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 only have to fertilize 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
Blueberry Bush Soil
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.
Ripe blueberries... Yummy!
It is 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 makes them less able to compete
with grass for water and nutrients. It also makes them sensitive to
excessive or insufficient soil moisture.
Blueberries resent heavy
clay soils, so you should till in about six 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. If
needed, 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 nitrogen recommendation until the
following spring when it will be of most benefit to the blueberries.
Growing of Blueberries
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 instead of continuing to grow as if they
were still in a container. If you did not do so at planting, that
could be another reason for their stunted growth. Since 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
three or four inches of organic matter to conserve soil moisture and
moderate soil temperatures. Aged, well-rotted sawdust makes an ideal
mulch for blueberries.