Above ground container production
The use of containers to
grow nursery stock is generally recognized as first beginning in
the early 1950's (1). Nurserymen in southern California, who had
considerable experience in growing plants inside greenhouses, were
first credited with taking plants outdoors in containers (2). By
having plants with foliage, and flowers, in a neat "package"
that was easily transportable, the sale of nursery stock could expand
beyond the typical dormant season. With the advent of the Federal
Highway system, and the expanding use of truck transportation, growers
were able to distribute their stock all over the United States.
The first containers used were recycled metal food containers, which
were often scrounged from schools and restaurants (3). With their
sharp metal edges, and straight sides, these early pots were difficult
to work with.
Dwarf Hinoki cypress
(Chamaecyparis obtusa 'Nana Gracilis') being raised
in decorative wooden boxes for the retail garden center trade
Container culture expands
During the early 1960's nurserymen started to explore all of the
factors associated with growing plants in pots. Studies looked at
using native soil (as opposed to modern container mixes), the time
the plants could be left in the containers, and the growth characteristics
of the contained plants. Today 80-90% of woody ornamentals produced
in the southern states of California, Texas, and Florida are grown
in containers. Plants that have small root systems and fast growth
rates are ideal candidates for containers. As for terminology, there
are different types of container plants:
- Potted stock
is used describe seedlings, rooted cuttings, or grafted plants
that are first started in small containers before they are put
out in the field as liner stock or re-potted into larger containers.
Examples would include flowering perennials, and rhododendrons.
stock refers to plants spend their entire lives in pots,
up to the time of sale. Examples would include many of the various
types of spring bedding plants, or vegetable transplants.
- Containerized stock
is used to describe the result of taking smaller field
stock (including trees and shrubs) and placing it into pots. Examples
would include global arborvitae and Japanese maples.
The nursery industry has a vast multitude of different containers
to choose from. Propagators will consider the following factors
in determining what type to select:
- Round or square shape
- Impact on root growth
Plastic nursery containers come in vast
array of sizes. This nursery has ordered them by the pallet
load. They should be kept shrink-wrapped untill they are needed
so that the wind does not carry them away.
As for durability most nurserymen use what are known as blow-molded
plastic pots (made from polyethylene, polypropylene, or polystyrene
resins). Blow molded pots are used for outdoor conditions as they
last longer, have greater strength, and can be easy stacked together
(3). For plants in the greenhouse, injection molded plastic pots
are more common. While there are versions that can stand shipping,
their lighter weight generally precludes their use to propagation.
Most pots come in either black or green. Black pots can heat up
excessively on hot days, which can harm root systems. Larger blow-molded
pots (#5's and greater) can be purchased with handles. Very large
pots (#45's and greater) can be ordered with forklift slots.
Nursery pots are available in a multitude of different sizes. In
the same volume class, deeper sizes are best for aeration and drainage
(4). The size of the plant determines the size of the pot it should
be raised in. Tables have been developed by the American Association
of Nurserymen suggesting the size of pot to use for different sized
stock (1). For ornamental trees over the height of 4' a 5 to 15
gallon pot will be needed. Most shrubs will remain in 1-2 gallon
pots. For globe narrow-leafed conifers a 2-5 gallon pot is required.
For a complete listing of the different sized pots turn to the Nursery
Supplies Incorporated web page.
Fiber pots are made from biodegradable wood fiber. As a rule fiber
pots promote healthier root systems as the roots with can breathe.
They also impart a cooling effect on root systems. Fiber pots are
known to increase rooting depth over that of plastic pots. When
the insides of treated fiber pots where treated with a water-based
latex coating containing copper hydroxide coating (Spin Out, Griffin
Corporation) root circling was reduced. Ruter (5) found that copper
treated fiber pots (from Western Pulp Products) could be shipped
across the United States successfully. Fiber pots appeal to retail
consumers who would rather purchase a biodegradable product as opposed
to one made from plastic.
One gallon pots
The most common size at the garden center is a 1 gallon pot, referred
to as a #1. In general round pots prevail over square Plant material
consisting of flowers, trees, and shrubs from liners, cuttings,
and flats typically go into #1's. Pot terminology is unique to the
nursery trade. A 1 gallon pot only holds 3 quarts of soil in terms
of liquid measure, but is still referred to as a #1. As for dimensions
a #1 pot measures 6" wide by 7" deep and has a capacity
of 183 cubic inches (6). Once the plant has been put into the pot,
and some space has been left at the top for water, ten #1 pots can
be filled with a cubic foot of soil. With 27 cubic feet of soil
in 1 cubic yard, a nursery can pot up 270 #1 pots with a cubic yard
of either soil or container mix. If #1's are placed pot-to-pot,
in rows 12 pots wide, with 2.5 foot alleys between, approximately
2,700 #1's can be set out on 1,000 sq.ft. of ground.
Herbaceous perennial producers often use 3-6" square pots
for smaller plants. Square pots are more space efficient that round.
If perennials are to be sold in #1's they will need to transplanted
from liner beds 6 months prior to sale in the spring.
Few tree seedlings are put into #1s as there is very little demand
for such a small tree. The only exception would be the multitude
of grafted Japanese maples. In the Pacific Northwest these small
trees are a common sale item at spring garden fairs.
#2s, #3s, and #4s
These larger pots are especially useful for herbaceous perennials,
and hybrid roses. Retail growers enjoy the sales of bedding plants
grown in 2-3 gallon fiber pots, which are sold as color pots in
the trade. Buy purchasing wholesale annuals in plug sizes, and fiber
pots and potting soil from a nursery supply house, a part-time income
can be generated during the months of March-May. By using an array
of annuals grouped together in wide, relatively shallow container
a grower create an excellent retail product for backyard decks and
apartment complexes, with very little investment. When a fiber pot
is selected with a wire hanger, growers can capitalize on the growing
interest in hanging baskets filled with bountiful spring and summer
annuals. Other common uses for 2-3 gallon fiber pots include the
sale of budded hybrid T roses during the months of February-May.
#5s, through #15s and larger
A #5 container is the generally the minimum size for the sale of
woody ornamentals at retail garden centers. This is also the minimum
size for commercial landscape construction. Tree seedling liners
are often put into #5s without first going into #1s. Larger liners
look better from a retailer's viewpoint in a #5 container, as opposed
to a smaller pot. A #5 container filled with mix and a plant weighs
approximately 25-30 lbs., thus making it is still manageable by
A #15 container can be an excellent choice for the smaller independent
retailer looking to capture the higher end of the specialty garden
trees such as Japanese maples, or weeping conifers. If growers have
the time to allow these plants to attain a larger size they will
be rewarded with a very high profit potential. Conifer growers who
have dug their trees as B&B will often pot up any stock that
did not sell in the spring into #15s for sale during the summer.
A #15 pot, filled with a plant and soil will often weigh more than
90 lbs. so that a dolly and extra help will be needed for loading.
Landscapers prefer #15s as they need at least 1" caliper trees
for their installation projects. By having access to these larger
container sizes they can plant good sized trees (6' or more) all
year long, as opposed to field grown bare root material in the spring
only. A complete guide to growing trees in #15s and larger trees
is available from North Carolina State University (7).
Above ground, open weave containers
In the last 10 years there has been a lot of interest in alternatives
to hard-sided plastic containers. The inherent tendency towards
circling roots in plastic pots has sparked investigations into engineered
porous fabric and plastic weaves that stop root by air pruning.
The RootMaker Products Company (8) has developed 10-30 gallon white
sided soft containers, referred to as RootTrappers®, that can
used above ground. Smaller woody stock is planted into these white-sided
containers and allowed to grow. Root death due to sun exposure is
minimized as the containers stay relatively cool. With time the
expanding roots fill the RootTrapper® tubs with a thick dense
mat of fibrous roots. Roots can penetrate the base of the RootTrapper®
containers so that they can take up some water from the soil (9).
By having roots anchored in the surrounding soil these above ground
fabric bags are less prone to blowing over. The resultant trees
can be planted all year long.
This company also markets a product known as RootBuilder®,
which is a product that growers build themselves out of a roll of
porous semi-rigid plastic that is 11"-28" wide. When cut
to length and stapled tubs of 12-1200 gallons can be built. This
product is designed to be holding unit for either container or field
stock, prior to landscape installation. Once again, by having a
porous weave, air pruning prevents circling root formation.
Another new above ground poly bag has been introduced by Nursery
Supplies Inc. Called the Plant Pouch these bags are made from durable
polyethelyene-covered mesh fabric. Available in sizes from #15 through
#200, these bags are designed for above ground use. Bags can be
ordered with drainage holes in the bottom or sides. Custom ordered
bags can made with air-pruning holes. In addition Plant Pouch bags
can be ordered in 3 different colors: black, white, or green, and
custom labeling is available.
The latest container developed by the nursery trade is known as
a tree box. By using these larger containers growers can either
raise very large trees for latter transplanting, or use them as
permanent, above ground planter boxes. Typically consisting of plastic,
these collapsible, square-sided units come in sizes of 35 gallons
(24" wide), 75 gallons (31" wide), 125 (38" wide),
and even 130 gallons (10). These containers are designed for use
with either high-end nursery stock sales at independent garden centers,
or for commercial and municipal applications where they can be used
for portable traffic barriers. They come ready to be moved with
forklifts. They are built with molded sidewalls that prevent root
circling, as well as with elevated bases to stimulate air root pruning.
Plastic versions can be disassembled for transport (11). For the
homeowner that wants instant gratification these products can be
a potentially lucrative item for the discriminating buyer.
1. Nursery Management: Administration
and Culture, 3rd Edition. 1994. Harold Davidson, Roy Mecklenburg,
and Curtis Peterson. Prentice
2. Production of Landscape Plants II (in the field). 2001. Carl
Whitcomb, Lacebark Inc., Stillwater, OK.
3. So You Want to Start a Nursery.
2003. Tony Avent. Timber Press,
and media for the nursery. 1991. Michael Schnelle, and Janet
Henderson. Oklahoma Cooperative Extension.
5. Cross-country containers. John Rutter. American
Nurseryman, Feb.1, 2000.
6. Growing Profits: How to Start and
Operate a Backyard Nursery. 2000. Michael and Linda Harlan.
Moneta Publications, Citrus Heights, CA. Distributed by Chelsa
Green Publishing, White River Junction, Vermont.
quality for a plant grown in a big container? Tom Bilderback.
North Carolina State University, Department of Horticulture.
8. RootMaker® Products
Company, Huntsville, Alabama.
9. Focusing on fabrics. David Morgan, senior editor with American
Nurseryman magazine. May 15, 2003.
Farms, Greenville, North Carolina.
Enterprises, San Diego, CA.