There are many of us who are up to the challenge of growing blueberries. It can be rather difficult, mostly because of our soil conditions in our area. It is much easier to provide 'new' soil rather then trying to amend the soil to the conditions that blueberries require in order to thrive.
Karl Foord, UMN Extension educator, tells us that plants have a soil pH range within which they function well; however outside this range plants can show signs of stress. This stress is often in the form of a pH induced nutrient deficiency. In blueberries an out of the range high soil pH will induce an iron deficiency. Traditional blueberry soils are sandy with low organic matter and pH of 4.5 to 5. In addition blueberries plants do not tolerate waterlogged or droughty soils. If the planting hole is filled with water and takes more than four hours to drain, the hole is not deeper than the compaction zone.
It will be a significant challenge to modify the pH 7 clay soil to the point where it will be amenable to blueberries. Clay soils tend to resist changes in pH and dramatic changes will be necessary to achieve a soil pH of pH 4.5. A pH of 4 is not three points away from 7 it is 1000 because the pH scale is logarithmic. Rather than attempt this change, the plan is to abandon efforts to change the soil and start over with a new soil. The soil mix proposed is as follows: Proposed blueberry soil mix: 50 percent Sphagnum peat moss - (pH of 3.6 to 4.2), 10 percent Original soil - (pH 7 clay loam), 10 percent Compost - (likely pH @ 7), 10 percent Sand Inexpensive, untreated sand used primarily in construction, and 20 percent Perlite
The peat moss will provide organic matter and be the source of low pH for the mix. It will have to overcome the high pH characteristics of both the compost and soil components of the mix. Perlite and sand will add drainage qualities to the soil mix. The only way to truly know if the soil mix is at the proper pH is to have it tested. Although tree leaves tend to be acidic, compost made from tree leaves and most yard wastes will likely be alkaline (pH between 7.0 and 8.0) due to changes in compost components during the composting process. Most manures also have a liming-effect (increase in soil pH) as the pH of cattle and sheep dung is typically >7.0.
To be extra cautious about pH and drainage, remove the soil creating an 18 inch deep by 3 foot wide bed. Fill the ditch and add enough mix to create a 12 inch high raised bed. Space the plants 3 feet apart to create a hedge. Because the blueberry planting is a low pH island in a high pH field with environmental conditions that will tend to increase the pH, fertilize with ammonium sulfate or urea to help maintain the proper pH. Amend any mulch you use with a small amount of elemental fertilizer. This particular mix will work as will many other combinations. Given the tendency for many of the soils in Minnesota to be alkaline (high pH), this method may also prove valuable for planting of other acid loving crops such as rhododendrons and azaleas. It bears repeating that the main thing to do is get your soil mix tested and be sure that it is at the right pH for blueberry and other acid loving plants.
There are many varieties to choose from including: Burgandy Lowbush, Pink Lemonade, Northblue, Northsky, Northcountry, St. Cloud, St. Cloud, Polaris, Chippewa, Northland, and Patriot.
Don't forget to mark your calendars for "Plant Yourself in the Garden" sponsored by the Lyon County Minnesota Extension service Master Gardeners. April 16th. Doors open at 11:30 am. The first topic at Noon will be on Native Grasses, 12:40 the topic will be Bees in the Garden; 1:25 Break 1:40 The Birding Landscape and at 2:30 Success Secrets from the Farmer's Market. The charge is $5.00 or $4 with an item for the food shelf.
For more information on gardening, you can reach me at Stephanie@starpoint.net