Hank
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Poster: Hank @ Sun Jul 05, 2009 12:46 am
Part 1 : the setup
Water management
Water management is key for success, especially in desert environments. One of the determining factors in water management is the overall slope of your site space. Observe where water flows and pools when it rains. The areas where water pools are ideal planting locations for root crops (carrots, beets, etc).
You can influence the flow of water by constructing "swales" along the elevation contour lines. "Swales" are geographical features that are constructed by digging along contour lines and mounding the removed soil on the lower-elevation side of the ditch, creating a depression and berm that guides water runoff. This method can be effective for minimizing water loss and guiding flow to where you need it - your planting beds with water-hungry crops.
Rainwater and 'greywater' harvesting are good ways to maximize the self-reliance of your urban agriculture project. Rainwater harvesting requires a well-designed gutter / catchment system and collection barrel. When deciding how to apply your harvested rainwater, be aware that if your house has asphalt / tar / composition shingles, the roof runoff will contain toxic residues from the shingles. Therefore, you don't want water that runs of an asphalt roof to be used on your vegetables; it's probably OK to use on trees and anything you don't eat (though there's some argument about whether you should use it on trees that bear edibles -- see note on toxin concentrations in fruit). Water that runs off tile, tin, concrete, ceramic, wood shingle, or other non-volatile roofing materials is kosher for all plant uses.
'Greywater' is relatively uncontaminated water that's been used once in your home - for example, to wash clothing or the dishes. By using biodegradeable, nontoxic detergents, the urban agronomist can collect that water -- which is quite a lot - and re-use it directly on trees or and non-edible plants. You'll need to plan how best to get the greywater from its source (e.g., the clotheswasher) to the destination (e.g, your orange tree). For example, a hose can be run directly from the clothes washer to the orchard or collection barrel; catchments and barrels can be used to store greywater before use. Note that since greywater can harbor bacteria, it should not be stored for more than 24 hours before use (unless cured by UV rays). For collecting greywater from the kitchen and bathroom sinks, the simplest way is to simply collect the water in bowls and decant it into a bucket to take outside; you can also do minor plumbing alterations to make it easier. There are numerous books and commercially-available systems on the market with more detail about how to install greywater systems in the home; be sure to consult local laws governing greywater before starting on the project.
Some municipalities offer irrigation as a city service. This provides very cheap and plentiful water, sufficient to grow even the thirstiest crops. The downside to this convenience is that irrigation always brings with it numerous seeds (such as Bermuda grass) and insects. Take care to be on the lookout for invasive species when using municipal irrigation. Avoid placing plants directly in front of the irrigation channel to avoid damage from water movement.
When using forced city water -- that is, tap water -- there are several concerns to bear in mind. The most crucial is that tap water is chlorinated and fluoridated; left untreated, it'll kill vital garden bacteria and fungal microrhizome 'residents.' If you have no bacteria, you'll have no worms, and no worms spells doom for vegetable gardens. Without symbiotic fungi, your plant roots won't be able to take in vital nutrients from the soil. Therefore, if you use tap water, install a filter system that's designed to eliminate chlorine and fluoride contamination. If a commercial filtration system is beyond reach, these harmful elements will also evaporate if you leave the water in an open barrel or bucket for 24 hours or more. It's been hypothesized that toxins in water are concentrated in plant tissue to a factor of ten, so prenez garde!
Sun and shade
As important as water management is the practice of solar planning. It's essential to plan your plantings with a mind to the patterns of the sun on your site and the needs / tolerances of your crops. Plants can be sunburned just like animals can.
Pay special attention to summer sun patterns. In arid climates especially, avoid planting vegetables in places where they'll receive direct solar radiation (cactus and desert succulents are OK in direct summer sun). This is one of the reasons why it's desirable to create a multi-tiered "canopy" with trees or trellised sun-tolerant vines providing shade for edibles below. Creating such a canopy system improves not only the soil and plant health, but also site air quality.
You'll note that the sun pattern in your space will vary considerably between summer (the sun will be directly overhead) and winter (sun will come in at more of an angle).
The best spots for planting on your site are those that are in partial shade in the winter sun pattern. Determine your sun patterns by carefully observing the shade patterns as they shift throughout a day. You can approximate the patterns of whatever season it isn't by drawing a bird's-eye-view map of the site, putting objects on it to represent shading structures (for example, a tissue box for the house and saltshakers for trees) and moving a bright flashlight over the model, imitating the sun's sweep, to see how the shade patterns move.
The ideal type of shade is "filtered shade" -- that is, shade that doesn't completely obscure the sun. For this, trees with smaller leaves such as mesquite, palo verde, and palo brea are ideal. These types of trees are also "nitrogen-fixing" plants -- that is, they take elemental nitrogen from the atmosphere and convert it into nitrogen compounds in soil that can be used by other nearby plants. Note : if you have a dead tree on the site, don't root it out - introduce a trellising vine like grapes to grow up it and provide shade. Using what you've got on hand -- like pre-existing structures -- is a key permaculture principle.
Understanding microclimates
Microclimates are local variations within a regional climate. For example, the Phoenix area has an overall climate that is hot and arid. However, variations in elevation and airflow patterns make the North East section of the valley significantly cooler and more verdant than the southwest section. The urban center is hotter than the surrounding areas due to to high concentration of heat-retaining structures and pavement. Likewise, there are microclimates within individual sites. It's a good idea to walk around the site in he middle of the night, making notes as differences in temperature, humidity, and wind movement are perceived. These microclimates will influence the planting layout.
Soil : analysis and composition :
Soil is composed of sand, silt, clay, organic matter, air, and water. It's what plants grow in, and is ultimately the source of all food. It's important to think about and analyze the soil on any planting site.
Typical Arizona soil is heavy with caliche -- a mixture of clay with mica and montmorillonite particles. The clay and mica particles lay flat against each other, making for poor permeability and drainage. It's hard to break up and very challenging to grow in. The type of soil that's ideal for planting is called "loam" -- an equal balance of all particle types and sizes with plenty of organic matter. This soil type is very "friable" -- that is, easy to plant in -- and is nutritious for nearly all plant types. Any soil type can be made to take on the characteristics of loam with the addition of time and natural soil amendments -- compost and mulch. Never use gypsum to break up clay deposits, as it will make soil terribly alkaline.
The site soil should be tested for pH before the project is started. A pH between 6.8 and 7.5 is considered to be neutral and good for most plants; desert soils tend to be alkaline (~8.5 pH); some soils are acidic with a lower pH. The correct way to manage soil pH that's too high or too low is to add plenty of compost, which will help neutralize the overall pH. Any nursery can test the site soil for pH.
If you believe that your site may be heavily contaminated with industrial toxins, motor oil, pesticides, or other hideous stuff, many major universities (such as U of A) will test your soil for poisons (for a significant fee). If you find that your soil is contaminated, but still want to plant, you can attempt to "bioremediate" it using liberal amounts of compost tea and / or so-called "Effective Microorganisms."
Note : never use raw manure or fecal material directly on your soil, no matter what you hear-- it will introduce pathogens and can potentially cause 'nitrogen burn' in crops. Compost all manure before applying to your soil.
How to determine your soil's composition : This is easy. Just fill a lidded jar halfway with the soil to be tested (it's recommended to test multiple parts of your site), fill rest of jar with water, shake it up well, and leave it to settle for 48 hours. The sample will then separate into layers and reveal its composition. The bottom layer is sand, the middle layer is silt, the next and lightest-colored layer is clay, and floating on top is organic matter. The composition of your soil samples will tell you what amendments should be added to optimize the soil's friability.
If clay is present in excess, coarse compost or mulch can be added to help make the soil more permeable over time. Clay does have redeeming characteristics -- for example, it's rich in plant nutrients, as is silt. If your soil is sandy, that's not necessarily a bad thing -- sand is vital for good drainage. Just add plenty of finished compost to amplify the nutrient value. If your soil is weak in organic material, add mulch and compost (the more, the better).
Getting started
A good plan for starting your urban agronomy adventure is to pick the best-shaded, well-watered spot on the site and create a 4 by 8 foot bed (planting your favorite native food crops using the companion-planting strategy -- more on that later). This functional size is manageable for the neophyte and is modular, so that your planting beds can be easily added together or rearranged. Once you have success in the 4x8 bed, create more. A key permaculture principle to apply here is "start small, get big."
Basic tools
The basic tools you'll want to embark on your planting experiment are :
- Gloves
- Shovel
- Rake
- Hoe
- Wheelbarrow
- Rebar stakes are useful for many things including water and air management
- Compost and compost sifter
- Velcro for plant ties
The bulk of this information was drawn from the lecture series "Designing a Vegetable Garden" as presented by Heather Welch, November 2008.
Part 2 to follow
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