CO-Horts Blog

Friday, April 29, 2022

Perennials: Why, When & How to Divide Them

Posted by: Judy Kunz, Master Gardener, Arapahoe County

Perennials are a great addition to any garden, but some may need to be divided after a few years. Make note if they are no longer blooming, have developed bare spots in the center, are floppy or they have outgrown their space. However, not all perennials should be divided at the same time. Spring is the ideal time to divide summer and fall blooming perennials while spring blooming perennials should be divided in late summer or early fall.

Dividing summer and fall blooming perennials in spring is preferred because the plants are not expending their energy to produce blooms at that time, and they tend to be smaller and easier to handle. Spring division also gives plants the upcoming growing season to direct their energy toward producing a healthy root system before blooming later.

Photo: North Carolina State University Extension

Some of the goals of dividing perennials are to improve the health and appearance of the plants by increasing the amount of light and air available, to increase flowering, to relocate plants that have outgrown their space or to increase the number of plants, more commonly known as plant propagation.

Before dividing existing plants, it is important to think about the feasibility of the new site. Consider the size and height of the new plants, as well as the amount of sunlight hours available. For ease in handling and transplanting, perennials should be divided just as new growth begins to emerge in the spring. To minimize plant dehydration, choose a cooler day in spring when the ground is moist and can be easily worked. Overcast weather is ideal. After dividing, rinse roots with a hose or dunk them in a bucket of water. Trim any dead growth and plant new divisions at the same depth as the parent plant. To minimize plant shock, it is helpful to have the transplanting hole prepared. Roots exposed to air can dry out quickly. Water in after planting and continue to monitor soil moisture during the growing season.

Photos: left,; top right, forsyth.ces.ncsu.edubottom right,

Perennials have three basic root systems that are handled somewhat differently at the time of division:

  • Plants with spreading root systems like ornamental grasses have thick, fibrous roots. They can be divided by pulling apart or by cutting with a sharp shovel or garden knife. Each division should have at least three to five shoots with roots included.
  • Hostas or daylilies have clumping root systems that can be divided by pulling them apart, by cutting through the crown with a sharp knife, or prying them apart using two back-to-back pitchforks facing outward. Each division should include several buds with roots.
  • Plants like iris have underground rhizomes that are actually thick, fleshy underground stems with roots attached. These plants require division by cutting with a sharp knife or shovel. Replant new divisions with the rhizomes at or slightly below ground level. In the case of iris, trim the leaves to prevent wind from uprooting the new transplants.

It will take several seasons for the new plants to reach their previous size, but dividing them now is well worth the effort. They will reward you with stronger, straighter stems, healthier foliage and more robust flowering.

By the way, don’t forget to share extra cuttings with friends!

Here is more information on perennial dividing, plus a PDF listing common perennials and when to divide them.

Thursday, April 21, 2022

Increasing Carbon Dioxide for More Productive Plants?

Musings of a Cell Biologist on the Way to Becoming a Colorado Master Gardener

Posted by Kristin Moore, Master Gardener Apprentice  

As gardeners we spend a lot of time trying to figure out how to make our plants grow as productively as possible. However, if we really boil down the major constituents that make up a plant, it comes down to a small number of chemical molecules and elements. Water, which is generally taken up through the root system of a plant, can make up 80-90% of a live plant’s mass. However, if we take water out of the equation, the chemical elements that make up the vast majority of the dry mass of the plant (the mass recorded after water has been dried out) are carbon and oxygen, which combined make up approximately 90% of the dry mass of a plant. Another 6% dry mass is made up by hydrogen. The remaining 4% of plant dry mass is made up of the other 17 essential nutrients that we spend lots of time (and money) supplementing our soil with (examples: nitrogen, potassium, and phosphorus). While those other 17 nutrients are absolutely essential to plant growth and productivity, I am going to focus on the 90% of the plant that is carbon and oxygen for this article.

Have you ever stopped to think about where all the carbon and oxygen that make up most of what we’d really consider to be a plant (leaves, stems, bark, etc.) come from? Your initial response may be that they come from the soil and get incorporated into the plant through the roots. If so, you are not alone in this assumption (See this video that asks graduating MIT students this same question). In reality, all of the carbon and most of the oxygen come out of the air. Photosynthesis, the unique trait of all green plants (and some bacteria and algae), is the process of utilizing energy from sunlight to convert gaseous carbon dioxide (CO2 - a carbon atom bonded to two oxygen atoms) into the sugars and structural molecules such cellulose that makes up the energy storage and fibrous tissue of most plants. Plants do not actually “suck up” carbon from the ground. That 90% of the dry mass of a plant came from converting the CO2 in the air into carbon-based molecules in the plant.

This fact then begs the question: in an era of increasing CO2 emissions and concentrations in our atmosphere, might plants actually benefit from increased concentrations of carbon in their environment? Could they grow bigger faster since one of their major nutrients is now in excess? As it turns out, the answer to this question is a lot more complex than it may initially appear. There is strong evidence that increasing atmospheric CO2levels does increase the photosynthetic rate of plants. This results in larger, faster growing plants. Higher CO2concentrations also results in less water loss for many types of plants. This is because plants have to open up pores on their leaves called stomata to let CO2 from the air into the plant. When stomata are open, not only can CO2 come in, but water can also escape out into the air. With higher CO2 levels these pores are open for less time resulting in less water loss from the plant.

That all sounds pretty great! Bigger plants with lower water consumption! However, the increased rate of carbon incorporation into plant tissues results in increased amounts of sugar (mostly made of carbon and oxygen) compared to protein (lots of nitrogen) in a plant. Thus, plants grown in elevated CO2 may not have the same nutritional value (more sugars and less protein) as those grown under current CO2 levels. There is evidence to indicate that insects feeding on these plants have poorer outcomes and cause more plant damage as they try to make up for these nutrient shortcomings. One way to fix this imbalance may be to increase nitrogen supplementation through fertilization, which can be costly and have other impacts. Additionally, the impact of having extra sugar molecules accumulating within the plant is unknown. While sugars provide energy and structure to a plant cell, they can also signal plants to make changes in the way they grow. We are just starting to gain an understanding of how the increases in sugar accumulation due to increased CO2concentration would impact this facet of plant physiology. Lastly, the overall increase in temperatures that accompany increased CO2 production as well as the changes in weather patterns will ultimately have a huge impact on plant growth and productivity. Many of the current predictions indicate that these will not increase plant yields.

Schematic from 'Preserving the nutritional quality of crop plants under a changing climate: importance and strategies' (Soares et. al., 2019). GHG = greenhouse gas; eCO2 = elevated carbon dioxide; Single letter chemical element abbreviations outlined in red boxes; OM = organic matter. 

Combined, all of these data indicate that the impacts of changing levels of atmospheric CO2 on plant physiology, production, and value remain…complicated at best. Although increased plant growth and decreased water consumption are consistent results in many experiments run under increased atmospheric CO2 concentrations, there is an upper limit to this increase. Furthermore, how these plants will adapt to their new environments (water availability, temperature, growth season length, etc.), and whether they will have the same value as those grown today is uncertain. What is certain, is that our changing environment will ultimately results in changes to plant productivity and their critical role in the global carbon cycle.

Tuesday, April 19, 2022

Old Mulching Technique

Old Mulching Technique
By CSU Horticulture Agent, Linda Langelo

                                  Liquidambar styraciflua 'Volcano'

                                             Photo credit: Anonymous

You might ask yourself, "Is the author for real?" This is not a cultivated variety. Unfortunately, the technique of volcano mulch practice is still alive and well. This practice was considered the best practice during my parent's lifetimes in the 1940's. As Maya Angelou has said, "When we know better, we do better." Hopefully.

Liquidambar styraciflua is commonly called Sweetgum. It grows in zones 5-9 on wet river bottoms, swamps that frequently flood and sometimes on drier uplands. According to the Colorado Tree Coalition there is a sweetgum that is The Colorado State Champion Sweetgum (DBH 17"/Height 57') in Fort Collins. Sweetgum can grow to be 80-120 feet tall and 4 feet wide. But this depends on many environmental factors such as growing it in a moist soil with no high winds, hail damage or temperature extremes from 75 degrees Fahrenheit to -5 within in a few hours. It is a medium to fast grower. In aklaline soils iron chlorosis is a problem along with webworms, scale, bleeding necrosis and leaf spots.

As a tree hugger, seeing the volcano style mulch I should have titlted this blog article, How to Kill a Tree in Two Years or Less. I might add the person who sent this to me is not a tree hugger but sensed that this was not the right thing to do. Knowing that we already have Sweetgum as a Champion Tree why not give Sweetgum Trees everywhere the same opportunity? Or for that matter any tree the opportunity to become a Champion Tree or just to be an old tree?

Here is what can happen when trees are mulched this deeply:

1)the foliage starts to yellow or become off-color

2)there are abnormally small leaves

3)poor twig growth and dieback of limbs

What happens when you bury the root flare? Because the root flare has different tissues than other roots, piling mulch heavily decreases the gas exchange stressing the inner bark. These are lenticels which are pores the tree uses for gas exchange. Blocking them or waterlogging them with a barrier of mulch begins to affect the health of the tree. When the inner bark dies, roots become malnourished and weak. It would be no different than planting the tree too deep. 

By having a volcano of mulch around the trunk, this encourages diseases. Bacterial and fungal diseases require moisture. These diseases are opportunistic and mulching like this gives them the conditions they need to survive and prosper. These diseases can stop both the flow and storage of sugars produced in photosynthesis placing the tree in decline. Many borers are known to be attracted to trees in decline.

As if oxygen deprivation and starvation are not enough in over-mulching a tree, excess heat is another issue caused as the mulch decomposes. The high temperatures again affect the inner bark. With young trees if the trunk flare is not hardened off before a hard freeze, this results in damaged tissues.

Lastly, rodents and field voles like cover whether it is tall grass or deep mulch. Add girdling the trunk to the list of possibilities. There is no way of saving the tree when this happens. 

What is the solution? Leave the root flare free of mulch. Mulch 2-3 inches on the edge of the shoulders of the root ball. Here are some links to proper tree planting and mulching:

Share this post. Spread the word. Help stop volcano mulching forever!

Monday, April 18, 2022

Going Drip

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

I love growing a vegetable garden. Ever since I can remember I have grown some type of veggie garden every year. I also have hand watered ever since I can remember.

Hand watering has its perks. Being out in the garden every day, up close and personal with your plants allows you to see any problems that may arise and be on top of anything that is ready to harvest right away. The issue, for me, with hand watering, is that I just don’t have the time. For the last couple of years, I have let my garden dry out too much and have had small harvests because of it.

My beds with the supply lines

That’s why this year, we are going drip. Drip irrigation has many benefits. The main one for me, is that I can turn it on and water the garden without spending the time filling up my watering can and watering by hand. I bought a fancy timer that I can work from my phone, so I can even turn on my drip system from the office, or my bed, I am so excited. Drip irrigation applies water right to the soil, where the roots are, so it is very efficient. Letting water splash on the leaves of your plants encourages disease, another reason drip is beneficial.

It has been a bit of an adventure getting my system set up. I did a lot of research and had my method down, in theory, but when you get to real life sometimes things don’t always go as planned.

When I had my sprinkler system re-done last year, I designated a couple of zones to use for drip systems. We had the water supply ran to where we wanted it, and installed a filter, and pressure regulator in an underground valve box. From there I had the water supply lines ran to my garden beds.

The valve box with the filter and pressure regulator

This is where I had some trial and error. At first, I used my quarter inch hole punch to tap into the water supply lines at each bed, and then attached drip tubing (with holes every 6 inches) using a barbed coupler. I looped the tubing around my beds and staked them down. At the end of the tubing, I used a barbed plug to close the system, and excitedly turned it on hoping to see water dripping from the holes. That is not exactly what happened. Water was barely coming out in the first bed and not at all in the second bed, and I was sad

Tapped into the supply line

Barbed coupler

All ready to go, or so I thought

I decided maybe I needed to tap into the water supply line more than once, so I made a couple more holes and ran three lines of drip tubing, instead of looping the one long line. I also decided to change one of the beds to a quarter inch soaker hose type of tubing rather than the drip tubing to see which one I liked better. I held my breath and turned on the system again, and it worked! Water was coming out of the drip tubing on one bed and the soaker tubing on the other.
Barbed plug

The end of the drip tubing, all plugged up

I plan to use the two types of tubing this summer and see which one I like better, and maybe there will be a follow up blog on the results of my adventure in going drip. I will add more pictures of the soaker tubing as well.

I hope if you are considering changing up your irrigation plan, this can help you have less error. Things take some figuring out, but in the end with some patience, and help from your local Extension office, you can get to irrigation paradise too!

Friday, April 15, 2022

The Magical South (and Scenes from a Cemetery!)

 Posted by: Alison O'Connor, Larimer County Extension

Earlier this month, I spent the best weekend with my mom in South Carolina and Georgia. It was a trip for the ages, because we attended the Augusta National Women's Amateur golf tournament at Augusta National (more on that!), but we also crammed in a lot of other things to fully experience the south in spring.

Azaleas in full bloom in Columbia, SC.

Fortunately for me, my mom loves cemeteries as much as I do and we kicked off our trip by visiting the First Presbyterian Church and Cemetery. The church was organized in 1795 (!) and is the oldest congregation in Columbia. Buried in the cemetery are Woodrow Wilson's parents and a couple of University of South Carolina presidents. Soldiers from the Revolutionary and Civil Wars are among those also buried here.

Aside from the rich history of the cemetery's interred were the amazing plants! Swaths of lilyturf (Liriope), flowering dogwoods (Cornus florida), and majestic live oaks (Quercus virginiana) wove through the cemetery grounds. Other friends included crepe myrtle (Lagerstroemia indica), camellias, and azaleas.

A live oak spanning across many gravesites at the First Presbyterian Cemetery in Columbia, South Carolina. 

For someone who learned their plant materials in the Midwest, it was fun to pull out the cobwebs to try to identify many of these species - plus, having a group of horties accessible via text helps too!

I blogged about the magic of Augusta National a few years ago and had previously visited the course in May after the tournament. But let me tell you - seeing it in April, in its prime, was a near-religious experience. As mom and I drove from Columbia to Augusta, Georgia early Saturday morning, I was emotional just thinking about it. Mom teased me and told me to hold it together. As we walked up the main gates to enter the grounds, I was overcome with emotion and had tears streaming down my face. [Side note: my family took bets on how many times I would cry; the final count was eight!]

The course was impeccable. The perennial ryegrass was like green carpet. The pine straw was neatly manicured, and the grounds were absolutely beautiful. The course was once a nursery, so hundreds of plant species line the fairways. And hilly! If you watch the Masters, don't be fooled. Hole 18 is straight uphill. Mom and I walked the entire course, adding 22,000 steps to our sneakers. It was a dream to watch some of the most talented amateur female golfers in the world and celebrate 16-year-old Anna Davis's win. We also saw Annika Sorenstam, Nancy Lopez, and Dr. Condoleezza Rice (who is a member). 

Phones are prohibited on the grounds during the tournament, so mom and I stood in line for our complementary photo in the front of the clubhouse. Southern hospitality was at its finest, as everyone on the grounds, from patrons, to staff, to the groundkeepers were so incredibly friendly. The city of Augusta loves hosting the Masters and the women's amateur and they are so good at it.

Mom and me at Augusta National in April 2022. We practiced our pose, but mom forgot the leg bend! Phones weren't allowed on the grounds during the tournament, so this is the only photo we have. 

The next day we drove to Charleston, which simply oozed southern charm and history. A walking tour through the city combined aspects of architecture, history, and more great plant life. Boston ferns (Nephrolepis exaltata) and cast iron plant (Aspidistra elatior) were used as filler landscape plants.
This porch in Charleston begs for lazy afternoons reading and drinking sweet tea.

It was such a great trip! The weather was perfect, the humidity was low, and it was fantastic to spend quality time with my mom. We both agreed we'd go back in a second if given the opportunity. Two thumbs up!

Thursday, April 7, 2022

April in the vegetable garden

Posted by: Cassey Anderson CSU Extension Horticulture Agent, Adams County. 

April is the month when many gardeners are really getting things going. Perhaps you’ve planted some peas or kale in the vegetable garden already, perhaps you’re just getting things underway. Regardless April is a busy month. You can plant your cool season crops: radish, spinach, lettuce, green onions etc. You can start warm season crops indoors: cucumbers, melons, squash, pumpkins etc.

Example of bolting lettuce from
Time for Cool Season Crops: 

What is the difference between a warm season crop and a cool season crop? Mostly it’s in the
temperatures they’re willing to tolerate, and those that they will grow well in. Cool season crops can tolerate cold temperatures, and some can even tolerate light freezes (defined as anything between 28 F and 32 F). These crops are also typically done with their season by the time we really warm up in July. Many of these crops have produced their final fruit or bolted, i.e. gone to seed, once daytime temperatures go up into the high 80s or 90s. If you didn't get your fix for cool season crops by the time summer heat hits, you can always replant for a fall harvest. Typically replanting can happen around mid to late July depending on crop maturity dates. 

Photo by Cassey Anderson
One thing that can be a little surprising for many of our cool season crops is that although they like to grow in cool temperatures, they germinate better and more quickly with warm temperatures. You can pre-germinate many of the cool season crops: peas, lettuce, kale, onions etc. Soak a paper towel and put it in a ziplock bag or other sealable container, place the seeds in with it for 12-24 hours at room temperature. You can get them warmer, many crops like to germinate between 70 and 80 F. See this Colorado Master Gardener Garden Note for specific crop temperatures:  

You can get your perennial garden going as well: asparagus, rhubarb etc. are good to get started in mid- to late-April.  Perennial crops may take a few years to get their feet under them before harvest, but you can subsequently enjoy even decades of low-effort production. 

Planting Asparagus:

Asparagus can produce for over 15 years in a vegetable garden. You can start from seed but buying crowns will give you some time advantage. Choose a sunny, well-drained area, preferably somewhere not prone to freezes in your yard (not low-lying for example). Amend the soil with a well-rotted compost if needed. Plant crowns deeply in a 6-12” trench, cover lightly and bury as the crowns grow up. Place crowns “head to toe”, root tip to bud tip, typically with the crowns about 12” apart. Water regularly so the crowns do not dry out. Plant seeds about 1” deep, they may take up to 3 weeks to germinate. Mulch well for winter.

Do not harvest for the first 1-3 years (sooner for crowns, longer for seeds), or until you begin to see numerous spears poking up. In the first year you should harvest for about two weeks and let the remaining spears turn into ferns that will feed back into the plant overall. In subsequent years you can harvest for 4-6 weeks, usually into mid-June or early July.

If you have specific questions be sure to reach out to your local county Extension office.

Happy Gardening!

Wednesday, April 6, 2022

Spring Frosts and Fruit Tree Buds


By Amy Lentz, Boulder County CSU Extension

One can grow several different types of fruit trees in Colorado with some performing better than others depending on where and at what elevation you live. Along the Front Range, apples and cherries used to be staple industries prior to the 1950’s. A few rough weather years along with changing market forces moved the industries to other states, but these types of fruit trees along with pears and plums can be quite fruitful (pardon the pun) along the Front Range. Other types of fruit trees will struggle in this region to produce a crop, whereas if you are on the Western Slope, several different types of fruit trees will give you a dependable fruit crop due to the benefit of warmer winds…perfect for growing those coveted peaches.

A lot of the potential to get a decent harvest from a fruit tree in Colorado boils down to phenology. What’s that, you ask? Phenology is a branch of science dealing with the relationship between climate and periodic biological phenomena (definition from Merriam-Webster) such as bird migrations and, in this case, flowering patterns of plants. In more simple terms, this is often referred to as bloom stage or growth stage. Fruit trees will go through various bloom stages as they wake up each spring. For example, apple trees have nine stages of blooms from dormant to fruit set as seen in this pictorial chart from Cornell University:

Apple Phenology Chart - Cornell University
Apple Phenology Chart - Cornell University

Back to why it’s not easy to have a productive fruit tree in Colorado…springtime frosts! It’s safe to say that you never know when that last spring frost will come in Colorado. And when it does, how low will it go? This is the key to whether or not you will get a decent fruit crop from year to year – it’s the combination of the low temperatures experienced in the spring and the stage of bloom at that time. For example, if your leaves and/or flowers are just starting to emerge (at the ‘green tip’ stage of development), your tree’s flower buds can take some pretty low temperatures and can easily survive a light frost. However, if you tree is in full bloom, you will lose many of those flowers if the temperatures dip a just a few degrees below freezing. The following chart shows the various bloom stages for tart and sweet cherry and peaches:

% Bloom Loss vs. Temperature vs. Bloom Stage - Utah State University
% Bloom Loss vs. Temperature vs. Bloom Stage - Utah State University

Notice for tart cherries that even at temperatures down to 15° F, only 10% of the blooms will be damaged or killed if they are just swollen and have not broken through yet. Conversely, with that same tree in full bloom, you will see around 90% of the blooms (and future fruit) damaged or killed if the temperature gets down to just 25° F. The relationship is similar for peaches and other fruit trees, as well. Simply put, the further along in bloom, the more susceptible the buds are to being killed by a spring frost.

Undamaged peach flower bud compared to damaged bud after exposure to very low temperatures (-15°F). Photos: Amy Lentz

Throw in crazy Colorado weather and it’s a fool’s bet! The timing of these stages will vary from year to year, making it hard to predict when your tree will be in full bloom. The following photos were taken in the Fort Collins area in 2017 for an apple tree. The dates of each stage of flower are marked above each picture taken of the same branch over time. Just one year later in 2018, the same tree was more than two weeks later in its timing for each bloom stage.

Pink Stage occurred on April 12, 2017. In 2018, the same stage occurred about 16 days later, showing up on April 28th. Photos: Amy Lentz

There are not many options to outsmart Mother Nature and prevent your fruit tree from receiving some damage during a spring frost and some trees will fare better than others. Apricots are usually the first to bloom, followed by peaches, cherries, plums, pears and apples will usually be last. Here is one tip if you haven’t yet planted your tree…place it on the north or northeast side of a structure or house; close enough that it’s shaded in the winter and far enough that it’s in full sun later in the summer when the sun is higher in the sky. This can provide more consistent winter temperatures, hopefully keeping the tree dormant for just a bit longer and delaying flower development. Even a week of two can make all the difference!