I’d like to offer something rather uncommon in the gardening world. It contrasts the core concept in other methods that managing soil is the basis for plant growth. That the soil plays a major role in plant growth is true, but it leads us believe, when looking at a plant, it is mostly made of minerals found in the soil. It’s not -or at least, not to the extent most people think. The strange truth is that plants really grow from air.
Very little of the plant you see came from the soil. In fact only 3-5% of what you see came from the soil. The rest -carbon, oxygen, hydrogen, nitrogen -came from air, either absorbed directly, or stored in the soil until it was absorbed by the plant. In short, fertile ground for plant growth does not come from under our feet, it is all around us. Sophisticated gardening is figuring out how to make this fertility available to plants. I would like to share three primary ways this is done, and in doing so, explain some of the core principles of PASSIVE gardens.
The first step, is to protect a site from wind.
Wind has much more detrimental effects on plants than most would imagine. For tall crops, such as corn, wind can cut yields as much as 45 percent. Aside from the beating from wind, wind dries out plants, creating a need for more water, while evaporating water from the soil.
Blocking wind increases the on-leaf temperature for plants. This is because sunlight that heats the leaf creates a layer of slightly higher temperatures around the plant, like a skin of warmth. Within this skin, the plant’s metabolism runs faster. It also protects plants and soil from frost, so you can garden earlier, and later in the year, with more lush growth all season long.
Hearing this, you might wonder if windbreaks could over-heat a garden. Thankfully the situation is more complex. Blocking wind allows many microclimates to form, some warmer, and some cooler than the ambient temperature. This is because places that are shaded, such as below plant leaves on the soil surface, stay much cooler when wind is not driving warm air across it. The water plants pull from the ground is likely to be cooler in this case, and there is likely more water for them to pull. Windbreaks help every part of a garden stay at optimal temperatures, for water conservation, and ideal plant and soil metabolism.
You can provide a windbreak by locating your garden near buildings, but it’s best to make windbreaks using plants. This is because plants power PASSIVE gardens, and take care of most of the work.
The second most vital part of a PASSIVE garden that effectively channels the air into plant growth is nitrogen fixing plants.
Nitrogen is one of the most vital nutrients for plant growth. All plants -and in fact every living creature- needs it. This is because nitrogen is a key component in the formation of DNA. Anything that has DNA to at least some extent needs nitrogen.
Nitrogen comes from the air. About 78% of the air around us is actually nitrogen; but in this state it is inert. Nitrogen in the air is locked up, and must be transformed by the bacteria nitrogen fixing plants host in their roots to a form plants can use.
Now I should address that nitrogen has a bad rap in popular media. This is mostly because, back in the early 1900’s, we figured out how to artificially pull nitrogen from the air. The form in which this nitrogen is derived has a hard time entering back into the natural ecology when applied to soil, much of it washing away into rivers, and evaporating back into the air, where it causes problems. This is because synthetic nitrogen is not well balanced. You could say it is overly pure, and has a hard time working its way back into the ecology after we have ripped it out.
Plants will not pull enough nitrogen from the air to throw a system out of balance. Many have an idea in their minds that nitrogen fixing plants exude nitrogen from their roots. These plants actually don’t let any of the nitrogen they make out of their grasp without first incorporating it into their own tissue, bound up with many other elements such as carbon, and hydrogen they have also pulled from the air. This small amount is very costly for the plant to get in terms of energy. The bacteria work hard to get it for the plant. Plants only let go of it when they lose a branch or root. In fact nitrogen fixing plants will not even take on the bacteria which fix nitrogen in their roots unless there is a deficiency of nitrogen in the soil.
Most soils could use more nitrogen, so that is not a problem. We can get large amounts of very nutrient rich mulch for our garden by planting nitrogen demanding plants around our nitrogen fixing plants. This depletes the nitrogen directly around the plants, encouraging maximum nitrogen fixation.
So a PASSIVE garden ideally has taller, woody nitrogen fixing plants, that create a windbreak for the garden, with non-nitrogen fixing plants around their base to ensure maximum quantities of nitrogen are entering the system. Together, these plants will pull many nutrients from the air, including the hard to get nitrogen, and pair them together in their tissue with small amounts of mineral elements from the soil. This way, the nitrogen applied to your garden will always be in proportion to the other nutrients plants need. Rather than poisoning the system, this kind of nitrogen makes gardens flourish.
Providing nutrients this way leads us to the third vital aspect of a PASSIVE garden, which is to create a soil rich in organic matter.
Organic matter is most any material of which carbon is its basis. We usually think of fertile, crumbly soil as dark colored. This color is caused for the most part by carbon in the soil.
Carbon in the soil is seldom utlized by the plants to build their tissue; they get most of that from the air. What carbon in the soil does, is hold on to the hard to get nitrogen, as well as other nutrients, such as the small amount of minerals a plant needs, and water.
The complex carbon structures of decaying plant material holds as much as ten times its weight in water between rains, greatly reducing the liklihood you will ever have to water.
Finally, high levels of organic matter often correlates to soil that is spongy, with lots of air particles in it. Healthy soil should in fact be about 50 percent porous airspace, the other fifty percent mineral soil and organic matter. This allows air to enter the soil, feeding the plants, the bacteria and microlife that feed the plants minerals, and facilitating many chemicals reactions a plant needs to have happen down below if it is to be healthy.
If these three steps are followed, most of the average garden’s problems disappear. Soil that is so full of organic matter is so crumbly it does not need to be tilled. Water is conserved to the point you never need to carry a watering can into the garden accept for watering young seedlings, or in extremely dry conditions. The amount of mulch generated from a planting that effectively blocks wind and produces enough nitrogen to feed annual vegetables drowns weeds when applied to the soil, so cultivating to remove weeds is seldom an issue.
In short, PASSIVE takes all the elements of an ecology -air and wind, nutrients such as nitrogen that feeds a vital, life filled soil, and a diverse array of nutrients held in carbon rich soil from plant matter, that together create the ecology our food needs to thrive. All we have to do is follow the simple concept that plants do not grow from any one part of the ecology, but every part interacting, starting with the air, and ending with the fruits of a well designed ecology.
Did you find this of interest? Check out this highlighted chapter from the book PASSIVE Gardening: