For the past 11 years I’ve been running a nursery at the University of Minnesota called the TRE (for Teaching, Research, and Extension) nursery where we research all kinds of fun stuff like Dutch elm disease, the dangers of mulching, and what happens when you plant a tree too deeply. One of the most interesting things we’ve done recently, though, is to install Missouri gravel beds into the nursery. Missouri gravel beds are called Missouri gravel beds because they were invented by Chris Starbuck, a professor at Missouri State. He mostly works with gravel beds above the surface of the soil, while here at Minnesota we work with gravel beds below the surface of the soil (the gravel bed below is 60 feet by 10 feet and filled with about 2 feet of pea gravel — we do have a system for recirculating the water — which we sometimes use and sometimes don’t because of clogs, algae buildup, etc.).
We take bare root trees and place them into these beds in spring (when bare root trees are available from nurseries) to encourage root growth and then plant them out into the field later in the season. The amount of beautiful fine roots for transplanting is just incredible, and the resulting plant can be planted bare root any time of year, instead of just spring when bare root plants in our area are usually transplanted.
Now to be a little more specific: I’m a tremendous fan of planting bare root plants, but I’m not a fan of planting larger plants bare root (at least not without Missouri gravel bed treatment), particularly what are known as B&B trees — trees that are harvested and held in a burlap and wire cage, such as those being harvested below from our nursery.
The reason that I don’t like taking a B&B tree and planting it after bare rooting it (by removing all of the burlap as well as the wire cage and then washing off the soil that surrounds the roots) is that, no matter how gently you wash off the roots, fine roots tend to be destroyed. When you harvest a root ball for a larger tree you are removing about 80-90 % of the roots. The additional roots that you remove by washing the ball will often make the tree non-viable. This is something that have I learned from experience with individual trees, as well as from replicated experiments using hedge maples and Turkish filberts. We used trees with a stem diameter of about 2 inches with standard sized root balls for that size tree, washed off the root ball for half (five trees of each species) and planted the other half using our more standard system (we removed the top portion of the burlap and wire, but not the bottom portion so as not to disturb the ball). All of the trees which we bare rooted from B&B died after planting and all that we didn’t bare root lived. This is further supported by some research coming out of the University of Illinois earlier this year by Andrew Koeser (and coauthors) which shows that handling the balls of B&B trees just isn’t that good for them.
So why am I spending so much time with this? Simple, this is an area where researchers disagree. In fact, based on what Linda has written in the past I’ll bet that she disagrees with me. And that’s a good thing. People always want the quick and simple answer, but often there isn’t a quick and simple answer. I can’t deny that sometimes bare-rooting a B&B tree before planting might be a good thing. But I think that, in the majority of cases, it’s a mistake. In terms of containers — We’ve got a big research experiment going on that right now — we’ll have results next year.