Healthy soil has the ability to store and process an amazing amount of water. Poor quality, depleted soil, on the other hand, will simply not hold water and will, in turn, leave your plants high and dry and ultimately dead. They key to healthy, high-quality soil is lots of organic matter, things formed by living organisms. These can be kitchen scraps, garden waste or animal manure. By adding organic matter to your soil you will dramatically improve its ability to hold and regulate water.
Keep in mind that soil is a living and dynamic ecosystem in and of itself. That ecosystem hosts spaces in between soil particles (otherwise known as pores) that allow for passage or retention of water and nutrients. For example, fine soil particles, such as those found in clays, hold water much more readily than the larger particles in sand. The amount of available water in your soil has profound consequences for your garden. Not only will that amount effect the health of your plants and the amount of water you use in irrigation but it will help balance soil surface temperatures and regulate the heat content of the soil which in turn effects seed germination and flowering activity. Organic matter is the key to water retention and good soil health.
Organic matter can be anything containing carbon compounds. That is, things formed by living organisms. Organic matter can be anything from lawn clippings and leaves to stems and branches, moss, algae, lichens, manure, kitchen scraps, sawdust, insects, earthworms and microbes.
While native vegetation are adapted to their soils, most garden crops prefer a loamy gardening soil composed of half solids high in organic matter and half porous space and with a neutral or slightly acidic pH. This kind of soil holds water without water logging. It also allows air into the soil so that roots and soil organisms can thrive.
As an aside…you may have heard the term ‘humus’ and wondered “what in the heck is that?” Humus us basically partially decayed organic matter. It is composed of complex organic compounds that have resisted decomposition and have accumulated in the soil. Humus is another useful ingredient when it comes to water retention in the soil.
So how do you get to the perfect water-retaining soil?
While some suggest mixing silly things like anionic polyacrylamide into your soil to improve absorption and retention I suggest you simply add organic matter. This is not rocket science and there are many easy ways to get it done.
You may want to start with compost. Compost is simply organic matter that is being decayed via aerobic decomposition. Anyone can build or buy a composting device or structure and put it right to work by adding food scraps and landscaping leftovers to a pile to allow it to decay into rich, dark soil. There are numerous composting websites such as this one, Compost Instructions, that will show you exactly how to make your composting effective.
In Permaculture design however, we often discourage compost in favor of a less intensive and more effective soil building method. When you compost, you decrease the nutrients in the organic matter by allowing them to go into the air or to be leached out of the compost pile. Think of grass clippings. When you pour them on the compost pile they are green. All that green is essentially nitrogen. A few days later those clippings are brown and dry. Where did the nitrogen go? Up into the air.
So instead of composting, we often avoid the compost pile in favor of putting kitchen scraps and other organic material such as grass clippings directly into the growing area and covering it with straw or some other moisture retaining material. You will be spreading the organic matter over a wider area and letting the decaying process occur at a slower rate on top of the surface of the soil. Fewer nutrients go up into the air and those that leach out then go straight into the soil. The decaying activity – a key part of the soil ecosystem – spreads across the whole of the growing area. This is a more effective way of building your soil.
You can also simply buy topsoil, different types of ready compost or a manure mixture to get your soil where you want it to be. Just remember that, by adding organic matter to the soil you alter the amount of nitrogen and other nutrients that is available to your plants, you alter the way soil aggregates and holds water and you increase the number and diversity of organisms in your soil.
Other Methods to Improve and Protect Your Soil:
Aerate compacted soil with a digging fork or vigorous root crops such as daikon radish or locust trees (if using a digging fork, loosen the soil but do not turn it so as not to wipe out the existing soil system).
Clay soils can be improved by adding finished compost and sand to the clay in a 1:1:1 ratio. Sandy soils can be improved by adding compost or other organic matter at a 2:1 ratio.
These allow you to control the soil quality as well as the amount of water used.
Tilling mixes up the soil, destroys the existing ecosystem and opens the soil to the drying forces of wind and sun. Tilling also causes compaction of the soil which decreases its ability to hold water. Spread your compost or mulch on top instead of tilling it in.
The roots of perennial species decrease erosion and anchor soils in place.
Try to avoid walking on your garden soil or running heavy machinery on it. Again, compacted soils cant hold water.
Create permeable pathways between your garden beds to allow precipitation to filter into your soil instead of running off. Slow the water down and keep it on your land!
Key Principals of Soil Biologic Fertility from Soil Health: www.soilhealth.com:
1. Soil erosion should be controlled to minimize loss of soil organisms,
2. Plant organic matter should be retained to maximize nutrient cycling and soil aggregation processes,
3. Some disturbance of soil is necessary to maximize soil biological diversity,
4. Nitrogen fixing bacteria should be selected that match the host, soil characteristics (such as pH) and environmental conditions,
5. Inputs of nitrogen fertilizer should be calculated to complement nitrogen cycling from organic matter
6. Inputs of phosphorus fertilizer should be calculated to complement and enhance the activities of arbuscular mycorrhizal fungi,
7. Any substance added to soil should be assessed in terms of its effects on soil biological processes and soil biological diversity,
8. Crop rotations and tillage practices should be selected to avoid development of soil conditions that enhance the growth and survival of plant pathogens,
9. The capacity of a management practice to produce a commercial product should be considered in parallel with its capacity to maintain and/or increase soil biological fertility,
10. Sufficient time should be allowed for establishment or restoration of a level of soil biological fertility appropriate for particular soils and land management.
Jim O’Donnell gardens in the mountains of northern New Mexico. A certified permaculture designer and ecological restoration specialist, Jim’s first book Notes for the Aurora Society was published in 2009.