BYGL Weekly News for April 9, 2018

Date Published: April 7, 2018
Authored by: Joe Boggs

Why in the name of all that is horticulturally holey do we continue to see mulch piled around tree trunks to stratospheric heights?  What is the appeal?  And, why can’t we stamp out these mulch monstrosities despite years of educational efforts?

The image below was taken 20 to 25 years ago by Jim Chatfield using a 35mm camera.  It shows Erik Draper’s size 12 shoes positioned to illustrate mulch piled over 2 feet high. The three of us used this image for years in numerous training programs to teach against this horticultural horror (volcano mulch, not Erik).

Of course, there have been numerous efforts by other Extensioneers, Master Gardeners, and our Green Industry to educationally eradicate mulch volcanoes (a.k.a. mulch mounds).  There has been some success.  I can count on provoking groans from audiences of horticulture professionals or Master Gardeners by showing them pictures of mulch volcanoes.  The impact is so profound, I commonly hear groans lingering throughout my presentations!

And yet, mulch volcanoes continue to erupt.

Indeed, this mulch rant was incited by a visit to a local hospital yesterday where my wife had a minor medical procedure.  Nothing serious, but I spent the wait-time cruising the hospital’s landscape.  Unfortunately, the most striking feature was new mulch formed into high mounds:  mulch volcanoes were erupting everywhere!

Adding insult to injury was the peculiar practice of digging a “mulch moat” around the base of the mulch stratovolcanoes.  Creating these mulch moats not only cuts existing tree roots extending into the surrounding soil, but the trench can prevent root regrowth into the soil beyond the moat.  In essence, each tree has its entire root system confined to the area beneath its mulch volcano.  ARRGHH!

I’m certain the hospital is staffed by some of the best medical professionals in our region.  However, as visitors and patients approach the hospital, they are greeted by clear evidence of far less than professional horticultural practices.

When It’s Done Right

Organic mulches such as aged bark mulch are a wonderful thing.  They moderate soil temperatures, preserve soil moisture, suppress weeds, and as the organic mulch slowly decays, it contributes to the organic content of the underlying soil.  The dark color of natural bark mulch also enhances landscape aesthetics.  Of course, the availability of organic mulch dyes makes other colors available; shopping for mulch can be like using an artist’s palette.

Last season, I highlighted an exemplary use of mulch in Glenwood Gardens, Great Parks of Hamilton County (see BYGL April 27, 2017, “Glenwood Gardens: A “Volcano” Mulch-Free Zone”).  They had followed all of the general recommendations for the proper use of hardwood mulch around trees.  The mulch rings were as large in diameter as practical and mulch depths were no more than 2 – 3 inches.  Mulch that found its way onto the tree trunks was pulled away from the trunk flare.

When It’s Done Wrong

Volcano mulch does not kill trees outright; if it did, people wouldn’t do it.  Instead, it produces subtle, long-term, ill-effects.  Although bark mulch may at first appear light and airy, it will ultimately compact as it degrades to interfere with oxygen reaching tree root cells.  Trees respond by growing roots into the mulch; however, the roots can become exposed as the mulch further degrades.

The slopes of mulch volcanoes cause roots to turn; they can’t grow into thin air!  Eventually these roots encircle the tree trunk and merge with the stem tissue.  As these errant roots increase girth, they gradually girdle the trunk and restrict vascular flow.  Thus, they are known as “stem girdling roots.”

As the mulch decomposes and dries out, it will eventually start to repel water; it becomes hydrophobic.  You can observe the hydrophobicity of dry organic matter when you try to moisten a bag of dry peat moss.  Of course, water repellency ultimately causes roots that have grown into the mulch to dehydrate.

The deleterious nature of volcano mulch is not immediately apparent.  Moisture starvation and vascular strangulation can ultimately kill a tree; however, along the way they produce tree stress.  This can induce trees to drop their defenses against infestations by opportunistic insect pests such as native borers or infections by plant pathogens.  Of course, pests and diseases get blamed if trees succumb, not the volcano mulch that made the trees susceptible in the first place.

William Shakespeare, in King Henry VI, Part III, provided the perfect quote:

“And many strokes, though with a little axe,

Hew down and fell the hardest-timbered oak.”

Volcano mulch is a little axe.

Date Published: April 6, 2018
Authored by: Amy Stone

Hairy Bittercress (Cardamine hirsute)

While temperatures remain cold, and even an occasional snow flake takes flight, there is weed that is giving it is all this spring. That weed is hairy bittercress. While it has been lurking in gardens all winter long, it is flowering its little heart out and setting seeds right now in northwest Ohio.

This weed sends out leaves in a basal rosette from seeds that germinated last year. Like other members of the mustard family (Brassicaceae), its tender greens are edible. You might be fooled by the common name—the plant is typically not bitter, but rather peppery in taste. Its flowers can be tough to chew, but the tender leaves are said to be a source of vitamin C, calcium, magnesium, beta-carotene and antioxidants.

Speaking of flowers, hairy bittercress produces a small cluster of tiny flowers each with 4 white petals. Narrow seed pods stand tall above the flowers. When dried or disturbed, the seed pods “explode” sending seeds in all directions.

This seed dispersal strategy is known as ballochory. Jewelweed and cranesbill also employ this as a strategy to spread seeds.

Removing plants prior to them setting seed is highly recommended. In northwest Ohio you will have to move pretty quickly as it doesn’t take much time for the seeds to develop. The use of a pre-emergent herbicide can help reduce future populations. Hairy bittercress can be a nuisance in the landscape, turf, greenhouse and nurseries.

Date Published: April 6, 2018
Authored by: Joe Boggs

Driving south on I-71 Wednesday, I was mesmerized by a deep purple veil creeping across fields like smoke on the water.  The purple haze, all in my eyes, made me wanna drive ’til I ran out of highway into the purple sky.

The annual bloom of Purple Deadnettle (Lamium purpureum) that is just getting underway in farm fields flanking Ohio’s southern highways was responsible for my nostalgic pop culture smash-up.  Even this weed’s name would be great for a rock band; think Deep Purple meets deadheads.

Purple deadnettle is a winter annual meaning that seeds germinate in late summer to early fall.  Members of this sneaky group of weeds grow throughout the winter and sing their flower song in the spring.  This isn’t a problem for farmers because winter annuals are easily plowed under in the spring so they don’t compete with summer annual crops.  In fact, in some ways, they act like winter cover crops.

However, winter annuals can create headaches for landscape and turfgrass managers.  Since preemergent herbicides are typically used to target the spring germinating seeds of summer annuals (e.g. crabgrass), winter annuals such as deadnettle can escape to reappear as harbingers of spring each year.

The beautiful purple display beginning to adorn Ohio farm fields is produced by both the flowers and new leaves of purple deadnettle.  The pitcher-shaped flowers range in color from pink to deep purple.  Older leaves are green to purplish-green while new leaves may be a deep, reddish-purple.

Henbit (L. amplexicaule) is sometimes mistaken for purple deadnettle, and vice versa.  Both are winter annuals and since both are members of the mint family (Lamiaceae); they have square stems.  However, henbit leaves are scalloped and evenly spaced along the stem; new leaves do not have a purple hue.  Plants tend to grow low to the ground and are seldom so prolific they cover large expanses of open ground.

The leaves of purple deadnettle are triangular to heart-shape and serrated along the margins.  They arise opposite of one another along the stem and new leaves may be deep purple.  Deadnettle plants may rise to height of 16 – 18″ and they commonly carpet open ground such flower beds, openings in weakened turfgrass, and of course farm fields.

Purple deadnettle can be controlled by hand weeding and cultivation.  A post-emergent broadleaf herbicide can be applied in early spring to control the blooming plant, but a pre-emergent herbicide will need to be applied in late summer to control the germinating seeds of this winter annual.  If you do choose to use an herbicide, be sure to follow and read all label directions.

Date Published: April 2, 2018
Authored by: Joe Boggs

Our slowly developing spring is a real boon to us procrastinators.  If you exercise caution by performing a close inspection of what lies beneath, there may still be time to make a non-selective herbicide application to control Poison Hemlock (Conium maculatum) without wiping out preferred plants that have not yet sprung for spring.

Poison hemlock is certainly a worthy target for early spring herbicide applications.  It’s one of the deadliest plants in North America.  You don’t want this nefarious non-native invasive weed flourishing in landscapes where people; particularly children, can come into contact with the sap, seeds, foliage, or roots.  It’s no exaggeration to say the outcome could be lethal; consider Socrates.

Death in a Tea Cup:  A Greek Tragedy

The plant contains highly toxic piperidine alkaloid compounds, including coniine and gamma-coniceine, which cause respiratory failure and death in mammals. Indeed, the infamous demise of Socrates is testament to the lethality of poison hemlock.  Plants and seed were imported to North America as an ornamental from Europe and West Asia in the late 1800s.  Unfortunately, this dangerously toxic plant is now common throughout much of Ohio.

The toxins must be ingested or enter through the eyes or nasal passages to induce poisoning; they do not cause skin rashes or blistering.  Regardless, this plant should not be handled because sap on the skin can be rubbed into the eyes or accidently ingested while handling food.  While the roots are more toxic than the leaves and stems, all parts of the plant including the seeds should be considered dangerous.

Death-Defying Identification

Poison Hemlock belongs to the carrot family, Apiaceae (formerly Umbelliferae).  It shares a number of characteristics with the non-native but non-toxic Queen Anne’s Lace (Daucus carota) as well as the non-native Wild Parsnip (Pastinaca sativa) which is notorious for producing sap that causes skin blisters through phytophotodermatitis.

All stages of the poison hemlock plant have bluish-green leaves that are 3-4 times pinnately compound, and the deeply cut parsley-like leaflets have sharp points.  Flowering plants have hairless, light-green to bluish-green stems that are covered with obvious purplish blotches.  Clusters of tiny white flowers are borne on structures called umbels that look like upside-down umbrellas.

Turning the Tables:  Poisoning Poison Hemlock

Poison hemlock has a biennial life cycle and spends its first year as a basal rosette; the stage that is currently very apparent.  During its second year, plants produce erect, towering stalks and multi-branched stems topped with umbrella-like flowers.  Mature plants can measure 6-10′ tall.

Poison hemlock can be managed by mowing and tilling; however, the most effective control and perhaps safest relative to avoiding the sap focuses on properly timed herbicide applications.  Non-selective herbicides, such as glyphosate (e.g. Roundup) or pelargonic acid (e.g. Scythe), applied now can eliminate the first season rosette stage and the second season flowering stage, before seeds are produced.  Selective herbicides, such as triclopyr (e.g. Triclopyr 4, Ortho Poison Ivy and Trough Brush Killer) or clorpyralid (e.g.Transline), may also be applied now, but are generally more effective once plants start initiating the flower stalks.  Of course, as always, you must read and follow the label directions when using any herbicide to maximize safety and product efficacy.