CO-Horts Blog

Tuesday, August 31, 2021

Cabbage Pests

By Yvette Henson, San Miguel Basin Extension

It’s been a tough gardening year.  My seedling plant starts got damping off disease, resulting in the loss of most of them.  I also had fungus gnats in the soil my seedlings were growing in.  The cabbage seedlings that survived damping off, got aphids.  Before planting them, I rinsed them in soapy water and removed aphids by rubbing them off.

Cabbages usually grow well in my 8,400’ mountain garden and although I’ve never had much of an issue with aphids, this year there have been quite a lot.  The hot weather may have contributed to this.  However, the cabbages have grown and so I haven’t done much about the aphids except try to keep the plants as stress free as possible by watering them well.  I give them a light fertilization with a complete fertilizer like 5-5-5 at planting and again every 4-5 weeks.  The cabbages I have harvested, I’ve soaked in salty water and the aphids came off in the water.   Purple cabbages are reportedly less susceptible to aphid infestation than green cabbages so if you have problems with aphids, try growing purple cabbages. 

Aphids and cast skins on cabbage leaf
(there's even a mummified aphid)

I’ve had infestations in the past of imported cabbage worms (Pieris rapae) on my cabbages and other brassicas, so I’ve kept an eye out for the adults-- white butterflies with purplish-black spots on their wings but haven’t seen any flying around.  I also haven’t seen any of the velvety green caterpillars with a single yellow stripe down their backs and two broken lines along their sides on my plants. They overwinter in an inch-long chrysalis that matches whatever it is on.  They can have several generations a year.
Imported cabbage worm

I cover most of my raised beds with row cover fabric held up and off the plants by hoops made from recycled irrigation tubing. This can deter the cabbage worm butterflies (and other pests) from being able to lay their eggs on the plants. 

Cabbages growing in a raised bed with row cover fabric on hoops

This year, although I haven’t seen any imported cabbage worms, the row covers didn’t prevent cabbage looper moths (Trichoplusia ni) from finding a way inside the cover to lay their eggs on my cabbage plants. Unlike the adult imported cabbage worm, which is a butterfly, the adult stage of the cabbage looper is a brown moth.  The caterpillars are green with several light lines down their back and sides.  The easiest way I’ve found to distinguish them from the imported cabbage worm is their distinctive “inch worm” crawl.   They overwinter in a white webbed cocoon on the undersides of the leaves, in plant debris or the soil.  They also can have several generations a year.
Cabbage Looper and feeding damage on Cabbage Leaf

Both Imported cabbage worms and cabbage loopers feed on the leaves.   They can do quite a lot of damage, making the plants unsightly and weakening them.  Cabbage worms sometimes bore into the heads.  It’s unappetizing when you boil a cabbage and several caterpillars float to the top of the hot water.  

 You can treat the plants when the caterpillars of both cabbage worms and cabbage loopers are young with Bt, Spinosad or some other insecticide (follow the label) but don’t use a broad spectrum pesticide that can harm beneficial insects. Because I usually have less than a dozen plants, I simply check the undersides of the leaves each time I water the plants and remove them by hand. Covering with row cover does prevent at least some of the adults from getting in and laying eggs.

Even though my gardening year got off to a rough start and my cabbages have been infested with aphids and cabbage loopers, I have still had a good harvest of some nice cabbages.  

Savoy cabbage harvested August 25, 2021



Friday, August 27, 2021

The Marvelous Monarch Butterfly

Posted by: Lisa Mason, Arapahoe County Extension

Monarch butterflies are an iconic species in the United States! These bright orange and black butterflies are known for their migration in North America. How do these small creatures make the 3,000-mile journey every year?


While the bright orange butterflies can be hard to miss, Colorado has a variety of orange-colored butterflies. You can identify a monarch butterfly by the black veins on the wings in addition to the bright orange color. They also have white spots on the edges of the wings. The wingspan usually ranges from 3-4 inches long. You can identify if the butterfly is a male or female by looking at the hind wing. If the butterfly is a male, it will have one black spot on each hind wing along one of the center veins. If the butterfly is female, she will not have a spot.

Monarch caterpillars have contrasting black, yellow, and white stripes on their body. Caterpillar size varies depending on what instar, or stage of growth the caterpillar is in.

A female monarch butterfly. Credit: Lisa Mason

Life Cycle

All butterflies including monarchs go through a lifecycle called metamorphosis that includes an egg, caterpillar, a pupa called a chrysalis, and an adult butterfly. When monarchs are caterpillars, their job is to feed as much as possible. They feed exclusively on milkweed plants (Asclepias spp.). Once they have fully grown, they will find a safe space to form a chrysalis. The chrysalis is a protective covering for the caterpillar while it transforms into a butterfly. It begins as a pale green color, then gradually turns black and orange as the butterfly gets ready to emerge. After emergence, the butterfly will soon search for a mate and the female will begin laying eggs on new milkweed plants. 

A monarch caterpillar on showy milkweed (Asclepias speciosa). Credit: Lisa Mason


Adult butterflies only live two to five weeks. The only exception is the overwintering generation of monarchs that can live up to nine months in Mexico. Once spring arrives, this overwintering generation will migrate north to Texas and surrounding areas. The females will lay eggs for the next generation. Once the next generation becomes adult butterflies, they continue to migrate north. After a few weeks, they will lay eggs for another generation further north. Typically, monarchs will have two to three generations throughout the summer season. Once fall arrives, the fourth generation, also known as the overwintering generation, will begin to migrate south back to Mexico. How does each generation of monarch know how to navigate migration? For other migratory species like Swainson’s hawks, they follow their parents and large groups of hawks to the overwintering grounds in Argentina. Scientists are still researching how monarchs are able to migrate to the same location every year. Recent research suggests they use a combination of the sun’s position in the sky, landmarks like mountains, and an internal magnetic compass. Genetics may also play a role in the ability to navigate.

Monarchs have two migratory pathways in North America. The eastern monarch population migrates from Mexico up north through the Midwest and eastern US. The western monarch population migrates from the Pacific Coast of California to the states west of the Rocky Mountains. While Colorado is not one of the main migratory corridors, you can still see monarchs throughout our state.

Butterfly Mimicry

Other species look similar to the monarch butterfly include the queen butterfly (Danaus gilippus) that hosts on milkweed and dogbane plants in the Apocynaceae family and the viceroy butterfly (Limenitis archippus) that hosts on plants in the Salicaseae family including willows, cottonwoods, and poplars.

These three butterflies look similar for one reason: mimicry! The contrasting orange and black colors serves as a warning to predators that the insect may be distasteful and potentially toxic. Milkweed is full of a compound called cardenolides. When a caterpillar feeds on milkweed plants, the cardenolides stay in the body of the monarch, which makes it distasteful and toxic to predators like birds. The predators learn to stay away from insects with the bright coloring.

For long time, scientists suspected viceroy butterflies mimicked monarchs in a form of Batesian mimicry meaning that the viceroy appeared toxic and distasteful to predators based on coloring and wing shape, but they were not actually toxic or distasteful. Further research indicates that the monarch, viceroy, and queen butterflies may exhibit Müllerian mimicry, meaning all three can be distasteful or toxic to predators and they mimic each other. More research is needed to fully understand this mimicry relationship between the butterflies because variations in the butterfly’s colors, wing shape, distastefulness, and toxicity vary among different regions and caterpillar host plants.

A queen butterfly has more white spots on the hind wings than a monarch. Colors can be variable but often they are a darker orange color than monarch butterflies. Credit: Lisa Mason

A viceroy butterfly can be differentiated from a monarch by the black, circular line through the hind wing that is perpendicular to the other black veins. Credit: Lisa Mason

Supporting Monarchs and Other Butterflies

You can support monarchs and other butterflies by providing food, habitat, water, and space in your landscape. Each species of butterfly has a different caterpillar host plant, for instance, monarchs rely on milkweed plants for caterpillar food. Black swallowtail caterpillars feed on dill and fennel. All adult butterflies will visit a variety of other flowers for nectar. Plant flowers that have different bloom times so you will have flowers all season. Butterflies need sunny areas and places to shelter from wind and weather. Planting a variety of trees and shrubs can help provide sheltering areas. Be mindful of pesticide use because they can harm caterpillars and butterflies.

Click here for more information on attracting butterflies to your landscape.

For more information on monarch butterflies, visit

To learn more about butterflies in Colorado, read this CSU Co-Horts blog post called The Fascinating Lives of Butterflies

Thursday, August 19, 2021

Change the Future: Plant a Tree

 Photo Credit: Bruce Marlin, Morton Arboretum


By CSU Horticulture Agent Linda Langelo

Trees are more valuable to us because they are an integral part of our lives.  Without trees we would have less oxygen since they take in carbon dioxide and release oxygen. Trees cool the atmosphere. Trees give us food and materials to build our homes and so much more. If you have space in your landscape, consider adding another tree. Here are two reasons why:

1)      It is good to have a diversity of trees in your landscape. If they are all the same, when one is effected by a disease the other trees are not a host to it.  But there are many more benefits to trees. They cool the air, land and water if strategically placed. According to the Arbor Day Foundation trees cool shaded surfaces between 20 to 45 degrees Fahrenheit below the peak temperature of any surface in full sun nearby.  

2)      As for larger towns and cities, trees can be used to cool the street and homes. Trees release water vapor into the air through their leaves cooling the town or city down 10 degrees Fahrenheit. In fact, one single small tree has the capacity to cool as much as 10 single room air conditioners over a 20 hour period. The best part is it doesn't impact your electric bill to cool the environment around you. Well almost. You do need to water the tree. Trees need water during extended periods of drought and during fall and winter. Here is a Colorado State University Extension Fact Sheet on Fall and Winter Watering:
Fall and Winter Watering (

On a global scale, forests remove about one-third of fossil fuel emissions annually from 1990 to 2007.  Trees remove pollution such as the 26,000 tons removed from Greater Kansas City each year. Wildfires occurring in the west and other places globally, lessen the capacity of forests to remove fossil fuels or add to the cooling capacity of the environment.

However, new research in a paper titled, "Trees, forests and water: Cool insights for a hot worldpublished in the journal of Global Environmental Change had 22 co-authors from the United States, Australia, Britain, France, Sweden, Norway, the Netherlands, Peru, Indonesia, Ethiopia, the Czech Republic, Italy, and Belgium all stated, the more important process that trees assist with in our environment is the redistribution of water. According to David Ellison, they redistribute water and simultaneously cool planetary surfaces. These scientists are determining that deeper roots, trees can maintain their cooling function even during long-lasting heat waves.  In Extension, we teach water deeply and less frequently with all plants from trees to vegetables.  Trees are a very important part of the hydrologic cycle. 

According to the Arbor Day Foundation, 180 million Americans depend on forest watersheds for their drinking water. The natural water filtration trees provide can lower costs associated with drinking water treatment.  

The U.S. Forest Service states that trees properly placed around buildings can reduce air conditioning needs by 30% and can save 20-50% in energy used for heating.  On a larger scale in Cincinnati community trees save the average household $56 annually in cooling costs by reducing electricity use. 

Overall, the U.S. Forest Service states “every dollar spent on planting and caring for a community tree yields benefits that are two to five times that investment. Why? Trees clean our air, lower energy costs, improve water quality and storm water control and increase property values”.  

If you are not sure of what trees to plant and where, then test the soil and find trees that do well in the soil in your landscape.  Be sure to place them with enough space for them to grow. If you need planting instructions here is a link:

If you need tree suggestions here is a link to Plant Select which has all types of plants that after being trialed are selected as some of the best plants for Colorado:

If you need suggestions for Small Deciduous trees, here is a CSU Fact Sheet:

If you need suggestions for Large Deciduous trees, here is a CSU Fact Sheet:

If you still have questions after reviewing the fact sheets and other materials, please contact your local Extension Office. We can help better inform you towards making the right choice.  I hope if you have the space that you decide to plant a tree.


Monday, August 9, 2021

Basil saves the summer

 By Carol O'Meara, Boulder County Extension


August is a time that separates the wheat from the chaff, when vegetable gardeners can tell if a season is successful or a bust.  Though you might not be hauling in record breaking harvests in everything you plant, usually you have a few items that are the stars of summer.

This year is particularly telling on a gardener’s skill, with a cold start followed by record heat, and as I assess my vegetable patch, one thing becomes clear:  I can’t grow a darned thing this season.  The peppers are puny and eggplant nearly nonexistent; the spinach, lettuce, and broccoli bolted so quickly I pulled them before we got to eat them.  My squash is beset by squash bugs and the potatoes - though sky-high in growth - probably won't yield much.

In response, I’m complaining about it, which in hindsight was not a good thing to do when talking about a paltry harvest.  Like scenting the weakest of the herd, other gardeners seized the moment, soothing my pain by gifting me with photos of their bountiful harvests.  Now I find myself bereft of garden produce and green with envy.

Thank heavens for basil, or I’d be petitioning the Governor to have my garden declared a disaster.  Basil (Ocimum basilicum) has boomed this summer, producing an abundance of fragrant, sweet leaves on plants that have shrugged off the extreme conditions.

Originally from the Asian areas of Thailand, Pakistan, and India, basil is popular in Italian, Thai, Mediterranean, and other cuisines.  Grown throughout history, it’s the root of interesting superstitions, such as being able to spontaneously transform into a serpent if crushed and left under a stone, or if eaten, turn into scorpions that infest the brain.  These things make me wonder why people eat certain foods.

Other cultures considered basil more fondly:  Hindus consider it a symbol of protection, Italians a sign of love but some use it as a pest repellent, which shows just how confusing love can be.    

Culinary basil comes in many forms, and cooks who enjoy diverse cuisines should indulge in planting sweet, dwarf, Thai, African, citriodorum, or purpurascens types.  Citriodorum, such as New Guinea or Sweet Dani, are lemony flavored plants; Purpurescens are the purple leafed varieties that taste like the classic green basil. 

If you’re interested in traditional sweet basil, pop in Cardinal, Pesto Perpetuo, Genovese, or super-size with Lettuce Leaf or Green Ruffles; their enormous leaves are excellent in salads.  Smaller leafed types can have a peppery kick to their leaves.

The Thai group, with varieties like Siam Queen or Cinnamon, has a surprisingly fruity, licorice-like, or spicy flavor.  The African group are boldly distinctive and often better suited to potpourris rather than food.   African Blue, a hybrid between Dark opal and Camphor basils, is stunning in the garden with spires of lavender-colored blooms.  

Most basils grow in full sun here, but a touch of shade is helpful during the hot summer.  Harvesting it is simple: pinch off the leaves just above the bottom two to four sets of true leaves.  Leaf flavor is best just prior to bloom, but you can pinch off and use the flowers in salads also.

Friday, August 6, 2021

Supporting Late Season Pollinators

 By Sherie Shaffer, Horticulture Agent, CSU Extension-Pueblo County

As summer starts to come to an end, gardening starts to leave our minds as we make room for fall and winter. For those that want to support pollinators to the best of their ability, it is good to remember that there are still species around in late summer, and early fall, who need habitat and floral resources to be able to make a new generation of pollinators. Here are some tips on providing for late season pollinators in your landscape.

Just like any living thing, pollinators need food, water, shelter, and space to thrive.

The large majority of native bee species in Colorado are ground nesting. This means that they dig into the soil and nest under the surface. To encourage nesting in your landscape, provide sunny, undisturbed ground in your garden that is free of mulch and plant material. You also don’t want these areas covered in landscape fabric or weed barrier. These will be great areas for ground nesting bees to create their future generations.

Andrenid female, Whitney Cranshaw, Colorado State University,

Some native bees nest in hollow stems and tunnels. You can leave your perennials untrimmed until spring and leave dead wood snags as well.

Butterflies like open sunny areas, but also need protection from wind. Windbreak plantings or other ways of sheltering an open area will encourage them to stick around your yard.

Pollinators also need water. You can provide a dish filled with pebbles and water so they can land and get a drink. You should dump and replace the water every couple of days to prevent mosquitoes from breeding in it.

Bees will also drink water from drip systems, sprinkler heads, fountains, and bird baths, so be sure not to use pesticides near these water sources to avoid poisoning our pollinator friends.

Male butterflies tend to congregate on moist sand or mud around puddles of water. Female butterflies will be in search of the proper host plant for their caterpillars, so they can lay eggs on it. This fact sheet lists some common Colorado butterflies and the plants that caterpillars and adults will commonly be found on:

Clouded Sulfur butterfly, David Cappaert,

Perhaps the most important thing you can do to support late season pollinators in your garden is to have floral resources for them. Early season plants are very important, most all of us have plenty of flowers in the middle of the season, but it is also important to make sure you have a few species that bloom later in the season as well. Below is a list of late season bloomers that you can incorporate into your landscape:

-          Rocky Mountain bee plant – Cleome serrulata

-          Common sunflower – Helianthus annuus

Common Sunflower, Lesley Ingram,

-          Goldenrod – Solidago spp.

Goldenrod, Howard F. Schwartz, Colorado State University,

-          Rabbitbrush – Chrysothamnus nauseosus

-          Blue Giant Hyssop – Agastache foeniculum

-          Plains Coreopsis – Coreopsis tinctoria

Plains Coreopsis, John Ruter, University of Georgia,

-          Hairy False Goldenaster – Heterotheca villosa

-          Spotted Gayfeather- Liatris punctate

-          Tansy Aster- Machaeranthera canescens

-          Chokecherry – Prunus virginiana

-          Boulder raspberry – Rubus deliciosus

It is best to plant these species together in clumps, that way bees and butterflies don’t have to waste as much energy flying across your yard to get to them. Also, don’t forget that pesticides can be deadly to pollinators, so use other IPM methods to control any pest issues in your garden.

Monday, August 2, 2021

Three quick steps for planning low water landscapes

 Posted by: John Stolzle, Jefferson County Extension

Note: Many vegetable gardens are in the midst of full production. If you find yourself with an abundance of excess produce, I would encourage you to look into CSU Extension’s Grow & Give program where you can learn helpful tips to grow produce and information about how you can share the harvest. More information can be found on the Grow&Give program's website:

This blog is not going to focus on vegetables, but instead present starter tips for planning a xeric or low water landscape. Across the state, summer heat is impacting our gardens and it has resulted in many common landscape plants struggling with heat and drought. Creatively designed and carefully planned landscapes which incorporate hardy xeric, or native plants can flourish under hot and droughty conditions.

Penstemon and sagebrush, Denver Botanic Gardens. Photo by Irene Shonle
Provided in: CSU Factsheet for Low Water Native Plants - SE Colorado.
Step 1. Planning & Plant Selection

The first step is to assess your landscape and begin selecting plants and to develop a general layout and plan. You’ll want to consider the amount of sun that your landscape receives; southern and western exposures particularly near buildings or pavement (with reflected heat) will often have the greatest losses of water – to address this, consider using plants that are especially tolerant of dry conditions. In exposed locations that are particularly steep or difficult to irrigate such as terraced areas, you might consider planting a xeric groundcover which can also help to prevent erosion. Once you have selected plants for your landscape, it can be helpful to group them by water requirements.

A great list of xeric groundcover plants to help get you started can be found at this following link:

Additional resources to help start planning a xeric garden can be found towards the end of this blog post.

Heat reflected by the sides of buildings can be especially
 stressful for plants not well adapted to heat and drought.

Step 2. Soil Prep and Irrigation Planning.

Once you have a plan in place for your landscape and plants picked out, you can help ensure the successful establishment of your plants by properly amending your soil when needed. If your soil is too sandy, nutrients and water can be lost to leaching below the root zone of your plants; if the soil is thick clay, a landscape can lose water to runoff. To cultivate a soil that is just right, you can add organic matter annually to garden areas to help improve moisture retention. Additional information regarding soil amendments can be found in this following link:

Drip irrigation isn't just for vegetable gardens,
it can be very effective for other landscapes as well.

Native and Xeric plants can withstand very trying conditions; however, they are vulnerable and more sensitive when first becoming established. This process can take up to three years after planting, and so it is important that newly planted xeric and native plants are provided supplemental water during their initial years in a landscape. If you have an irrigation system already installed, you may wish to conduct an irrigation system self audit; if you do not have a system installed, you may be interested in setting up a drip irrigation system. Drip irrigation can be much more efficient than standard above ground sprinkler systems.

Irrigation System Self Audit:

Drip Irrigation:

Step 3. Just add mulch.

Mulch can greatly help to conserve soil moisture, it can reduce soil temperatures, the amount of soil exposed to wind, and help manage weeds. Wood chips and pea gravel can make a great choice for trees, shrubs, or perennials; but stone mulch should be limited to less than half and inch in diameter for weed management and water conservation. Black rolled plastic, or woven ‘weed fabric’ can interfere with the flow of oxygen and water between the soil and air and this can sometimes harm plants. These types of mulch are not recommended for many landscape situations; however, they can be effective in vegetable gardens when used very carefully. You can find a reference link with more information on using fabric mulch in vegetable gardens, below.

If you are interested in learning more about xeriscaping or hardy drought tolerant plants, I would encourage you to look through the follow links for additional information on these topics.

A view of the Jeffco Plant Select garden. Plant select is a program
run in partnership with Colorado State University and the Denver Botanic Gardens

More information about Xeriscaping:

Retrofitting a Yard:

Low water native plant guides for all areas of Colorado:

More detailed overview for creative xeriscaping:

Native & Xeriscaping Plant Lists:

Perennials and Annuals:


Trees & Shrubs:

Native Trees & Shrubs:

Native Herbaceous Perennials:


Mulches for vegetable gardens (includes information on fabric mulch):

Mulches for home grounds:

Mulching trees:


Fall and winter watering during drought:

And as always, best of luck in your gardening endeavors!