In the last post I talked about improving soil mineralization.
Now I want to discuss another aspect of organic soil health that is important for so many things: organic matter in soil.
Organic matter refers partially to living things like roots and fungi, but in this context it mostly means everything that used to be alive.
That means fresh fallen leaves and recently deceased snakes and beetles, to the coarse mulch layer when these things are partially decomposed, to the very stable humus when they’re fully broken down which stays around in the soil for years.
Creating organic matter in soil is something the forest excels at because it recycles everything – all of the leaves (deciduous and coniferous) eventually fall to the ground, becoming mulch and then soil organic matter and then humus.
Whole plants grow up and die back annually and contribute to this. Roots constantly grow and die back, becoming soil organic matter, too.
I should mention, while the forest is a good recycler, prairies actually create much more organic matter in soil because grasses have substantially more root mass and die back almost entirely every year, whereas trees just drop leaves and end up housing a lot of that carbon in their trunks.
But wherever you are in nature, plant recycling is happening.
Then there are the kingdoms other than plants – animals and microorganisms are recycled back into the soil when they die, and even as they’re living and leaving excrement wherever they go. It’s all recycled.
And then it goes to work. Organic matter in soil is important for so many reasons, such as:
- Fertility. Organic matter holds onto nutrients, stopping them from draining out of the soil, and making them easier for microorganisms and plants to use. Plus, organic matter is composed of many nutrients and other nutritional substances itself, especially carbon which is a primary plant nutrient.
- Water/Air. Just like with nutrients, organic matter holds onto water, stopping it from draining out of the soil. It also facilitates bigger pore spaces that hold onto air, which soil organisms and plant roots need just like us.
- Structure. It helps give organic soil a nice tilth, a nice structure. That’s what allows it to hold the right amount of water and air as mentioned above, but also contributes to decreased compaction and erosion.
- Soil Life. Organic matter provides homes for soil life, mostly because of all of the above points. Organic matter is food, water, air and habitat. It probably has many important functions for energy movement in the soil, too.
So how do we mimic nature to improve soil organic matter? Well we often do some things that are admittedly somewhat unnatural but nonetheless helpful, especially if we’re starting a new garden.
For example, we may bring in some compost, which is basically made by forcing organic matter to break down very quickly so we can work it into the soil for the many benefits it brings. We may also bring in some manure, although that is best composted first.
On the soil surface, we want to provide a mulch just the way nature does it. Leaves are the best, and a small amount of grass clippings are okay, too. When we don’t have leaves, we may bring in straw as a reasonable replacement for now, although we hope to get leaves in the future.
When you look in the forest, what you won’t find is 2 inches of bark and wood chip mulch. Although popular in the garden, these mulches really aren’t ideal. They can cause nitrogen shortages in the soil and most bark contains toxins, especially the coniferous barks like cedar and fir that are commonly used.
It can certainly be used sparingly in an ornamental garden, but let’s just be clear that it’s not how nature does it. In the forest, there are some sticks and seeds and mostly leaves in various stages of decomposition.
So composts and mulches are ways to quickly bring organic matter in soil, but we can also get even closer to the way nature does it, through our plants themselves.
When designing your garden, it’s a good idea to use some plants that create lots of mulch. That means plants that grow quickly and create a lot of leaves which (for most of us) they drop in the fall.
It also means planting densely and using ground covers. Many groundcovers are deciduous evergreens, and they can still improve the soil, but I’m especially thinking about clovers and perennials that are at home in a more natural garden design or an orchard.
Speaking of clover, in the vegetable garden we use cover crops during the off season to enrich and protect the soil. Clovers and vetches are legumes that bring in nitrogen, while grasses and other covers provide other benefits. Even allowing certain weeds to grow in your garden will improve the soil.
So you can see how nature gives us some good tips on how to improve soil organic matter. Mulch-making plants and cover crops are the long-term, sustainable way of doing this, while bringing in compost and leaves are a way to ramp things up quickly.
In the next video, I’ll discuss the third factor of establishing a healthy soil ecosystem.