CO-Horts Blog

Friday, October 25, 2013

The Science behind Autumn Leaf Colors

Special post by: Nika Reininger, Master Gardener in Larimer County (uploaded by Alison O'Connor)
Colorado's fall color: Oak leaves (upper left) appear green while continuing to produce chlorophyll during the growing season. When chlorophyll production stops in autumn, yellow carotenoids in this maple leaf (center) become visible. An ash leaf (right) growing in dappled sunlight develops vivid red hues on parts of the leaf exposed to bright sunlight, as a result of anthocyanins. Shaded leaf surfaces remain yellow. Frost has turned a linden leaf (lower left) from a brief autumnal yellow to brown, as leaf tissues succumb to necrosis. (Photo by Nika Reininger, CMG in Larimer County)
     The shorter days and cooler temperatures of autumn signal deciduous trees to reduce chlorophyll production, leading to brilliant displays of fall foliage color. During the growing season, trees produce food for themselves by converting water from the soil, carbon dioxide from the air and energy from sunlight into sugars and starches. This chemical reaction, called photosynthesis, occurs in chloroplasts, specialized structures within a plant’s leaves and green stems. It requires the presence of chlorophyll, a pigment which reflects green light. Smaller amounts of other pigments are also present in plant leaves during the growing season, but are primarily masked by chlorophyll. This is why leaves typically appear green to the eye.
     In autumn, deciduous trees prepare to lose their leaves and slow chlorophyll production, allowing other pigments to become visible. Yellow and orange leaf colors are due to xanthophyll and carotene pigments, also located in chloroplasts. These pigments help the plant to capture more wavelengths of light for photosynthesis. Many native Colorado trees turn various shades of yellow before the first severe winter frosts. Some tree species produce anthocyanins in response to shorter days and cooler weather. When anthocyanins are present in leaves containing ample plant sugars and exposed to bright sunlight, bright red and purple hues result. Tannins impart a brown color to leaves.
The fall color of Autumn Purple ash (photo by Bill Monroe, CMG Larimer County)
     Why is autumn color variable from one year to the next? A number of factors determine the timing and intensity of leaf color changes, including plant genetics, moisture, temperature and sunlight. Periods of late summer drought may postpone the start of autumn color changes for a few weeks. Warm, dry, sunny days, followed by cool nights, favors development of water-soluble anthocyanins.  During warm fall days, sugars are produced in the leaves, but cool nights prevent normal flow of sugars and water through the petiole (where the leaf attaches to the branch). Increased concentrations of sugars trapped within leaves results in increased anthocyanin production. Because carotenoids are always present in leaf tissue, yellow autumn foliage remains more predictable from year to year than anthocyanin-based red coloration. While bright, sunny days do favor development of dramatic red and purple colors, excessive drought during a tree’s cessation of chlorophyll production can lead to premature brown coloration and leaf drop. Freezing temperatures result in death of the leaf tissue. Genetics can also influence fall color displays. Within a species or local population of trees, individual trees may develop more dramatic foliage colors than their neighbors. Recently developed cultivars of many tree species offer attractive fall foliage, extending seasonal interest in the garden.
     To learn more about the botany of fall color, check out the following articles:

CMG GardenNotes #141, “Plant Growth Factors: Photosynthesis, Respiration, and Transpiration.”
Planttalk Colorado #1728, “Why leaves change color in the fall.”

University of Tennessee Agricultural Extension Service publication #SP-529, “Changing Colors of Leaves.”
USDA Forest Service publication, “Why Leaves Change Color.”

Tuesday, October 22, 2013

In Celebration of the Vining Weeds of Colorado

By Linda McMulkin, CSU Extension-Pueblo County
I just got back from the Mississippi Delta where I was introduced to kudzu (Pueraria montana).  For years, I’ve heard stories about this invasive plant growing over parked cars and killing the trees it climbs, but it took seeing to believe. 

Kudzu has taken over a road cut on US 49 in
Phillips County, Arkansas.  It is trying
 to cover an abandoned house and has
 smothered every plant from the road to
 the top of the hill.  It's invading
more territory by crawling
 up the cell phone towers.
The area I visited is on the Mississippi River in eastern Arkansas, about an hour south of Memphis.  There are many cotton, soybean, and corn fields in the area, and we observed the crops and harvest techniques on our sightseeing drives on both sides of the Mississippi River.  Along the road, there were unfarmed areas where a mix of trees, shrubs, and grasses thrived.  But interspersed with the fields and natural areas were kudzu patches of a green so thick and uniform you could not see what used to grow underneath.  The vines covered everything, including the tallest trees, smothering every plant underneath.

Using my handy smartphone, I looked up details about Pueraria montana and found that the plant is native to Asia, was introduced as an ornamental and for erosion control, is in the Fabaceae (Pea) family, has an extensive root system that is the major source of new infestations, fixes nitrogen and can be used to break up and enrich heavy soils (please don’t try this at home), and is on the noxious weed list in 21 states (and present in 8 others where it isn’t on the noxious list).  I realized I had seen the plant on other trips, just not covering such enormous areas.

In Colorado, we often complain about vining plants such as bindweed, Chinese clematis, Virginia creeper, or calbazilla growing over fences or plants in our landscapes.  After seeing kudzu at work, I’ll think twice about criticizing even the most obnoxious weed in my landscape.  I’ll embrace my bindweed patches and celebrate that kudzu hasn’t come to live with us. 

Are Your Ash Trees At Risk?

Alexis Alvey, Horticulture Agent, CSU Denver Extension

Imagine if every tree on your street had to be cut down.  Would it still feel like home?  Would it still feel like your neighborhood?  Would you be prepared to pay for extra air-conditioning and heat?  Would you be prepared when the value of your home decreased?  This has actually happened in numerous communities throughout the country where streets lined with Ash trees have been decimated by an invasive insect pest called Emerald Ash Borer.  At the end of September, this lethal insect was discovered in Colorado for the first time in Boulder.

How many ash trees do you see in this photo from University Blvd. in Denver?

Invasive insect pests and new fatal tree diseases are seriously impacting our nation’s forests, our community’s street trees, and our own backyards.  Over the past century, global trade has greatly expanded and has inadvertently facilitated the introduction of invasive pests into this country through various means including wood packing materials.  Insect pests and diseases that are native to other areas of the world are able to cause an alarming amount of damage to our trees.  Because our trees did not evolve with these new insects or diseases, they did not develop a natural defense mechanism and succumb easily.  Our native trees have died by the millions due to diseases like Dutch Elm Disease and pests like Emerald Ash Borer.  It is estimated that over 53 million ash trees have died or are dying due to Emerald Ash Borer.

Currently, plans are underway to assess the extent of the infestation of Emerald Ash Borer in Boulder.  You can be sure that other municipal forestry departments throughout the Front Range are going to ramp-up their efforts to survey for this insect.  We will let you know about the status of Emerald Ash Borer as new information becomes available.  In the meantime, I would encourage everyone with an ash tree in his or her yard to educate him or herself about this lethal insect.  For national information, visit: and for Colorado-based information, visit:

Ad from the national campaign to slow the spread of Emerald Ash Borer

Also, please be sure to not move firewood – this is one of the main pathways that Emerald Ash Borer has spread around the country, beginning new infestations at campsites.  Make sure that your firewood is heat-treated (which kills any larvae developing in the wood) before you transport it, or that you simply buy firewood where you are going to burn it.

If you think you have Emerald Ash Borer in your ash trees, or if you have any questions or concerns, or would like additional information, please contact the Colorado Department of Agriculture at 888-248-5535 or email

The culprit - Emerald Ash Borer
Photo source: David Cappaert, Michigan State University,

Friday, October 18, 2013

Tempted by the Cutting Edge?

Posted by Tony Koski, CSU Extension

In the past few months I’ve received a bunch of calls and emails about a “revolutionary” (the company’s words) product – CuttingEdge grass seed. I had never heard of this stuff. I’ve been asked…”What is in it?”… “Should I buy it?”….”Is it better than what I have now?”…. “Isn’t it just grass seed?”…. and “It sounds too good to be true…Can it really be that good?”.  Beyond what they found on the company website, people could find no information on it anywhere on the Internet. So I did what we do in Extension: I tried to find out what I could – especially any research-based information.
Surprisingly, I could find little on this product as well – except on the company website (  One look and I understood why all of the questions. This stuff is incredible! It (Cutting Edge Grass Seed) not only has “unique characteristics that revolutionize the way grass seed and turf management is viewed today.”, but it is “one of the most environmentally responsible grass seed mixes sold anywhere in the world.”.  Those are pretty big claims? But…wait… there is more! A lawn planted to this grass could allow you to STOP (their emphasis) “constant” (their word) watering, fertilizing and mowing. It will grow roots up to 48 inches deep. It is salt resistant, endophyte-enhanced, self-repairing, grows in sun or shade, and is resistant to gray leaf spot. It comes with an OMRI-approved “hydration and mycorrhiza” coating. You can even earn points towards LEED Certification by planting it (intriguing, though that link was dead). Wow! Amazing! I’ve got to try it!

Just as I was about to click that big red “Order Now” button that promised an extra FREE 1 pound bag (Well…free, except for more shipping and handling…) if I bought 1 pound, a thought crept into my head: what IS this stuff? I scoured the flashy (and really slow) website. All I could find was that it is a “patent-pending mix of Kentucky bluegrass and other top-performing seed.”.  Hmmm…now I’m suspicious. And annoyed. Really annoyed. I hate it when a company won’t say what is in their product – especially when it’s required by law. 

Instead of the “Order Now” button, I clicked “Contact” and dialed the information number. I got a live, knowledgeable, friendly person – Kristin – who answered all of my questions. (Disclaimer: I told her up front that I was gathering information for this blog) I asked what, besides Kentucky bluegrass, was in the mix (I was told perennial ryegrass, hard fescue, Chewings fescue, and tall fescue). When I asked about cultivar/variety names, Kristin said the company doesn’t reveal those. I asked if the mix contained VNS seed (stands for “variety not stated”), and was told “yes, it is VNS seed”. Ahhh...the reason they can’t tell you the cultivars – because they are not sure of what those cultivars are! To be fair, VNS is not always “bad seed”; it CAN be very good seed, in fact. But buying VNS seed is like ordering “running shoes” from Zappos and not being able to specify size, brand, style, or color. You will get running shoes, but will they fit your feet, fit your needs – will they be what you want? Kristin also kindly sent me a sample label for one of their seed lots (the seed lots will differ slightly, she told me, depending on where in the country you order your CuttingEdge seed).

The company recommends a seeding rate of 4 pounds per 1000 square feet – which is about 1.6 pounds of seed (because of the coating on the seeds…which is about 60% of the total weight). This would be a low rate for bluegrass alone, much less for the larger-seeded rye and fescues (which comprise about 80% of the seed in this mix). To end up with a turf of acceptable density using this product, it should be seeded at a rate of 12-15 pounds of the coated seed per 1000 square feet – not 4 pounds.

To seed 1000 square feet, using the company’s recommended seeding rate, it would cost about $40 (if you buy the 10 lb. professional kit; about $72 if you buy the one pound bags). To seed at a rate that would give any chance of producing good quality turf, it would cost about 3-4 times as much ($120-280….to seed 1000 square feet of turf!).

If you were to instead buy a comparable seed mix (bluegrass/fine fescues, or bluegrass/ryegrass) from a reputable local seed company like Pawnee Buttes Seed ( and seed at a rate of 6 pounds of seed per 1000, it would cost $12-18 dollars for seed.

Though it’s possible that the VNS seed sold by CuttingEdge is of good quality, the product cost (quite high) and recommended seeding rate (quite low) make this product an unwise buy. And the idea of mixing grass species like bluegrass, ryegrass and fescues is far from “cutting edge” or revolutionary – much less a patentable one. It’s far wiser – both agronomically and economically – to purchase seed of excellent quality and known cultivars from a local, reputable seed company. You will know what you are purchasing, get the best quality seed, and won’t have buyer’s remorse later. It may not seem sexy or cutting edge, but it’s smart. CuttingEdge grass seed: another case of “If it sounds too good to be true….”

Fall in the Air, Pumpkins on the Brain!

Kurt Jones, Chaffee County Extension Director
(Excerpts from Libby Colbert, Arapahoe County Extension)
I came home yesterday to one of my favorite treats…a home-made pumpkin pie!  So much for my self-imposed diet.  I also love roasted pumpkin seeds this time of year; luckily both are readily available this time of year.  I won’t even dwell on the pumpkin-infused beverages that keep tempting me!
The pumpkin has been a longtime favorite of children, featured in their literature (Cinderella's coach) and in song (the keeper for Peter Pumpkin Eater's wife). The Jack-o-Lantern is their Halloween celebrity. In China the pumpkin is still called the emperor of the garden.
Pumpkin technically belongs to the squash family, but works so well as pie filling it is often considered a fruit. It is also a good main course vegetable and an ingredient in soup, quick breads, cookies, cakes and pudding. It is an excellent source of many nutrients including Vitamin A, iron, potassium, Vitamin C and others. It is low in calories, sodium and fat.

Historically, pumpkin seeds have been used medicinally: American Indians chewed them to ward off kidney infections and parasites, and they were an official drug in the 19th century as a diuretic and worm remedy. They are rich in phosphorus, iron and some B vitamins, including niacin, are thirty percent protein and forty percent unsaturated fat. They can be purchased raw or roasted, or you can prepare them yourself. They are a great snack and the kernels make a crunchy complement to cooked dishes and salads.

Harvesting and storing
Pumpkins are ready to harvest when they are orange in color and the skin is hard, anytime before frost. The rind should not be easily penetrated by a thumbnail. Smaller varieties of pumpkins are best for storage and cooking. They store best when part of the stem is left on and carefully handled. By storing at about 55 degrees F. in a dry place they have a two to three month storage life. Prepared pumpkin pulp may be frozen, canned and even dried for future use. Pumpkin must be canned in a pressure canner as cubes, not mashed or pureed. A five-pound pumpkin will yield about 4 1/2 cups of cooked, mashed pumpkin. About 2 cups of cooked pumpkin is required for a 9-inch pie.

Roasting pumpkin seeds
Rinse two cups pumpkin seeds until pulp and strings are detached. Boil seeds for ten minutes in six cups of water with 1 teaspoon of salt added. Drain and dry seeds on paper towels. In a bowl add 1 teaspoon Worcestershire sauce, 3 tablespoons melted butter or margarine. Add pumpkin seeds and stir well. Spread on baking sheet. Bake at 325 degrees F for about 30 minutes or until seeds are light brown. Seeds should be crisp when fully roasted.

Preparing cooked pumpkin
An easy way to prepare pumpkin for recipes calling for cooked pumpkin is to cut the pumpkin in half, scoop out the seeds and stringy pulp, and cook the halves face down in a conventional or microwave oven until pulp is tender (about an hour in a 350 degree F oven, or 6-7 minutes per pound in the microwave). After the cooked pulp is scooped out of the shell it may be mashed or put through a mill or strainer. It is then ready to be used in a recipe, or frozen for later use.

I now need to get back to my pie before my kids catch me and want to share!  I can always go back on the diet next week...

Monday, October 7, 2013

CSU Announces “Best Of” Winners from 2013 Annual Flower Trials

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

The votes are in and ballots counted after two evaluations.  One was held on July 29 and another on September 6, 2013 to decide the 2013 “Best Of’s”.

The 2013 “Best of Show” annual is Lantana ‘Lucky Sunrise Rose’ from Ball Flora Plant.  The brightly colored colored flowers were prolific against the dark green foliage making the flowers really “pop”.  They had consistent display of blooms throughout the entire growing season.  These more heat and drought tolerant plants need to be grown and planted more throughout Colorado.
Lantana 'Lucky Sunrise Rose'
Lantana 'Lucky Sunrise Rose'

Petunia ‘Cascadias Indian Summer’ from Danziger took the “Best New Variety” award.  This petunia is a real color breakthrough since it has unique shades of pink, yellow and orange.  The flower color is reminiscent of a water color painting of a southwest sunset.  The flowers are abundant throughout the season with a nice cascading growth habit.  This variety will be a must for Colorado landscapes in 2014. 
Petunia 'Cascadias Indian Summer'
Petunia 'Cascadias Indian Summer' in a container
In the “Novelty” category Pennisetum ‘Graceful Grasses Fireworks’ from Proven Winners took top honors.  This ornamental annual grass is unique due to the colorful foliage.  The narrow leaf blades are an attractive combination of green mixed with white and pink streaks running the length of the grass blade.  Foliage color varies throughout the season depending on light and temperature.  It is an overall attractive annual grass when in bloom or not. 
Pennisetum 'Graceful Grasses Fireworks'

Foliage of Pennisetum 'Graceful Grasses Fireworks'
Twenty-three additional genera had a “Best Of” chosen in their category.  Descriptions and photos are on our website at

A few of the genera include:

Best Coleus – ‘Kong Jr. Rose’ from Ball Ingenuity
This coleus had very attractive green leaves with rose markings that make a high color contrast.  Plants had great vigor and a uniform growth habit.  Possibly another shade alternative for seed impatiens infected with downy mildew.
Coleus 'Kong Jr. Rose'
Best Geranium (zonal) – ‘Dynamo Red’ from Ball Flora Plant
The solid green foliage created a dramatic backdrop for the rich red colored flowers resulting in a spectacular overall appearance.  Growth habit and flowering was very consistent throughout the growing season.
Geranium 'Dynamo Red' flower

Geranium 'Dynamo Red'
Best Mandevilla – ‘Sun Parasol® Giant Pink’ from Suntory
This fairly new entry into our annual trials caught people’s attention while still growing in the greenhouse in early spring all the way to the fall.  The consistent flowering throughout the season and trailing growth would make it an excellent choice for a trellis in a container or let it trail out of the container.  Plant loves the heat and gives that tropical look to the garden.
Mandevilla 'Sun Parasol Giant Pink'
Best Petunia (veg spreading) – ‘Surfina Purple Majesty’ from Suntory

The constant bloom throughout the season made this plant go to the top of its class.  The fading flowers created a pleasing bicolor contrast.
Spreading petunia 'Surfina Purple Majesty'
Flowers of spreading petunia 'Surfina Purple Majesty'
Best Sun New Guinea Impatiens – ‘Sun Patiens Compact Electric Orange’ from Sakata Seed
The orange flowers are so abundant that foliage is hardly seen.  The orange color appears to glow and does not fade.  Plant growth habit is very uniform.
New Guinea impatiens 'Sun Patiens Compact Electric Orange'
New Guinea impatiens 'Sun Patiens Compact Electric Orange'

For a more complete report and photos of all the winners go to

Friday, October 4, 2013

Cover Crops: They look cool and serve a purpose

Posted by: Alison O’Connor, horticulture agent, Larimer County Extension

As the weather cools, my thoughts turn to comfort food, good books, warm fires…and cover crops?  Ok, I never really gave planting a cover crop in my garden a second thought, until my poor veggies were smushed to smithereens in August from hail.  With my garden sitting fallow and sad…and the fact that I’ve never tilled, amended or fertilized my garden…I decided to plant a cover crop. 

What’s the purpose you ask?  Well, the Colorado Master Gardener site has an excellent publication that will answer your questions.  But essentially, I did it out of sheer curiosity and to do a good thing for my soil and plants next year (free nitrogen from the legumes!).  Lesson learned: planting a cover crop is really easy.  Easier than growing tomatoes, that's for sure.

So here’s what I did…enjoy the photographs!

Step 1. Buy your seed.  I happened to get mine from Johnny's,
but you can buy from your favorite seed company.  I bought
a mix of clover, annual and winter ryegrass, peas, oats and vetch. I bought
about 2.5 pounds of total seed for my 400 square foot garden.
Step 2. Upon opening your seed packets, promptly spill them
on the garage floor.  ARRGHHH! 
(You're impressed that I got a photo of this, aren't you?)
Step 3. Mix all the cover crop seed together in a clean container. 
This is only necessary if you bought your seed separately and not as a "cover crop mix."
Step 4. Make sure your beagle is handy to carefully watch and keep you on track. 
(That's Willow. She's my gardening buddy and has an affinity for tomatoes. )
Step 5. I had straw on my garden to help combat weeds,
so I worked in sections to rake it back.  You'll want to make sure you don't
walk too much on the garden during the seeding process, so divide it up if possible.
Step 6. Using my favorite garden tool (I call it the "scuffle hoe"),
I roughed up the soil surface.  This is also an excellent workout. 
It's whole body--abs, arms, back and legs!  Forget the P90X...just try gardening.
You don't have to scuff much...just enough to loosen the soil.
Step 7. Spread your seed!  Toss the seed in an even coat across
the soil surface.  It's not a science--just make sure you have
enough seed for the entire garden area.
Step 8. Using a steel-tine rake, gently spread the seed evenly across
the soil surface.  This also helps ensure soil-seed contact which will help
with germination. 
[The beagle who was watching is now being watched.]
Hazel (the one standing) was a puppy mill dog and tries to "mother" Willow. 
She does this all the time to protect her.  From what you ask? 
Well, we have really friendly rabbits and lots of sparrows.  It's a jungle out there!
Step 9. Back to the cover crop!
I then re-spread my straw over the top of the seed to help with moisture retention.
If you don't have straw, leaves or grass clippings, Step 8 will be even more
important to ensure good soil-seed contact.

Step 10. Water! I watered my cover crop with a "back and forth"
sprinkler for about a week for 10-12 minutes a day.  Just enough
to keep the seed moist, but not wet.  My drip irrigation wouldn't have
worked, since you need even moisture distribution.
Step 11. Success!  Nine days later, the cover crop has germinated
and is starting to fill in.  I'll leave it until next spring when I'll till it into
the soil as a green manure.
Wait 'til next year, Willow!  We'll have the best tomatoes ever!