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Improving Your Soil

Healthy plants come from healthy soil. Make sure your garden is providing the right nutrients in the right proportions for optimum results; too much or too little of soil nutrients can affect how well your garden grows.The structure of your soil is important. Loose, crumbly soil that contains organic matter will allow plants roots to grow deeper, provide nutrients, channel water to pant roots and hold water more easily. Healthy soil will also contain micro-organisms that convert organic matter into nutrients plants need to grow.


Soil Structure This determines how water drains and is held in the soil, the amount of air space, and if nutrients are easily released for use by plants. Add organic matter to improve soil structure: 1 inch of fine compost or manure each year, 3 to 4 inches of bulkier materials like straw or leaves. (Turn leaves, other non-composted material into your garden in the fall, so it will have broken down by the time you plant in the spring.) Avoid compacting soil by walking on your garden beds, or working soil when it is wet.

Nutrients Plants need macro-nutrients like nitrogen, phosphorus, potash (the N-P-K in fertilizers) calcium, magnesium and sulfur to thrive and other minerals in smaller amounts (iron, manganese, copper, zinc and others). The availability of nutrients in the soil is affected by ground and air temperatures, moisture levels and soil pH. Organic fertilizers slowly break down in the soil make nutrients available to plants as they need them.

About pH Plants require certain ranges of acidity-alkalinity (pH). A 5.5 to 7.5 pH range allows essential nutrients to be available to plants. In general, soils in Minneapolis are alkaline, and city water is a pH near 8. Organic materials such as conifer needles, sawdust, peat moss and oak leaves will slowly help to acidify your soil.

Have your soil tested by the University of Minnesota Soil Testing Lab (information: 612 625-3101) to determine the percentages of nitrogen, potassium and phosphorus present in your garden, amount of organic matter and its pH. Add amendments to your soil to replace missing nutrients.

Organic Fertilizers

Apply dry organic fertilizers in spring before planting, in amounts recommended by your soil test results. Spread evenly over your garden and work them into the top 4 to 6 inches of soil. Common organic sources of macro-nutrients are:


Compost is a combination of organic matter that is decomposed to form humus. It improves soil structure, helps retain moisture and contains a balance of macro-nutrients. Add 1 inch of fine compost each season (a little more if your need to improve soil structure) or use compost as a mulch. Make "compost tea" to feed plants when you water.

Animal Manures

Animal manures provide nutrients and organic matter. They must be well composted before using in the garden, or risk damaging your plants. Make "manure tea" to feed your plants when you water.

Using Cover Crops to Fertilize

Cover crops, also known as green manures, are any green plant tilled back into the soil. Cover crops can add nitrogen and organic matter to the soil, catch nutrients and moisture that have leached deep into the soil, loosen compacted soil and reduce soil erosion over winter. They may be planted in late summer/early fall to mature in the following spring, or sown as a living mulch. See Using Cover Crops


A mulch covers the soil, moderating temperatures by insulating the soil from extreme heat and cold, preventing erosion, retaining soil moisture, and improving soil structure. Mulches help keep crops clean and disease free, and act as a weed barrier.

When mulches are made from organic materials, they will gradually add nutrients and organic matter to your soil. Adding a 3 to 6 inch layer of mulch to soil that has been thoroughly weeded will discourage weeds from growing. Mulches made from wood chips or sawdust tend to remove nitrogen from the soil as they break down. Mulches from non-organic materials like plastic provide better weed control, but do not allow healthy air exchange in soil, may build up heat, or not allow for sufficient water to pass through.

More About Compost

Make compost in your garden or backyard from plant waste and food scraps. Combine "green" materials (higher in nitrogen) with "brown" materials (higher in carbon) in the right proportions, add water and let microorganisms such as bacteria and fungi break down your plant wastes. Layer green and brown materials, with a little soil between layers, and water so pile is the consistency of a wet sponge. Periodically turn the layers with a pitchfork to provide air and speed decomposition. A properly constructed and maintained compost pile will not smell. Your compost is ready to use when it looks like soil.

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