Yard and Garden: Preparing Garden Soil

March 28, 2018, 4:13 pm | Richard Jauron, Willy Klein

hands holding soil.AMES, Iowa — Most soils in Iowa are well suited for vegetables, flowers and turf; a few may have special problems needing correction before planting. Gardeners often have questions whether or not to amend the soil so Iowa State University Extension and Outreach horticulturists offer tips on soil management. 

Should I apply lime to my garden?  

In Iowa, gardeners should apply lime to gardens and lawns only when recommended by a soil test. A soil test will indicate the current soil pH and, if necessary, the amount of lime to apply to the area. Liming materials include ground limestone, which is mainly calcium carbonate, and dolomitic limestone,which contains calcium carbonate and magnesium carbonate.

Lime is applied to acidic soils to raise the soil pH. The soil pH is important because it affects the availability of essential nutrients. The pH scale runs from 0 to 14. Any pH below 7.0 is acidic and any pH above 7.0 is alkaline. A pH of 7.0 indicates a neutral soil. The optimum pH range for most flowers, vegetables and other horticultural crops is between 6.0 and 7.0.  Lime is applied to acidic soils with a pH below 6.0 to raise the pH into the optimum range. However, an application of lime to an alkaline soil can raise the soil pH to excessively high levels, reducing the availability of plant nutrients and leading to poor plant growth.  

Will an application of gypsum improve a clay soil?  

Advertisements for gypsum sometimes claim that gypsum will help loosen heavy, clay soils and improve soil drainage. However, the addition of gypsum to Iowa soils is of little benefit. Gypsum is chiefly used to amend sodic soils. Sodic soils are mainly found in arid regions of the western United States.  

Core aeration is the best way to improve growing conditions for lawns established on clay soils. The core aerator should remove soil cores that are approximately three-fourths of an inch in diameter and 3 inches long. There should be 20 to 40 holes per square foot. April and September are the best times to aerate lawns in Iowa.  

Vegetable and flower gardens can be improved by applying and incorporating organic matter, such as compost, into the soil. Work the organic matter into the top 8 to 12 inches of soil.  

What type of fertilizer should I apply to my garden?  

Conduct a soil test to determine the nutrient levels in the soil. Apply and incorporate the recommended type and amount of fertilizer (based on the soil test results) into the top 6 to 8 inches of soil prior to planting in spring. If the fertility level of the soil is unknown, apply and incorporate 1 to 2 pounds of 10-10-10 or a similar analysis fertilizer per 100 square feet in spring.  

Can I apply barnyard manure to the vegetable garden in spring?  

Barnyard manure contains nitrogen, phosphorus, potassium and other plant nutrients. It is also a source of organic matter. However, manure also contains pathogens, such as E.coli and salmonella that can cause infections in humans. For food safety reasons, there should be at least a three-month interval between the manure application and the harvest of vegetables from the garden. In home gardens, fall is the best time to apply and incorporate manure into the garden.  


About the Authors: