Underused Trees and Shrubs You Can Plant in Your Landscape

By Sherie Shaffer, Horticulture Agent, CSU Extension-Pueblo County

Planting a new tree is a great thing to do, but planting an underused tree is even better! For one, it increases the biodiversity around us. Having a variety of plant and animal species increases the overall health of an ecosystem.

Another thing to consider, is the positive effects using an underused tree would have if there were a pest outbreak. Right now, we are dealing with the potential of the Emerald Ash Borer coming to Pueblo, and many places around the state are currently dealing with EAB outbreaks. Where the EAB is present, there is a potential to lose a whole lot of Ash trees. Since Ash trees have been widely planted for decades this could cause many of our neighborhood trees to be gone. If we had a greater variety of tree species, one pest could not wipe out such a large number of trees.

If you are thinking of planting a tree, look around and don’t choose a tree species that you see already planted near your home. Here are some ideas, from CSU Extension PlantTalk scripts, for underused trees and shrubs you can plant to increase the tree biodiversity in your neighborhood:

•         Aesculus flava (octandra) or Yellow Buckeye- Has an oval shape at maturity and can grow up to 50 feet tall. Yellow flowers appear around May. Has a great orange color in the fall. Ideally it would like a moist, well-draining soil, and it can adapt to our alkaline soils.
  
•         Quercus muehlenbergii or Chinkapin Oak- Grows up to 45 feet tall and can spread just as wide if not wider. The leaves have a nice rust color in the fall. Being an oak, it will have an acorn that will mature in the first season.
  
•         Pyrus calleryana ‘Whitehouse’ or Whitehouse Callery Pear- Has a columnar/pyramidal form. The leaves are glossy green, and long and narrow. Leaves turn reddish-purple earlier in the fall than other clones. The white flowers are a little later than other clones of Callery Pear.
  
•         Crataegus x lavallei or Lavalle Hawthorn- It grows 15-20 feet tall and has a round to oval crown. The leaves are glossy green in spring and summer and copper red in the fall. It has white flowers that bloom in May or June and a red fruit that will last through winter.
• 
          Maackia amurensis or Amur Maackia- Grows to about 20-25 feet tall and wide and has a round crown. The interesting bark peels when mature. It blooms in June and July with fragrant white flowers.
• 
          Lacebark Pine Pinus bungeana- Lacebark pine has attractive exfoliating bark in patches of green and brown which makes it a good single or multi-stem specimen tree.Needles are medium to dark green about 3 inches long. It tolerates moderately alkaline soils and is hardy to zone 4 to 5.  This tree will reach a mature height of about 30, with a 15 foot width.
• 
      Harvest Gold® Linden Tilia x ‘Harvest Gold’- This hybrid of littleleaf and Mongolian linden develops reliable yellow/gold fall color and is more resistant to linden aphids. As a younger tree itis less prone Harvest Gold Lindento winter sunscald than other lindens. When mature, the bark becomes mottled. You can expect this linden to reach approximately 35 feet tall and 25 feet wide. It is hardy to zones 3-4.
  
•         Crimson SpireTM Oak Quercus x ‘Crimschmidt’- This hybrid of white oak and columnar English oak is a good choice where there is a need for a tall, narrow tree. Crimson Spire™ oak has attractive blue-green leaves that are resistant to powdery mildew. Leaves turn rust-red in October for 2 weeks. The leaves then turn brown and persist into early spring. Hardy to Zone 5, you can expect this oak to reach 35 to 40 feet tall and 12 to 15 feet wide.  It has shown some intolerance to wet soils.
  
  

In addition to these great underused trees, native species are always a wise choice. You can find a list of Colorado native trees here: https://extension.colostate.edu/topic-areas/yard-garden/native-trees-for-colorado-landscapes-7-421/  , and a list of native shrubs here: http://extension.colostate.edu/topic-areas/yard-garden/native-shrubs-for-colorado-landscapes-7-422/

 

Battling Japanese Beetles

Posted by Lisa Mason, Arapahoe County Extension

If you live in certain parts of the Denver Metro area, you are probably very familiar with this pest. Littleton and other parts of Denver are inundated with this insect starting around mid-June.

Japanese beetle population levels in Colorado. Source: Colorado Department of Agriculture

This invasive beetle has two unique challenges: 1.) Japanese beetles cause damage during the larval/grub stage in turf grass, and adults cause damage by feeding on a variety of landscape plants and trees, and 2.) adult beetles feed on blooming flowers at the same time pollinators and beneficial insects are pollinating those flowers, which limits control options.

Japanese beetles were first introduced in the United States in 1916 and has spread throughout the US via nursery stock. The beetle was brought to Colorado in the 1990s but only recently have populations grown considerably. The larval stage feeds on the roots of turf grass, and the adult beetles feed on vegetation, including popular plants such as roses, crabapples, Virginia creepers, and linden trees. They can feed on over 300 plant types.

Japanese beetle life cycle. Source: University of Minnesota

A Japanese beetle larva. Source: David Cappaert, Bugwood.org

An adult Japanese beetle. Source: David Cappaert, Bugwood.org

You won’t see adult Japanese beetles appear until around mid-June, but now is the time to start planning for their return. Here are some things you can do:

For now and longer-term:

• Keep your plants as healthy as possible. A healthy plant will be able to sustain more damage. Practicing good cultural care will help reduce the stress on your plants.
• Keep turf as healthy as possible, too. A strong root system will be able to tolerate more feeding from grub.
• We are providing a perfect environment for Japanese beetles: well-irrigated turf provides their habitat and a wide variety of plants provides their diet.
• Consider planting other cultivars or plant varieties in the landscape. Research which cultivars are not susceptible to Japanese beetles.
• Be creative with plant selection! Evergreens, annuals, perennials, some vegetables, and many tree varieties are not susceptible to the beetle.
• Research your options for biocontrols and pesticides.
• Choices can be limiting depending on if pollinators are foraging on the same flowers that the Japanese beetles are feeding on. Pollinator-safe options include Bacillus thuringiensis var. galleriae (marketed as beetleGONE!, beetleJUS!) and chlorantraniliprole (marketed as Acelepryn SC).
• Look for plants that do not produce flowers or their flowers bloom at a different time than when the adult beetles are active. For example: crabapple trees bloom in the early spring when adult beetles are not active and other treatments may be an option.
• Remember the label is the law! If you chose to apply pesticides, the directions must be followed exactly.
• For a complete list of control options on foliage and turf and how they affect pollinators, see the Japanese Beetle factsheet.

When the beetles arrive:

Hand picking Japanese beetles off roses. Source: Lisa Mason

• Hand-pick Japanese beetles to your hearts content! You can squish them or dump them in a bowl of soapy water. This effort may seem tedious, but keep in mind each female beetle can lay 40-60 eggs. Hand-picking will also reduce the volatile attractants produced by plant wounding.
• Think twice before using Japanese beetle traps. Research shows that traps can attract more beetles to the area. As they fly towards the trap, they may find new food sources along the way. If you choose to use traps, place them at least 30 feet from any vegetation that the beetles will eat.
• Make sure you have grubs in your turf before treating the turf with products. Checking can save you time and money. Grub damage looks very similar to other turf issues. Try doing a “tug test”. If you tug on your turf and the grass pulls out of the ground immediately, then you have may have grubs that have been feeding on the roots. If the grass is rooted into the ground, you may have another issue.
• If you do have grubs, consider drying out the lawn when the grubs are active. They need well-irrigated soil to survive.

A native bee and Japanese beetles on a rose. Source: Lisa Mason

Are geraniums a plausible solution? Not likely. Research indicates that if Japanese beetles feed on geranium flowers (not leaves), they become paralyzed and rarely recover. However, geraniums are not a very favored host plant and if more attractive plants are nearby, such as roses, Virginia creeper, or lindens, then they would not visit the geraniums.  Also, if they do feed on geraniums, they mostly feed on the leaves, which are not toxic.

Japanese beetles are here to stay, unfortunately. With some longer-term landscape planning and persistent treatment efforts, we can try to disrupt the perfect environment we have created for them. 

More questions on Japanese beetle? The Japanese beetle factsheet is a great resource! You can also call your local county extension office.

Best of luck battling the beetles this summer! 

Arbor Day is Coming: Tree Planting 101

Posted by: Alison O'Connor, Larimer County Extension

My body hurts. Carol was right. I spent the day in the garden, doing my spring clean-up and towards the end of the day, I thought to myself, "Well, I might as well plant that linden."  You might remember my previous linden, the one that was a hot mess--sunscald, girdling roots, planted too deeply. Through an act of utmost generosity, Dr. Klett donated a linden to me to replace the one that met its fateful demise. I'm bound and determined to make sure my new linden has a healthy and long life. Just like all the trees you may plant this spring for Arbor Day.

So how do you plant a tree? Well, it really is more than digging a hole. If you're a Master Gardener, you've probably sat through my 3-hour lecture on tree planting, but here's an overview (with pictures!) to help you plant your tree correctly for long-term success.

Before you even THINK about planting, make sure to call 811 to have your utilities located. This is very, very important, especially since March Madness is occurring and cutting your neighbor's cable line will be bad news.

First of all, my tree had some structural defects, so I did some pruning to remove broken branches, those that were rubbing and picked a new central leader. In most cases, you should not have to do this. Your tree should come properly pruned from the nursery. With this tree, the need for pruning had been overlooked for a couple seasons.  I removed quite a bit of branches, but for me, it's easier to prune prior to planting to correct these problems than wait until they are a major issue.

I knew the site I wanted to plant my tree in (the same place as the old linden) and the first step was to determine how deep my hole needed to be and also how wide my hole needed to be. So I measured the height of the root ball and also the width of the root ball. The hole should be about three times as wide as the root ball, so just multiply by three. The depth of the hole needs to be 1-2" shallower than the root ball. Yes, the tree will sit 1-2" above the soil grade (trust me on this). The reason for this is because we want the structural roots to be right at grade (not too deep or too shallow).  Roots need oxygen to function, and in our clay soils, the deeper you go, the less soil oxygen is available (due to small pore space). So make sure your tree sits above grade.

You should also check to make sure that the structural roots (the big 'uns) are only 1-2" deep within the root ball. Use a thin screwdriver to check. You'll know you've hit a structural root because your screwdriver will meet a solid point of contact.  In my case, this linden was planted properly and the structural roots are 1.5" down in the root ball, so when I plant this tree, the roots will be at grade when I finish.

Now that you've determined your depth and size of the hole, start digging. And digging. And digging. The root ball on this tree was enormous and the hole was nearly 6 feet wide, tip-to-tip. The hole should be saucer-shaped and more shallow than deep (the hole width is key to rapid root regeneration). Make sure you check your hole depth from time to time, to ensure that you don't dig too deeply. Lay something flat across the hole and measure the depth. The soil at the bottom of the hole should be firm--stamp on it with your foot. If you leave the soil fluffy and loose, the tree can sink as gravity takes over and you water.  Again, the tree needs to sit on firmed/un-dug soil.

Remove the tree from its container. Wiggle off the container...or cut it off if it's being stubborn. If you're planting a balled-and-burlapped tree, leave the wrappings on the root ball until you get it into the hole--you don't want to risk the root ball shattering and potentially damaging the root system.

And what do we see after removing the container? Jeepers creepers, a mess of circling roots on the outer periphery of the root ball!

The old recommendation was to take something sharp and slice through the roots. Unfortunately, research proved that this was ineffective (check out Jeff Gillman's blog on the subject; also see Ed Gilman's work). The new recommendation is to shave off about 1 inch of the outer periphery of the root system to physically remove the circling roots. Let me get my saw...

So I shaved the root system (bottom too). I know, it seems...wrong. But truly, in the long run, it's going to be better for the tree. Be ruthless. The thing with circling roots is that those little roots will get bigger. They can turn into girdling roots, which can affect the tree's health. In fact, there's a thought that many tree failures are now a result of girdling roots, which act like a boa constrictor on the trunk, cutting off water and nutrient transport. Plus, circling roots (the existing ones) will not grow laterally into the site soil. After shaving, I had a pile of roots:

Now that I've shaved the root ball, the tree is ready to plant. Heave ho into the hole! Check it from several angles and make sure it's nice and straight. Also make sure the root ball is sitting 1-2" above grade.

Once you're satisfied, add a shallow ring of firmed soil at the base of the root ball. Doing this will eliminate the need to stake in most cases. Yes, it's true! The shallow ring of soil is going to keep the tree in the ground and prevent it from rocking back and forth.

Staking can actually damage the tree. There are really only three reasons to stake following planting: windy sites, near people activities or for a tree that cannot support its own weight. For the most part, a tree in a homeowner's yard should not need to be staked.

Then add your backfill. I always get the question about amending backfill soil, and really, science has proven that it's not beneficial long term. The rule of thumb with organic matter is to have 5% in your soil. Adding a "rich compost" to the backfill is essentially planting your tree in a container. Plus, too much organic matter can be detrimental. It can hold too much water and decomposes more rapidly. So I'm not an advocate of adding copious amounts of organic matter to the backfill, unless you have a really awful soil. It's more important to plant the tree correctly than to rely on organic matter to make things better. You'd be surprised at how successful roots are at growing into site soils.

When you're backfilling, do not put any soil on top of the root ball. If you do, there's a good chance that when you water, the water will skirt around the root ball. Water is lazy. It's going to take the path of least resistance, which means it doesn't want to go through soil texture interfaces, like the one with the root ball (dark, rich soil) and the native site soil. Keep the soil off the top of the root ball.

After adding the backfill, water gently to allow the soil to settle. Then add more backfill, water and repeat as necessary. You may have to do this several times to get the tree to final grade.

Finally, add organic mulch. It helps keep weeds down, stabilizes soil moisture and also adds organic matter as it breaks down. Just like the backfill, keep all mulch off the top of the root ball. The mulch should come up to the edges of the root ball, but not cover the top. Mulch on the top of the root ball will not decrease moisture requirements, but it can increase circling roots. When you're finished, you should clearly see the root ball, which makes it easy to water, since you can focus your efforts for the first season on just watering the root ball. After a season or two, start watering the planting hole and beyond. The rule of thumb is to apply 1-2 gallons of water per inch trunk diameter as needed (don't let things dry out), maybe 3-4 days/week, depending on the temperature and wind.

And you're done! Congratulations! The CSU Garden Notes also have a great publication on Tree Planting Steps. Don't worry....I will remove the tree wrap by mid-April.

Infrared Fun

Posted by Eric Hammond Adams County

I acquired an infrared thermometer recently.  It’s a really neat toy tool that measures the surface temperature of any object you point it at.  It has all sorts of practical uses such as checking windows or duct work for air leaks and is even used in horticulture research to help quantify things like stress by measuring leaf temperature.      So, 

Ryobi infrared thermometer  

what is the first thing I do with it (well second thing actually- I now know my dog’s nose has a temperature of 81°F- does that seem low)?    I walk around pointing it at different elements of my and neighbor’s landscapes while they undoubtedly watch me through their windows wondering exactly what kind of crazy I am.   

To set the scene, it was partly cloudy day earlier this week with little direct sunlight and I took all of the temperatures around two in the afternoon.  According to what I’m sure is my highly accurate car thermometer the air temperature was 43°F.  So, all in all it was a pretty mild day for January in Colorado.  No direct sunlight and not crazy warm or cold.   Even so, seeing the temperature of various things in the landscape depending on their composition and orientation was pretty interesting.  (Disclaimer: This is all antidotal.  It’s based on data collected on one afternoon with the cheapest infrared thermometer the Home Depot sells.)

Air Temperature	43°F	Littleleaf Linden Trunk	82°F
Dormant Turf	53°F	Rock Facade  (Southwest facing)	66°F
Concrete Driveway	55°F	Home siding (South facing)	62°F
Wood Mulch	53°F	Home siding (North Facing)	45°F
Caddo Sugar Maple Trunk	47°F	Dogs nose	81°F

 

Even though some of the temperature differences were not as dramatic as I would have guessed the relative temperatures of the elements do illustrate the importance of good landscape design and management.

Rock façade facing Southwest.
A tuff site to for a plant.
 

 I think the temperatures of the rock façade and composite siding would have been higher if the weather had been less cloudy and more shortwave radiation was reaching them but, even the 20°F difference I observed serves to illustrate the danger of planting to close to brick or concert structures with South to West exposures.   The added heat load can be stressful to plants in both the winter and the summer, especially to evergreens.   

Sunscald on Littleleaf Linden

The most interesting thing to me was the high temperature of the lower portion of the trunk of the Littleleaf Linden.  On a 43 °F day it had a temperature upwards of 80°F.  Its only one tree and the temperature could certainly have been influenced by other factors such as the site the tree was planted in but, it struck me as noteworthy because Lindens are often prone to sunscald (also known as southwest disease).  This is a condition that is caused by rapid fluctuation in the temperature of the bark.   The reason we recommend wrapping young tress, especially those like lindens which have smooth and\or thin bark is to mitigate these fluctuations.  The difference between the Linden and Caddo Sugar Maple might be attributed to several factors including the sites the trees are planted in and color of their bark.  The linden was planted along a parking lot while the maple was in turf.  The maple also has a much lighter colored truck than the Linden.  It will be interesting to return and see what the temperatures are on a warmer day with more direct sunlight.

 






Even Horties Make Mistakes: Tree Planting

Posted by: Alison O'Connor, Horticulture Agent for Larimer County Extension

This is my linden.  Looks pretty good, huh?  Nice and straight, beautiful canopy.  Was in full bloom a few weeks ago—and I would argue that lindens have the most fragrant flowers in the landscape.  I love this tree and planted it in my yard five years ago, after the Windsor tornado leveled most of my landscape (except for the honeylocust behind it).

[Cue Roberta Flack’s song “Killing Me Softly”]

When you get a little closer, you can see that my perfect tree isn’t so perfect.  Oops.  Sunscald.  I should have remembered to wrap it a little more consistently when it was younger. 

Wait…what’s that?  Is that a…gasp…circling root!? The ones that I preach about in Master Gardener training?  The ones that are known to cause tree failure as they start to girdle the tree?  The ones that can essentially strangle a tree like a boa constrictor?  Nooooooo.
 

So what happens when you have a 4^th of July party and invite other horties over?  They assess your yard.  They start digging around your plants.  They find a massive, 2” thick circling root just below the soil surface of my prized linden.  Uh oh. 

Time for me to investigate and I find the worst.  Not only are the circling roots bad…they are devastating.  To me and the tree.  My husband and I decide to dig out the tree on a Friday night (I know…what a “date”!) and my stomach gets a twisted, sinking feeling as we excavate.  

 

If the first and second offenses were the sunscald and the girdling root, the third offense is that I planted this tree horrifically low.  We’re talking 8” too deep.  I am red-faced and shamed as I write this, as this is the #1 thing I teach when I talk about tree planting.  “Make sure your hole is saucer-shaped and shallow, with the root ball sitting 1-2” above grade.”  I am pretty sure I never said, “Hey!  Dig a huge, deep hole and toss your tree in.”  Wince. (Robert Flack sings, “I felt all flushed with fever; embarrassed by the crowd.”) 

As we dug, I asked my husband, Gil, if he enjoys that every project in the garden ends up being scientific research.  “No, Al.  Not really.”  But…this is so cool!  In a sad, depressing way. 

We got the tree out of the ground and check out the root system.  Remember, this tree has been in for FIVE YEARS.  Does it resemble anything to you?  Does it kind of have a black plastic container-esque look?  

So here’s where I went wrong.  I bought this Greenspire linden at a local nursery.  I didn’t do my due diligence by checking the root system before I planted it.  I obviously should have taken a closer look and either corrected all these circling roots (by washing off or shaving the outer perimeter of the root ball) or selected a different tree.  To be honest, this tree was probably a little large for its container at the time of purchase.  I could have asked more questions, but at the time, I just wanted a tree for my barren landscape.

  There’s been a lot of research on how to deal with trees with circling roots.  Linda Chalker-Scott from Washington State suggests making the tree bare root by washing all the soil off.  While this method may not be practical for those planting dozens of trees, this would have been a great solution for me and my one tree.  Jeff Gillman has looked at shaving the outer periphery of the root ball (removing 1” of soil/roots), shaping the root system into a box.  This had great success in Minnesota.  More importantly, research has found that “scoring” the outer sides is statistically equal to just planting the tree in the ground.  There is also a large study at Michigan State University looking at several planting techniques and an update on the latest findings.   

Woody roots have lots of lignin, making them more difficult to correct once they’ve matured, compared to herbaceous plants.  Teasing and slicing woody roots helps, but doesn’t fix the problem totally (obviously the case with my linden).  Plus tree root balls are large and it becomes cumbersome to try to do this with your hands or knife.   

I don’t know what the final solution is—research is ongoing—but you can guess when it comes time to replant, I’m going to carefully examine and manipulate that root system.  Oh, and find a ruler so I don’t plant the thing too deeply again.  I’m happy I was proactive and removed this tree, since it would have easily become hazardous in the near future (if it wasn’t already).  Those girdling roots cause pressure points at the base and wind in the canopy could have caused the tree to snap.  Did I mention that my neighbor parks his truck just on the other side of the tree?  Girdling roots have been found to be suspect in many tree failures. Want to read more?  The University of Minnesota has an excellent website on all things stem girdling roots.

I’m also glad I removed it, as the next day we had a 30 minute hailstorm that flattened everything.  There was a good chance this tree could have failed then and caused even more damage.  The hail was far more painful to experience than removing my linden…while I technically “killed” a tree, it was for many good reasons. 

Holy hail. 
They had to bring out the snow plows to clear the streets.
Windsor, Colo. August 3, 2013

So the next question is…what should I replant?  A linden?  Ok, will do!  I’ll keep you posted on my next science project.