covers such as clover, increasing the nutrient content of the soil. › Pest suppressors. Certain plants generate pest suppressing compounds and can be strategically intercropped to provide protection to their neighbors. For example, plants in the allium family (onions, garlic, leek) are generally pest repellent due to their strong odor. › Structural support. Some plants can be used as natural trellises. A well known example is growing corn together with beans, allowing the bean stalks to climb the corn. Competition for nutrients is minimized because beans fix nitrogen in the soil. Trees can also be used as a structural support. › Shading, windbreaks, shelter. Shade loving plants can be grown underneath bushes, trees, or taller plants. This creates a natural micro-climate without the need for mechanical shading. ECOSYSTEM STABILITY Some polyculture principles that particularly apply to outdoor cultivation include: › Reducing tillage and soil disruption to reduce the growth of weeds and maintain a living soil structure. › Maintaining ‘permanent’ ground covers in untilled areas to improve soil structure, retain moisture, and reduce unwanted runoff of nutrients. › Using cover crops under perennials to increase moisture retention. Ideally these are also nitrogen fixing cover crops. Increasing crop diversity to disrupt pest growth. INTEGRATED PEST MANAGEMENT › Integrated pest management is a goal of polyculture design. Stress is applied to pests by interrupting their life cycle, removing alternative food sources, and enhancing populations of beneficial insects. To maintain biological crop production, agrochemicals are avoided. As suggested in the designs here, leaving greenhouses unheated in winter can also help disrupt some pest populations by reducing favorable conditions for their survival. Regular crop rotation also breaks the reproductive cycle of pests. ASSEMBLAGE CONSIDERATIONS Key factors in designing a successful polyculture are how crops and other elements are arranged within the system. All elements should be easily accessible when needed. Time also plays a factor in ideal spatial arrangements. Companion plants can be planted near trees, blocking easy access to the tree, as long as they are harvested before the fruit from the tree itself needs to be harvested. Nitrogen fixers: › clovers › › eleagnus acacia › beans › peanuts › › vetch Alfalfa Dynamic accumulators: › › › › › › comfrey nettles yarrow borage chicory dandelion Ground covers: › › › › › alyssum clover yarrow mint strawberries Pest suppression: › › › alliums dill coriander › parsnip › › cumin › › › › anise carrot most herbs marigolds calendula Insectary: › clover fennel › lemon balm › › › › › borage alyssum comfrey linden Windbreaks / shelter › › › › › › sunchoke fig loquat mulberry acacia elagnus Pagina 12
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