CO-Horts Blog

Thursday, August 29, 2013

It Doesn't Get Any Fresher: Farmers' Markets

By: Alison O'Connor, Horticulture Agent...and manager of the Larimer County Farmers' Market in Old Town Fort Collins
Some of you may not know this, but I moonlight as a farmers' market manager.  Ok, it's actually part of my job in Extension and while it's a lot of work, it's also a lot of fun.  Especially this time of year, when EVERYTHING is in season.  I have to restrain myself when I'm working the market, as it's easy to have my eyes (and wallet) feast on the latest offerings from our vendors.  If you haven't visited your local market lately, check it out!  The Colorado Department of Agriculture has their Farmers' Market listings online.  If you're in the Fort Collins area, visit the Larimer County Farmers' Market, open Saturdays, 8am-noon trough October 26 at the Larimer County Courthouse (200 W. Oak Street in Fort Collins).  Stop and say "hi" to the hard-working Larimer County Master Gardeners who ensure the market is open each Saturday....and try to stump them with your gardening questions.  Don't have one?  Then try to stump the Master Food Safety Advisors!

Why should you shop at a market?  There are so many reasons.  Interested in canning or preserving?  Vendors sometime offer discounts for bulk quantities (hello peach jam in the middle of January).  Looking for some new greens to perk up your salads?  Vendors have 'em.  Want a 1.3 pound heirloom tomato?  Look no further than your farmers' market. 
It's a meal in itself. Cherokee Purple in all her glory.

And if all of that doesn't tempt you to shop at your local market, then maybe these photos will...  (I'll let you grab a tissue to wipe the drool.)  Many of us have wonderful gardens, but none of us can grow everything.  Special thanks to Master Gardener Michelle Wilde for her fantastic photos!

Sometimes I wonder why I don't eat tomatoes...
especially when they look as good as these.

Going to a dinner party? 
What impresses the host more than fresh cut garden flowers?

Eggplant parmesan...where's the homemade tomato sauce?

Apples means that fall is coming, but there's still plenty of summer left.

Confession: I have consumed 7 (!!!!) watermelons this summer. 
By myself.  Thank you very much.

Sweet corn is like candy on a cob.

I made strawberry jam last weekend and there's nothing better. 
Strawberries are also a great snack!

Peaches are the current darling of the market.
So visit your local farmers' market.  Give them a high-five for their hard work.  Challenge yourself to make a meal from the market...I bet you can do it.  Most markets also have bread, meat, eggs, dairy, honey, salsa, sauces and even wine.  And I'm sure you'll find dessert too.  Or just eat more sweet corn.
The vendors are always glad to see you.

Friday, August 23, 2013

Native Plants for Sustainable Gardens

Alexis Alvey, Horticulture Agent, CSU Denver Extension

I hail from the East Coast and moved to Denver last year.  By no means am I an expert yet on Colorado native plants, but having gardened all my life, I AM an expert on making gardening mistakes and learning how to fix them.   And during the past year, I’ve learned that there are a lot of things that can go wrong when trying to garden in Colorado!

Like many Coloradans, in my spare time, I enjoy going up to the mountains and going hiking or trail running.  I love checking out the vegetation and the stunning landscapes that Colorado has to offer.  And I always think, oh, wouldn’t it be so awesome if I could recreate this in my own backyard!  How nice it would be to have wildflowers blooming in my garden like these on the trail to Mt. Evans….  

Or how relaxing it would be to create a meadow instead of lawn like this alpine meadow near Dillon….

Or how enchanting it would be in the fall to have a grove of aspen outside my window like these at Willow Creek Reservoir, near Granby.  

And based on all the inquires we get at the Denver Extension office, I know that I am certainly not alone in my desire to recreate a little piece of natural Colorado in my backyard.  But unfortunately, what we want, we often do not get, especially when it comes to native plant gardening.  For example, this aspen which is in the front yard of an avid Denver gardener is nearly dead. 

To learn some tips on how to garden successfully with native plants and avoid common pitfalls, click on the link below to listen to a free, recorded webinar I just did on this topic!

Monday, August 19, 2013

On the hunt for interesting garden paths and benches

Posted by Linda McMulkin, CSU Extension-Pueblo County
August 19, 2013

          I’ve been looking at gardens in a slightly different way lately.  Traditionally, my focus has been on the plants that inhabit a garden.  But my husband pointed out that many pretty gardens are missing two things that enhance the experience of touring gardens for him--paths and places to sit.

A meandering path that leads to a bench at SECWCD.
Photo by O. O'Callaghan
Mike’s point is valid, but I’m usually so distracted by plants that I rarely realized why some gardens feel more inviting than others.  I don’t mind standing on the edge of a flower bed and looking in, but winding through the flowers is even more fun.  And benches inside beds are always an invitation to sit and observe the details of the garden. Now I notice paths and benches in every garden I visit.
           In a 2011 article for our From the Ground Up newsletter, Elizabeth Catt, SE Colorado Water Conservancy District (SECWCD) garden manager, wrote, “Pathways can be an alluring hardscape feature, enticing you to move further into a garden either directly or indirectly. In a formal garden, a path can direct your view straight across a vista to bring your eye (and sometimes your feet) through it to another object: perhaps a fountain, a bench, an ornamental urn. At other times a winding path calls to your sense of curiosity; what can be around that next bend? 

The colorful pattern is repeated on the patio
and other terraces.

I’ve visited several private and public gardens recently and observed plant choices and maintenance practices, garden art and retaining walls, and the results of drought stress and crazy weather.  All of these observations have been done from a pathway and I’ve started noting construction materials and how the path itself fits into the garden design.  Does it tempt me to continue exploring or not?
One of my favorite garden paths is at a Pueblo home that was on the xeriscape tour in June.  The homeowner uses recycled materials and colored concrete to build paths to the many terraces on his property.  The paths are necessary and could have been just functional, but he has made them works of art.  Other pathways I’ve seen were less colorful but constructed in ways that invited the visitor into each garden.  My favorites are the paths that tempt me into an as-yet-unseen part of the garden or to a place to sit and relax for a moment.
          Places to sit in gardens can be constructed from any number of materials.  I’ve seen benches and chairs from local furniture stores, homemade seats, and recycled items.  I find that I admire any seating area that incorporates recycled materials, found items, or whimsy. 

A seating arrangement for everyone in the family. 
This photo was taken at Spring Creek Garden in
Fort Collins in 2009, perhaps the
 beginning of my fascination with benches.
An interesting, recycled seat in the same garden
 as the colorful path above.


This bench was constructed
by the homeowner,
a local artist.
This seating area was constructed with wood recycled
from the homeowners family farm. 
So I’ve ended up with a new garden obsession, one which Mike has been forced to share.  I’m on the lookout for the most tempting path and a seating area that is so inviting that I want to linger instead of rushing to the next view or bed.  Any suggestions on where I should visit next?

Thursday, August 15, 2013

Is Ignorance Bliss when it Comes to Noxious Weeds?

Posted by: Kurt M. Jones, Chaffee County Extension Director

My family and I are currently relaxing on an end-of-summer vacation. Well, we are relaxing as much as one can when vacationing with a 5 and 6-year old.

One of our excursions was to ride a chairlift up the ski hill, and I tried to ignore the beautiful noxious weeds that I kept seeing. Overhearing the comments from other tourists reflecting on the beautiful "wildflowers" that were blooming, I kept glancing at the musk thistle, yellow toadflax, and myrtle spurge. I can only assume they were looking at the same flowers that I was.

Reaching the top of the ski lift ride and grabbing our alpine slide sleds, we walked along the weed-lined path. Uugh! I did wonder what it would be like to be the overheard tourists still admiring the beautiful flowers. Unfortunately, I know the environmental damage these weeds will and are causing, lowering the aesthetics of the flowers we are seeing.

I climb into the sled with my excited 5-year old, and note the beautiful carpet of field bindweed next to the slide track. We listen to the bored teenager give us our safety lecture, something he has done hundreds of times this summer. He said the most dangerous part of our ride is the burn we would get from touching the slide walls while we are moving. Soon, we are off.

Since I am allowing my 5-year old to run the brake, we are off at a snail's pace down the mountain. It allows me time to view the musk thistles overhanging the slide we are paralleling. Luckily, it grows to about 6 feet tall, so the sharp thorns surrounding the purple flowers are above us as we rocket past at about 5 mph. I don't recall the thorns from the thistles in the safety lecture!

At the end of our ride, I note another teenager running a weed eater along the bottom of the ski hill. He was standing amongst the rosettes of the thistles, cutting down some Canada thistle, ester, and curly cup gumweed. While mechanical controls like mowing work well for many weeds, he probably is stimulating the spread of the Canada thistle. Sigh!

We get out of the sled and the kids are very excited. I'm a bit depressed that such a pristine mountain environment is under siege from a variety of problematic weeds. Of course, maintaining a diverse crop of desirable plants can be difficult with the number of people recreating on these slopes, but recreating in a field of Canada thistle or musk thistle doesn't sound like much fun either.

Oh well, time to look up the hills to the droughty gamble oaks, turning their fall colors early. The oranges and reds are quite nice, highlighted by the wildfire smoke from the dry thunderstorm which moved through earlier in the day. I again think about ignorance being bliss, and make a quiet wish for it to rain on our vacation.

Though it may not sound like it, we are having a wonderful time, relaxing in the Utah mountains. Our kids are still commenting about the bike ride and short hike to the Bridal Vail falls. The freestyle ski jumping show was amazing at the Olympic Training Center. Just turn an ignorant eye to the noxious weeds that may be joining you on your vacation. Or better yet, learn about noxious weeds and take steps to keep them from growing in your home landscape.

Monday, August 12, 2013

Summer Love Songs

By Carol O’Meara, CSU Extension Horticulture Entomologist, Boulder County

When insects sing their summer songs, love rises to a crescendo in the garden. Valentines day can’t hold a candle to the trills, chirps, clicks and drums that form a symphony of sound in the height of heat. Who are these plaintive lovers singing for romance? Bend an ear to the different calls and you’ll find love comes on many splendored wings.

Horn section
Dog Day Cicadas (Tibicen spp.) are well known for the band-saw-like serenades of males advertising their appeal. Resting on branches, occasionally sucking sap from twigs, the males call by vibrating a membrane, called a tymbal, in their abdomens.

The females pass judgment on male suitability by the quality of their song, but how they can distinguish one male’s notes from another is baffling when they sing in unison. Buzzing in concert with each other, male cicada song can be very loud, occasionally rising to shrieking pitch before quieting down.

Cicadas are often confused with locusts, but have a squat body with wide-set eyes and large, clear wings. You’ll find them gathered on trunks and tree branches late in summer.


Some insects use their wings in a modified version of a violin, holding one wing aloft while drawing the other over it. The wing acts as an amplifier, channeling sound into the night air to woo females close. Snowy tree crickets (Oecanthus fultoni) are one of the most beloved night singers in the region.

Thanks to Hollywood movies using their song as the epitome of night sound, these rarely seen crooners hang out in trees, shrubbery and vines. Chirping in concert with the heat, their song becomes faster as temperatures rise. Clinging to the undersides of leaf or branch, snowy tree crickets blend into surrounding vegetation and are difficult to spot. Look for pale green crickets with long antennae whenever you hear their call. Listen to it at the Singing Insects of North America site,

True Katydids (Pterophylla camellifolia) are newcomers to the Front Range music scene, bringing with them a unique file-on-metal sound females find irresistible. These raspy voiced Romeos are laid back musicians, slow moving and loath to fly, and can be found in the tops of deciduous trees. Singing solo, their song is often slow and easy, but in chorus the tempo is more upbeat with nearby males playing off one another to form a quick tune.

To find them, look for tall, narrow, green insects resembling a leaf.


Many arthropods use drumbeats from foot or abdomen to pound the earth and gain attention, including wolf spiders, Mormon crickets, or grasshoppers. Their repertoire isn’t limited to simple beats; some use a combination of taps and rubs that keep up a percussive rhythm. The garden should be very quiet to hear this sound and many in urban or suburban yards will miss it altogether due to background noise.


No concert is complete without a diva, and female Culex tarsalis mosquitoes are headliners of sound. When Culex enters the summer stage, she sets off a whine no male can ignore. Using her wings to belt out a song, the female draws crowds of hopeful suitors to her side, where they form a cloud-like entourage to follow her about.

Like most prima donnas, gardeners would be better off without the antics of female mosquitoes, but they are a staple of summer evenings and serve a purpose in the larger food chain. If you choose to search for summer songsters, take precautions against being bitten by wearing long sleeves and slacks while out after dusk, and use repellants if they don’t cause you allergic reactions.

Sunday, August 11, 2013

What the Hail!? Plants that Stood Up to the Ice Bombs

Posted by: Tony Koski, Professor and Extension Turfgrass Specialist, CSU

Golfball and baseball-sized hail
Unfortunately, I don’t live in the idyllic area where Darrin lives…where unicorns and lemonade waterfalls co-exist together.  No, I live in northern Colorado—Wellington to be exact—and hailstorms are frequent.   And on August 3, parts of northern Colorado suffered from one of the worst hailstorms in recent history.  Pea-sized hail is laughable…the hail we got was baseball-sized (and a lot of golfball-size).  This storm paved a swath of destruction from Wellington to Windsor, dropping hail and copious amounts of rain in a short time. 
When life gives you hail,
you collect it for show and tell.

While Windsor had to get out the snowplows to clear the streets, the hail in Wellington wasn’t as plentiful, but much larger.  And it got me thinking as I cleaned up my garden…are there plants that do better than others when pelted with these ice balls?  According to Wikipedia, the size of the hailstone determines the rate of speed at which it hits the earth.  A hailstone less than ½” will strike ground around 20 mph.  If you increase the size to 3”, the speed increases to 110 mph.  That means my baseball-sized hail ricocheted to the ground faster than Wyoming drivers race down I-25. 

Since Alison and I both had extensive damage to our gardens (we are seeking donations of any garden produce), here’s the list of plants that fared well and those that are now compost:

Plants that survived the hail
  • Ornamental grasses (Janey—note for your thesis!)
  • Hawthorn with hail damage;
    a little light pruning is all that's necessary
  • Lavender
  • Sage
  • Parsley
  • Rosemary
  • Groundcover thyme
  • Most small-leafed trees (honeylocust, linden, maples and crabapples/apples)
  • Broccoli
  • Kale
  • Cosmos
  • Lilacs
  • Pines (they lost a few needles, but look good)
  • Spruce (tips were pruned, but overall fared well)
  • Junipers (shocking, I know)
  • The sandcherry just laughed at the hail.
  • Lamb’s ear
  • Vines trellised to fences/structures (honeysuckle, silver lace vine)
  • Cholla cactus
  • Opuntia cactus
  • Coneflower
  • Scabiosa
  • Yarrow
  • Dogwood
  • Sandcherry
  • Agastache
  • Turfgrass (another reason to have turf!)

The turf says, "Hail?  What hail?"
Plants that bit the dust
Zucchini...I think.  Pretty sure.  Hard to tell.
  • Squash, cucumbers and other cucurbits
  • Eggplant
  • Peppers
  • Tomatoes
  • Dill
  • Beets (but may recover, since edible part grows below ground)
  • Rhubarb
  • Hops
  • Russian sage
  • Upright sedums
  • Cleome
  • Zinnias
  • Coreopsis (tickseed)
  • Fleshy-leaved sedums are a hail favorite
  • Iris
  • Daylilies
  • Peonies
  • Big-leaf trees (catalpa)
  • Heuchera (coralbells)
  • Hosta
  • Blue-mist spirea
  • Winecups
  • Jupiter’s beard
  • Shasta daisy

Sniff...there goes the beer :(
Hops vines totally denuded of leaves.

Darrin’s blog covered how to handle hail-damaged plants well, so I won’t repeat that.  And we’d love to hear from you about the plants in your garden that have prevailed after hail…anything we missed? 

Sungold cherry tomato = no likey hail
The Russian sage was in full bloom.
Now it's a hot mess.
Onward and upward to greener pastures!
Green space downtown Toronto, Canada.
These cows don't make cowpies!

Monday, August 5, 2013

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 4th 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.

Saturday, August 3, 2013

A Great Time to Visit Color

Posted by: Jim Klett, Professor and Extension Specialist, Department of Horticulture and Landscape Architecture

Window boxes of annuals accent this property in Vail, Colo.
Late July through Early August is an ideal time to visit many sites throughout Colorado to observe annual flower color.  All along the Front Range and many mountain communities are bursting with fantastic color from annual flower plantings.  It is a great time to visit city displays of annuals along with more formal plantings at botanic gardens and the trial grounds at Colorado State University.
Petunia Cascadias Indian Summer
The CSU Trial Grounds is located on College Avenue and Lake Street next to the University Center for the Arts (1401 Remington Street, Fort Collins).  These Trials include about 1070 different annual varieties with over 500 different containers including over 250 new varieties for 2013.  Many new petunia colors are planted which include some major genetic breakthroughs along with exceptional Sun Impatiens.  Petunia ‘Cascadias™ Indian Summer’ has an outstanding mix of flower color along with a new distinct yellow petunia called ‘Suprise Yellow’.
Petunia Surprise Yellow
Numerous lantana varieties are planted but one called ‘Lucky Sunrise Rose’ has an extremely attractive flower color that your eye goes to immediately. 
Lantana Lucky Sunrise Rose
The annual flowers in Old Town Fort Collins are exceptional with many great combinations in containers and beds. 
CSU Annual Flower Trial Gardens
1401 Remington Street, Fort Collins

In the Denver metro area the Denver Botanic Garden has a great display of newer varieties along their York Street entrance.  Inside the gardens annuals are planted throughout the garden and especially in their All American Display area.  They have also displayed most of the ‘Best Of’ winners from the 2012 CSU Trials.

Parks and parkways throughout the City of Denver have excellent annual displays.  The formal Mount Vernon Garden in Washington Park along with their large display of annual color as you enter the park are places to visit for mass use of color.  Sixth, Seventh and Seventeenth Avenue parkways have excellent color displays along with displaying proper use of height in their displays.

Mountain communities, especially Vail, has outstanding annual flower displays.  Many of the displays have incorporated numerous perennial and ornamental grasses to add distinct color and texture contrasts.  Containers, hanging baskets and flower boxes are throughout the business area making a very enjoyable shopping visit.  The flower boxes around many of the restaurants show outstanding uses of color.
Window boxes of annuals dress up this entrance
Try to take some time at this time of year to visit some of the outstanding use of annual colors throughout our beautiful state.

Thursday, August 1, 2013

The Mid Summer Leaf Drop Blues

Posted by Mary Small and Curtis Utley, Jefferson County Plant Diagnostic Clinic

Ah, sweet mid-summer! Long, warm evenings spent on the veranda listening to the sounds of leaves dropping. Huh?!  leaf drop in late July/early August?

Yep, you read that right. We’ve been getting inquiries and emailed photos about, and observing this very phenomenon.  Well, “phenomenon” probably isn’t quite the right term when you consider we see it every year, usually beginning mid-July.  Several situations cause this by themselves or combine with others into a “perfect storm”.  Tree leaf drop is probably the number one problem we encounter in our clinic every summer. So why do trees drop leaves in the summer?

Trees often form more leaves in the spring than their systems can support later in the season.  The hotter, dryer weather of summer signals plants to drop leaves as a defense mechanism against water loss.  There may not be enough available or transpiration rates are so high that trees just can’t keep up. So they drop leaves to cut water losses and keep the rest of the system going.

Drought stress causes leaf drop.  Some of the tree canopy is shed to balance water intake and “outgo”, similar to the above situation.  And, even though it looks like a lot, as much as 10% of leaves can drop without causing serious injury.

Newly transplanted trees (including those planted last year) frequently drop leaves to compensate for root loss and reduced water absorption.

Overwatering, poor soil drainage and too-deep planting results in root oxygen deficiency. Poorly functioning or dying roots can’t absorb needed water, so again the tree drops leaves to reduce transpirational losses.

Insect pressure causes leaf drop. It’s not unusual for so-called “healthy-looking” trees to drop leaves all of a sudden.  Lilac-ash borer and the banded ash clearwing are common culprits.  These insects spend a good chunk of their lives tunneling in and through wood underneath the bark a couple of inches deep.  In addition to physically weakening the tree, the activity can interfere with the flow of water, stressing the tree and inviting attack. Leaves are shed as (you guessed it) trees try to cut their transpirational losses.

Then there’s hail and wind that physically knock leaves (and branches) out of trees. Sometimes the full extent of damage doesn’t show up until a bit after the storm, when damaged petioles and leaf blades succumb to dehydration following tears or dings. 

Aspen trees begin their Marssonina-infected leaf drop in mid to late July. Infection occurred in spring, so there’s nothing to do until leaf raking season.

Trees lose leaves for many reasons in late summer but the question behind the question for most folks is, “is the tree okay”?  Check the quality and quantity of new growth by looking at the annual growth increments, the general size of the leaves and remaining canopy density. If all of these things check out, then the tree is probably going to survive to see another spring…and summer.