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Nursery-Production

Trees are a part of the urban forest; Most municipalities have tree planting programs to ensure that their canopy continues over time. 

New trees are also needed in urban capital projects. Arborists and Urban foresters play a role in this process.

The majority of planted urban trees are large. Landscape size (at least, 30 mm; frequently >60mm diameter).

Nurseries have developed production techniques to produce large numbers of these trees at reasonable cost. However, propogation, production, harvesting, delivery, handling, and planting processes provide many opportunities for error. 

Most urban trees are produced in one of the three production systems:

  • Container Grown
  • Balled and burlapped (B & B)
  • Bare root

Some nurseries will use all of these systems (or variations on the systems). Other nurseries specialize. Field nurseries (necessary for B & B and bare root production) require lots of high quality agricultural land. 

How a tree is produced

Year 0: Lots of work goes into the selection of a tree

  • Seed hunting
  • Breeding
  • Selection and evaluation

Sent to Liner Grower Year 1: Tissue culture or cutting Year 2: Outdoor liner bed Year 3: Lining out in field Year 4: Established Central Leader Year 5: Root Prune & Develop branching  

Sent to Nursery Production. Year 6: Prune Roots & Canopy; Plant in field Year 7 - 8: Pruning, staking, Limb- up Harvest. 2"-3" Tree Year 9: Harvest 3"-4" Tree

Typical end users include municipal, small to mid scale residential & commercial. Retail nurseries, personal consumers.

Sent to Large Tree Nursery Production Year 10-14: Transplant or Root Prune; Canopy Prune; Harvest 5"-6" Tree Year 15: Harvest 8" - 10" Tree

Typical end users include high end residential & commercial. Specimen, focal, point trees for institutional projects.

Production Types

Balled and Burlapped (B & B)

Trees are grown directly on the ground and are harvested with the surrounding soil to keep part of the roots intact. The root ball is then wrapped tightly in burlap and is secured by nails and twine or wire baskets.

Pros

  • Large plant specimens can be planted
  • The tree will have a healthy natural appearance after transplanting, including good taper.
  • Is the default technique for municipalities

Cons

  • 5 - 10% of roots harvested
  • Best to transplant while dormant
  • Summer t'plant not recommended
  • Can't really tell what's deep in the ball - hard to inspect
  • "Deep in the ball" - only getting a very tiny portion of the roots at the bottom half of the ball.

 

Harvesting

Roots ball is dug up and placed in a sack.

  • Manual harvesting is slow but can often capture a higher quality rootball.
  • Mechanized harvest is faster but can lead to the defect of "deep in the ball"
    • happen when a large soil ball only contains a small root system concentrated at the bottom and most narrow portion of the ball.

 

Mechanized harvest has reduced the individual attention that each tree gets and makes it possible to dig too deep more easily (something that rarely happens when harvesting by hand). 

Bare Root Planting Stock

Bare root trees are trees where the soil has been removed from the roots. They are typically dug in late fall after leaf senescence and then stacked and stored in coolers with the roots kept moist. They are planted in very early spring while dormant. 

  • Plant while dormant
  • Usually smaller trees (5 cm caliper), some shrubs, daylilies, roses
  • Deciduous trees
  • small part of root system harvested
  • Not suitable for all species

Advantages

  • Inexpensive
  • Lightweight, easy to handle
  • Doesn't take soil from nursery
  • Can observe root system easily
  • No interface of different soil textures

Disadvantages

  • Must plant while dormant
  • Some species will not tolerate
  • Most of root system is gone, very few fibrous roots
  • Prone to desiccation during handling
  • Not suitable for most large specimens (some exceptions)

Container grown (not containerized)

  • 100% of root system
  • Usually smaller plants (<5 cm caliper), often whippy
  • Plant whenever ground is not frozen

NOTE: Distinguished from "containerized" trees, which are bare root trees placed in containers with growing media for re-sale.

Containers take on many forms

  • Most popular in NA: Black plastic pots with semi-composed bark;
  • Boxes
  • Cans
  • Growing medium is any light-weight media (i.e., rice hulls or coir)
    • Driven by local availability and customs

Pot in Pot systems (PIP)

Increases the range of container production by allowing it to occur in colder regions.

  • Prior to pot in pot systems, container growing could only occur in warmer temperatures

They:

  • Protect roots from the cold
  • Capture water run-off
    • Can be recycled
  • Countless other benefits

 

Advantages

  • Entire root system present
  • Can plant anytime so long as ground isn't frozen
  • Relatively lightweight
  • Possible solution for "difficult-to-transplant" species

 

Disadvantages

  • Only relatively small sizes (most of the time)
  • Must water very frequently (every day) after planting
  • Soil interface always present
  • Prone to circling roots
  • Often lack trunk taper
  • Have unappealing branching habit
  • Nursery must be attentive to prevent pot bound plants

 

Harvesting

Just pick up the pot, place the tree in the ground!

Architecture of a nursery root system

Root shank: Portion of the tree that isn't entirely clear if it's root or shoot tissue.

  • If the tree wasn't grown in a nursery, roots would likely have grown in this place.

 

Container grown trees

Pot bound roots are an issue. Roots start circling the pot.

  • Very difficult to get a high-quality pot grown tree
    • Need a very professional / expert grower to achieve this.
    • One solution:
      • Coat inside of pot with copper paint (i.e., spin-out™) .

How to inspect a tree for good quality

  • Two-thirds rule
    • Enough canopy covering enough of the tree
    • Lollipoping will stress out the tree and is bad for new plants.
      • Lollipoping is where the lower branches are pruned away
  • Central Leader
    • Multiple leaders / forked trunks can be difficult to correct for. Leads to splits and diseases.
  • Last minute corrections via pruning

Ensure that they follow standards & guidelines