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University of Illinois Extension

Now is the Time to Prepare Blueberry Beds

October 22, 2008

Blueberries offer important nutritional benefits, and in the home landscape, they provide a spring show of flowers, fruit and brilliant fall color. Blueberry plants can survive 25 or more years with proper care. But to successfully grow blueberries, you need some advance preparation.

The planting site needs to be prepared in the fall so that the soil pH (acidity) can be reduced, thus allowing the plants to thrive. It can take up to a year for this soil chemical change to occur.

"As you prepare your planting area this fall, consider building permanent raised beds," suggests Tony Bratsch, University of Illinois Extension horticulture educator. "Blueberries are sensitive to wet soil conditions. If your soil is heavy and predominately clay, or less than well drained as many Illinois soils are, the extra effort will be worth it."

Like rhododendron and azaleas, blueberries prefer an acid soil with a low pH of 4.7 to 5.2. Most Illinois soils have a higher pH. Depending on location, the pH can range from 5.5 (or lower), to 7.0 or higher, at which soils become alkaline.

Bratsch says the best way to reduce soil pH is by adding elemental sulfur. Peat moss, which is acidic, can also be added to the planting area to help reduce soil pH and add organic matter that is beneficial for blueberries.

Start by taking a soil test to determine the pH and the amount of sulfur needed for the planting area. A soil test will also provide information on fertility, namely phosphorus and potassium levels. If the natural soil pH is above 6.5, consider an alternative crop rather than blueberries. It will be too difficult to initially lower and keep the soil pH down to an acceptable level over time.

Take several random samples across the area to be planted. Cut slices of soil, approximately 8 to 12 inches deep, with a clean spade. Remove grass and surface debris, and mix the samples together in a clean bucket. Collect about two pints of soil and place in a clean plastic bag.

Take the sample to your local Extension office or to a local agriculture service center that offers soil testing. State that the sample is for a garden blueberry planting. Request that soil pH, and soil phosphorus and potassium levels be tested. For an additional fee, you can also request a soil textural analysis, which tells you what "type" of soil you have. This is usually expressed by the percent of clay, silt or sand that predominates -- for example a clay-loam or a silt-loam soil.

Once your sample is analyzed, it is time to determine the amount of sulfur needed to reduce soil pH. Usually this is done on a square footage basis. Calculate the area of your bed by taking the length times the width. For example, a 10-foot by 20-foot area is 200 square feet. Charts, based on soil type, are available to estimate the amount of sulfur needed, usually for every 100 square feet of bed area. Contact your local U of I Extension office to obtain this information.

"When purchasing sulfur, avoid aluminum sulfate because it can be toxic to plants," advises Bratsch. "Instead, buy elemental sulfur which will be sold as a powder or in small pellets."

Evenly apply sulfur across the area and deeply till in a couple of directions to maximize sulfur contact with soil particles. Do not apply more sulfur than the soil test recommends. Remember, pH adjustments take time, and a spring re-test may be necessary to determine the effectiveness of the treatment.

While adding the sulfur, also add organic matter such as peat or compost to the soil. In addition, fertilizer containing phosphorus and potassium should be applied, depending on soil test starting levels. A general analysis fertilizer, such as 12-12-12 can be used, and 1 to 2 pounds of this material per 100 square feet is a good base application if starting phosphorus and potassium is unknown. Spade and till organic and fertilizer amendments in deeply; this can be done when adding sulfur.

Next, determine your planting bed and pathway layout. Using soil from the pathways, form the raised beds 4 to 5 feet wide, and 4 to 8 inches high. Pathways between beds can be 12 to 15 inches

wide. To ensure water will not be "held-up" by the beds if they are on a slope, orient beds with the slope and not across it. Beds should be raked flat across the top. Use straw, newspaper or bark chips to fill in the shoveled pathways.

If pH has been reduced in the spring, you will be able to plant your blueberries in the well-drained, raised beds without having to wait until wet spring soils are dry enough to till.

Because soils tend to revert back to their natural pH over time, Bratsch says a soil test should be taken every few years. Our efforts to lower (or raise) pH are temporary at best. Apply sulfur on the soil surface to keep pH low. Blueberries also need regular fertilization, and a fertilizer such as ammonium sulfate is a good choice because it provides both nitrogen and sulfur.

For more information, pick up the Small Fruits in the Home Garden circular 1343 at your local U of I Extension office. Or, visit the Small Fruit Crops for the Backyard website at www.urbanext.uiuc.edu/fruit/.

Source: Anthony Bratsch, Extension Educator, Horticulture (Serving East-Central and Southeastern Illinois), bratsch@illinois.edu

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