Monthly Archives: May 2017

The Season Of Vigilance: Noxious Invasives, Introduced Weeds And You

-Olivia Wylie, Master Gardener Denver

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The saying goes ‘a weed is a flower whose virtue hasn’t been found yet.’
But you have to wonder with some of the weeds in the garden. What exactly, you think as you sweat and tug, is the virtue of bindweed’s strangling grip on other plants and your garden? What’s the virtue, you think with nervous venom as you pull on your gloves, of a spurge that can give you blisters, kill your dog, and is invasive?!

Unfortunately, the virtues of these plants are exactly what makes them weeds. Adaptability. Tenacity. Ability to survive harsh conditions. It sounds like a compliment when you’re reading a garden catalog, but with the wrong plant in the wrong place, it’s a recipe for disaster on a garden-wide, city-wide or even state-wide level.

Sadly this disaster has played out many times, and today we carry the burden of our forbears’ horticultural mistakes across the country. To combat this issue, a Federal Noxious Weed act was passed in 1974, and our own Colorado Noxious Weed Act was passed in 1996. The Act supports the creation of programs to combat the invaders, and the Department of Agriculture maintains a list of plants to look out for called the Colorado Noxious Weed List.

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This list is invaluable as a resource, and is broken down into several sections. Quoting from the Colorado Department Of Agriculture,

List A Species in Colorado are designated by the Commissioner for eradication.

List B Species are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, develops and implements state noxious weed management plans designed to stop the continued spread of these species.

List C Species are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, will develop and implement state noxious weed management plans designed to support the efforts of local governing bodies to facilitate more effective integrated weed management on private and public lands. The goal of such plans will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions that choose to require management of List C species.

Watch List Species that have been determined to pose a potential threat to the agricultural productivity and environmental values of the lands of the state. The Watch List is intended to serve advisory and educational purposes only. Its purpose is to encourage the identification and reporting of these species to the Commissioner in order to facilitate the collection of information to assist the Commissioner in determining which species should be designated as noxious weeds.’

But we all know what happens when we leave the work up to the government and sit on our laurels. It’s up to every gardening citizen to know your noxious invasives, your invasives, your introduced weeds and what to do about them!

Know Thy Enemy

We could spend entire articles on the exact definition of invasive species, and in fact a wonderful white paper on the subject can be found at this link. But here’s the skinny.

niNoxious Invasive- the long winded definition is quoted from the 1974 Act, and runs ‘Noxious Weed means any living stage, such as seeds and reproductive parts, of any parasitic or other plant of a kind, which is of foreign origin, is new to or not widely prevalent in the United States, and can directly or indirectly injure crops, other useful plants, livestock, or poultry or other interests of agriculture, including irrigation, or navigation, or the fish or wildlife resources of the United States or the public health.’

Put plainly, not only will Noxious Invasives make you livid, they can make you sick. These are the true thugs of the plant world. Generally these beasts will be found on the Commissioner’s A list. These include vile things like Myrtle Spurge/ Donkey Tail Spurge, Euphorbia myrsinites. Originally introduced as a ‘lovely and tenacious rock garden addition’ (a direct quote from an old seed catalog, the company shall remain unnamed!)  it was indeed tenacious. TOO tenacious. And if you decide to pull the stuff, it retaliates with sap that causes painful blisters. Get it in your eyes? You’re taking a trip to the ER my friend. Dogs that encounter the sap can actually die. Not such a great addition after all, and if you see it in your garden it needs to be eradicated by (almost!) any means necessary. Before you tackle it, PLEASE pull on goggles, a long sleeve shirt and pesticide-grade gloves. In fact, I prefer to pull on a thin pair of fabric gloves and my nitrile pesticide gauntlets go on over those. You can never have too much protection.

dtInvasive Species-  an invasive species is best defined as a non-native plant that could cause harm to the native ecosystem by competition pressure. When you pull prickly lettuce before it smothers your lovely little columbines, that’s a perfect example. These plants are tougher, more prolific, easier spreading or in some way advantaged over other plants, and if allowed will run roughshod over our native flora.
Dalmatian Toadflax is the classic example. I’ve taken out of town friends on a drive through the foothills and heard them exclaim ‘oh look at that yellow field!’ I look over and give a heartfelt groan, because I know that field has nothing living in it save a single invading species that has choked out native plant life.

isIntroduced Species-Where list A Noxious Invasives could be compared to a plant felony, plants that fit the Introduced Species are more of a misdemeanor: they’re trouble, but not ecological disaster. Defined as ‘an organism that is not native to the place or area and has been accidentally or deliberately transported to the new location by human activity’ in the 1974 Act, they’re your neighbor’s old mint bush sending shoots into your yard. In my Capitol Hill neighborhood, the quintessential example is the Cap Hill Weed (no not THAT weed),Campanula rapunculoides or Creeping Bellflower. Local lore says it was introduced in the 1920s to grace the great old mansions that once stood in their majesty along these streets, and it’s been with us ever since. It wanders from garden to garden in the older parts of town, sneaking under trees and into small areas, worming into bare spots in the grass and gaining a foothold most anywhere. Some people have simply accepted it as a garden plant like their grandmothers did, but most of us fight it tooth and nail because we’d like to have a garden with more than one plant in it!

Fighting The Good Fight

Delving into reclamation and eradication tactics for species that are toxic, invasive or introduced pests is a paper in itself, and many have been written. The Colorado Noxious Weed Species List has details on the treatment of every species it lists. But here’s some general tips.

  • Safety First. Wear gloves, wear long sleeves, wear safety glasses or goggles if you run any risk of getting poked in the eye or sprayed with sap
  • Get The Root!  Pulling does little good if there’s a root stocked with nutrients ready to shoot up new leaves under there. If you use pesticides, make sure your choice specifies ‘kills the root’.
  • Tenacity Is A Virtue. Don’t get discouraged if the plants come back again and again. keep using your favorite eradication method, and you can wear these invaders out!

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Pretty Tough Plants Book Review

I love the name of the new book by the experts at Plant Select. Pretty Tough Plants describes the family of Plant Select plants perfectly.

If you’ve grown any of these beautiful plants that are so well-suited to our gardens, then you know what I mean. If you haven’t grown any Plant Select recommendations, what’s stopping you? These are the plants that can help you be a more successful gardener.

Plant Select calls itself “a nonprofit collaboration of Colorado State University, Denver Botanic Gardens, and professional horticulturists.” I call it one of the best plant testing and introduction programs in the country.

Pretty Tough Plants: 135 Resilient, Water-Smart Choices for a Beautiful Garden (Timber Press, 2017) is a follow-up to Durable Plants for the Garden: A Plant Select Guide published in 2009.

This new edition seems to be more user friendly, both by its manageable size and in the plant presentations. Plants are divided into groups that include tender perennials and annuals, petites, groundcovers, perennials, grasses, vines, shrubs, and trees and conifers.

Each Plant Select description includes its scientific name, common name, mature size, flower type, bloom time, and best features. Understandable icons give details on sun and water requirements, as well as if the plant attracts pollinators or if deer resist browsing it.

The “Landscape Use” information is meant for gardeners who have difficulty matching plants to place or are unsure of how to combine plants for the most striking effect. The descriptions make suggestions for perfect placement and the best Plant Select companions.

Many of the gorgeous, full-color images show both a close-up view of the plant and a shot of how it looks in the landscape when in full bloom. One of my favorites is Redleaf rose (Rosa glauca) shown as a fabulous specimen plant, and closeups of the star-like single pink flowers and brilliant red hips.

An especially nice feature for this volume is the Plant Reference Guide in the back of the book. This guide provides a quick resource for matching the right Plant Select plant to the right spot in the landscape.

Besides the typical categories, there are two additional and interesting categories: Special landscape use and North American roots. Not every plant has a special landscape use, but when a plant is recommended for “dry shade, cold hardy,” like Denver Gold columbine (Aquilegia chrysantha), gardeners can trust the endorsement.

Prairie Jewel penstemon (Penstemon grandiflorus) is one Pretty Tough Plant in my xeriscape.

I’ve grown many different Plant Select recommendations in my perennial beds, and I can vouch for their resilience – one of the seven qualities a plant has to have to be added to the program.

In addition to being able to stand up to a challenging climate, Plant Select plants have to thrive in a variety of conditions, be water smart, have that “it” factor, resist insect pests and plant diseases, offer long-lasting beauty, and aren’t invasive.

I can tell Pretty Tough Plants was a labor of love by a group of passionate plant people. The photo credits read like a list of area Who’s Who, from well-known horticulturists to CSU Extension Master Gardeners. Pat Hayward and David Winger had the happy task of sorting and selecting images, including many of their own.

By Jodi Torpey
A Denver Master Gardener
(Timber Press provided a complimentary copy of Pretty Tough Plants for this review.)

Sheet Mulching Re-visited

Last week’s blog included a link back to our October 2016 blog on experimenting with sheet mulching (also known by some as “lasagne gardening”) http://wp.me/p5JEJY-YZ so I thought we ought to re-visit and see how that worked. Sheet mulching is the layering of different kinds of compostable garden waste (sometimes with old newspapers or cardboard as well) on the surface of poor garden soil. The aim is to quickly add organic matter to the existing soil, improving drainage, water retention and fertility.

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I had several questions in my mind last fall when this experiment was carried out:

1. Will the cardboard decompose?
2. Is the “green” and “brown” balance right?
3. Will the raccoons and skunks churn it all up?
4. Will there be a crop of new weeds from the imported materials?
5. Will the cold Colorado winter simply stop any decomposition from taking place?
6. Will there just be a smelly slimy heap to remove next spring?
7. OR, will we have achieved that elixir of gardening – fertile, well-drained, moisture-retentive soil???

The experiment has been going on for some eight months now and these are the answers, so far:

1. YES. Some digging about at the base of the layers revealed no sign of cardboard except for a few stray bits of plastic tape that didn’t get removed when I broke down the cardboard boxes.
2. Probably YES. Though close inspection revealed that in some parts the grass clippings were laid too thick and would have done better if they’d been mixed in more with the dried leaves.
3. NO. Apart from a few little exploratory digs by some critters, the layers remained intact.
4. NO. Initially there was some germination from seeds (unidentified grass/cereal) which were in the chicken coop material I used, but these were easily pulled in the first couple of weeks. Since then not a single weed has appeared.
5. NO. Digging into the layers revealed pretty well composted good, brown material though not everywhere. Lots of worms too. Straw seems to have been the hardest to break down and is still recognizable in some places.
6. NO. See 5.
7. Well, MAYBE ….

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The native grey clay soil is still there beneath the sheet mulch

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Well on the way to being compost

There is no doubt that we now have deep layers of composted garden waste on our borders. The layers have not been totally absorbed into the soil below. They have shrunk in depth by a couple of inches which is probably mainly due to gravity and the reduction of air pockets. I accept that these borders may remain as “raised” borders for some time.

So, what happens next? I expect these sheet mulched borders to continue to decompose over the summer and, perhaps, by next spring will no longer be “raised”.

But I can’t wait until then to get new plants in.  Already, I have a planted a Japanese maple and some hellebores in one of the beds (both should benefit from the rich compost.  I dug holes in the compost layers, put in some native soil from elsewhere in the garden and planted and watered.

I was concerned that the compost itself would not hold the plant roots securely which is why I mixed in garden soil from elsewhere to give weight. It will also provide mineral nutrients that may not be present in the compost/mulch. Now, some six weeks later, the new plants are all well rooted and looking good.

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Japanese maple and hellebores just planted

So, is it worth doing? I’m giving the experiment a qualified “yes” at this stage.

I think it works for areas that have been neglected or are being cultivated for the first time. There is an initial effort in gathering the materials and building the sheet mulch layers, but then you just sit back and wait.

Does one big “hit” of compostable material work better than cumulative additions over the years? I don’t know. Time will tell as I compare these borders with others in the garden. Certainly, I got a lot more compost onto the borders than I could generate annually from my compost bins. (You don’t get a lot of kitchen waste from two people; and a modest-sized, young garden doesn’t produce much waste either.)

It might have been less work to simply go out and buy bags of compost from the garden center or big box store. That would have been expensive (my materials were all free). There are no regulations on what goes into bagged compost for retail sales.  At least I knew exactly what was in mine.

Aside from these thoughts, there has definitely been a great sense of satisfaction in doing the experiment.  It was interesting.  It was good exercise.  It was free.  I turned what other people thought was just rubbish messing up their yards into useful, re-vitalizing material for our garden and plants.

Anne Hughes/A Denver County Master Gardener