevent erosion.
Arthropods are bugs. Bugs do not have backbones. Instead, they have exoskeletons. Arthropods include insects, crustaceans, and arachnids. Common insects include ants, beetles, and springtails, while sowbugs are crustaceans. The arachnids include spiders, mites, and millipedes. Arthropods eat a variety of foods. Some types feed on fungi, while others prey upon worms and other arthropods, and yet others are herbivores. As they feed, arthropods aerate the soil, aid in decomposition, and keep other populations in check. At the same time, arthropods can damage root systems.
Bacteria are one-celled organisms. They are so tiny that they can enter a plant through a broken hair, or trichome. It is estimated that there is one ton of bacteria in every acre of soil. That’s the weight of two adult cows, or half of your car. A teaspoon of productive soil may contain anywhere between 100 million and 1 billion bacteria.
Most bacteria are decomposers that prefer more tender fare. As they breakdown carbon-based life forms, they make those nutrients available to plants and improve soil structure. Other bacteria are mutualists, which means they work together with plants to everyone’s benefit. This group includes the bacteria which convert atmospheric nitrogen into a form available to plants. Another group of bacteria, called lithotrophs, break down hydrogen, iron, nitrogen, and sulfur compounds, rather than carbon, making those nutrients available to plants. The fourth group of bacteria are pathogens. This group includes Erwinia (fireblight) and Xymomonas diseases, and gall-forming Agrobacterium.
Recent research has shown that a certain soil bacteria, Mycobacterium vaccae, improves mood and reduces stress. See, gardening really is good for you!
Earthworms are popular decomposers, improving soil structure as they feed on organic matter and move through the soil. Earthworm poop, or casts, is a fermented batch of plant material, bacteria, and fungi that forms nutrient-rich soil aggregates. Earthworms improve soil structure, porosity, infiltration and drainage, as well as make life a lot easier for plant roots. Earthworms are also credited with reducing erosion and runoff.
Fungi are single and multi-celled organisms that grow as long threads, called hyphae. Those hyphae may cluster into groups called mycelium. Yeast is a fungi. So are mushrooms and dog vomit mold. Fungi help bind soil particles together, improving soil water holding capacity and infiltration rates. Most fungi, called saprophytic fungi, are important decomposers that can break down harder materials than bacteria can, such as tree trimmings, and hold those nutrients in the soil, rather than allowing them to be lost to the atmosphere through erosion and runoff.
Other fungi (mycorrhizae) are mutualists that live on and in plant roots, bringing soluble nutrients to your plants. Plant roots can only come into direct contact with approximately 2% of the surrounding soil. With the aid of fungal threads (hyphae), those roots then have access to all the water and nutrients found in 20% of the soil. There are pathogenic fungi, such as Pythium, which cause blackleg, seed rot, and cavity spot, Rhitozoctonia, and Verticillium, which cause Verticillium wilt, among others. Parasitic fungi feed on insects and nematodes.
Nematodes are worms without segments. Some are large enough to see, at 1/20”, but most are smaller than that. We know surprisingly little about beneficial nematodes. Most research has focused on root feeding omnivores that parasitize our plants. In the world of nematodes, life is hard. There are nematodes that feed on bacteria, fungi, and other nematodes and protozoa, while those same creatures prey upon and parasitize the nematodes. This whole process can either spread or control disease, depending on who wins that particular fight. Nematodes benefit plants by releasing excess nitrogen into the soil, like protozoa. As bacterial and fungal feeders, nematodes keep those populations in check while, at the same time, expanding their ranges by carrying microbes with them. There are usually 100 nematodes per teaspoon of soil.
Small animals, such as gophers, moles, rabbits, snakes, and voles are the giants of this microscopic world. As amphibians, birds, mammals, and reptiles scratch at and burrow through the soil, they help reduce compaction. They can also destroy plant roots. While both predators and prey aid in nutrient cycling, some are more beneficial to your garden than others. In my opinion, snakes, lizards, and toads are preferable. That’s just me.
Bottom line, like any other food web, everything gets eaten by something else. Your soil is no different. As things are eaten, the elements that make them up get broken down into smaller bits. These smaller bits get eaten by something else until, ultimately, plant roots absorb those nutrients to help them grow.
The Earth’s crust is a living, breathing entity whose health dictates our own. Do right by your soil, and your garden will thrive. The greater biodiversity in your soil, the healthier we will be.
If you have access to a microscope, I urge you to collect some samples of your garden soil and take a closer look at what is supporting life in your yard. What life forms can you see in your soil?
How would you like to transform your soil from compacted concrete (or lifeless sand) for free?
You can, with tree trimmings!
Tree trimmings, also known as arborist chips or Tahoe chips, consist of coarse, medium, and fine wood chips, pine needles, twigs, leaves, and bark. It isn’t the pretty, uniform stuff you buy in bags from the garden center. This is what’s left over after a hard day’s work of trimming trees.
Professional arborists chip everything they cut off a tree into bits. These tree trimmings either go to a landfill or civic composting center, for a fee, or to someone’s driveway, for free.
Benefits of mulching with tree trimmings
Tree trimmings make an ideal mulch. The green leaves and new buds break down quickly, while medium-sized twigs and stems break down a little more slowly. Coarser pieces take longer to breakdown. This process creates a time-release of nutrients and organic material that provide a wealth of benefits, including:
But, what about toxins or disease? Let’s learn the truth.
Toxic wood chips
You have probably heard rumors about the way certain types of wood chips are toxic to garden plants, preventing germination or killing them outright. In nature, this form of chemical warfare is called allelopathy and black walnut is usually the first to come to mind. It is true that black walnut trees produce a compound, called juglone, that can kill off competitors. But juglone only affects some shallow-rooted plants and black walnut is too valuable as lumber to end up chipped. Other commonly accused chips include cedar, redwood, and Douglas fir, but there has been zero scientific proof that trimmings from these trees negatively affects other plants. They do, however, inhibit some fungi and bacteria, and repel or kill clothes moths, termites, cockroaches, ants, and carpet beetles.
What to look out for
Before accepting a load of wood chips from your local arborist, be sure to ask if the load contains any palm tree trimmings. New palm trees can grow from these pieces. This is not what you want in your garden. Believe me. Here in California, we call palm trees ‘rat hotels’ for good reason. If the load contains palm tree, let it go somewhere else.
Many people are concerned about diseases and pests being transferred through tree trimming loads. For the most part, this fear is unwarranted. In nearly all studies, pathogens such as Verticillium, Cytospora, Thyronectria, were found unable to move from the mulch layer, into and through the soil to plant roots. They simply couldn’t do it. So don’t worry about tree trimmings bringing disease to your landscape, unless you make the mistake of digging the chips into the soil. It is far better to just dump them on top of the soil and let nature do all the work.
[Note, most pathogens are already present. They become a problem when plants become unhealthy enough to be susceptible. Mulching with tree trimmings helps your soil and plants be healthier, and less prone to disease.]
Speaking of work, moving wheelbarrows full of tree trimmings from your driveway to your landscape is work. It’s not backbreaking, but be sure to wear sunscreen, a hat, and gloves. You can skip the gym.
Tree trimmings and nitrogen loss
As mulch of any type breaks down, the microorganisms responsible for decomposition consume nitrogen. This makes nitrogen temporarily less available to nearby plants for 6 to 8 weeks. This is only true for the most shallow-rooted plants and has no effect on deep-rooted, established plants. You may need to add a little extra nitrogen during this time if you apply tree trimmings near vegetable plants. In the long term, as the wood continues to break down, it will add nitrogen and other nutrients to the soil.
And if you happen to see white fungal threads spreading through your tree trimmings, fear not! These fungi are a blessing to your soil and should be celebrated for the good health they bring to your plants.
Tree trimmings and fire safety
Some mulches are more flammable than others. If you want to improve soil structure, retain moisture, and reduce weeds, tree trimmings are your best choice. A group of fire and gardening professionals got together in Nevada to test various types of mulch for fire safety. The material you are most likely to get from an arborist is rated with moderate flames and spread, compared to shredded rubber, which burns the hottest (630°F) and flames the highest (over 3 feet), and composted wood chips, which is the only material that did not “demonstrate active flaming combustion”. So, as your tree trimmings break down, they will go from low risk to no risk.
How to get tree trimmings
Most arborists are happy to give away full or partial truckloads of perfectly good mulch. Simply give them a call and let them know you are interested. They will put your name on a list and call you when they have a load available. Then, park your car somewhere else for a few days and get ready to transform your landscape!
And be sure to gift your friendly, neighborhood arborist with the fruits of your garden labor. You will want another load in a few years!
Spread those tree trimmings 4 to 6 inches thick and let the magic happen. As always, keep mulch several inches away from trunks and stems to avoid diseases, such as crown rot.
Now, go call your local arborist!
You can grow a surprising amount of food in your own yard. Ask me how!
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