planting – Page 5 – The Garden Professors™

Baring it all, again.

Earlier in this blog we had a rather robust discussion about the merits of transplanting trees bare-root. Bare-root transplanting has had a renaissance in arboricultural circles, based in large part on the work of Dr. Nina Bassuk and her colleagues at the Urban Horticulture Institute at Cornell.

As our bloggers noted, transplanting trees bare-root has advantages over balled and burlap trees (larger portion of the root system stays with the tree) and over container-grown trees (more natural root system development). One disadvantage of bare-root trees is the need to protect roots from desiccation during storage and handling. Also, some trees respond better to bare-root treatment than others. Nevertheless, I think we will continue to see increased interest in bare-root planting. One notable trend is planting relatively large-caliper (4” and larger) trees bare-root. This phenomenon has coincided with the development of the air spade, a tool which produces powerful a jet of air that allows arborists or nursery workers to carefully excavate an entire root system with minimal disturbance. Unlike digging a tree with a traditional tree spade, the air spade allows nursery workers to maintain virtually the entire root system when lifting a tree. Last week, my esteemed colleague, Dr. Tom Fernandez, and his Nursery Management class at MSU worked with Paul Swartz, MSU campus arborist, to lift a 10” caliper weeping white pine from our campus nursery. Members of the class took turns using the air spade to excavate the entire root system of the pine. Since the class is divided into lab sections that meet throughout the week the process was spread over several days. After each lab period exposed roots were covered with wet burlap to prevent drying. By the end of the week the tree was ready for lifting and was transported via flatbed truck to its new home at the front entrance to the MSU Horticulture Teaching and Research Center. Paul Swartz reports that he has successfully used the air spade to move several large specimens on campus and the technique is especially useful for moving trees from tight spots that can’t be reached with a mechanical spade. As more and more arborists acquire air spades look for this technique to become more common.

NOTE: Photos courtesey of Dr. Tom Fernandez.

The air spade uses a stream of compressed air to excavate roots.

Note the extent of the root system. A 90″ mechanical spade would have missed at least half the roots of the tree.

Once the roots are excavated the tree is ready for lifting.

The pine resting comfortably at its new home.

Health care reform (of trees)

Nothing is more frustrating to a gardener than watching a newly installed tree or shrub slowly die. In performing “post mortem” analyses on failed landscape plantings, I’ve identified four common errors that can be easily avoided:

inadequate root preparation
improper soil preparation
planting below grade
inadequate aftercare

This blog entry will be dedicated to the first point – but before I do so, we need to understand how nursery plant production has changed over the last several decades.

A brief history of propagation
Many years ago the only way to obtain young trees and shrubs was as bare-root plants. Plants were field grown, then dug up during dormancy for storage and shipping. Bare-root trees and shrubs are usually only available during a narrow window of time, but in general these plants are healthy and structurally sound. Most importantly for our discussion, growers can see the woody root system of bare-root plants and cull those that are not well formed.

The development of containerized production methods meant that plants could be grown and sold year around. When plants are grown in a production greenhouse, they are generally started in small liner pots and gradually moved through a succession of increasingly larger pots. Ideally this is done before roots become potbound, or the roots are corrected when “potted up” (moved to a larger container). What we found, unfortunately, in a study of nursery plant quality, is that root systems are often ignored in an effort to produce large quantities of plants quickly and cheaply. It is not considered to be cost effective to examine and correct root flaws during potting up, so the entire root mass is moved into the new container. Structural root flaws are not self-correcting and will become more severe the longer they are ignored.

Based on our study, as well as evidence collected by numerous researchers and arborists, it is apparent that poor root quality is a significant problem in containerized and balled-and-burlapped trees and shrubs, at least in this part of the country. Therefore, we need to correct root flaws before installing woody plants into the landscape.

A quick intro to correcting poor root systems
Balled-and-burlapped plants have a clay rootball; despite its appearance, it is fairly easy to remove the clay simply by removing the burlap and twine and soaking the entire rootball in water. You can facilitate the process using your fingers to work out the clay, or use a gentle stream of water (Figure 1).

Figure 1.

Once the clay is removed the root system can be evaluated. If you find woody roots that are circling, girdling, or in general not growing horizontally and away from the trunk (Figure 2), they should be pruned (Figure 3). You want to develop an evenly distributed structural root system.

Figures 2 and 3 – before and after

The pictures in this post are from my own Cercis tree, which I planted in April of 2004. This is not a great time for planting, since Seattle has notoriously dry summers. Nevertheless, that’s when I planted and as you can see from Figure 3, I had to remove close to 70% of the root system. I mudded it in well (which eliminated the need for staking), mulched, and kept the root zone well rooted. It sat for about 3 months and did nothing (Figure 4), except of course the flowers died quickly!. In July it leafed out (Figure 5), and 3 years later had doubled in size (Figure 6). It is now close to 15 feet tall and is in excellent health. Given its initial root system, it’s doubtful it would have done this well without intervention.

Figure 4 – April 04 Figure 5 – July 04 Figure 6 – July 07

(I have performed radical surgery on hundreds of tree and shrub root systems and have only lost one small shrub, whose root system is in Figures 7-8. Kind of tough to prune something as fatally flawed as this.)

Figures 7 and 8 say so much more than I can.

Bare Root Trees

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.

Bad roots and deceptive marketing

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.