After writing recently about some concerns about water being a non-renewable resource, I thought that I should address water conservation concepts. As I asserted before, water come from only one source: rain. Rain tends to come during certain times of the year, especially in regions like the southwest, and it often comes down too fast, such as thunderstorms in the east. The result is either months of dry skies or flashfloods. The issues involved here are the ability of the ground to absorb and hold the rain as it falls.
In our region, the ground can absorb about one inch of rain in 24 hours. Any more runs off, and sours the local farmers who see those additional drops going unused. In more developed cities and suburbs, run off occurs not just because of the ground composition, but because much of the ground is covered by buildings, roads, parking lots, and maybe even swimming pools. Hard surfaces do not give water any means to enter the soil. Parking lot catch basins and percolation ponds are a couple of ways to capture rapid flows of water and contain them for slower release or ground absorption. Rain gardens around parking lots and roads can add a feature of containing and breaking down oil and road grime, if the grasses and plants have this characteristic, allowing cleaner water to enter a nearby stream or groundwater systems.
While public roads and parking areas need to be hard surfaces for public safety and to meet building standards, if you are designing a driveway and pathways in your yard, you have the possibility of using alternative materials that allow more absorption of water. A gravel driveway is much more compacted than the garden, but more absorbent than a cement pad. Stone pavers (basically bricks) can be set over a bed of gravel and sand, at least allowing water to slip into the cracks between the pavers. Gravel or paver driveways have frost heave risks if you live in a cold climate. But, the same climates will crack asphalt or cement, which is more difficult to fix than adding some gravel to a pot-hole or leveling pavers. Pathways around the yard can be treated in a similar manner with walkway stones and decorative gravel, rather than pouring cement walkways. There may be regional variations of hardscape, too, such as using shells on driveways in New England.
The next soil condition to avoid is soil compaction. Any weight on the ground from feet to tires, presses on the ground, eliminating small spaces that contain water and oxygen. Some surfaces, such as driveways and paths, need to have a degree of compaction to avoid becoming mud holes, from which you would need a winch to extract your vehicle or self. But, the flowerbeds, vegetable garden, orchard, and field should have light, open soil.
Reducing compact soil relates to the material in the soil and the pressures that we put on the soil. Heavy clay soils have the most compact structure. When dry, clay particles lock together, requiring some time for moisture to penetrate the clay. When wet, clay particles swell, leaving little room for more moisture. Sandy soils have nearly the opposite characteristic of being very porous. Sand does not hold water long. A solution to both soils types is to add organic matter (i.e. compost). While over time compost will break up the sticky clay and bond together the loose sand, worms and fungus will break down the compost. Here in the Appalachian Mountains we have plenty of extra leaves and silt run off in our dirt road ditches and culverts. But, if you do not live in the woods, you will need to find other sources, such as municipal compost or your own kitchen scrap compost bin. The amount that you will need depends on the size of your garden or how many potted plants you put on your deck. On a side note, I read a report that claimed that someone studied municipal compost piles for evidence of pesticide residues. According to these researchers, the chemicals broke down when the pile’s temperature stayed above 160F, which is usually the level at which harmful bacteria are erraticated (remember Louis Pasteur?).
Commercial products can also be used to increase water retention in soil. These generally need to be turned into soil, so are best added when setting up perennial flower and herb beds. Various nut shells (e.g. walnut, hazelnut, coconut, also called coir) are sold in crushed or shredded forms. These work well for containers and pots. They work by breaking up the soil, leaving spaces for water and oxygen, and as with coir having the property of expanding when wet. Wet the product before mixing it into the soil. Once we put a brick of coir into a drywall bucket, added water, and split the bucket in a couple of hours, as the material soaked up the water and expanded.
Expanded aggregate is a new product that I read about recently, which does not break down as organic materials do, and can be used on large scale landscaping projects. Expanded aggregate is made from slate, shale, or clay by heating the material to 2000F. This baking process permanently enlarges the pebble size pieces, and forms small pockets, which again can fill with water or oxygen. Expanded aggregates can be turned into the soil, put down in a layer below the soil in which the plants will grow, or used as a decorative landscaping element on the surface. Turned into the soil, it will gather and release water directly to the roots of the plants. Under the soil later, it will create a reservoir of water than can move upward as the soil dries. On pathways or around plants, it will capture the water and then release it more slowly into the soil or evaporate to create humidity.
Once you have gathered the compost or material to turn into the soil, the technique that you use to turn it in can affect how compact or light the soil will be. Rototillers actually create a hard-packed layer when the turning blades beat the ground below the clods turned up. This essentially gives you a garden in a bathtub. The hard sub-layer traps the water and can drown the plants. Hand turning the soil with a spade is the most efficient method, especially if you use a double digging method (dig out a trench and set this soil aside; turn the next row into this trench, creating a second trench; keep turning one trench after another, then add the first trench full of soil back in).
If you are not inclined to break the surface, building up the garden soil can work. This can start as a “lasagna garden”, in which you layer various layers of brown and green compost. Then, each year you add layers during the winter months. “No till” gardening is a variation on the lasagna garden, in which, rather than turning the garden soil, you add layers of leaves or straw in winter, or grow a cover crop, such as winter rye, barley, or clover. In spring you make holes just for your seeds or seedlings, then cover the spaces between the rows with more organic cover. The layers of leaves or straw cool the soil, reduce evaporation, and will break down into next years top layer of soil, at which time the cycle begins again. Two major benefits of no till gardening is that you expose fewer weed-seeds and reduce the risk of erosion by breaking up the soil. On the other hand, some advocate turning the garden in later winters to expose grubs and insect eggs to some late freezes.
A final suggestion to reduce compaction in seasonal gardens is to create portable pathways. We make wooden pathways, 1’ x 4’, that we can configure each year, based on the garden layout. Standing on these distributes our weight, not on the two soles of your shoes, but across the whole pathway. These sit lightly enough that we can run soaker hoses under them when crossing from one bed to another, without pressing on the hose.