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Bare root plant production
is typically used for herbaceous perennials (including ornamental
grasses), small groundcovers, and small deciduous shrubs and trees
(4 years or less to harvest). In the past many trees were established
in rows in fields, allowed to grow, and then were dug up when they
were still small during the dormant season. While this practice
is still in use it has been succeeded by balled and burlaped production,
as well as tree spade harvesting of larger plants.
Conifers are propagated bare root for Christmas tree planting and
reforestation. The thriving Christmas tree industry has lead to
a good demand for high quality seedlings for establishing new plantations
as well as restocking established ones. Growers interested in exploring
conifer seedling production are advised to visit an established
propagator and observe the seed sowing, transplanting, and eventual
harvesting practices. The Pacific
Northwest Christmas Tree Association maintains a list of seedling
producers. One of the most important requirements for a conifer
seedling nursery is well drained lighter textured soil that enables
field equipment use during the dormant season. Heavier ground soil
sticking to the root systems of seedlings can interfere with harvesting.
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Field grown shade trees,
lifted bare-root during the winter, are a common sight in
the north Willamette Valley of Oregon
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Larger deciduous trees and evergreens are generally not harvested
bare root as there is simply no way to prevent excessive drying
out of the foliage (referred to as desiccation).
Considering field production vs. container
production
Many small nurseries started out with field production as they had
less labor supply (1). Field grown crops can generally be left alone
in terms of watering; righting containers that are blown over by
the wind; pest control; and the need for winter protection. Shade
trees grow quickly in the field as their roots are not restricted.
If field grown stock is grown in properly spaced rows, mechanical
weed control, as well as registered herbicides, can relieve the
grower from the inherent difficulties of hand weeding plants in
containers. Supplemental nutritional needs are often reduced especially
if the production beds are situated on heavier ground (2).
Once dug the smaller bare root trees and shrubs can be shipped
easily as there is not the weight of container media to deal with.
The light weight of bare root stock makes them easy to handle by
planting crews, notably volunteers helping with urban renewal programs.
Their lower price tags can promote better sales. If handled during
conditions of cool wet weather very high planting success rates
are often achieved. Bare root production is the preferred technique
for native trees and shrubs destined for riparian restoration and
storm-water retention ponds.
The best method (as well as least expensive) of producing larger
shade trees for commercial and public projects is to simply establish
the trees in the ground and allow them to grow naturally to a size
where they can still be dug up with a mechanical tree spade. As
consumer wealth has increased over time, as well as a demand for
more immediate satisfaction, many customers welcome the opportunity
to purchase these well established trees.
Field production is better suited to growers that don't have access
to surface or ground water. While the stock can benefit from supplemental
irrigation during the initial years, once established they can generally
survive summer drought. Also, by having the roots in the ground
there is no chance for summer heat stress that can burn the roots
of container plants, especially those in black pots.
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Field grown arborvitae
that may latter be dug balled and burlapped or placed into
a container
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In areas where winter temperatures drop down towards zero degrees
Fahrenheit, field stock survives untouched while above ground container
stock can suffer root injury. Field stock does not require the use
of cold frames or greenhouses for protection during a dip in temperatures.
Challenges during harvest
While field grown stock is certainly easier to manage during its
growing cycle, harvesting has to be done when the plants are dormant
(3). This of course limits the time during which the plants can
be dug and sold. Once dug, bare root stock such as Christmas trees
and reforestation seedlings have to be kept in cold storage until
fields are ready for spring planting. Under cold storage conditions
trees and shrubs can only be kept for a limited period of months
before they succumb to decay.
There will have to be some consideration for soil on which bare
root plants are produced. A demanding soil rebuilding program will
have to be employed to restore soil fertility, tilth, and texture
as the heavy machinery is used. Cover crops or compost can become
useful, especially when tree spades are employed to mine trees as
well as soil.
The short season for digging bare root stock comes during the time
of year when the weather is still inclement thus impacting machinery
operation (4). The weight of the shade tree root ball can exceed
one ton with larger trees! The short marketing season certainly
limits sales at retail garden centers where customers expect to
find container stock for much of the year. Only the very smallest
trees can be dug from the field and placed into containers. Field
grown roots have generally spread out too far to be potted into
the 5-10 gallon containers which are commonly used in retail settings
unless root pruning has been employed in the field.
The expense of either purchasing or leasing a mechanical tree spade
and the truck that transports both the equipment as well as the
tree has to be accounted for. The shipping distance for such trees
is limited by the size and weight of the tree and root ball.
In summary
While field production has it's place in certain aspects of the
nursery trade, notably with small conifers, trees, and herbaceous
perennials, the challenges of harvesting plant material during a
limited window has greatly increased interest in more easily handled
container stock. The profit potential that comes with a longer marketing
season and larger stock sizes has made container sales the brightest
star for garden centers.
References
1. So You Want to Start a Nursery. 2003. Tony Avent. Timber
Press, Portland, OR.
2. Getting
started in the nursery business: 1.) Nursery production options.
June, 2002. Gregory Eaton and Bonnie Appleton. Virginia Cooperative
Extension, Publication 430-050.
3. Locating the
nursery. Michael Schnelle and Janet Henderson. Oklahoma Cooperative
Extension, F-6702.
4. Alternative
field production methods, 2002, Robert R. Tripepi, University
of Idaho, Nursery management lecture notes for Plant Science Course
# 340.
First posted:
December, 2004
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