American Nurseryman -Jan 2012

A DV E RT I S EME N T advertisememt Germination Root Pruning is most effective when it occurs four inches below the seed a few days after germination hen a seed germinates in nature the fundamental objective is to extend the primary or taproot as deep and as fast as possible in order to secure the young plant in place and access moisture critical to survival Every seed e v i t c e j b o e m a s s i h t s a h s e i c e p s y r e v e f o With some species dominance of the taproot is short lived With trees and some other species taproot dominance may continue for years As long as the tip of the taproot remains active development of secondary branch root production is suppressed However in the long term anchorage of a tree and gathering of water and nutrients to support energy production by leaves the secondary branch root system in the top 10 to 12 inches of soil is far more important There is a practical and economical way to skip the multi year dominance of a taproot and go directly to the much more supportive multi branched secondary root system The key is air pruning the taproot while it is still soft and actively growing If you miss this opportunity you cannot go back When older roots are cut using antique ways an open wound is s n e g o h t a p f o e c n a r t n e r o f l a e d i d e t a e r c In addition older tissue is much less responsive to pruning and secondary root production When an older root is pruned new roots develop mostly around the face of the pruning cut By contrast when a very young root is air pruned no open wound is created The dehydrated root tip is much like a cauterized wound and unsuitable for pathogens When a soft and active root tip is air pruned very quickly typically in only a day or two secondary and more horizontal branch roots begin to grow from the short vertical axis of the taproot And importantly these secondary roots develop around the entire circumference of the taproot However the zone of primary influence of air pruning only extends back on a root about four inches This four inchrule appears to apply to all root tips airpruned or trapped so they can no longer extend For example in a bottomless sleeve type container 12 inches deep secondary roots develop mostly in the bottom four inches and all are oriented to grow down In this case the taproot from the soil surface to a point about eight inches below functions like a conduit transferring water and nutrients y t i l i b a t s t n a l p o t g n i h t o n t s o m l a s d d a t u b On the other hand air pruning seeds at a depth of four inches plus air pruning on container sides provides the most m e t s y s t o o r e v i t c e f f e d n a e v i t r o p p u s RootMaker propagation containers are four inches deep for this precise reason Pruning the tip of a taproot at four inches and developing a fibrous network of secondary and more horizontal roots is only Part 1 in developing a sound root system Part 2 which is equally important to long term plant anchorage and health is keeping young roots poised to grow mostly horizontal and avoid having a wad of roots growing in a circle around the inside of a conventional plastic pot Larger RootMaker containers are designed to air prune at the container sidewall and maintain roots poised to grow horizontally immediately following transplanting This is done with a series of ribs and ledges that stop root circling and direct roots into g n i n u r p r i a d e u n i t n o c r o f s g n i n e p o Not only does this stop root circling but it creates a root system throughout the volume of growth medium and not just in a congested layer at the sidewall iming of transplanting is very important Because RootMakers create many new roots the volume of growth medium fills faster than regular containers Do not slice or otherwise abuse the root system of a RootMaker grown plant as this will damage root tips waiting for the opportunity to grow To gain full benefits from this unique system transplanting earlier is better than later especially out of RootMaker s r e n i a t n o c n o i t a g a p o r p Adapted from Dr Carl Whitcombs book Plant Production in Containers www rootmaker com W T