Fertilizing your vegetable garden

When it comes to fertilizing your vegetable garden this spring, don’t guess – soil test!

Spring is here and soon gardeners will be busy planting their 2013 vegetable gardens. I can’t wait for the tomatoes, sweet corn, melons and all the other delicious selections I will plant this year. I’m sure you’ve heard it before, but I’ll say it again: smart gardeners begin by taking a soil sample to determine the nutrient needs of the crops, and April is a great time to do it.

Michigan State University Extension offers a soil test kit that can be purchased online at the MSU Extension Bookstore. After receiving the kit, follow the directions for collecting the sample and mailing for analysis. When the results have been returned, go to MSUSoilTest.com and select the “Understand Your Soil Test Results” bar for further instructions and recommendations for timing of applications.

Once you have determined the amount of fertilizer needed, broadcast over the entire garden all of the required phosphorous, potassium and two-thirds of the nitrogen. This should be done seven to 10 days before planting. Six to eight weeks after the garden is up and growing, apply the remaining one-third of the nitrogen. It should be applied by sidedressing. Place the fertilizer in a band 2 inches to the side of the plants and lightly cultivate or water it in.

The ideal soil pH for the garden should be about 6.2 to 6.8. A slightly lower pH is better when growing potatoes. With a higher pH, 7.5 for example, potato scab – a fungal disease – can become a problem. As the pH approaches 6, the occurrence of this disease diminishes.

A higher pH can be lowered using sulfur or iron sulfate (Ferrous sulfate). The amount needed is based on how far the pH is to be lowered and garden soil type. More sulfur is required to lower the pH on a clay soil than a sandy one. Apply the product to lower pH in the fall while the soil temperature is still warm. The microbial activity for pH conversion works better when the soil temperatures exceed 55 degrees Fahrenheit. If the pH is too low, lime will be required. It may be added in spring before planting or in the fall.

Most commercial granular fertilizers contain only nitrogen, phosphorous and potassium, but plants also require calcium, magnesium, zinc, boron, manganese and other elements. Micronutrients such as boron, molybdenum and zinc are required in very small amounts, but plants continually remove them from the soil as they grow. If they are not replaced, the soil will eventually become deficient and certain plants may develop problems such as hollow heart in broccoli. Using liquid fertilizers with micronutrients, animal manures or other select organic fertilizers can help to prevent the development of deficiencies.

To determine the levels of certain micronutrients such as zinc and boron in the soil, MSU’s Soil and Plant Nutrient Laboratory provides separate tests for an additional charge.

If you need assistance, contact your area MSU horticulture educator by calling 888-678-3464 or visit the Gardening in Michigan website and submit your question to the Ask an Expert tool.

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