CO-Horts Blog

Thursday, September 27, 2018

Have You Seen These Non-Native Insects?

Posted by: Jessica Wong, Broomfield County Extension

By now you are probably aware of emerald ash borer and Japanese beetle, two invasive insects that threaten Colorado landscapes. However, these are not the only non-native insects that you should be on the lookout for. 

The Asian mud dauber (Sceliphron curvatum) is a wasp originally from areas in India, Pakistan, Nepal, Tajikistan, and Kazakhstan. It is not a garden or agricultural pest, but all non-native species have the potential to disturb an ecosystem. The distribution of Asian mud dauber in North America currently includes Quebec, Ontario, and now Colorado. Within Colorado sightings have been reported in El Paso, Douglas, Denver, Larimer, Mesa, and Boulder Counties. It is likely that these wasps are in more than just these six counties, which is why we need your help finding them.

A female Asian mud dauber. Photo credit: Whitney Cranshaw
Female Asian mud daubers build nests out of mud along elongate crevices. In the Front Range they have been seen using the edge of windows as nesting sites. They hunt for spiders, which are put into the nests to provision a single larva. Asian mud dauber can be mistake for the closely related black and yellow mud dauber, an insect that is established and found throughout Colorado.    

Asian mud dauber nests in a window frame. Photo credit: Betty Cahill
The next non-native insect you should watch out for is a leafminer of Siberian elms originating from China. The insect is a small moth currently known only by its scientific name, Stigmella multispicata. It has become widespread across the eastern part of North America since it was first found in 2010. It is possible that Stigmella multispicata is already in Colorado.

Leafmines made by Stigmella multispicata larvae. Photo credit: Daniel Gilrein
The larvae of this moth are tiny green caterpillars. These caterpillars create snake-shaped leafmines that get progressively wider as they grow. Once the larvae are fully developed, they exit the leafmine, spin a line of silk and drop to the ground where they will pupate. The leafmine pattern, the size and color of these caterpillars, and their use of silk are characteristics that distinguish this leafminer from the other elm leafmining insects established in Colorado, such as the European elm flea weevil or the elm leafminer.

Stigmella multispicata larvae. Photo credit: Daniel Gilrein
If you see any signs of Asian mud dauber or Stigmella multispicata, take pictures and send them to CSU entomology professor, Whitney Cranshaw, at, and don’t forget to tell him what county you saw the insects. 

Monday, September 17, 2018

Bringing Herbs Indoors for Fall and Winter Use

Posted by:  Mark J. Platten, Teller County Extension Director

Many of us gardeners also love to cook, and all summer we’ve enjoyed cutting fresh herbs to use in our recipes. With summer over and the first frost imminent in the high country, how can we continue to enjoy them? One solution is to buy herbs at the grocery store, although that can be expensive and they may not be fresh. A better solution is to bring our herbs indoors so you can enjoy using them year-round. 
Herb Garden in a Raised Bed
 From every walk of life and corner of the globe, humans and herbs have shared history. Some of the earliest herb gardens have served us with medicinal, religious, and culinary staples; they’ve perfumed bodies, disinfected houses, and repelled insects. Herbs are defined as any plant, or plant parts, valued for “medicinal, savory, or aromatic qualities.” By this definition, herbs can be trees, shrubs, herbaceous perennials, annuals, vines or lower plants.

The best time to bring your herbs inside is before the first frost, which is the middle of September, or earlier, in many of our mountain communities. Perennial herbs such as parsley, sage, tarragon, oregano, mints, lavender, thyme, and chives can be divided in the fall. Use a shovel to cut the plant into sections taking as much root as possible. When dividing, place some back in the garden and pot one or two of the healthiest for your indoor herb garden. Pot the herbs in fresh, commercial potting soil and water them well.

Chocolate Mint
If your herbs are already in pots, check to see if they need re-potting. Fresh soil and enough room for the roots will help them make the transition indoors. Before bringing plants indoors, check each plant for pests by in­specting the stems and leaves. It’s a good idea, once you have them in the house, to keep them away from other plants, just in case they have any insects or eggs you might have missed.

Coming indoors can be traumatic to your herbs. They’ve been used to direct sunlight, rain, wind, and tem­perature variations. Before permanently placing them in your home, first set the plants outdoors, out of direct sunlight, for a few days to get them used to indoor conditions. Then bring them in for a few hours to get them used to the indoors. If you have time, and they’re not in danger of frost, repeat this process for up to a week.

Herbs need at least six hours of direct sunlight each day. A sunny windowsill works great. Turn your herbs regularly so they’ll grow evenly. If you don’t have enough natural light, use an inexpensive fluorescent shop light with a cool fluorescent, or grow, bulb. Hang the light about six inches above the plants and give them several hours of light each day. This lighting method also works great if you’re starting herbs from seed.

You can add to your herb collection by taking cuttings and starting new plants. You can propagate lavender, comfrey, horehound, oregano, peppermint, tarragon, thyme, lemon balm, scented geraniums, sage and rosemary from cuttings. Healthy tip growth makes the best cuttings. When taking cuttings, snip off a 4-5 inch length of stem, remove all but the topmost leaves, and insert into a loose potting soil. Keep the cuttings moist until they become rooted, then transplant to larger containers. Fertilize sparingly and water regularly.
Indoor Herbs courtesy of Andrea Dunn
Herbs can be beautiful indoors and nothing can replace fresh herbs in your home cooking. Imagine an indoor garden of basil, thyme, parsley, sage, rosemary, and chives. So have some fun and save some money by bringing your herbs indoors this fall.

Sources include Colorado Master Gardener Garden Notes:; Penn State Extension: , and Teller County Master Gardener Katie Geist.

Thursday, September 13, 2018

Best plants to create habitat

One of the best reasons to grow native plants is that they do more to provide ecosystem services than non-native plants.  With pollinators and birds in decline, it’s a great way to help. While everyone remembers from basic science classes that plants are at the bottom of the food chain, it is important to realize that some plants pull more weight than others.   For starters, many non-native plants don’t support any insects at all. This is because about 90% of herbivorous insects are specialists to one degree or another.  The insects simply don’t recognize the alien plant as food.

Here is where a functional definition of a native plant can be useful. Entomologist Doug Tallamy (author of Bringing Nature Home) uses this one: is a plant or animal that has evolved in a particular place long enough to be able to establish the specialized relationships that are nature.   Alien plants just have not been around long enough to develop these relationships with the local fauna.
Further research by Tallamy’s lab bear this out; they have found that some oaks have up to 557 species of moths and butterflies, Prunus like wild cherry and plum can yield up to 456 species; and maples support up to 297 species. Introduced species such as Bradford pears have almost no species on them. When it takes over 6,000 caterpillars to raise one brood of chickadees, it is clear which species will help birds  and other insect-eaters the most.

Clearly, the moral of the story is that to support pollinators and birds, plant native plants.  But even within native plants, some species are more helpful than others.  Tallamy’s research has found that just five percent of the local plant genera produces about seventy five percent of the insect food that drives food webs. Including these powerhouse in your garden (even if you otherwise have lilacs and petunias) will do much to support bird species.  And the birds will keep the caterpillars from overrunning your plants. If you have breeding birds in your yard, you won’t see many caterpillars because the birds will have eaten them.

So, how to figure out which species are the powerhouses in our area? A really cool site where you can find native plants for your zip code – ranked by how many caterpillar and moth species they host- can be found at (based on collaborative work with Dr. Tallamy).
Typing in the zip code for Boulder as representative of the Front Range, I get results for both herbaceous plants and trees in order of how many insects they support.  Granted, this website is still in Beta format, and is not perfect, but it is nonetheless a terrific start.

So, the winners of the best habitat plants in the herbaceous category for butterflies and moths for the Front Range are….. drum roll….

Goldenrod (Solidago spp.)
Sunflower (Helianthus spp.)
Strawberry (Fragaria spp.)
Lupine (Lupinus spp.)
Sagebrush (Artemisia spp.)
Violets (Viola spp.)  (We do have native violets, although they are hard to find in nurseries).
Rabbitbrush (Chrysothamnus spp).
Goldenrod lights up the late summer garden and is fantastic for habitat

And in the woody category they are….

Willow (Salix spp.)
Poplars – aspen, cottonwoods (Populus spp).
Prunus (chokecherry, plum) (Prunus spp)
Oak (Quercus spp – esp. Quercus gambelli here)
Pines (Pinus spp)

Chokecherries have fragrant spring flowers and edible fall berries 

You may even have some of them in your yard now, but it couldn't hurt to plant more.

Monday, September 10, 2018

Plant Diseases Have Tartans, Too!

Posted by
Mary Small
State Colorado Master Gardener Coordinator
I went to the Longs Peak Scottish-Irish Festival in Esters Park this past weekend. So colorful! And so many tartan patterns identifying the different clans.
My mind wandered. Instead of thinking about my ancestry, it hit me that clan tartans are similar to some classifications in the plant disease world. Patterns of damage help us identify what “clan” a plant's problem belongs to.

For example, to the left is a picture of lupines. Can you see how some of the plants look  okay and others don’t? The pattern of damage is random – pointing us to the biotic clan. This means that the cause of the damage is probably a living one – like fungi, bacteria or viruses. I think it’s probably a fungal root rot and I would love to look at the roots more closely to help confirm that. But I don’t think digging up plants in this garden would be appreciated, since it’s a public one.

Apple scab on crabapple
Look at the crabapple leaves here on the right. A number of them have scattered spots. You can also see that some of the leaves in the background don’t have spots. The spotted pattern on the two main leaves is not identical, either. This problem is apple scab, which is a fungal disease. An interesting feature of these leaf spots is that they have “feathery”, not solid margins. Apple scab also belongs to the biotic clan.

Fireblight on crabapple
Can you see the random pattern of damage in the  crabapple to the left? Most of the leaves look normal, but there are some scattered twig tips with dead leaves. This is fire blight, which was a huge problem in 2019 largely due to the late spring/early summer rains that helped splash the bacteria around. The disease belongs to the biotic clan.

Leaf scorch on linden
What do you think about the pattern of damage on this linden (right)? All the leaves have the same damage – brown leaf edges and tips. The pattern is uniform on all of the leaves, which points to the abiotic (non-living) clan. The poor tree had two major strikes against it. It was growing in a non- irrigated area (I hesitate to even call it a “lawn”). On top of that, much of its already struggling root system was severed during driveway and street construction. No (or few) roots to absorb water and hydrate the canopy and you get the pictured leaf scorch.  

What happened to this oak (below)? All of the newer leaves (near the twig tip) look dark green and healthy. But all of the older ones are distorted, paler and have some cool-looking fringe at the tips.  The leaf damage was caused by herbicide injury. The older leaves were exposed to herbicide, but the newer ones were not. It’s another member of the abiotic clan.
Herbicide injury to oak
 Next time you’re out and about, see if you can identify which "clan" a plant problem belongs to. By the way, I belong to Clan Ross (tartan below).

The Ross tartan

Friday, September 7, 2018

Tree Seeds of Fall

Posted by: Alison O'Connor, Larimer County Extension

The end of August and early September can be pretty "blah" in the garden. While we're harvesting zucchini and tomatoes up the wazoo, the perennials and shrubs are looking tired. That is, until we start seeing some fall color.

But the tree seeds have been growing all year and will soon be fully mature. They are beautiful in their own right and some can be quite attractive and showy. Some seeds are persistent through winter, adding interest.

Here's a few of the common tree seeds you'll see around the landscape:


There are two groups of oaks--red and white. Red oaks include the red oak (Quercus rubra), pin oak (Q. palustris), and scarlet oak (rare in Colorado) (Q. coccinea). Red oaks have pointy leaves and the acorns are usually in pairs on the tree, taking two years to mature. The red oaks, in general, have a "classic" acorn. Red oaks are not always a great choice for Colorado landscapes, though some species, like Texas red, are more tolerant to high soil pH.
Pin oak leaves and acorns
The white oak group includes bur oak (Quercus macrocarpa), swamp white oak (Q. bicolor) and English oak (Q. robur). These species tend to have lobed leaves and are MUCH better choices for Colorado landscapes. They are more tolerant to high soil pH and do better with dry climates. The acorns of white oaks vary, but take one year to mature, and leaves from these trees can persist on the tree through winter. Fall color for white oaks is usually yellow and they don't get the brilliant reds and maroons of red oaks.
Bur oak and acorn. 
The bur oak acorn is very large (macrocarpa is Latin for "big fruit"). The cap of the acorn (scientifically called the involuchre) nearly covers the entire nut and is very hairy. As the acorns mature, the cap and seed will turn brown/tan.

English oak and acorn.
I adore English oak for many reasons, but I find the acorns to be particularly endearing. They are long and skinny with a small cap on top. The way I remember this tree are two-fold: 1) the leaves have "earlobes" at the base where the petiole (stem) attaches to the tree. I was taught to remember Prince Charles's earlobes; 2) the acorn, being long and skinny, reminds me of a tall Frenchman with a beret on his head. England, France....both located across the ocean. We don't have a French oak, so this is my association.

The acorns of bur oak (top left), English oak (bottom) and pin oak (right).

Buckeyes and horsechestnuts are great trees for Colorado. They have showy flowers in early spring and are tolerant to our soils. The Ohio buckeye (Aesculus glabra) is a fairly common species, though could be planted more. (And for the record...Go Bucks!)

Buckeye fruit has small spines. Towards the end of the fall, the capsule will break open and reveal the shiny brown nut inside--keep one in your pocket for good luck. Squirrels go crazy for these nuts and bury them all over. If you have a buckeye in your landscape, you'll likely get volunteer seedlings.
Ohio buckeye leaf and fruit (seed not mature).
Horsechestnuts are very similar, but the fruit capsule has more spines and there are multiple fruits in one capsule.


Catalpa (Catalpa speciosa) is one of the bigger trees in our landscapes. Mature catalpa can reach heights of 50 feet or more. They are very showy with their white orchid-like flowers in June. Catalpa are drought tolerant with huge leaves and cigar-shaped fruit. (Disclaimer: Growing up in Minnesota, our neighbors had a catalpa in their front yard and we would either pretend to "smoke" the fruit or use them as swords--neither practice is recommended.) Many find the leaves and fruit to be messy, but it's just something to consider before planting.

Catalpa leaves and seed pod. The leaves can be much larger than this, about the size of an adult's face. The seed pods will mature and turn brown, but often hang on the tree through late fall and into winter.

Oh maples (Acer sp.). I do love this tree, even though it's one that can get sickly in our dry, high pH soils. Seeing the sugar and red maples along the St. Croix River bluffs on the Minnesota/Wisconsin border in fall was always a highlight. Most everyone knows maples have samaras (you may call them "helicopter-whirly-gigs") but samaras come in all shapes and sizes. Tatarian maple (A. tataricum) has small cherry red samaras in clusters; Norway maples (A. platanoides) have wide samaras that you can perch on your nose.

Norway maple leaf and samara--the one you can perch on your nose.

Ash (Fraxinus sp.) are still a very common landscape plant in Colorado and this year, the green ash (F. pennsylvanica) had a seed heyday. This happens every few years--generally when we have good spring moisture. The ash seed is also called a samara, but it's a single fruit, unlike the maple. Many of the newer ash planted are male clones, which do not form seed.

Leaves and seeds from green ash.
Kentucky coffeetree

Another drought tolerant, tough-as-nails tree for the landscape, Kentucky coffeetree (Gymnocladus kentukea) has amazingly thick, chunky seed pods that are retained through the winter. The structure of the tree is very coarse, so the seed pods give it great winter interest. The green seed pods turn into a chocolate brown color. Squirrels also love the seeds. The leaves of this tree are considered as doubly compound, where the leaf branches twice. If you grow this tree, be patient. It doesn't look like much for a few years.
Kentucky coffeetree leaf (one leaf!) and seed pod.
There are many other trees in the landscape with interesting seeds, leaves and fruit. Take a closer look into the tree canopy and see what you find. If you ever need help identifying trees in your landscape, contact your local Extension office!
Maple the Beagle. Not the tree.