Dr Darby McGrath
Dr. Darby McGrath, research scientist with Vineland Research and Innovation Centre.
From the time it is a seedling, how a tree’s roots form and grow are an important indication of future health and production. Dr. Darby McGrath, research scientist in nursery and landscape plants with the Vineland Research and Innovation Centre wants to create a better propagation tray to allow seedlings the best opportunity possible.
Knowing that trees are often planted in less than perfect conditions and encounter sometimes violent environments, ensuring a propagation tray sets the tree up for improved vitality is essential. In 2013, McGrath began looking at roots to see where, in a tree’s development, root deformations that impact growth, health and strength begin.
“We obviously aren’t the first group to look at this,” she says. “There is a lot of interest in this right now because when we plant trees we plant them in less than ideal conditions. There is an optimal root architecture for trees.”
McGrath explains that in ideal conditions a root ball will grow out in all directions, much like the rays of the sun. This radial distribution allows for optimal collection of nutrients, water and other essential elements for healthy growth. However urban soils tend to be very compact, creating challenges for trees that don’t have the best root structure established.
“If you grow a tree seedling in a propagation tray, you pass that root deformation down,” she says. “There are a lot of negatives associated with that. At the plug stage, you can correct root deformations.”
With others having explored the idea of propagation trays to create better root systems already established, McGrath and her team started with a review of what was available. They tested a variety of trays and found that none promoted the ideal radial style of root development. Even trays from forestry, nursery and other subsectors were studied but no matter how much air exposure there was with the tray, there was always a plastic structure that made contact with the substrate which would cause root deformation.
Tree Comparison
Red oak seedlings grown in the Vineland propagation tray on the left and in an industry standard tray on the right.
“After testing trays from all sorts of different subsectors, there isn’t really a tray out there to promote this ideal root architecture,” McGrath says of her team’s review. “Anchorage is always an issue in urban soils. Especially with the storms we’re seeing now. Some of the solid sided trays often promote driving roots down and that’s not good either because you have the roots terminating at the bottom of the tray.”
She further explains that while there were some “decently okay” trays, none of them met the needs of real production growers due to high costs or awkward structures. Growers were looking for something new but there weren’t many options that fit what McGrath and her team wanted to see in terms of features.
The obvious solution was to develop a new propagation tray. It couldn’t be just any tray however, it had to be affordable enough and manageable for real production environments. In 2015, a prototype was developed using air-root pruning to promote branching and create a greater root mass. It also incorporates other key elements – like strategically sized and shaped holes – the team knew would allow for ideal root growth.
Propagation Trays
Propagation trays used at the Vineland Research and Innovation Centre.
“We want to see a natural root system that is uninhibited,” she says. “Where there are no impediments in the soil because that’s the best advantage it [the tree] can give itself. Our tray did very well in terms of root production.”
Trials are done with oak trees because if conditions aren’t ideal, an oak will simply send down a tap root. The initial prototype caused a root deformation, but now, in the second iteration of development, the team has found that the angle of the cup at the bottom of the tray is an important consideration.
“Our trays don’t make contact with the substrate anywhere,” McGrath says. “Growing in something like this can actually promote accelerated production for fruit nursery stock. There’s been a lot of work done on air-pruning and the influence it can have on bearing fruit nursery stock.”
More trials of the propagation tray are planned with fruit nursery stock and the tray is expected to be released into the market in spring 2017. ■