Soil prep will help blueberry efforts bear more fruit
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Q. I planted blueberries four years ago, being careful to purchase different varieties to ensure cross-pollination. However, they have never grown. They are still only about a foot tall but otherwise healthy-looking. How can I push them to grow? I use Mir-Acid fertilizer as recommended. Should I use a different fertilizer?
A. I would start with a soil test to make sure the pH is in the proper range, between 4.5 and 5.0. Blueberries are acid-loving plants, and a higher pH stunts their growth because necessary nutrients become unavailable to them, even if they are present in the soil.
I would also switch to a granular fertilizer rather than using Mir-Acid so that you have to fertilize only once in the spring. If you have properly prepared your planting beds, blueberries generally only require nitrogen once they become established. The Mir-Acid may not be enough, especially when we have a lot of rain. Nitrogen leaches from soil easily under such conditions, especially when none of what is applied is in a slow-release form.
You do not mention how you prepared the soil prior to planting. Ideally, you should start the fall (September) before you want to plant by getting rid of the existing vegetation. You can strip sod by hand, smother it with black plastic (start in July) or kill it with a non-selective herbicide such as glyphosate (Round Up, Eraser) or herbicidal vinegar.
It's wise to create a planting bed rather than planting individual plants because of blueberries' specialized requirements. Also, they have shallow, fibrous root systems that lack root hairs (the fine roots that increase a plant's ability to take up water and nutrients), which make them sensitive to excessive or insufficient soil moisture and less able to compete with grass for water and nutrients.
Blueberries resent heavy clay soils, so you should till in about 6 inches of organic matter (compost, aged manure, peat moss or aged sawdust) to lighten our clay soils. At the same time, you should till in soil amendments such as sulfur according to your soil test recommendations. It takes time for sulfur to lower the pH to the optimum range, so it is best worked into the soil prior to planting. Both sulfur and phosphorus move very slowly through the soil and should be tilled in when you prepare the planting bed so that they are present in the root zone where they are needed. If you prepare the bed in fall, hold off applying the recommended amount of nitrogen until the following spring, when it will be of most benefit.
If your plants were grown in containers, it is important to gently break up the circling roots so they move out into the surrounding soil. If you did not do so at planting, that could be another reason for their stunted growth. Because they still look healthy, you can dig them up, break up the roots and replant them once you are certain the soil pH is in the appropriate range.
It is also good practice to mulch blueberries with 3-4 inches of organic matter to conserve soil moisture and moderate soil temperatures. Aged, well-rotted sawdust makes an ideal mulch for blueberries.
First Published February 25, 2012 12:00 am
