Is Fall Really a Great Time to Plant Trees?

One of the joys of working on a university campus is that construction never seems to end.  As near as I can tell there are about 3,000 orange construction barrels that permanently reside on the MSU campus that simply get shuffled from one end of campus to the other every few months.  Along with all the construction comes a never ending series of new landscape projects.  Driving by one of the most recent projects the other day got me to thinking about the myth of Fall planting.  In numerous extension bulletins and certainly in nursery sales advertising we hear that “fall is the perfect time to plant trees”.

Photo: Dana Ellison

The recent fall planting job on our campus gave me pause to think about this.  I haven’t had a chance to completely survey the carnage but I suspect about a third of the trees will need to be replaced.  Obviously there are lots of things that may have gone wrong here, irrespective of when the trees were planted and one exception doesn’t prove the rule.  Nevertheless when I look back on the planting disasters I’ve been called in to inspect over the years a disproportional share (I’d say by a factor of two or three to one) are fall planting jobs.


What gives?  Well, the notion that fall is a great time for planting is built in a faulty premise, at least for this part of the country.  Probably the most commonly cited reason for fall planting is that trees grow a lot of roots in the fall.  This assumes that since there’s no shoot growth occurring, trees automatically shift reserves below-ground.   There is certainly a ‘pecking order’ of carbohydrate distribution within a tree based on relatively strengths of sources and sinks.  But there’s one factor that trumps all others: temperature.  Soil temperature is the biggest driver of root growth.  Measurements of new root growth in a cottonwood plantation in Wisconsin provide a classic example.  As temperatures decline in the fall, new root growth essentially ceases.  For trees that are well established, this is no problem.  For trees that have just been transplanted and need to re-establish root-soil contact this is a tough row to hoe.  Throw in a tough Michigan or Wisconsin winter and the tree’s facing an uphill climb.


New root growth of eastern cottonwood (top) and soil temperature (bottom). Source: Kern et al. 2004. Tree Phys. 24:651-660.

Again, most planting failures have multiple causal factors.  Even if the trees on this site had been planted in the spring, they may have still experienced problems.  My point is that a more accurate statement is “Fall is an OK time to plant trees”; not the ‘best’ time or even a ‘great’ time.  I think these statements are often driven by the fact the fall is a slow time for nurseries and landscapers.  When homeowners or landscapers ask me about fall planting the first thing I ask is if there is any reason why they can’t wait until spring, the real ‘best’ time for planting.

Protecting existing trees – what a concept!

I just got back from a trip to Pullman where I guest lecture once a year for the Landscape Plant Management class.  It’s also a chance to get some new photos for my Wall-O-Shame.  Here’s my latest:

Pin oak (Quercus palustris) doesn’t drop its leaves in the winter – instead, they hang on until the following spring.  So it’s really easy to see which part of this tree is alive (i.e., has last year’s leaves).  It’s apparent that most of the crown has died, with only some lower scaffold branches remaining.

How did this happen?  Take a look at how new that concrete is around the base of the tree (and how small the tree well is.  This construction was done in 2004:

Note the complete lack of root zone protection.  Not only has the majority of the tree’s fine roots been destroyed in preparation for pouring concrete, but only a very small space under the tree is “protected.”  I guess the cup at the base represents the irrigation system.  To top it off, this construction was done in August, when coincidentally I was there as well.  It was blistering (as it usually is in the summer in eastern Washington), and the remaining leaves on this tree were wilted:

So why would anyone be surprised when, 6 years later, this tree looks like crap?  And why doesn’t WSU insist on tree protection standards when construction bids are submitted?

“Being wrong” counterpoint

I haven’t finished with the water droplets story yet – but I just had to add some more evidence to the tree planting discussion from last week.

Consider this series of photos below.  This is a street tree in Kennewick, WA (in the southeastern part of the state, where summers can be intensely hot and dry).  Every spring, this tree leafs out just fine – and every summer the leaves suffer marginal and tip scorch.  This is a classic symptom of chronic drought:

As an amenity, the tree fails.  Even though the landscape is well-watered, as shown by the healthy turf in the next photo, the canopy is sparse and dry.

An excavation of the roots explains why:  the tree was planted too deeply and has developed a secondary set of  roots:

Note how sparse these roots are – which is typical of many adventitious root systems.  While the roots are adequate for water uptake during the cool spring weather, the hot dry summers suck away more water from the leaves than this puny root system can absorb, even when well-watered.

My point:  sure, trees might survive being planted too deeply.  But thrive?  Not in this case – and this is a well-managed landscape!  With less care this tree would have died long ago.  The only solution here would be to replace this tree – correctly.

Friday puzzle solved!

Great discussion over the weekend, with some very astute observations.  If you looked at the brown needles under the tree in Friday’s picture, you may have noticed that some of them weren’t needles:

Not only was this tree planted too deeply, as several of you pointed out, but the burlap and twine were left intact.  It appears the nylon twine has already started to girdle the trunk, based on the trunk swelling just above where the twine is wrapped.

I’ve ranted about this practice already, so I’ll just sigh and move on to the first question – what directly caused the needle drop from the lower part of the tree?  It’s a young tree facing west so the lower half gets plenty of sunlight.  And though needle drop is normal with all conifers, the upper portion of the tree does not show the same drop with its interior needles.  My guess is that ethylene gas is responsible.

Plant roots under stress often release ethylene, a natural plant growth regulator more commonly associated with fruit ripening.  It also induces leaf drop, so as it percolates out of the soil it affects the lower leaves, but dissipates before it reaches leaves higher in the crown.  It’s a common phenomenon with over-watered house plants.

Thanks to all of you who participated in the diagnosis discussion – this is more fun than my 20 years of college teaching!

Inspecting nursery plants, part lll

By now you’re probably ready to stand up, brush off your pants, and stretch your back after crawling around looking for surface roots and root crowns.  Not so fast!  There’s one more thing to look for – and to avoid.

Take a look at these two photos:


You can easily see the suckers at the base of these trees.  Whether or not they are actually suckers (coming from the roots) or watersprouts (coming from the base of the trunk) doesn’t matter.  Their presence in single trunked species warns of problems underground.  You’ve probably seen landscape trees respond to crown stress by suckering.  In this situation, my diagnosis is that the roots are so stressed (buried too deeply, structurally malformed, etc.) that they are unable to provide enough water to the crown.  Thus, the plant responds by creating a shorter crown (the suckers) which is easier to keep supplied with water.

In both of the above cases, these were the only individuals of their species in the nursery that were suckering.  That makes it easy to avoid purchasing them and their stressed root systems.

This is not such a problem with species that tend to form thickets, like our native vine maple (Acer circinatum) below:

Bottom line:  know the natural habit of your trees and shrubs before you buy them.  If they are single trunked species, don’t be a sucker – avoid suckers!

Advice Requested!

Greetings, all!

I am not a tree-care expert, having invested most of my mental capital into herbaceous plant stuff.  But I know enough to be dangerous: spiraling/strangling roots and narrow crotch angles are bad news. But at what point do they become “unfixable”? So I’m asking my illustrious colleagues and diligent readers (a.k.a “all y’all) for advice.

We have a lovely specimen in our campus Horticulture Garden…Acer ‘White Tigress’ – a hybrid between A. davidii and A. tegmentosum – also known as snake-bark maple.  Probably been in the ground for 18 years or so. Lovely buttery fall color, gorgeous stripey bark.

This tree, as we say in Georgia, “has more problems than a show dog.”

Scroll on down…

Bit of constriction there, mid-way up.

Some interesting crotch angles, too…

But here’s the kicker (I can hear Linda hooting it up from here…)

This poor gal is obviously a “what not to do” teaching tool.

But the question is:
Can this tree be saved? Discuss.

Inspecting nursery plants, part ll

Well, I’m recovering from this simply horrific chest cold or whatever it is and feeling brain function returning.  The last time we were at our virtual nursery, we were looking for root flare and inspecting the trunk for damage from improper bagging.  Since we’re already down on our hands and knees, let’s consider roots.  In general, you really don’t want to SEE roots, except where they meet the trunk (the root flare).  The presence of coyly crossed “knees” in this photo is a clear indicator of a plant that wasn’t potted up quickly enough:

Likewise, while the fused, circling woody root mass in this next photo might be aesthetically interesting, it sure doesn’t make a functional root system:

It’s pretty easy to avoid these types of plants, because you can see the root problems before purchasing.  The hidden root problems, such as those I’ve shown in earlier posts, are tough to find until (or if) you take all the extraneous stuff off of the root ball.

Finally, there is a new production practice that really fries my potatoes.  What really makes me angry is that these trees had absolutely LOVELY roots – a nice flare, woody roots spreading radially – and then they were butchered – and left unprotected:


I can think of no legitimate reason for this practice.  I’ll be curious to hear my colleagues’ thoughts, as well as those from the blogosphere.

Inspecting nursery plants, part 1

I’m frequently asked to give seminars on selecting healthy plants at the nursery, especially trees and shrubs which can run hundreds of dollars.  (Nobody seems to want a seminar on how to pick out a flat of petunias.)  I routinely visit nurseries with my camera so I can record examples of good and not-so-good choices.  What better forum to share these than on our blog?   I’m also curious whether the problems we see in the Pacific NW are found elsewhere in the country, or in the world for that matter.  So today we’ll hunker down on our hands and knees and inspect root flares.

The root flare (or root crown) is the point where the trunk meets the roots and should be wider than the rest of the trunk.   The photo below shows this clearly:

In balled and burlapped trees and shrubs, you might not be able to find the root flare as soil and/or burlap cover the root flare.  The tree below is burlapped far above its root flare:

Over time, many trees and shrubs buried too deeply will develop trunk rot.  You can inspect for rot by gently peeling back the burlap from the trunk and looking for damage.  Don’t worry, this doesn’t hurt the root ball or the trunk:

The tree in the above example already has some red flags – the presence of weeds on the soil surface suggests that it’s been in this pot for a long time.  (And no, you don’t want to buy this tree.)
The most dramatic example of the problems that can occur is this weeping larch, which has been completely girdled by the rot induced by the burlap and twine around the trunk:

Lesson:  It’s cheaper to wash your now-dirty pants than it is to buy (and eventually replace) a poor quality plant.

The Flap Over Burlap

This month’s issue of the Oregon Association of Nursery’s Digger magazine includes the second part of a two-part article on urban foresters’ perspectives on nursery stock.  It was interesting to note that some urban foresters felt they were in a quandary because their specs require removal of burlap from B&B trees, yet many nurseries will void their warranty if burlap is removed from the root ball.

Removing burlap from B&B trees is a practice that is widely recommended, yet there is little, if any, data to support it.  The logic, of course, is that burlap will prevent root egress into the surrounding soil after planting.  But is this really the case?  We conducted a study a couple of years ago using 3” caliper B&B green and white ash trees as part of a trial on the movement of a systemic insecticide (imidacloprid) for treatment for emerald Ash Borer.  Since we were using radioactive carbon-14 as a tracer, safety regulation required us to keep the trees contained.  The trees were dug with a 36” tree spade and placed in burlap-lined wire baskets by a local nursery (Discount Trees. Inc.) using their standard procedures. For the study we placed the root balls in large orchard boxes backfilled with top soil.  We removed all ropes and the top of the burlap.  The trees were used for a study that lasted two growing seasons.  At the end of the second season we conducted whole tree harvests on a sub-sample of the trees.  My vision for the root system harvest was that we would simply chain up the baskets and pop the trees out of the boxes; the burlap would help contain the roots, right?  Wrong.  Separating the root balls from the boxes became a major ordeal that involved a whole lotta shakin’ with the front-end loader.  Once the root balls were finally extracted it was obvious that the burlap provided little resistance to root egress into the surrounding soil.

burlap roots
My former grad student, Grant Jones. “He said it would come out easier than that…”

Mike Kuhns at Utah State University conducted a trial several years ago (J. Arbor. 23:1-7) in which he observed a similar phenomenon.  Mike compared root egress of B&B maples with burlap removed versus a single or double layer of burlap by calculating a RTRATIO which was based on the amount of the total root system weight that was found outside the original root ball.  There was no difference in the RTRATIO between trees with single burlap and trees without burlap at any date during the 2-year study. Double burlap decreased RTRATIO initially but there was no difference by the end of the study.    Annela et al. (Arb. & Urb. For. 34:200-203) compared various growth parameters of baldcypress, plane tree, and freemani maples transplanted bare-root or B&B with only the top of the burlap removed.  After two years the only statistically significant difference was an increase in shoot growth for the B&B maples.

So what does it all mean?  My personal opinion is that when it comes to establishing trees in the landscape we spend way too much time worrying about trivial matters like this.  (Digging a planting hole 3X the width of the root ball and amending backfill are others but we’ll save those for another post).   Matching species to site, quality planting stock, and proper after transplant care – especially mulching and irrigation – are way more important but still neglected.  If we plant quality plants in the right place and take care of them properly the first two years after planting we would eliminate 80%+ of the transplant issues I see.  Burlap or no is a tempest in teapot.

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.