Keep the Momentum
Depending on your production goals, there are multiple container options to consider, guided by the “4-inch Rule.” Research has shown that when a root is pruned, root branching typically occurs at the tip and up to four inches back. This is why RootMaker® propagation containers are four inches deep. When plants are moved to a larger RootMaker® container with a sidewall difference of less than four inches, root branching will be excellent but may quickly fill the container, possibly requiring another transplant. On the other hand, shifting to a container with a sidewall difference greater than four inches may lead to missed branching opportunities.
The 4-Inch Rule
To illustrate the 4-inch Rule, this large root ball of a 3.5-inch diameter lacebark elm, grown in an 18″ diameter RootBuilder® for 1.5 years, was cut in half with a chainsaw. The white lines highlight this tree’s first-year root systems from the RootMaker® 18-Cell Tray and the RootMaker® 3-gallon container. Notice how each container size complements the next, promoting an exceptionally fibrous and well-branched root system.
Transitioning to Gallon Containers
After propagation, many nurseries transition seedlings to a 1, 2, 3, or 5-gallon RootMaker® container, typically between May and early July. This allows the seedlings to establish in these containers until fall planting in the field or the next container upgrade. Each model of the 1, 2, 3, and 5-gallon RootMaker® is equipped with multiple openings designed to promote air-root pruning. This encourages root development throughout the entire volume of the growth medium, preventing root congestion along the sidewalls and fostering a well-distributed, fibrous root system.
A Good Mix
For above-ground RootMaker® containers, an good soil mix starts with ground pine bark, peat, and sand 60/20/20 by volume. To this base, add 1.5 pounds of Micromax® micronutrients and 14 pounds of 17-7-12 Osmocote® slow-release fertilizer per cubic yard. The optimal amount of dolomite will depend on the mineral content of your irrigation water, as pH adjustment can vary by location. Additional amendments may also be needed depending on specific site conditions and plant requirements.
RootBuilder® Kits
RootBuilder® containers are designed with a root-directing bottom disk and are available in Pint, Quart, 1-, 2-, 3-, and 5/7-Gallon sizes. This innovative design enhances ease of handling while promoting an exceptionally fibrous root system, creating stronger, healthier plants.
Cinder Blocks
One of our most popular methods for liner production involves using concrete cinder block cavities, into which our 5″ bags fit snugly. This design effectively eliminates blow-over and insulates roots from temperature extremes. Additionally, it supports ongoing root branching through either root-tip trapping or root constriction, promoting healthier and more robust plant development.