planting – Page 2 – The Garden Professors™

Container planting: intuition vs. reality

I’m just starting to think about getting my containers planted for the summer and happened to get an email on the topic from a blog reader. John was frustrated with a local columnist’s advice on using gravel in the bottom of the containers for drainage. When challenged, the columnist refuted John’s accurate comments with “logical thinking.” (You can find the posting and comments here.)

Here’s part of the post: “I like to cover the hole with a layer of gravel to improve drainage. Plants need to have their roots exposed to air in the soil to survive and thrive. If the container has no holes for drainage, it will fill with water and drown the plants very quickly. It is better to keep your plants on the drier side than to keep them constantly moist or wet. The big danger in using pots is drowning plants.” Later, he goes on to explain “The potting soil plugs up the drain hole and the water is trapped behind the plug. The layer of gravel creates an area for the water to drain through to escape. The creation of drainage commonly involves a layer of gravel.” This reasoning is part of what he calls “Logical thinking 101.”

As my husband pointed out, this isn’t logical thinking: it’s intuitive. It’s what we think is going to happen in the absence of any evidence. And in this case, it’s wildly inaccurate.

Jeff and I have both discussed the phenomenon of perched water tables in containers as well as the landscape in previous posts and on our Facebook page. The fact is, when water moving through a soil reaches a horizontal or vertical interface between different soil types, it stops moving. Here’s a photo from a very old research paper on the topic:

A layer of silt loam sits above a layer of sand, and water from an Erlenmeyer flask drips in. Intuition says that when the water reaches the sand, it will move more quickly through the sand because the pore spaces are larger than those in the silt loam. But intuition is wrong, as this series of photographs clearly demonstrate. Water is finally forced into the sand layer by gravitational pressure, after, of course, saturating the silt loam.

Intuition has its uses (I am quite proud of my own intuitive powers), but it doesn’t trump reality.

**This is an older post, so I’ve added this link to a peer-reviewed publication on the topic by Dr. Jim Downer and myself.**

Five little lavenders…four years later

If you’ve been following us for a while, you might remember a post from August 2009 when I got cranky about a pot of lavenders with horrendous root systems. I intervened with my Felcos and planted out the patients, hoping for the best.
Lavender #2 before root pruning

In July of 2010, I gave an update on their progress. At that point, one of the lavenders had died but the other four were perking along. And now it’s time to show them in their floral glory:

Root washing is still controversial, as is corrective root pruning. However, all five of these plants would have died had I not corrected the spiraling root systems. Published and ongoing research at several places around the country continues to support the practice of bare-rooting and correcting root flaws of woody plants.

Is this a practice that the landscape industry will adopt? Probably not on a large scale: it is time intensive and requires careful work. But home gardeners can do this themselves and have done so successfully.

If you’re interested in more information on how to do this, you can download this fact sheet. Until production nurseries change their practices to avoid these fatal root flaws, it will be up to home gardeners and a handful of landscapers to repair the damage.

Buried alive – the roots version

Bert’s post yesterday inspired me to share one of my own timelines that I followed for 7 years. As many of you know, I am a proponent of bare-rooting container and B&B shrubs and trees. One of the benefits is that you can prune away malformed roots, but another is that you can ensure the roots come into contact with the native soil as soon as possible. It’s interesting to see what happens over time with the more typical “pop and drop” method.

I saw this rhododendron being planted in 2002. If you look closely, you can see that it was originally balled and burlapped – the burlap is up around the multiple trunks. Then the burlapped bag was put inside a contained filled with media. You can see that, too. So a hole was dug that exactly mirrored the plastic container and the whole works was lifted out and plugged in.

Visualize a giant jawbreaker with different colored layers. At the center, we have the roots surrounded by clay. This is encased in burlap and twine. Then there’s a layer of container media. And finally we have the native soil. Rather than making it easy for this rhododendron to get established, we now have several barriers for new roots to overcome.

The primary problem here is all of the different textures of stuff in this planting hole: clay, soilless media, and native soil. Water doesn’t move easily through different soil types (remember Jeff’s demo on drainage?) and if water doesn’t move, neither will the roots. And as you follow this time line, it becomes quite apparent that the roots never established into the native soil. Look in particular at the size of the leaves (they are markedly smaller as time goes on – a great indicator of chronic drought stress). The line in the masonry wall makes it easy to see changes in height – or lack thereof.

Installed in 2002 (year 0)

Early 2004 (Year 2)

Late 2005 (Year 3)

Early 2007 (Year 5)

Note the leaf necrosis from chronic drought stress. Having a ground cover competing for water does not help. And neither does pruning off dead parts of leaves.

Now unfortunately I was not able to make it back again until 2009. And here is what I found:

Another WOW (why oh why) – “biodegradable” mesh for plugs

David Hobson, a garden columnist, sent me this great photo of his petunia planted earlier this year. Take a look at the root growth (or lack thereof):

I’m not sure where this particular product came from, but it looks a lot like a FERTISS propagation plug. Here’s a description from their website of this product.”FERTISS is a ready-to-use, pre-filled propagation tray system. Cuttings are placed in a mixture of peat and perlite wrapped in a non-woven fabric. Roots of young plants will easily penetrate this fabric and enter the airspace between the fabric and the plastic cell wall. Roots are naturally air-pruned, resulting in a faster and better take, increased lateral branching, and improved transplanting performance.”

It sure doesn’t look like roots “easily penetrate” this fabric, at least when gardeners get them potted up at home. And though I can’t see the top of the plant, I’m guessing it didn’t show “improved transplanting performance,” especially compared to a plug from a traditional liner pot.

Nowhere did I find what this “non-woven fabric” was made of (though there are allusions online to it being biodegradable), but it’s just one more impediment for plants – and gardeners – to deal with.

When all else fails…

As someone who has had a foot in Horticulture and a foot in Forestry throughout most of my career, people often ask me to compare the two disciplines. One of the truisms that applies in both cases is, “When all else fails, blame the nursery.” I’ve seen this following seedling die-offs in industrial forest plantations and I’ve seen it many, many times after street tree or landscape planting failures. In fact, if you believe some people, tree nurseries are responsible for every plague and pestilence to ever afflict mankind. Are some tree failures related to things that happened in the nursery? Of course. But there are lots of things that can go wrong between a nursery and a tree’s final destination; and even more things that can go wrong after it’s planted.

I know a lot of people don’t believe this, but nursery growers want their trees to survive and grow well after they leave their care. Growing trees is like making cars and any other business. You need satisfied customers if you expect to have repeat business. The best growers are always looking at their production practices for ways to improve their product. Last week I visited Korson’s tree farm in central Michigan. Korson’s grows Christmas trees and B & B landscape conifers. Rex Korson, the owner, has been concerned over the impact of root loss during transplanting of landscape trees. So much so, in fact, that he is conducting his own trial on root pruning.

For those that are not familiar, root pruning of B & B trees is usually done a couple years before harvest by using a tree spade to severe tree roots. The spade used for pruning is slightly smaller than the one used for harvest, so that new roots stimulated by pruning are harvested with the root ball. Does it work? I did a root pruning trial a few years back to see if it could improve survival of fall-planted oaks and had mixed results. For Rex’s trees, however, the initial results were pretty impressive. In the first photo below are root systems of Norway spruce trees dug with a 30” tree spade. The second photo shows the root systems of trees dug with the 30” spade that had been root-pruned last October with a 24” tree spade. The response in one-year’s time was dramatic. At this point there no out-planting data but, other factors being equal, increasing the amount of roots harvested with the tree should increase transplant success.

I should hasten to point out that Rex is not alone. I work with many other growers in the state that are constantly tinkering with this or that in their production systems; sometimes on their own, sometimes with university specialists or extension educators. I’m not so Pollyanna to think that everything is always rosy in the nursery world but most growers, especially the better ones, are aware of the issues out there and are working to build a better tree.

Spruce dug with 30″ spade without root pruning

Norway spruce root-pruned in Oct 2011 with a 24″ spade and dug Oct 2012 with a 30″ spade.

Close up of new fine roots

Tree spade mounted on excavator for root pruning. With this system an operator can root prune 8 trees in 5 minutes.

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Opening up a can of roots (or worms as the case may be)

Blog reader Alan Haigh asked if we could start a discussion about tree planting recommendations. He sent along these guidelines from the Colorado State Master Gardener Program.

While I’m glad to see that the consensus now seems to be that burlap, wire, twine etc. do not belong in the planting hole, there’s still plenty of issues to contest. Here are just a few that I found on my first read:

1) Not mulching over the root ball;

2) Assuming that all B&B trees are “field grown,” which I *know* is incorrect for so very, very many B&B trees;

3) Not including the root-washing technique for B&B, which is not only research-based but is actively promoted through the International Society for Arboriculture’s workshops (see this posting for instance). This is the only way to find and correct circling and girdling woody roots, and the easiest way to find the root crown for planting at grade.

Without root washing you’d have to dig through 10″ of clay to find the root crown (the duct tape marks the top of the clay root ball prior to washing)

I’ve written about this topic before. And many people argue that it would “take too much time” and “be too expensive” to root wash specimens. But when you read this publication, note that it takes 13 pages to describe how to plant containerized and B&B trees.

It takes 1 page to describe how to plant a bare root tree.

Be a Part of History!

Here at the Garden Professors we pride ourselves on being on the cutting edge of technology. In fact, we’re so tech savvy we didn’t even whine when FaceBook foisted a new homepage format on us for no apparent reason. So it’s only fitting that we offer you, Mr. and Ms. Garden Professor Blog reader, an opportunity to participate in the first ever landscape horticulture research project designed by social media.

Here’s the deal. My current research project on water and nutrient management of trees in container production has left us with over 100 ‘Bloodgood’ London planetrees in 25 gallon containers. What I need from you are ideas for a study plan on what to do with the trees next.

Of course, as with any major research project, the first step in the rigorous scientific process is to come up with catchy acronym for the study. I propose “the SOcial MEdia DEsigneD TRansplant ExpErimental Study” or SOME-DED-TREES for short. Needless to say, I am willing to consider alternatives. In any event, we have a unique opportunity to investigate post-transplanting growth, development and physiology of landscape trees.

So here’s what we have: Approximately one hundred, 2” caliper trees, grown in containers in a standard mix of 80% pine bark and 20% peat moss. Trees have been grown for two years in essentially standard nursery culture – daily irrigation and 60 grams of Nitrogen per container. The subject of the original study was fertilizer source; half the trees were fertilized with Osmocote and half received the same amount of nutrients from organic fertilizers. After two years we have not seen any difference in growth or foliar nutrients between the treatments. Nevertheless, I will need to include the prior treatment as a blocking variable to eliminate any potential confounding effects. Beyond that it’s wide open. We could have 6 treatments x 2 blocks x 8 trees = 96 trees. I strongly suspect in the final analysis the block effect will be non-significant and we can consider there to be 16 replicates, but life is full of surprises.

So, what tree establishment or tree care question is burning a hole in your brain? “Shaving” or “butterflying” container rootballs? Fertilizing at time of transplant? The latest biostimulant? Crown thinning at time of transplant? Frequency of post-planting irrigation? Width of the planting hole – how wide is wide enough? Send me your suggestions and we will set up a poll to vote for the top choices.

WOW again (Why oh Why?)

I’m going along with the “dead tree” theme of the week, but doing a little prognosticating at the same time. Bert and Holly showed you tree demise on site; I’m going to show you tree demise in the making. We can call this “dead plant walking.”

I’ve done a few WOW postings in the past, often with a focus at what you might find at a nursery or big box store. Here’s a recent find at an unnamed BBS, in the “topiary” section:

Unless you intend to have a giant stake as part of your topiary statement, this tree (actually a juniper) will morph into a prostrate form before your very eyes. Fortunately, it probably won’t live long once transplanted since it’s so overdue for potting up that the pot has split:

You can just imagine the nest of woody roots fusing into a functionless mass, can’t you?

Run, don’t walk, away from nursery plants like this. You’ll be glad you did.

Getting to the root of the problem

After getting off to a cool and soggy start, summer has come with a vengeance to Michigan, with heat indices expected to push 100 degrees by Wednesday. Along with warmer temperatures, summer also means our research season is getting into full swing as well. One of our biggest efforts these days involves our project to look at pre-plant storage and handling on shade tree liners.

As many GP blog readers are aware, emerald ash borer (EAB) has dominated the conversation regarding shade trees in the Midwest for the past 6-8 years. Ashes made up 20 to 30% of the shade tree cover in many urban and community forests, so their loss has been devastating. A major thrust of our extension programming during this time is to promote a wide range of ash alternative to increase species diversity. One of the challenges we find in making this pitch is that many of the species we recommend (oaks, hackberry, baldcypress) are trees that nurseries often find difficult to grow from standard bare-root liners.

My graduate student, Dana Ellison, is in the second year of a project to look at some of the practices that growers use on the difficult to transplant species and some of the underlying causes of poor transplanting. Dana is looking at a variety of attributes including plant water relations and carbohydrate status, but the order of business these days is roots. Specifically we’re evaluating root growth potential of oak, baldcypress, and hackberry. We’ve also included white ash, which transplant easily, as a positive control.

Graduate research assistants Dana Ellison (right) and Brent Crain (left) and undergraduate assistant Arriana Wilcox (center) pot up shade trees for root growth potential testing.

Root growth potential (RGP) is a common parameter in evaluating quality of reforestation seedlings but is measured less often on larger liner material. The logic is pretty straightforward; a plant’s ability to initiate root growth after plating and re-establish root-soil contact is one of the biggest determinants of its ability to survive and grow. A variety of systems have been used to evaluate RGP for seedlings – most involve growing seedlings for a set time (3 weeks is standard) in an aeroponic system and then counting or measuring new root growth.

Growing the trees in pea gravel makes it easy to get a look at new roots.

For Dana’s shade tree liners (5’-6’ whips) we’ve adapted a system based on the Missouri gravel bed system (which I first got to see in person at Jeff’s research nursery in Minnesota – thanks Jeff!). Dana and her helpers pot the trees up in pea gravel in 25-gallon containers. The trees are grown on for three weeks in a greenhouse while the roots are kept moist with spray stakes operated by a mist system timer. After three weeks, we dump out the gravel, wash the root systems, and carefully count the number of new, white root tips.

Dana washing roots.

So what have we learned? Well, the work is still on-going but some trends have emerged. Baldcypress may experience some transplant issues but they don’t appear to be related to producing roots. We had several baldcypress trees that produced 400 or more new roots during the RGP test – and, yes, we counted them all! Red oak and northern pin oak, on the other hand, are very slow to put out new roots. For hackberry trees, our other measurements suggest their transplanting issues may be related to their inability to re-hydrate after lifting, storage and transport. These insights should help us provide some guidelines to growers to help them produce a wide pallet of trees for the landscape market and increase species diversity in the wake of EAB.

Counting roots. Almost as much fun as it sounds…

The defending champion baldcypress: 614 new roots.

Harvesting an Experiment

This has been an exciting week for me. On Monday we started cleaning off 72 rootballs of various tree species that had been planted 5 years ago for a study. These trees had been planted in containers and become potbound at the nursery from which we received them. We treated them in one of three ways. Either we did nothing (in other words we just dropped the pot bound tree in a hole), we used the standard methods that Universities recommend for slicing potbound roots (Four deep slits down the sides and a deeply cut X across the bottom), or we cut off all of the circling roots by cutting the pot bound root system into a box shape.

A root ball cut into a box shape

The plan was to harvest after 4 years to see what happened – we decided to wait 5 – and boy did we see some interesting stuff. At this point our results are preliminary – we need to run statistics before we can say anything conclusively – but this is what my eyes tell me.

Trees that had their roots cut into boxes suffered reduced growth the first few years, BUT, their root systems look as good as any root systems that I’ve seen – almost no circling.
We planted our trees with the surface of the soil at the same level as the surface of the media in the containers – which is too deep in most cases. For trees with circling roots this created a severe problem as the circling roots often surrounded the stem – potentially causing suffocation of the tree later in life.
Root systems that were cut using the 4 slit method didn’t look much different from those that weren’t cut at all.
The number of large roots emanating from all of the treatments appeared to be about the same (we’ll need to run the stats before I commit to this one). This is particularly interesting because many people expect large roots that are circling to continue circling — but that isn’t what usually happens (unless the hole where the tree is planted has hard sides which can force the roots to circle just like the container did).

This root system was from a control — no root pruning at all, but still plenty of large roots.

No matter what the results/statistics end up saying there will be more questions. For example, all else being equal, how damaging are circling roots to the health of a tree if the tree is planted properly (no stem tissue under the surface of the soil) and the circling roots are under the surface of the soil? If the answer is that circling roots under the surface of the soil aren’t very damaging (after all, there’s no stem tissue for them to crush) then why are we bothering to try to root-prune pot bound plants at all – what we should really be concentrating on is planting at the proper depth.

All the above is hypothetical though – I just enjoy thinking about this stuff as the data starts to roll in. As we get more definitive answers and start to run the statistics I’ll let you know more.