Sunday, August 21, 2016

The Annual Weeds of Summer

Posted by: Alison O'Connor, Larimer County Extension

Though we're approaching the end of the gardening season (I know...I don't want to think about it either!), most of us are still battling the sea of weeds on our gardens. As I was walking Maple the other day, I took photos of a few persistent and common annual weeds that we see in our gardens, lawns and landscapes.

It's important to note these are annual weeds and germinate in spring and complete their lifecycle in one growing season (just like petunias or geraniums). Most summer annual weeds will germinate after soil temperatures warm to above 60 degrees. This year, we had a slow start to spring...and our soils stayed cool, so we didn't see weed growth as early as normal. But once temperatures heated up--BAM! Weeds. Everywhere.

There's a few approaches to weed control. One is to pull the weeds. Persistent and regular pulling will prevent the weeds from going to flower and seed (very important) and help keep the weed seed bank at bay. I'm sure most gardeners do their share of pulling weeds throughout the year. Another control option is to use an organic mulch (wood chips, grass clippings, leaves). Granted, this isn't possible in all areas of the landscape, but a thick layer of mulch in planting beds and vegetable gardens does wonders to prevent weed growth. Most weed seeds need light and exposed soil to germinate. Take away these two things and you'll have fewer weeds.

Using chemical options is also an option. For post-emergence weeds (those that have germinated), there are only a few options in our landscape areas (far more in lawns). These options include glyphosate and some organic products (like acetic acid (vingear) and oils). These tend to be non-selective products. Glyphosate is absorbed via the foliage, which does kill the root of the plant. Acetic acid and oils are burn-down products, which means that the foliage dies back. It also means that repeat applications may be necessary.

There are pre-emergence herbicides that you can use in the early spring, such as treflan (sold in Preen), isoxaben (sold in Ferti-Lome Broadleaf Weed Control with Gallery) and corn gluten meal. All  of these products can work, but may need to be reapplied. Always follow the label on the product you plan to use. And a note about corn gluten meal: While it has VERY LIMITED, SHORT-TERM weed control capabilities, it has proven, by research, to be a much better fertilizer than herbicide.

So let's look at the Weeds of Summer:

Crabgrass (Digitaria sanguinalis)

Large crabgrass
Good ol' crabgrass. Here it is in all its glory. Other plants get called "crabgrass" but this is the one and only. Crabgrass won't germinate until soil temps are above 60 degrees. In a lawn, the best defense against crabgrass is to keep the lawn healthy (well-watered and fertilized). In this situation, crabgrass found a great place to grow in rock mulch along the sidewalk. It's nice and hot and ideal for growth. Crabgrass has a very distinct seedhead, which is finger-like (hence the genus Digitaria).
Finger-like seedhead of crabgrass.
Prostrate spurge (Euphorbia maculata)
Prostrate spurge
Prostrate spurge has had a very good summer. It's everywhere. This mat-forming weed can reach impressive size by late summer if left uncontrolled. Fortunately, it's easy to pull. The one caution is that like other plants in the Euphorbia genus, the plant has a milky sap, which oozes when stems are broken. The sap can be caustic and an irritant. If you have sensitive skin, wear gloves and be sure to wash your hands following weeding.
White latex sap of prostrate spurge
Close up of prostrate can make out the teeny-tiny flowers, which all form viable seeds!
Purslane (Portulaca oleracea)

Purslane is a pretty mild's edible, after all! And I haven't seen as much purslane this summer, but I might not be looking that hard. Purslane can be confused with spurge, but there is no milky sap...and this weed has thick, red stems. It's a succulent, so it can tolerate dry conditions with occasional moisture. I see it most often in my vegetable garden, near the drip irrigation lines.
A very mature purslane plant.
Puncturevine (Goatheads) (Tribulus terrestris)

Ugh! By far the WORST of the summer annuals. This beastly plant is just nasty and mean. If you aren't familiar with puncturevine, consider yourself lucky. The seedheads can pop bicycle tires, injure dogs' paws and wreck havoc on bare feet. This is one weed that you should 100% remove and prevent from growing. It can reach widths of feet if left to grow undisturbed...yikes!

One (yes one!) puncturevine plant.
That same plant pulled from the ground.
Puncturevine has yellow flowers and the seedheads start off green, hardening into sharp, pointed, vicious seedheads by late summer.
Yellow flowers of puncturevine.
Nasty, mean and cruel seedheads. The plant is called "goathead" because the seedhead resembles a goat's head.
And poor Maple, my faithful beagle pal and gardening buddy, was afflicted by a stray puncturevine seed on our walk. Poor thing hobbled for a few feet before sitting down, lifting her paw in the air. It's because of this that I just despise this weed. So pull it already!
Maple's paw with puncturevine seed stuck in the pad.
There are many other weeds of summer that I didn't mention, like kochia, but we can cover those another time. Happy late summer weeding, folks!

Thursday, August 11, 2016

The Power of Plants!!

Posted by: Deryn Davidson, Boulder County Extension 

The power of plants. We eat leafy greens packed with vitamins and minerals to fuel a healthy body. We use their fiber for clothing and building materials. We use the shade of trees to cool ourselves and our homes and we search seas of parking lots looking for that sliver of shade to park our cars under. Plants prevent erosion, they clean stormwater, this list goes on and on! Given some sunshine, water and occasional feeding (if they're lucky) plants just do their thing and we reap the benefits.

So where is all of this musing about the awesomeness of plants coming from? Well, at first I was going to write this blog about all of the lovely plantings that towns along the Front Range do to pretty up their streets and make them more appealing. Fort Collins is becoming known for their lovely Old Town alleyways (when I was growing up, they were not so lovely...), Denver and Boulder put time and energy into making their public spaces planty. And Niwot, CO does a great job with this. Petunias spill out of fun and unusual containers that line the streets and a dedicated crew of folks drag a water tank around and water them regularly throughout the hot summer months.

Niwot, CO 

So, as I was thinking about all of these lovely summertime streetscapes, I started thinking about WHY towns and cities do this. It's because of the power of plants!! Plants (nature) make us feel good. Plants make a space feel more comfortable and calming and happy. Study after study shows that time spent in nature has a profoundly positive effect on us. A University of Michigan study showed that students who took a walk through the campus arboretum performed better on a short-term memory test than those who walked down a city street (I'll go ahead and assume it was an un-planty city street). Spending a brief amount of time in a natural setting can restore our mental energy know that metal foggy feeling? Research has shown that just looking at a picture of a nature can help clear that fog (looking at picture of cities did not have that effect). And we all know that gardening is a stress reliever!! 

When we go outside (or even look out a window at a bit of nature) our cortisol levels drop (the hormone associated with stress), our blood pressure drops and it can help us improve our concentration skills. Nature can even help our bodies heal. In a landmark study done in the 1980s, Roger Ulrich found that patients recovering from gallbladder surgery who had a room with a view to a small stand of deciduous trees had a shorter postoperative hospital stay, took less pain medication and had fewer post-op complication than another group whose view was to a brown brick wall. The power of plants. 

Niwot, CO
So thank you to the towns and cities who include summertime streetscaping into their budgets. Believe it or not, by bringing that little bit of nature to our daily lives as we get to work and run our errands, they are helping us all feel more calm and brightening our days! 

Thursday, August 4, 2016

Sample some Love Apples

Posted by Carol O'Meara, Boulder County Extension

  My neighbors might be catching on that living near a gardener is a good thing.  Sure, there are a few quirks to put up with, like earsplitting shrieks when squirrel damage is noticed on pumpkins or alarming noises as I rise up from crouching to weed.  But these small eccentricities fade once harvest sets in, because they know I’ll start sharing the bounty with those who wander by.
As they stroll past with their pets, I call them into the garden with friendly invitations like “you, with the Shih-Tzu, want some beans?” or “Hey, parrot-walking man!  I’ve got plenty of kale to share!”  I've contemplated tying bags of produce to cats' collars so they take them home with them, but those rascals are harder to catch than the dogs are. 

Most neighbors have gotten produce from me before and accept it with smiles, even though they know I’ll toss in a zucchini for good measure.  Right now the beans are coming in like there’s no tomorrow, but fast on their heels is a bumper crop of tomatoes.   And once they start, everyone in the neighborhood gets love apples. 

Big, little, red, yellow, purple, and orange – we’re entering tomato season with its wealth of rainbow colors.  Cherry tomatoes like Green Doctors, Isis, Sungold, and Jasper may be little in size but big in flavor.  Each of these tasty morsels is sweet enough to woo new devotees to growing them.  Matt’s Wild Cherry, a currant type, is a tiny, prolific tomato about the size of a pea. 

Salad tomatoes that shake your kitchen up with new flavors and colors are Green Zebra, Lemon Boy, or Japanese Black trifele.  Each has bold enough flavor to stand on their own, but combined in a colorful Caprese salad, they shine. 
I’m experimenting with paste tomatoes this year, because I sauce a lot of them and an Italian-American friend told me, proudly, that for real Italian sauces, you need San Marzano tomatoes.  But I love the flavor of Amish Paste and you can’t beat Roma for performance. 

Although I’m a tomato geek and love them big and small, I will admit that when the beefsteaks come in, it’s my favorite part of the summer.  Huge, brightly colored, and heavy with the promise of outstanding taste, the beefsteaks are the late season love apples that finish summer with a bang.
Of the big ones, it’s hard to beat Brandywine, but Pineapple, Amana Orange, Black Krim, Cherokee Purple, and Paul Robeson give it a run for the money.  Sweet and balanced with acid, Pineapple is a large yellow tomato streaked with red. 

Gardeners, if you’ve wondered what those tempting tomatoes taste like, but don’t have room to grow them all, head out to the Taste of Tomato in Boulder.  Sponsored by Harlequin’s Gardens and Colorado State University Extension in Boulder County, the Taste of Tomato is an opportunity to sample the love apple in its many forms - stripes, color, shape, and size.
Scheduled for Saturday, August 27, 10 am to 1 p.m. at Gateway Park 4800 N. 28th St. in Boulder, the Taste of Tomato is where gardeners can bring their tomatoes for others to try and sample the products others are growing.  Each year, tomato enthusiasts gather to taste nearly 100 varieties and vote on the tastiest of the lot. 

Entry is free if you bring three or more medium to large tomatoes or 10 cherry tomatoes of one kind, with the variety name on a card, to donate to the tasting. All entries must be home-grown.  If you have no tomatoes to bring, there will be a $5 entrance fee. 

Thursday, July 28, 2016

What is a weed?

By Irene Shonle, CSU Extension in Gilpin County

What is a weed? I think most of us have seen that cute little quote “A weed is just a plant whose virtues haven’t been discovered yet.”  This quote aggravates me to no end because it implies that any plant that has a known virtue cannot be a weed. And that all plants in all ecosystems are fine; we just have to look for their virtues.

Most savvy gardeners and people who manage open space, rangelands, or agricultural lands know that this is not the case.  There are definite bad actors that aggressively spread and cause harm to ecosystems and agricultural settings.  Plants that have the previous two characteristics AND are alien plants meet the criteria for a state-listed noxious weed, and thus become illegal to grow or sell in Colorado.  For more information on these weeds, please go to the Department of Agriculture website:
Leafy spurge - a list B noxious weed in Colorado

Not all alien plants are noxious weeds or even weeds at all.  Some can be fairly aggressive (field penny cress, small yellow alyssum, dandelion) but still not rise to the level of a noxious weed.  Some are merely nuisances in our landscapes (Shephard’s purse, prostrate knotweed).   Many are nicely behaved garden plants (Delphiniums, Iceland poppy, tulips).
Prostrate knotweed, an alien nuisance weed

But in our quest for novelty in our gardens, some of the alien ornamental plants we have brought in have turned out to be noxious weeds – even though they have the virtue of being pretty.  And they quickly spread outside the bounds of a garden, finding niches in soil disturbed by construction, travel, recreation, etc. When they grow unchecked, they can displace native plants, reduce biological diversity and alter ecosystem processes. These impacts affect birds, pollinators and mammal populations which depend upon native plants for food, shelter, and protection from predators.

The worst ornamental invaders across all of Colorado include: purple loosestrife, ox-eye daisy, Russian olive, tamarisk, Bouncing Bet, Dame’s rocket, Dalmatian toadflax, yellow toadflax (aka butter and eggs), Mediterranean sage, common tansy, bouncing bet, scentless chamomile, and myrtle spurge. 
Oxeye daisy - a list B noxious weed

What makes the weeds so invasive?
There are five key traits that allow them to dominate natural plant communities: they have abundant fruit and seeds, effective dispersal mechanisms (either by seeds or strong, creeping roots), they are rapidly and easily established, they grow quickly, and they have aggressive, competitive behavior. Even if they are well-behaved in their country of origin, they arrive in this country without any of the mechanisms that keep plants in check, such as insects, disease, and competition.

Is it possible to plant invasive ornamentals responsibly?
Not really. As soon as the "responsible" gardener who knows about the plants invasive characteristics is out of the picture (moves away, gives away cuttings or transplants, goes on vacation), the plant has the chance of becoming a problem. Often seeds can be eaten by birds, carried by cars, dogs, or the wind and then get established in new locations, unbeknownst to the gardener. Gardeners, no matter how diligent, cannot control for natural processes, most of which rule the world of plant invasions.

Dame's rocket - a list B noxious weed, often found for sale in seed catalogs as an "old fashioned favorite."
What can you do to help?
Become familiar with invasive species and report their presence on public lands to the agency in charge.

Choose native (natives (they will never become noxious weeds since they are not alien) or non-invasive plants for your garden, and remove any invasive ornamentals in your garden. It is usually possible to find visually similar plants to use in place of invasives.   The Garden Smart guide was specifically written to help with this: Both the Native Plant Master Program ( and the Colorado Native Plant Society ( are wonderful resources for people wanting to use more natives in their landscaping.

Ask your local greenhouse and/or nursery to stock more natives. Report any noxious ornamentals to the Department of Agriculture (it is illegal to sell ornamental noxious weeds in Colorado – even if you get seeds by mail order.)  If you do see an invasive ornamental in a seed catalog/website, you can politely and pleasantly inform the company that they need to add “not for sale in CO” to the plant.

Monday, July 25, 2016

When Plants Go (somewhat) Rogue

Posted by: Alison O'Connor, Larimer County Extension

I really enjoy weeding my landscape. Call me crazy, but I enjoy plugging my ears with my iPod, making things tidy and dumping five-gallon buckets of weeds in the trash. It's a real sense of accomplishment. I also enjoy seeing what's new in the garden...did my newly planted perennials survive? Do the shrubs need water? And seeing what's gone rogue.

Uh oh. Plants gone rogue. The potential to be invasive. Plants you want to avoid with a ten foot pole (mint, anyone?). But is "going rogue" a bad thing? In some cases, no....I actually enjoy plants that gently go rogue. Those that randomly pop up and say "Hello! Here I am! Aren't I cute?!" And those that are easily to pull out and remove.

An example of a plant that's gone rogue and is NOT easy to mitigate is Russian sage. Yet I have it in my landscape. CO-Hort blogger Eric discussed this topic a couple years ago (and offers great suggestions to alternatives). But as big of a pain as this plant is, it does have a place...and in my yard, it is a border between my landscape and our neighbor's gravel driveway. It adds some nice separation. It's also a honey bee magnet. But sadly, Russian sage doesn't care about property lines, so I'm constantly pulling it from their gravel. Ugh. Russian sage--a bad rogue plant.
Russian sage growing in my neighbor's gravel pad. You can also see where I whacked it back to stay on our side of the property.
But some examples of gentle roguers (a new word?) include:

Petunia! Maybe this is common for you, but I've never had a petunia reseed. This one took up residence in my flagstone path, which is a great spot. What I'm trying to remember is if the petunia hanging basket I had last year was white? This petunia is so cute!
White petunia that found a home in the flagstone path.
Portulaca! Another annual, and one that commonly reseeds. I planted a few plugs a number of years ago and every year since, the portulaca fills in gaps in the flagstone and nearby beds. Fine by me! It's easy to pull and has great flowers that only are open during the day.
Portulaca that reseeds every year in the flagstone. The only problem is it's hard to distinguish from purslane (they are in the same genus).
Lamb's ear! I feel this may be controversial for some, since lamb's ear is a love it-hate it plant. Personally, I love lamb's ear, and while it's in the mint family and can be invasive, I find it easy to control by ripping it back whenever necessary. But what I find absolutely adorable about this lamb's ear is that this one is in my vegetable garden, a good 20+ feet from where the lamb's ear is planted. I can't bear to remove it, so I'll leave it for awhile and admire its perniciousness.
Lamb's ear roguing it in the veggie garden. So cute! And my garlic (on right) is nearly ready for harvest.
Angelina sedum! I have blogged about how much I love this sedum in past posts, so I won't belabor the point, but this sedum is lime green in summer and copper in fall. And it creeps and fills in. I started with a very small 4" perennial and it's grown to fill in a pretty big spot. I've also found it near my shed, rooted in a path and happily growing wherever it sees fit. Don't like where it's moving? Pull it and replant the roguers.

Maple was so excited to be in this photo with the Angelina sedum.
Coneflower! I feel like this one blindsided me. I guess I should have known, seeing as how coneflower is a native, but wow. Talk about prolific. I'm going to label this one a "medium roguer" since it's not as easy to relocate or remove. I originally planted coneflower in a sunny spot near a path and some other perennials. They quickly grew to be five feet tall and reseeded everywhere. In the path, across the yard and a few other spots. But can you really dislike coneflower? It's sturdy, a great bloomer and a friend to bees. So I deal with it.
The original coneflowers.

This coneflower was not planted, but found a home by the lavender. I like it! 
Sunflowers! And other bird seed! The birds in my yard go crazy for black oilers. So do my beagles for that matter. And if you feed the birds, you'll get some of the seed germinating below or nearby the feeder. It's inevitable. I have sunflowers. You might get corn. Or millet. All of these are annuals that may or may not be your cup of tea. I remove a lot of the sunflowers, but also let a few grow because they are nice.
Why not let these grow? The mulch path is for the dogs, and they provide some obstacles to run around.
Another that just came to mind is columbine...but mine all are tired and sickly-looking, so I'll spare you a photo. So tell me...what in your garden is a gentle roguer? Or even an aggressive roguer that you happen to love? I'm all (lamb's) ears!

Thursday, July 21, 2016

A Lost Hope?

Posted by: Curtis Utley, Jefferson County Plant Diagnostic Clinic

On a recent tree evaluation visit I discovered more fallout from the historic polar vortex freeze event in November 2014. Many of my contemporaries said we would continue to see more damage in otherwise apparently unaffected species and sure enough, now two seasons later, green ash trees are pushing off large sections of damaged bark. 
Bark loss from Callery pear observed in 2015
This damage and the resulting recovery is similar to what we are seeing on ornamental pears but the symptoms have been delayed do to the difference in bark thickness of green ash. The South or Southwest facing sides of green ash trunks and branches had not gone dormant when the freeze event occurred and these portions of the vascular cambium were killed. 
Green ash with loose bark on the south side of the tree.
White ash trees were not affected but green ash trees growing in warm locations, in this particular case street trees growing on a south facing slope show considerable damage. 
Thinning canopy and dieback on ash from the November 2014 polar vortex freeze event.
The marginal cambium that did not freeze is now trying to grow over the damaged section of trunk wood and is pushing the dead bark off in its attempt to close the wound. Another concerning symptom that is explained by this freeze damage is the thinning canopy and decreasing growth increments in affected trees. 
Ash tree attempting to close wounds from freeze injury.
We have had two cool wet springs that should have resulted in fantastic growth in green ash and to see the opposite has had me concerned. The elephant in the room anytime we discuss symptomatic  ash trees is of course the possibility of finding emerald ash borer, especially in trees that are losing chunks of bark, have thinning canopies, and dying crowns. The difference between freeze damage induced bark loss and bark loss as the result of the exotic emerald ash borer is the absence of a zig-zag or meandering pattern visible both on the loose pieces of bark and exposed wood caused by EAB larval feeding. Learn more about emerald ash borer at:
Emerald ash borer feeding (photo courtesy of University of Minnesota Extension)

Monday, July 18, 2016

A Reason For Optimism After Hail

Posted by: Linda Langelo, CSU Horticulture Program Associate, Golden Plains Area
This squash plant emerged after the hailstorm.

We stood and watched two-and-a-half-inch hail devastate the landscape around us within minutes.  All efforts of the growing season gone.  Yet, in the aftermath, there is reason for optimism.  Most vegetables are resilient.  Take the local community garden for example, even the broad-leaved plants in our landscapes most affected can be resilient.  The silver lining is if 50 percent or more of the leaves remaining on the broad-leaved plants, they have the opportunity to produce food for the plant to survive.  Broad-leaved plants such as daylilies can survive.  In fact, at various public places I’ve worked, we intentionally cut the daylilies back after they bloomed then watered and fertilized them.  They produce a second bloom by late August and September.  I don’t recommend this every season.   This is forcing a plant to bloom out of season and not the best cultural practice. 
The native coneflower came through the storm like a champ!
One other optimistic note after a severe storm, is if you have lots of native plants in your garden, it seems that they did better than any of the non-native herbaceous perennials, biennials and annuals.   Amazingly the native plants of the Plant Select™ Program fared the best in the Sedgwick County Courthouse Colorado, landscape. These include:

  • Diascia integerrima ‘P009S’  Coral Canyon Twinspur
  • Penstemon x mexicali 'P008S', Red Rocks Penstemon
  • Clematis scottii, Scotts Sugarbowls that faced the wind and hail head on came through with only a couple of seed heads pruned off the plant.
  • Fallugia paradoxa, Apache Plume
  • Ceroearpus intricatus, Littleleaf Mountain Mahogany
  • Ratibida columnifera, Prairie Coneflower
  • Nepeta “Pskite” PP 18,904 made it through with some tattered leaves as well.
  • Echinacea purpurea, Purple Coneflower also made it through with just a few leaves tattered. 

There are a lot of other natives that would do well, these are just those we can testify to in the hail aftermath.   Natives do not need any fertilization.
Apache plume is tough as nails....what hail?!
There are many methods to heal what is wounded by storm damage; I would suggest the following:

Herbaceous perennials that had prolific flower stalks: prune those back to good growth if there are any good leaves left on the stalks. If there are basal leaves or a rosette at the base of the plant, just prune the stalks to just above the basal leaves or rosette. If the rosette or basal leaves are damaged give a light fertilization.  This will give plant further energy for growing new leaves.   
Master Gardener Joe Stan examining garlic following the hailstorm.
Annuals: you may just have to call it quits, especially if nothing grows back in a week.  Examine them to see if there is anything left to grow and fertilize.  Sometimes with petunias, snapdragons and violas, you may find that they get severely damaged, yet there is still a mass of leaves to grow again and flower.  With the petunias, pruning will be helpful.  Other annuals such as zinnias can be pruned.  There is still enough time in the season.  I am recommending to lightly fertilize annuals once a week. 

On that note, too much nitrogen in the soil increases the mineral salt content.  Excessive salt can dehydrate the plant.  The symptoms would be burning or yellowing of the leaf margins.  The best thing to do is to water and wash the excess nitrogen in the soil.  Nitrogen moves quickly through the soil.  Excess nitrogen will slow root development. 

Our garden of greens following the hail.
Biennials: enjoy what is left because if they are flowering this will be the last year you will see them.  You will need to start over next season.

Shrubs: prune out what is damaged and during the very hot days of summer give them a deep root watering.  The timing for pruning won’t be perfect for some shrubs and you may lose next year’s flower buds. 

Trees: prune out what is damaged and during hot dry periods such as an extended drought give them an extra deep root watering, but do not fertilize them.  It makes sense to remove the branches that are hanging first and make nice clean cuts.  Then examine the tree for any other severe hail damage and prune properly.  Even if your tree looks very thin, give the tree time, it will grow new leaves. 

Fruit trees: remove the damaged fruit.  The damaged fruit will attract pests.  Again, look to see if there are any hanging branches and other severely damaged hail wounds on limbs that might not heal quickly.  Open wounds are an easy entry for pests and diseases for trees and shrubs. 

In answer to the question, “a reason for optimism after hail?” We have witnessed the wounds of severe hail, now we can apply optimism towards what remains on the landscape and heal.  It is hard work, and that, in part, is what gardeners do!