Another good reason to mulch

Posted by Bert Cregg

Researchers often get accused of concluding the obvious.  At some point we’ve all scoffed at headlines like, “Study finds cell phones and driving don’t mix” or “Researchers discover high heels make your feet hurt.”* But even when a study demonstrates something we already know, sometimes there is still value in being able to put hard numbers on the scope of the problem – and hopefully spur some action.

A case in point is a recent study by Justin Morgenroth, Bernardo Santos, and Brad Cadwallader at the New Zealand School of Forestry, “Conflicts between landscape trees and lawn maintenance equipment – The first look at an urban epidemic” Urban Forestry and Urban Greening 14:1054-1058.  Morgenroth and his colleagues surveyed over 1,000 trees in public greenspaces (parks, cemeteries, campuses) in and around Christchurch, New Zealand (pop. 375,000) to assess the amount of damage to trees by lawn equipment.  Their conclusion: Lawn equipment is hell on trees.  This conclusion, of course, surprises absolutely no one that has ever looked at trees near turf in a public place on this planet.

lawn mower blight 2

 

Morgenroth et al. claim their survey is the first systematic look at this issue and their data are staggering.  Nearly two-thirds (63%) of the trees they surveyed had at least one wound.  The proportion of trees with wounds was fairly constant regardless of type of planting (i.e., park, campus, cemetery, roadside verge), though trees in parks and campuses tended to have more wounds per tree than trees in nature reserves or roadside verges.

Not all the news was bad, however.  Morgenroth et al. found that grass cut-outs or mulching around trees significantly reduced the number of wounds per tree.

So, not a conclusion that should take anyone by surprise, but some sobering data to put some scale on the size of the problem.

 

*actual conclusions from real studies

Just post some pretty pictures or something

Posted by Bert Cregg

A little over six years ago Jeff Gilman called me out of the blue and asked me to be part of a new blog about the science of horticulture that he was embarking on along with Linda Chalker-Scott.  I was reluctant – I didn’t know much about social media at the time and was plenty busy already.  Jeff explained that he was recruiting others and how we would rotate posts. I asked Jeff, “What if I don’t have anything to write about?”   Jeff replied, “Just post some pretty pictures or something.”  So with that long ago conversation as backdrop, here are a few photos from this week’s trip to Hidden Lake Gardens near Tipton, Michigan.

Sugar maple fall color
Sugar maple fall color
Entrance to the Harper Collection of Dwarf and Unusual Conifers
Entrance to the Harper Collection of Dwarf and Unusual Conifers

Taxodium distichum "Pendens' cones

Taxodium distichum “Pendens’ cones

Pinus contorta "Chief joseph'. With apologies to Joseph Tychonievich...
Pinus contorta “Chief joseph’. With apologies to Joseph Tychonievich…

Sassafras albidum fall color

Sassafras albidum fall color

The long and winding road...
The long and winding road…
Sciadopitys verticillata 'Joe Kozy'
Sciadopitys verticillata ‘Joe Kozy’
Abies koreana 'Icebreaker'
Abies koreana ‘Icebreaker’
Taxodium distichum 'Pendens'
Taxodium distichum ‘Pendens’

 

Native vs Exotic: Not as simple as it seems

Lots of discussion recently over on the Facebook side regarding the recent publication in Ecological Letters by Karin Burghardt and Douglas Tallamy, “Not all non-natives are equally unequal: reductions in herbivore β-diversity depend on phylogenetic similarity to native plant community.” http://onlinelibrary.wiley.com/doi/10.1111/ele.12492/full
While there are certainly some things to nitpick in the paper (see Linda’s comments on the Facebook discussion), I think this paper may go a long ways re-shape, and possibly even begin to end, the debate over native versus exotic.

How was the study conducted. In 2006 Tallamy’s group established a series of test landscape plantings. Each planting fell into one of four groups: non-native congeners (species that are not native but have native relatives in the same genus); non-native non-congeners (plants from non-native genera), native congeners and native non-congeners. In 2008, when the trees were about 6’ (1.8 m) tall, they conducted a census to identify and quantify the adult and immature insect herbivores they collected. They analyzed the data to determine the amount of insect herbivore diversity within each planting type. Specifically they looked at what ecologists refer to as beta-diversity, the amount of species diversity among sites. If you’re interested and want to learn more check out https://methodsblog.wordpress.com/2015/05/27/beta_diversity/

So, what did they find? Like every good study on host-insect interactions; the answer is, “It depends.” (BTW, if you’re following along at home the key figure in the paper is Fig. 3). When Burghardt and Tallamy looked at the differences in diversity between adult herbivores on native and non-native congeners, they found no difference. When they looked at differences in diversity between immature herbivores on native and non-native congeners, they found no difference. When they looked at differences in diversity between adult herbivores on native and non-native non-congeners, they found no difference. When they looked at immature herbivores on native and non-native non-congeners, they found a small but statistically significant difference, with higher total diversity for native non-congener.

As an aside, it is also instructive to look the version of Figure 3 presented in the article’s supplemental materials, which has been re-scaled to include zero. Including zero on the scale helps to give a better perspective on the actual variation among means. It’s a little like the “Truth in lending statement” that comes at the end of your credit card bill.

tallmay re-scaled

So, a possible alternative title for the paper could be, “Do native or non-native plants increase herbivore diversity? Most of the time it doesn’t matter.” That said, I think this paper makes a number of contributions and will start to shift native versus non-native debate, and perhaps even signal the beginning of the end. First of all it demonstrates that that non-native species of native genera contribute equally to herbivore diversity. However, I think some of the most insightful information in the paper is buried between the lines and in the supplemental information attached to the online version of the paper. The authors briefly mention that they also looked at guilds (i.e., chewing insects, sap feeding insect, xylem feeders, etc.). Once again the answer of whether natives contribute more to species diversity is, “It depends.” For xylem feeders, for example, diversity was the same for congeners and non-congeners.

To me, this is the level of resolution we need to work to gain a true handle on the situation. I’m not an entomologist and I’ve never played one on TV but I’ve been around these questions long enough to know that different types of insects are attracted to or repelled by different plants by different mechanisms. In one case it’s an attraction pheromone, in another it’s a defense chemical, sometimes it’s leaf toughness or a tree is able to produce enough resin to drown boring insects. An old axiom states that ecosystems are not more complicate than we think; ecosystems are more complicated than we can think. As this paper demonstrates, to think that all the complex interactions between plants and insects can be boiled down to something as simple as native or exotic is hopelessly naïve.

Pretty in Pink

It’s October. Fall is such an underrated time in the garden, and much pink can be found. In fact, flashes of pink are everywhere!! Got my ma’ams grammed last week; thanks for the reminder, NFL.

Muhlenbergia ‘Pink Flamingo’.
Aye yi yi. Alleged hybrid between M. capillaris and M. lindheimeri. Five feet tall and as wide, huge plumes of pink. Looks like nothing important the rest of the year, then, blammo!!! Sorry, folks north of Zone 6. Actually, it only works here  (Z. 6a) because of outstanding drainage; it’s planted in a pile of gravel. Mine has lived through two winters with -20 F days.  Place where the sun will rise or set behind it for maximum effect. Bunny the Whippet not included.

muhleypinkflamingo

Salvia involucrata – Rosebud Salvia
Big ol’ gal that will not favor you with blossoms until September. Absolutely not hardy here, or anywhere north of Zone 8.  Take cuttings, ’cause baby she’s worth it. The furry, hot pink flowers will thrill any hummingbirds left zipping around (I read ours the riot act this weekend, they have GOT to hit the road soon). Note there is some hullabaloo as to S. puberula vs. S. involucrata vs. some hybrid amongst the two.  Will report back.

salviapink

Chrysanthemum x whatever ‘Venus’ .
Am so tired of the taxonomic uncertainty. ChrysanthemumDendranthemum…  Whatever you call her, ‘Venus’ is a wonderful “real” garden mum (not those heinous meatball things) that brings the pink blooms in September, then fades to palest of pink, but not before every bee in the neighborhood visits.  Fairly compact (2-3’) and pretty darn hardy (Zone 5). Tuck Venus amongst things you know will be done before fall – bee balm, phlox, etc. to keep the show going!

chrysvenus

So there you have it, some pink for our October gardens.  In loving memory of my sister Carlene.

Mitchella repens … Partridge Berry … an Evergreen Native Groundcover for Shade

NaturalSetting1

Partridge Berry in its Natural Setting

One of the questions that came up regularly when I was working the hotline at the local county Extension office, is a recommendation for an evergreen ground cover for shady spots.  I had the same issue when I created my own shade garden … something that would have year round interest, but complement my desire to emphasize native species, although that was only one consideration.

The solution was literally right next to me, as a walk in my woods revealed with the lovely plant Partridge Berry, or Mitchella repens.

Not only is Partridge Berry (Mitchella repens ) beautiful, evergreen, shade-loving, and native to Eastern North America, but there’s also a fascinating aspect about its flowers and fruit, from a botanical, and evolutionary point of view.

According to the U.S. Forest Service Celebrating Wildflowers website, the “… genus name Mitchella was given to this plant by Linnaeus for his friend John Mitchell, a physician who developed a method of treating yellow fever. The species name repens refers to its trailing or creeping habit.”

Berry1

Here’s the part I found fascinating: The plant is dimorphous, meaning “occurring in two forms”:

In late spring, two beautiful white flowers (with one calyx) each open their four petals to entice insects to collect their nectar. Each blossom has one pistil and four stamens. The pistil in one is short and the stamens are long. In the other it is just the opposite. … Because of this no flower can fertilize itself–all flowers must be cross-pollinated by insects, and both flowers must be pollinated to get a single healthy berry. A berry will stay on the vine until after the blooms appear in the spring unless a hungry bird finds it nestled among the fallen winter leaves.

How cool is that?  The twin flowers produce, together, only one berry.

Berry2

Here’s a closeup, where you can see residual evidence of the fusion.  The berry is edible, and persists through the winter, assuming it is not consumed by “ruffed grouse, northern bobwhite, sharp-tailed grouse, and prairie chicken.

The fruit is also “frequently eaten by raccoons and red fox” and it has been reported that “partridgeberry made up 2.9 to 3.4 percent (dry weight) of the summer and fall diets of white-tailed deer.”

June2014Bloom1

Here’s a picture of the two flowers in bloom.

It’s easiest to spot the plant in its natural setting while hiking in late Fall, or early Winter before snowfall, or early Spring after snowmelt.

Back to the Forest Service article:

Some gardeners consider Partridge Berry a must for winter gardens. During the cold days of late winter Partridge Berry is a treat to the eyes with its deep, dark-green leaves and occasional scarlet berries. In a garden setting this evergreen prefers shade, accepting the morning sun. Partridge Berry is extremely difficult to propagate from seed.

The best way to introduce this native into your garden is through 1 year old cuttings or by division. In the garden situation they will form a thick, substantial ground cover. Once established they are relatively trouble free with the only required maintenance of keeping garden debris from covering the mats.

As always, do not wild collect plants from public lands and only from private lands when the landowner grants permission. Partridge Berry is a commonly available plant from native plant nurseries especially those who specialize in woodland plants.

I love the symmetrical variegation in the evergreen leaves, a bright, light yellow line bisecting each leaf, and the delicate, less visible veins.

It’s a great alternative to Vinca, an introduced species from Europe that appears on invasive species lists in our area.

A Google search will reveal many potential on-line sources for buying Partridge Berry plants, or check with a local nursery, or independent gardening center in the native plant section.

Confessions of a Lazy Gardener

NeglectedBed1

I admit it.  I can’t keep up … I’m not as industrious as most of my gardening friends are when it comes to the effort necessary to manage my 6 acre landscape.

It can get overwhelming, especially when there are previous beds that came with the property that had been neglected for 10 years or more by the elderly lady who owned the property before us, and where perennial weeds are well established.

I make a valiant effort in the Spring, with all the enthusiasm of the new season to clean them up … dig the perennial weeds … plant something new (usually a division, or a naturally layered specimen, from elsewhere, or one shared from friends), but by mid-July or so, I have to redirect my efforts to the places that I’ve created … the shade garden … the rock (mostly sedum) garden … mulching the new trees and shrubs, and of course my tomatoes, so these previous places don’t get the attention they deserve.

But then again, some surprisingly beautiful, and beneficial results can happen in spite of (because of?) the neglect …

NeglectedBed2

This is a “pre-me” bed of mostly Japanese Anemone stretching between two arbors, with Trumpet Vine (Campsis radicans) (pre-existing), and Climbing Hydrangeas (Hydrangea anomala) (me added), anchoring each end.

The Goldenrod (Solidago) and White Snakeroot (Ageratina altissima I think) now dominate, along with Sweet Autumn Clematis (C. terniflora), a non-native introduction that appears on watch lists as an invasive species in our area.

Syrphid1

Yet look at the insect life.  Scads of hoverflies (some species of Syrphid), who in addition to their role as pollinators as adults, are voracious consumers of aphids in their larval stage.

Scoliid

Scoliid wasp, predatory on Japanese Beetles.

Ailanthus Moth

An Ailanthus Webworm Moth (Atteva aurea), which uses the invasive Tree of Heaven (Ailanthus altissima) as its larval source for food.

Honeybee

And my, and most folks favorite these days, honeybees (Apis mellifera)

Hydrangea

And if I kept up the weeding of this neglected bed, would there be a self-seeded Hydrangea paniculata available to transplant elsewhere?

So, probably a rationalization to justify my laziness … but looking on the bright side, there can be beneficial results from my neglect.

Don’t just stand there like a statue

Posted by Bert Cregg

 

Reading through Linda’s recent article in Arboriculture and Urban Forestry “Nonnative, Noninvasive Woody Species Can Enhance Urban Landscape Biodiversity” (Arb. & UF 41:173-186) reminded me of some thoughts I had while I sat through a talk by Doug Tallamy at the New England GROWS conference back in February.  As most GP blog readers are likely aware, Tallamy is the author of Bringing Nature Home.  The basic premise of the book is that native insects only feed on native plants and therefore the use of exotic landscape plants will cause ecological food webs to collapse and the end of the world as we know it.

 

Looking at things critically, there was certainly plenty to nitpick in the talk.  For example, to illustrate that insects feed more on native than non-native genera, Tallamy contrasted Quercus, a genus that includes hundreds of species distributed across the northern hemisphere, to Ginkgo, a monospecific genus (heck, a monospecific order) with a limited native range in China.  Tallamy also compared the food value for birds of seeds of five native shrubs with five Asian exotics.  The North American plants all had higher nutrition, which leads to one inescapable conclusion: If you’re a bird-lover in Asia you need to plant more exotics from North America.

 

But, as I said, those items are nitpicking.  In an apparent effort to appease critics, Tallamy addresses the question of whether it’s ever OK to plant exotics.  He says yes, but think of them as “statues” – nice to look at but devoid of any ecological value – and then put up a slide of a landscape with a bunch of statues photoshopped in.  All analogies break down eventually but the ‘exotics as statues’ model fell apart before the slide hit ever the screen.  First off, native insects, birds, and other wildlife do utilize nonnative plants and I’ll refer you to Linda’s review and her 100+ citations on that point.  But just as importantly, nonnatives can also provide many of the same environmental benefits as native plants.  Statues, on the other hand, don’t cool buildings, sequester carbon, reduce stormwater run-off, and create vertical structure and cover for wildlife – OK, statues provide perches for pigeons, but that’s about it.  Landscape plants, and trees in particular, can provide a myriad of ecological services – but they can only provide these functions if they are alive to do so. Despite the intuitive appeal of, “Native plants are adapted to our local environment”, in many urban, and even suburban, environments this is simply not true due to urban heat island effects, top-soil removal, compaction and other site disturbances.

 

In his talk, as in his book, Tallamy demonizes the typical suburban landscape showing a photo of an expansive lawn with a lone Bradford pear tree.  OK.  Is the problem here the pear? If we changed the pear to, say, a lone shagbark hickory would anything change dramatically?  No, but this does bring me to a point of agreement with Tallamy.  The fundamental problem we face in our landscapes is lack of diversity; not only species diversity but also structural diversity and age class diversity.  If we can build diversity and generate ecosystem services with natives; great, go for it. But we need to understand that our list of suitable native trees is shrinking (as an aside, ignore Tallamy’s recommendation to plant green or white ash if you live in eastern North America). Vilifying, or even banning, nonnatives will ultimately reduce diversity in urban and community forests and their ability provide ecosystems services, not enhance it.