About this time last year I posted photos of the installation of my new pollinator gardens (all perennials). As you can tell from the photos below, all of these plants have not only survived but thrived with their midsummer rootwashing.
The only ones that didn’t make it were the six Lavandula stoechas ‘Bandera Purple’ (see above). They did fine through the summer and well into winter. But with our surprise snowstorm in February (along with a 20-degree temperature drop in one night – from 33 to 14F), all but one of these marginally hardy plants (USDA zones 7-10) gave up the ghost. I won’t make that mistake again. But I will continue to root wash ALL of my perennials before I plant.
And since it’s Independence Day here in the US, I thought I’d continue with the “free your roots” theme and discuss the medieval torture system that passes for recommended B&B tree installation practices. I’m talking about the burlap, the twine, and the wire baskets that are left on the root ball and cunningly hidden underground to do their damage over the years.
There is a great deal of disagreement about what to do with all the foreign material that’s used to keep tree root balls intact during shipment. To be clear, that is the ONLY thing they are intended to do. There is no research that shows leaving them on benefits the tree at all. The reason they are left on is because it’s more economically feasible for the installation company to do it this way. Personally I think that’s a pretty crappy reason, particularly when you are looking at trees that can cost hundreds or thousands of dollars.
Most studies that have addressed the issue have been short term: two or three years, rarely longer. Irreversible damage to roots can take years to develop. It’s useful, therefore, to look at the landscape evidence to see what happens with all these barriers to root growth and establishment.
Arborist and landscape designer Lyle Collins recently excavated the remains of trees that had been installed in 1991. The trees had died years ago and certainly hadn’t grown much as evidenced by their trunk size.
But while the trees didn’t survive, the burlap, wire basket, and webbing were all still there almost 30 years later.
The clay rootballs are nearly intact as well. That’s not what you want to see. Roots must establish outside the rootball into the native soil, or they won’t survive.
Eventually I’m convinced long-term research will show the folly of leaving foreign materials on the rootballs of B&B trees. In the meantime, I’ll continue to plant trees in a way that ensures their roots are in contact with the native soil and free from any unnatural barriers to growth.
I am always pleased to see Dr. Chalker-Scott addressing this topic. As a bonsai practitioner of more than 30 years, I have repotted thousands of woody plants with a success rate at the doorstep of 100%. I’ve found it is helpful to others if we carry a message emphasizing it is important to draw distinct delineation between repotting and potting up as they relate to conventional container culture. Repotting, which includes bare-rooting, root pruning, and correction of obvious root issues (girdling/ encircling/ crossing roots, roots growing straight up/ down/ back toward the center of the root mass) ensures limitations associated with root congestion and other spatial root problems, all go away. It doesn’t matter if this is a Ficus in a favored indoor spot or a tree in a nursery can intended for market. Potting up (bumping a plant to a size larger pot) ensures all aforementioned problems remain limiting factors until the day human hands actually get into the root mass and make corrections. Limitations associated with root congestion start to become conspicuous about the point in time where the root/ soil mass can be lifted from the container intact, and become increasingly severe as the congestion increases. Once the roots of any containerized plant have been allowed to reach that degree of congestion, even if the plant is eventually planted out, it’s highly unlikely it would fail to suffer significant loss of potential or worse for the lack of attention to roots, often arising from the good of the tree being sacrificed on the altar of the dollar.
Extremely large measures of growth (often >90%), vitality, appearance, and yields, are sacrificed to root congestion and other root problems, no matter the plant has been planted out or still in a container. Most growers will identify the significant increase in growth rate that follows a repot, and the lesser increase that follows potting up, as a ‘growth spurt’, but not so. What seems to be a growth spurt is normal growth ….. or more nearly normal growth if we include consideration of the potential for limitations resultant of unrelated cultural factors. A plant’s genetic growth potential does not change because the plant was repotted/ potted up. The “growth spurt” is but visual confirmation of the limitations being levied by pre-rootwork cultural conditions, and illustration of how the plant might have been growing all along had the grower acted sooner to correct the issues.
I’m sorry – I’ve strayed, as is not unusual. Hopefully there will be value found in the offering and I won’t be seen as taking advantage of Dr.’s platform. “Transplanting” by separating a tree from a nursery can and dropping it in a freshly dug hole or digging a hole and burying the rootball of a B&B tree are a parallel to potting-up in conventional container culture. It is much easier, but surely does the tree no favor, and the root problems remain. I think it a significant service to the gardening community that we have those intent on drawing an often much needed distinction between what’s done conventionally verses correctly. I appreciate Dr. Chalker-Scott’s efforts.
since learning about root washing, we have moved to southern Utah – St. George area, much different from the Pacific Northwest. i have been told that the principles of root washing/pruning do not apply here since this is a hot dry climate – different climate from where this research was done. I do not agree with that statement, but was wondering how you would respond to/counter that argument. thanks for your time.
The same plant physiology and soil science prinicples apply regardless of the location. Roots MUST be in contact with the native soil to establish in that soil. Circling roots MUST be corrected upon planting or they will becoming girdling roots. Anyone who tells you differently does not understand basic woody plant physiology. Ideally you will plant in the fall, but regardless of when you plant, ensure that roots are kept cool and moist, soil is well mulched with coarse wood chips, and plants are well watered throughout their first growing season.