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/

 

Time for Rust

Posted by Mary Small, Colorado Master Gardener Program Coordinator



Rust on clippers

You’re probably familiar with rust – the kind like you see here on the grass clippers (right) that were left outside all winter!

Plants get rust too, (although not for the same reason as the clippers) and it is appearing on landscape plants now.

Here’s rust on my Zephirine Drouhin rose (below).  I just had to have this plant with the beautiful, fragrant, pink flowers, few thorns and intriguing name. Since Zephrine is a climber, I planted it next to a 4 foot picket fence, imagining how the canes would spread along its length. This antique rose is classified as a “Bourbon” rose and dates from 1868. In spite of all the positives, it has poor rust resistance.

Rust pustules on rose

Rust is a fungal disease that overwinters on fallen leaf debris and canes.  It infects susceptible roses in moist mild weather when the pustules (that form on leaf undersides and canes) release their spores. The disease is tough to control once the symptoms develop. And since you can clearly see the orange pustules as well as yellow spots on the upper leaf surfaces – it is obviously well underway.

Fortunately, it is primarily an aesthetic problem in our climate. Cultural strategies can help manage it – proper siting, keeping the canopy thinned to promote rapid leaf drying and sanitation (removal of diseased leaves and canes.)


While I’ve had moderate success with the cultural strategies I recently learned about a situation in my neighbor’s yard that might be sabotaging my efforts. For some reason, their sprinkler system ran one weekend day when I happened to be looking out a window. One sprinkler head directly targeted poor Zephrine, along with the lawn. I think a conversation and a sprinkler adjustment will help improve the leaf drying situation!



Rust on hawthorn

Here’s a photo of rust on hawthorn (left). I’m not sure which rust this is, but regardless, the rusts that appear on hawthorn (and related species) are more complex than the one on rose.

These rusts have a two- host life cycle, which starts with the maturation of fungal structures on a juniper host. The spores produced by them in the spring blow to alternate hosts, which includes hawthorn, crabapple, apple and others. Years with mild, humid spring weather will produce a large amount of infections.
  


Tentacle-like reproductive structures

Symptoms appear as yellow-orange spots on leaf surfaces - as soon as flowering is over. Fruiting structures that look like small tentacles develop on the undersides of the spots. When mature, they produce spores that blow to juniper hosts and cause infection. The rust fungus must have both hosts to complete its life cycle. Under the right conditions, the two hosts can be a mile or more apart and still be infected!

Generally, these rust diseases are most obvious on the deciduous hosts because of the colorful spots and premature defoliation of infected leaves. The best way to manage the disease is to select plant species that have rust resistance. You can also remove one of the alternate host plants – three hundred yards up to 3 miles is the standard recommendation. In a landscape setting this is usually impossible.  Generally, the disease is more of an aesthetic than plant health problem in our area.





Rust on mallow - upper surface

Finally, here’s a rust I found on a weedy mallow hiding between a raised bed and fence. It’s the same rust that infects hollyhocks as they are closely related.  Unfortunately it’s not a health issue for the mallow (rats!), but the disease can prematurely defoliate hollyhocks and make them look just plain ugly later in the season. The fungus overwinters on dead leaf and stem tissue of mallow and hollyhock, so sanitation goes a long way to reduce the inoculum for next year. Guess I better get my weed knife out and get rid of this guy.



Rust pustules on mallow - lower surface