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Propagating quality liners from seeds and cuttingsgood root structure

Most shade trees begin as seedlings or rooted cuttings; some are produced using tissue culture techniques such as mircopropagation. Trees are propagated in field soil beds, in open trays, or in small propagation trays or small containers in a greenhouse. Containers range in size from one to several inches across and a few inches deep. Roots quickly reach the bottom and sides of the containers and deflect down or around the pot. If deflected roots are not too large they can be cut to improve root system quality. Roots on some species in field soil grow primarily down at a steep angle. Trees with most roots directed downward by propagation practices may not be as well suited for urban landscapes. Therefore, focus on producing at least some shallow horizontally oriented lateral roots in addition to deep roots.

Poor root systems

Good root systems

circling mahogany root
Tap root on mahogany circles bottom of smooth sided plastic propagation pot. See this tree one year later after shifting to larger container.

air pruned mahogany root

Tap root on mahogany was air pruned which generated many straight lateral roots right up to the substrate surface. Elle pot (constructed of very thin paper) allowed lateral roots to grow through paper and air prune. Result was few deflected roots. Copper hydroxide applied to interior container surface can develop similar root systems. See this tree one year later after shifting to larger container.

air pruned bald cypress root

Tap root on baldcypress was air pruned by an open bottom liner pot which encouraged lateral root growth. Lateral roots hit the smooth plastic sides and were deflected downward placing most root tips at bottom. See this tree one year later after shifting to larger container.

 air pruned bald cypress root
Tap root on baldcypress was air pruned which generated many straight lateral roots right up to the substrate surface. Elle pot (constructed of very thin paper) allowed lateral roots to grow through paper and air prune. Result was few deflected roots. See this tree one year later after shifting to larger container.

maple roots deflected
Two lateral roots on maple deflected by the plastic container wall are likely to become stem girdling roots later. See this tree one year later after shifting to larger container.

 

straight lateral maple roots
Lateral roots on maple are straight and not deflected. See this tree one year later after shifting to larger container.

deflected maple roots

Roots on maple are deflected down, up, and around the smooth sided plastic propagation container. See this tree one year later after shifting to larger container.

maple roots from elle pot

Maple grown in Elle pot (constructed of very thin paper) allowed lateral roots to grow through paper and air prune. More roots hit the sides at an angle resulting in more deflected roots that seeds grown in paper pots. See this tree one year later after shifting to larger container.

roots directed downwards
Roots are directed mostly downward because tap root was pruned (see below). This root system is poorly adapted to at least some urban soils (photo courtesy Keith Warren).

roots growing laterally
Roots growing more laterally and close to surface may be better adapted to urban landscapes with poorly drained and compacted soil (photo courtesy Keith Warren).

Two examples (mahogany left, baldcypress right) below of liner root systems with ample lateral roots produced by growing in a container with sides and bottom comprised of 90% air and 10% plastic. This liner root system may produce a finished nursery tree well adapted to urban soils due to amply lateral root growth. Testing is underway (April 2010).

Good root system

good root system

Good root system

good root system