Q. I'm considering growing some blueberry bushes but
don't know how they will do around here since it seems they grow up
north. I have been considering growing them in outdoor containers if
possible. What are my chances of success and are there any other
tips you would offer?
Blueberries (Vaccinium spp.) grow very well in our area as long as you pay
careful attention to soil preparation for them. They require an
acidic, evenly moist yet well-drained soil rich in organic matter.
If you choose to plant them in the ground, start with a soil test so
that you can incorporate enough sulfur to get the pH into the
preferred range of 4.5 to 5.5. Many gardeners spend a season getting
the soil prepared and plant the following spring, but much depends
on the existing soil conditions in your yard.
Winter cold can be
the limiting factor when growing perennial or woody plants in
containers in our climate. Many plants simply do not tolerate having
their root systems completely frozen the way they can when grown
above ground in a container, even if they are winter hardy here when
planted in the ground. One way to get around that challenge is to
choose plants that are much hardier than our coldest Zone 5a.
Blueberries (Vaccinium spp.) are hardy to USDA Zone 3, so
that is in your favor. Use the largest containers possible if you
intend to leave them outdoors over the winter. Since blueberries are
large plants – those that grow four to five feet tall and wide are
considered compact growers - you will need to use large containers
to support their growth anyway. At minimum something as large as a
half whiskey barrel. It is critical that the containers have good
drainage to avoid ice building up in them during freezing winter
weather. You will have drill holes in the bottom of whisky barrels,
if you choose to use them.
Another way to protect container-grown plants over the winter is to
move them into an unheated garage in late fall. That allows you to
control the water. You will need to water them periodically over the
winter, perhaps only two or three times. It is important to monitor
soil moisture through the winter storage period. Blueberries are
shallow-rooted plants that require good drainage but resent drying
out completely, too. They lack root hairs, the structure on most
plant roots responsible for absorbing water and nutrients. This
makes them extremely sensitive to too much or too little water.
Your container soil mixture will be important to success. Be sure to
fill the entire container with the soil mixture, rather than filling
the bottom of the container with gravel or any other material. To
make your soil mixture, start with a good soilless mix that contains
a high percentage of peat moss. Amend it with an equal amount (by
volume) of homemade compost (avoid mushroom compost here because it
tends to have a high pH, around 8.0). You should also mix in small
pine bark chips for some longer-lasting organic matter, about half
the volume of potting mix or compost. Finish with medium chicken
grit for sharp drainage, about one-quarter of the volume of potting
mix or compost. Chicken grit is pH neutral and does not break down.
Chicken grit is available at farm supply stores such as Agway. You
can also mix in a coated release fertilizer such as Osmocote®
Azalea, Camellia, Rhododendron Smart Release® Plant Food, according
to label directions. This also contains an acidifying agent, which
will help keep the pH in the desired range for blueberries.
ANNUAL CARE OF BLUEBERRIES
blueberries are planted, topdress the containers with the same
fertilizer annually. Avoid the temptation to use more than the label
rate of fertilizer; that could burn their shallow roots. You should
also avoid less expensive, quick release fertilizers in containers
because the relatively small soil volume cannot buffer the strong
salts they contain. You may want to purchase a quick soil pH test
kit to monitor the pH so you can amend it as needed to keep the pH
low enough for the blueberries. Sulfur is the preferred material to
lower soil pH, but it moves very slowly through the soil profile.
Sulfur is best incorporated prior to planting, if needed. Although I
would typically recommend a
Penn State soil test kit over the
do-it-yourself types, translating the recommendations from “X amount
of fertilizer per hundred feet of row” to an amount appropriate for
a container is difficult.
The typical recommendation is to plant two or three different
blueberry cultivars to ensure good cross-pollination, which will
increase fruit set. This also allows you to spread out the harvest,
by choosing early, midseason, and late ripening cultivars. Some
cultivars that would be good for your use include Patriot (early),
Blueray (midseason), and Elliot (late).
Once they are planted, water them thoroughly and mulch with an inch
or so of the same small pine bark chips you used to incorporate into
your soil mix. This will help conserve soil moisture and moderate
soil temperatures. It can also help keep weeds down, but weeds
generally are not a big problem in containers. Place the containers
in full sun, reasonably close to one another to ensure good
pollination. Once the plants begin to set fruit, you will have to
cover them with netting to keep birds from devouring the ripening
fruits. Monitor the blueberries’ water use and provide supplemental
water as necessary. As the shrubs mature and their leaves spread
over the edge of the containers, you may be surprised that you have
to water, even if it rains, because the foliage will shed rainwater
outside of the containers.
Blueberry pruning and care