Hank
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Poster: Hank @ Sun Jul 05, 2009 5:51 pm
Re-shaping the land : how to work with rock
Many sites are landscaped with rock and pavement. This creates what is known as the "heat island problem" -- that is, the rocks and paved elements absorb and hold solar heat, raising the temperature of the site, permitting little vegetation or evaporation. Another common landscape approach, xeriscaping, attempts to simulate a natural desert environment by using no deep-rooted plants, but only things like cactus and succulents. The problem with this approach is that it leads to erosion and a soil that is heavily leached and will not retain water; this is not conducive to growing food.
In contrast, permaculture-style landscaping that features a variety of rooted plants and water-managing features raises the water table and, though it requires more water input, may actually conserve water in the long run by cooling the site and creating more in-site moisture recycling (whereas xeriscaping creates a hotter, more arid environment by retaining little water). Plants cool a site, while rocks heat it up. So what's a person with rock on their site to do?
Don't remove the rock -- it's expensive and laborious to do so, and recall that 'using what's on hand' is a guiding permaculture principle. So, instead of removing the rock, redistribute it. Rock's heat-retaining characteristic is directly proportional to its surface area. Therefore, we want to arrange the rock in a way that minimizes the surface area and yet is useful.
The best way to do this is to use the rock on hand to create narrow, deep pathways around your planting areas such that the planting area will be sunken relative to to paths. This will help conserve your precious water -- the water will drain over and through the rock paths and be collected in the sunken beds. Sunken-bed agriculture has long been favored in desert Africa and other arid climates as a key water-management strategy. Repeat : sunken beds and raised paths are the best approach for growing food, especially in hot and arid climates. Raised beds will fry the roots of your crops when the sun beats on them.
Sidebar : the horror of Bermuda grass
Bermuda grass is a 'marginal' or 'fringe' plant -- it exists when land has begun to fail due to erosion and desiccation. It's an especially hardy species that is highly invasive, and is very difficult to control in an edibles-growing setup.
The 'conventional' approach to removing Bermuda grass is to use an herbicide, but smart people know that herbicides are poison and don't use them near their food crops. Instead, use the 'brute force' method : obtain a sod-cutter, "bobcat," or strong shovel (for the Calvinist) and remove the offending grass before planting. Attempt to scrape it off the top of your site. Due to its omnipresence and hardiness, it will continually stage comebacks, but this step will give you a head-start on it. If you're serious about keeping this hardy grass out of your planting beds, don't include removed Bermuda in your regular compost, as some of its seeds may survive the 140-degree temperature and come back to haunt your garden.
One tactic that has proved successful for keeping Bermuda grass at bay is the introduction of red clover, another 'marginal' species that is likewise invasive but has two advantages over Bermuda grass : 1) it attracts bees, which are vital for pollination of your crops, and 2) it smells better than Bermuda grass.
The 'Pre-Landscaped' problem
Many sites will already be landscaped with trees, shrubs, etc, before you arrive. This can be seen as an obstacle to your planting design, but the smart urban agronomist will incorporate existing green features into their plan. Rather than remove existing trees, remember that bees like trees and you need bees. Therefore, introduce gourds, grapes, and other hardy vines to grow up on and around the pre-existing features (including rocks of all sizes). This will create a photosynthesizing, water-producing heat barrier that requires little watering (because these thrive in dry conditions) is excellent at counteracting the effects of the urban "heat island."
Achieving microbial balance
Healthy plants are abetted by numerous symbiotic worms, insects, microbes and fungi living in the soil. Each type of helper organism lives in a certain "trophic level" -- that is, stratum -- of the soil. Microorganisms often move through fungal networks around plant roots to enhance crops' nutrient uptake. Helpful organisms come in several classes :
- Bacteria
- Fungi
- Nematodes
- Protozoa
- Arthropods
- Annileds
- Birds and animals are also in symbiosis wit your crop, but we'll treat them elsewhere in this series.
Soil trophic levels are an important consideration in urban agriculture. It's important to work with the organisms in each level, rather than against them, to maximize yield and minimize the amount of work you have to do. The first rule of working with these trophic-level-dwellers is : 'don't upend, displace, and massacre them with a rototiller.'
To dig or not to dig?
Tilling displaces the organisms in each tropic level, disturbing them and causing them to die quickly. A few inches means a lot to microbes and tiny animals. The "no-till revolution" currently under way in urban agriculture allows the trophic levels to remain healthy and undisturbed by specifying that rather than digging and tilling. it's better to layer mulch and compost on top of existing levels to allow the natural action of symbiotic-critter level adjustment as these new mulch and compost layers are watered in and self-percolate.
The "traditional" method of bed preparation, "double-digging," is wherein soil is dug up from one end of the bed and moved to another end. This is disastrous for microbe and fungal colonies and, even worse, is very hard work.
The new method : "Lasagna gardening"
I wish that "Lasagna gardening" was a way to grow lasagnas, but alas, it's only a slang term for building up soil in a layered fashion and avoiding disturbance of the native soil's trophic levels. Here's how to do it :
1) Spray / soak the site liberally with compost tea or "effective microorganisms" to bacterially control pre-existing environmental toxiins
2)Put a layer of black-and-white (only) newspaper over the selected bed site. This is nontoxic and will discourage pre-existing weeds from erupting in your planting beds. (note : stay at least 3 inches away from trees )
3) Layer equal thicknesses of mulch and compost on top of each other. Ideally, you want an ultimate planting depth that is equal to your root size; this is roughly the same as the height of the above-ground plant greens (hence the old saying "as above, as below"). This may seem daunting and silly, but after the first couple of seasons, the new material will be integrated with the original soil and the landscape will even out.
4) add new layers of mulch and compost after each harvest to continue enriching the site soil.
Kelp meal is a phosphorous-containing soil amendment that many have found to be beneficial to this process. However, those who live in landlocked areas may object to adding sea-based additives to their soil.
Coming soon : Part III
This information principally drawn from the lecture series "Designing a Vegetable Garden" as presented by Heather Welch in late 2008 courtesy of the Phoenix Permaculture Guild.
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