Unfortunately I can’t put this into the comment thread for Jeff’s post since it involves a link. Bonnie Appleton sent her 2007 American Nurseryman article on root washing that readers might find interesting. Thanks, Bonnie!
Can’t resist…must add photo…
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.
I guess today’s blog should be entitled “The Cranky Garden Professor.” Really, I’m not always cranky, and when I am I go outside to do something constructive in my garden. Last weekend I finally tackled a 5-gallon container of lavender that I’d bought several weeks ago. I had intended to wait until fall to transplant it, but I was watering it every day to keep it from wilting. I figured I might have better luck getting it into the soil where a good mulching would help keep the soil moist without daily watering.
So I carefully slid the lavender out of its pot and into my root-washing tub (Figure 1). (If you’re not familiar with root washing trees and shrubs, be sure to check out my web page. I’ve got a fact sheet and some myth columns on why it’s important to bare-root containerized and B&B woody plants before installing them in the landscape. Please visit www.theinformedgardener.com to access the entire site, or this link for a fact sheet.
Figure 1. Five little lavenders.
As I worked the potting media out of the root mass, I suddenly discovered why I was using so much water to keep the lavender happy. It wasn’t one plant. It was 5 separate lavender plants all placed in the container to LOOK like one large plant. Worse, all 5 plants had some of the crummiest root systems I’ve ever seen (Figures 2-6). They were poked into the pot like little carrots. Most of the pot was filled with untouched potting media.
Figures 2-6. The beehive is back!
What you see in these figures are root systems that look like upside down beehives. They were obviously left in their original small pots too long and developed circling root systems. So rather than growing outwards into the soil, they stayed in these little spirals and eventually would fuse into woody knots. They don’t miraculously straighten out when they’re put into larger containers (or the garden). If they did, they would have rapidly spread throughout the big container to soak up all that water I was pouring on daily.
Sigh. Now I was cranky again. These lavender roots were just like those I’d seen on hundreds of landscape plant failures over the last 10 years. Since these roots were so tightly woven together there was little hope of untangling them. So I made one vertical cut through each of the root masses (Figure 7), spread them out horizontally (Figure 8), and planted them (Figure 9).
Figure 7. The cut. Figure 8. The spread. Figure 9. In the ground.
This is the worst possible time of year to transplant trees and shrubs (it’s August, after all) and I most definitely put a world of hurt on these roots. But I will say that since I moved them I have been able to reduce irrigation, since the soil holds moisture better than the potting media. I’ll keep track of their progress through the next 12 months. I’m hoping they make it through this summer – if so, they stand an excellent chance of growing a decent root system over the fall and winter.
Back to the cranky part. I really resent nurseries that deliberately bunch small shrubs together in one pot to make them look like one big plant. It certainly cost more to buy this one pot than to buy five smaller pots. If this isn’t deceptive marketing I don’t know what is.