How to Kill Buckthorn

Last year we completed a small research study on how to kill buckthorn.  If you live in the upper Midwest then you’re familiar with this plant as a shrub which has escaped cultivation, been spread by birds, and generally made a nuisance of itself, particularly at the edges of forested land.

Buckthorn is notoriously difficult to kill after it gets more than about a foot high.  It laughs at single applications of roundup. If it’s pulled out of the ground any roots that don’t come with it have a good chance of sprouting shoots themselves, and it seems to enjoy being treated with organic herbicides like vinegar.  So, to try and kill bucktorn, we used an herbicide which had the active ingredient triclopyr.  This is an active ingredient which is usually great against all manner of weedy vines like poison ivy.  This herbicide is labeled for homeowner use and is available in most garden centers.

We applied this herbicide to buckthorn in the spring, summer and fall, and we used a few different application methods including painting the herbicide onto cut stumps and spraying it onto the leaves of uncut bushes, as well as painting the product onto the lower portion of stems.  Some of these application methods were experimental.  Do not attempt to apply an herbicide in any way besides that which is listed on the label!

That said, we found that the fall was by far the best time to apply the herbicide and that spraying the foliage wasn’t nearly as effective as other application methods, particularly painting the cut stem with the product after cutting it down.

Sheet mulching – benefit or barrier?

Alert reader Matt Wood pointed out a recent article in the NY Times on mulching with newspaper and wondered about my take on the topic.

For use on landscapes, I do not like sheet mulches of any stripe.  They tend to hinder to air and water movement, most especially in unmanaged landscapes like restoration sites.  A classic example is the use of cardboard or newspaper covered with wood chips.  The chips are easily dislodged, exposing the sheet mulch which quickly dries out and becomes hydrophobic.  Thus, the roots of desirable trees and shrubs lose out on the water, while the weeds surrounding the edges of the mulch benefit from the runoff:

Published research on sheet mulching in landscape settings confirms the drawbacks of sheet mulching.  But the article in the NY Times is about vegetable gardens.  This is a different situation – more akin to agricultural production than to landscape horticulture.  Vegetable gardens are routinely managed during planting, thinning, weeding, and harvesting.  Newspaper sheet mulches in these situations rarely dry out and, when kept buried and moist, do break down quickly.

So – keep the sheets on the (vegetable garden) bed where they belong!

It’s a Bird! It’s a Plane! It’s a …Butt?

So we last left off discussing the issue regarding the fact that the point is incumbent on us that one can’t refer to a native as "invasive" withou…


What’s that??!
There! Amongst the Pachysandra!

Is it a freshman? Perhaps passed out in our campus garden in despair after yet another stinging defeat of the Hokies?

Nay, ’tis a pair of Calvatia gigantia – Giant Puffballs.

'Tis not a butt

Pretty impressive, though. Note toes for scale. Unfortunately, with all the foot traffic in our garden, there’s little chance they will make it intact to the "fun stage" (official mycological term for when the exterior turns dark ‘n crispy and the internal spores floof out in huge clouds upon poking).

I fully expect our Pacific Northwest people to be all "You should see the size of OUR Calvatia species!"
Bring it.

Another W.O.W.

We’ve been beating up nurseries over Why-Oh-Why (W.O.W) do they sell things like Scot broom.  Here’s one of my  favorite W.O.W’s from the landscape side (Homeowner division).

Why-oh-Why do people think grass clippings make a good mulch?!  This photo comes from near my home.  The homeowner put the clippings down about two months ago.  All the trees were dark green and healthy before the clippings were put down.  Note how chlorotic the trees in the middle have already become and the dead lower limbs where the trunks were covered.   We’re all for mulch but this ain’t it!

A freakin’ violet

Friday’s puzzle scared you off!  Matt was correct – this is an African violet (Saintpaulia spp.).  But unlike other African violets, this one never opens its flower buds (Sandy nailed it!).  Originally cultivated in Germany, these plants are marketed in the US by Optimara Violets.  That’s all I can tell you about this quirky little cultivar.


Friday puzzle – from Dallas!

I’m in Dallas for the next 4 days attending the GWA (Garden Writers Association) annual conference.  (I get to give a talk on Horticultural CSI on Sunday!)  Tonight we had a slew of vendors to explore, and among the offerings I found this plant:

So today’s question – what is this plant?  And what makes it so unusual?  The first question might be easy – the second one, not so much.

Answer and more info on Monday!

Are Fertilizer and Insecticide Spikes a Good Idea?

One of the products that I often hear gardeners raving about are their fertilizer / pesticide combination spikes which are supposed to not only feed your plants, but also kill all of the insects which attack them.  I, personally, have not used these products, but I’m generally the kind of person who says “If it works for you then keep using it”.  Still, these spikes bug me a little.  Here’s why.

First of all I should point out that I’m not opposed to fertilizer spikes by themselves.  I’m a little concerned that fertilizer should be spread out instead of concentrated in one place, but still, I don’t consider them that bad.  The insecticides used for these spikes is where I have the problem.  Once upon a time these spikes were made with a chemical called disulfoton (aka disyston) which is bad news.  It’s a water soluble chemical which is highly toxic to people.  If you have an old package of fertilizer / insecticide spikes around there’s a good chance they were made with this chemical.  Do yourself a favor and get rid of them.  This stuff is really toxic and not to be messed with.  On the other hand, if you’ve purchased fertilizer / insecticide spikes recently, then the active insecticide in those spikes is probably imidacloprid.  Imidacloprid is a mixed bag when it comes to safety.  It’s not nealy as toxic as disulfoton, but it’s not non-toxic.  It has been banned in Europe for a variety of reasons, the most important of which seems to be that it was implicated in the collapse of bee hives (imidacloprid is systemic insecticide so it will get into a plants pollen where honey bees could eat it).  At this point it hasn’t been ruled out as having something to do with hive collapse here in the states — though if it does have a role it does not seem to act alone.  It can also affect other beneficial insects who feed on pollen.  Additionally, it has been known to control some pests while allowing mites to go crazy — in fact, it may even increase the rate of mite egg laying.

But imidacloprid is an effective insecticide which works against a wide range of insects which you that you might find on your plants.  It is much safer than many of the older systemic insecticides, and it isn’t readily translocated to fruits (a problem that many people are concerned about with systemic insecticides is the movement of these insecticides into the fruit itself where it can’t be washed off — Imidacloprid is translocated to fruits –just not that much — it moves in the xylem and fruit takes up mostly phloem).

So these spikes are one of those things that I’m wary of.  Not to say you shouldn’t use them, but be aware of what they are and what they could do before you buy them.

W.O.W. (aka Why oh why do nurseries sell this plant)?

Since we’re back on the alien train (spaceship?), I thought I’d bring up another of my least favorite shrubs – Scots broom – as our next installation of WOW (why oh why?).

Scots (or scotch) broom (Cytisus scoparius) is a much-reviled intruder in the western and eastern United States.  Originally introduced as a sturdy ornamental, this legume quickly invaded disturbed areas and is labeled as a noxious weed in several western states.  In Washington, it’s quarantined.  Research dollars have been dedicated to studying best methods of eradication.  So it doesn’t take a rocket scientist (or even a garden professor) to figure out that it’s probably not a wise addition to one’s landscape.

But apparently some nurseries either (1) haven’t paid attention or (2) don’t care.  In a quick look at the internet, I found nurseries in many states, including Oregon and California, that sell this species.  Many will argue that they are selling “less invasive” or “sterile” cultivars, which is a poor excuse in my opinion.  Readers of this blog know by now that cultivars often revert to wild type, and there’s no reason to assume that broom cultivars are exempt from this ability.  Furthermore, we know that plants have the ability to extend their ranges past what we think they are (hello kudzu?).

Just popping in to say hello

There are many ornamental alternatives to Scots broom that can easily be found online or in print.  I’d love to hear some rational arguments from nursery owners, landscape designers, or anyone else justifying the sale of this plant.

Defining Your Terms

Loyal reader and thoughtful commenter Ray Eckhart posted a while back (something along the lines of) wouldn’t it be nice if we could come to some agreement on all this “what’s invasive” terminology.  This has been flitting in and out of my brain but has not found sufficient gray matter to come to rest. Regardless, here goes.  I’ve attempted to capture these concepts in as few words as possible. My opinions in no way reflect those of the Garden Professors, blog host Washington State University, or anyone else important, for that matter.

Native. From these here parts.
Or this half/region/corner of the Continent, depending on your definition. And there are LOTS of them.  We had this discussion in my Herbaceous Landscape Plants class last week. My students alone came up with 10 different definitions and/or criteria, all probably legit.  I teach a plant as native if it is found east of the Mississippi (these are garden plants, it’s not a botany class). I try to describe its “nativeness” more in terms of whatever biome it came from (tall grass prairie, deciduous piedmont forest, etc.) as cue to how to best use it in the landscape.  If it’s found even closer to home, I find myself describing it as “really native” which makes no sense, but I can’t seem to stop.

Alien. Not from here (wherever here is).
Is a broader term than “native” because “here” seems to refer to land masses, whether continental or island. Alien has a rather negative and even inter-planetary vibe to it. “Must…thinkofway… to… eliminate… Japanese Privet. Helpme…, Spock.”

Non-native.  The kinder, gentler alien.
As in, Hosta are not going to take over the planet. Even though non-native is often used in the same breath as alien, we need it to stand on its own in this case:  what do you call a Calochortus (Mariposa Lily) in Virginia? It’s not native to the east coast, but species of the genus are native to the western part of continental North America and further south.  So I deem it non-native, but not alien. Maybe “mail-order” should be a category.

Exotic.  An attractive but promiscuous alien.

Invasive. Aliens amuck.
Lists are created, but are unfortunately often ignored (see previous post on ligustrum). There are lots of good invasive plant definitions out there. But can native plants ever be invasive? Or are they just “vigorous” or “aggressive”? See below.

Vigorous. This has positive connotations. Holds its own in difficult situations, makes lots more of itself, can share with friends.

Aggressive. See vigorous, but cue theme to Jaws. Makes a WHOLE LOT more of itself. Can share with unsuspecting friends.

Passive-aggressive.  Just when you think “I don’t know what all the fuss was about”, BAM you’re pulling out it of every nook and cranny. I can think of many examples – good fodder for a future post.

Based on these definitions, I see a few of our favorite garden natives as aggressive or passive-aggressive. You’re not sure whether to be pleased or perturbed that a delightful, wildlife-friendly native is reseeding all over your garden.  Two examples right here in our campus garden: Joe Pye (Eupatorium purpureum) and Cup Plant (Silphium perfoliatum). Completely out of hand.

I am no authority on this stuff, just happy to be part of the conversation. Feel free to agree/disagree. But please be gentle; I’m suffering from a late night of watching the Hokies get splatted by Boise State (invasive Broncos).

Volunteering for duty

One of the advantages of having a couple acres (and not being especially fastidious about weeding) is that sometimes you get your landscape plants for free.  I always keep an eye out for interesting plants that may turn up on their own – or a least get left behind by our bird friends.  Here are some volunteers that have shown up recently at Daisy Hill farm that I’ll work into the landscape.


Sassafras (Sassafras albidum) are notoriously difficult to transplant.  I’ll leave these sassafras volunteers where there are and relocate the shrubs in the bed.  I’m looking forward to some awesome fall color in a few years.


The native range of redbud (Cercis canadensis) only extends into the southernmost counties of Michigan but they generally do fine here in the Lansing area (just north of the end of the native range).   We have an old redbud in the front of our house so we get volunteers from time to time.  This one is on the edge of our patio so it’s easy to keep an eye on.  I’ll let it grow on another year or so and then find it home.


Most people probably wouldn’t get too excited about eastern redcedars (Juniperus virginiana) showing up on their own.   When I was with the US Forest Service, my grad student and I did research on seed germination of eastern redcedar and Rocky mountain juniper (J. scopulorum).  Ironically they can be difficult to grow as seedlings in nurseries because the seed are doubly dormant (they have a tough seed coat that requires scarification and the embryo is dormant and requires cold stratification).  I’m planting conifers as a screen on the south side of property. I’ll move these guys and a couple of their friends in the spring.