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Growing Fruits in Containers
By Dr. Leonard Perry, Extension Professor,
University of Vermont

If you have poor soil, limited time or a small space for fruit gardening,
limited mobility, or want to garden creatively or on patios, then you should
consider growing fruits in containers.  

Half-high blueberries, blackberries, raspberries, dwarf fruit trees, and even
grapes can be grown in containers.  All grow best in full sun, although
brambles will tolerate light shade (with less yield).  Keep in mind that
blueberries and most fruit trees need at least two different cultivars,
blooming at the same time, for cross pollination and fruiting.

The Challenges to Growing Fruit  in Containers

Perhaps the main challenge to growing fruit plants in containers in cold
northern climates is getting them to survive through winter.  Plants in the
ground benefit from the stored heat, and if their roots freeze it isn’t to the
very low levels that roots in pots above ground can experience.  

Easiest is to move containers to an unheated shed or garage that doesn’t get
much below freezing during winter.  Rolling supports with casters helps
move large and heavy pots.  Another option for milder climates is to pile
soil, compost, or straw around the pots, combined perhaps with partially
sinking the pots in the ground if they aren’t too large.  In even milder
climates, a large wooden tub insulated on the inside with a solid foam
material as used in construction may be sufficient.
Pick the Right Size Pot, Soil

Minimum pot size is a 5-gallon pail or pot, but 15- to 20-gallon is better.   
Many large containers will work for fruits, ones that are 18 to 24 inches wide
and at least 12 to 16 inches deep being ideal.   If deeper, you can add a false
bottom or fill with lightweight material such as wood chips.  I use plastic
pots turned upside down.  A large plastic pot is easier to move than clay
ones, or consider a whiskey barrel half or lightweight plastic tub.

Potting soil for containers has very different physical properties than garden
soils, so you don’t want to use garden soil that also may introduce diseases.  
Best is a potting mix of half peat moss and half bagged topsoil or potting
soil.  Some mix in weed-free compost as well.  Leave a couple inches on the
top when potting for an organic mulch, or adding a bit of new compost
yearly.  Plants may need re-potting every 3 to 5 years to keep them vigorous.

Keep plants watered well after planting, reducing water in late summer each
year.  Then over winter keep the soil barely moist.  Fertilize with a low
analysis fertilizer such as fish emulsion, weekly the first year and monthly in
subsequent years.  Stop fertilizing in midsummer so plants can harden by
winter.   Other low nitrogen fertilizers, as used in gardens, can be used.

Growing Grapes

Grapes lend themselves to growing on a trellis or one of the many decorative
structures now available such as obelisks.  Although grapes in containers
will be smaller plants with lower yields than if grown in the field, they’re
both attractive and a good choice if not otherwise possible.  Grapes, as many
plants, will only grow as large on tops as the roots can support, so fewer
roots means smaller tops above ground.  Since these can get heavy, you’ll
need to fasten the trellis or support to the pot sides with wires or similar.

If the pot becomes top heavy later in the season with older vines, you may
need to anchor it to the ground or hold it upright with cinder blocks.  Unlike
many potted plants, grapes prefer a sandy loam soil.  If making your own, a
recipe that should work consists of equal parts (by volume) of good topsoil,
peat moss, and compost.  If using up to 20 percent or so of sand for weight,
just make sure the mix drains well.
Grape cultivars (cultivated varieties) best for containers have their fruit
clusters close to the trunk rather than at the ends of canes.  Seedless cultivars
include Canadice and Interlaken, while seeded cultivars include Early
Muscat, Seyval and Swenson Red (the latter being a hardy cultivar bred in
Minnesota).  Sweet Lace is a cultivar particularly suited for patios and
trellises, good as both a table (eaten fresh) and wine grape.

You’ll need to prune your potted grapes, the goal being to develop a trunk
with several shoots (canes) over the first couple of years.  Prune off all but
four shoots (off the main trunk) the second and future years.  Then, during
winter, prune these shoots back leaving “spurs” with two or three buds on
each.  These will develop into the next year’s shoots.  To help the plants get
established in the first two years, putting their energy into growth and not
fruit, you’ll want to remove all flowers clusters.  In the third and subsequent
years, only allow 10 to 15 flower clusters for a 5-gallon pot (more for larger
pots, less for weak or slow-growing plants).  Grapes tend to produce many
more flowers than their roots can support, especially if in pots.

Growing Blueberries

Since blueberry bushes can get quite large, look for the lowbush cultivars
that only get one to 2 feet high and are quite hardy such as the cultivar
Tophat.  Slightly taller, and also hardy, are the half-high hybrids such as
Northland (3 to 4 feet tall), North Sky (one to 2 feet), and Patriot (3 to 4 feet).

Be sure and check the pH or acidity of the growing mix, as blueberries
require an acidic soil.  They grow best with a pH of 4.8 to 5.2.  Sulfur can be
sprinkled lightly on the surface, or mixed in, to help lower the pH.  An acidic
fertilizer, as sold for hollies and azaleas, may be all that is needed.  Make
sure and keep roots moist, as blueberries produce many near the surface that
are sensitive to drying out.  Browning leaf edges may indicate drought.

Raspberries & Blackberries

Brambles such as raspberries and blackberries can be grown in containers,
but expect less yields than if grown in the field.  The popular Latham might
be a good first choice for the summer bearing, with Heritage and the hardy
Fall Red for fall bearing.  Prune as for those growing in the ground, perhaps a
bit heavier if they get too large for the container.  Since many brambles like to
spread, you should divide and repot in spring every couple years to keep
plants vigorous.  Use only one plant per container, and use a container wider
than deep. If growing near a walk or patio, consider thornless cultivars such
as Canby and Encore.

Dwarf Fruit Trees

Dwarf fruit trees are ideal for containers, the size being determined partly by
nursery pruning, sometimes by the plant genetics, but in large part by the
“rootstock” onto which the desirable cultivar is grafted.  Many popular
cultivars are available as dwarfs, just make sure to choose ones best for your
area.  Descriptions in specialty catalogs and local nurseries are a good source
of this information.

Prune potted dwarf fruit trees as you would those growing in the ground.  If
you have a narrow space, or want to create a vertical design, try one of the
new popular columnar or pillar apples and peaches.  While the pillar
peaches such as Sweet-n-up, Crimson Rocket, and Summerfest have less
spread than their dwarf kin, nevertheless you may need to prune branches
back each spring to about a foot to keep the columnar shape. Northpole is a
columnar apple with fruit similar to McIntosh, Scarlet Sentinel apples are
green-yellow with a red blush, and Golden Sentinel tastes like Golden
Delicious apples.

Distribution of this article is made possible by University of Vermont Extension and
New England Grows--a conference providing education for industry professionals and
support for Extension's outreach efforts in ornamental horticulture.