Groundcovers for gaps

I promised on last week’s post that I’d mention some other low-input methods of keeping weeds out of the gaps between paving stones.  Here are a few photos of my own yard, where we’ve been installing flagstone pathways and terraces.  (Money-saving hint: check out craigslist and/or freecycle for free pavers and other types of stone.  We got all of ours free – just had to pick them up.)

We bought flats of groundcovers, such as woolly thyme, Irish moss, and blue star creeper.  In sunny areas, these plants thrive and spread quickly. But in shadier, moister areas they haven’t done so well.  Instead, we’ve allowed nature to fill the gaps for us.  Naturally occurring mosses, ferns, and other small plants keep out annoying weeds yet are small and attractive in their own right.

You can jumpstart the process by making a moss “milkshake” to spread between pavers.  There are recipes on the web, so I won’t bother repeating them here.  I prefer to let nature take its course (or maybe I’m just lazy).

Hot new method of weed control?

There’s a new report out from University of Copenhagen on killing weeds between paving stones. What they recommend is burning or steaming the weeds lightly and repeatedly. Boiling water, steam, even flamers can be used to wilt the leaves over the course of several treatments (six was recommended). This process damages the leaves beyond repair, slowly starving the roots to death.

I’m not sure exactly how I feel about this study (which is getting a lot of attention on the internet). On one hand, it is a chemical-free way to kill weeds…but on the other hand, it’s pretty labor intensive and requires energy inputs for generating heat. Moreover, what does one do once those weeds are gone? Those bare patches of sterilized soil are just going to be recolonized by new weeds.

Several years ago I had a Master’s student look at different methods of killing English ivy. She also tried the steam treatment.  Ivy laughs at steam. Aggressive perennial weeds like English ivy or blackberry or Japanese knotweed are unlikely to be much affected by blanching, and certainly not by half a dozen treatments.

But most of us probably don’t have big, woody-rooted weeds amongst our paving stones.  In my own garden, it’s a mixture of species that fill these gaps and some of them – like mosses and some smaller ferns – I actually enjoy.  So I pull out the things I don’t like, leaving the desirable species to fill in the gaps.  It’s simple and requires no special equipment.

Am I missing something here, or is this really much ado about nothing?

How open-minded are you? No, really.

Admitting you’re wrong is difficult.   For exhibit A see the recent discussion between me and Jeff over alternative nursery containers.  We all like to think we’re open-minded but  when push comes to shove we all end up like the Fonz on Happy Days when it comes time to say ‘I was wrrrrr… I was wrrrr….  I was not exactly right.”   As scientists we’re supposed to be objective and base our judgments on verifiable data and careful and repeatable observations.  But, as humans, we all have biases and preconceived notions that are hard to get around.

So here’s a challenge for our Garden Professors readers (and my fellow  GP’s too).  Give an example of a case where you’ve changed your mind about a landscape or gardening practice or product.  And what did it take to change your way of thinking and make you say, “Ya know, maybe I was not exactly right.”

I’ll start.  I have long been dubious about is the use of plant growth retardants (PGR’s) on landscape plants.  PGR’s are chemicals that reduce plant growth, usually by inhibiting shoot elongation.  There are a variety of PGR’s on the market but most work by inhibiting plant growth hormones such as gibberilin or auxins.  PGR’s have long been used by bedding plant producers to make plants more compact and easier to handle and ship.  One PGR, paclobutrazol, has been heavily marketed in recent years to control growth in landscape trees and shrubs.  The effectiveness of paclobutrazol at controlling plant growth has been well established in the literature, though there are some exceptions.  My long-held skepticism toward the landscape application of PGR’s stems from a couple factors.  First, the marketing claims are pretty fantastic: Not only does it control growth but it improves drought tolerance, heat tolerance, insect resistance, and disease resistance (no word on how it does on getting spots out of rugs).  Second, just because something works on containers of annuals in a greenhouse doesn’t mean it will work on trees and shrubs in the field with variable soils, weather, etc.  Third, why bother?  If something is growing too fast; back off the fertilizer, head it back with the Felco’s, or take it out and put something more appropriate there.

What changed my mind.  I’ve seen a couple of effective applications of PGR’s on trees and shrubs that have made me re-evaluate my opinion.  One was at a program at the Indiana Arborists Association a couple years ago.  The study tracked pruning cycles following utility line clearance pruning.  They found that treating trees with paclobutrazol following pruning reduced re-sprout growth and extended the cycle time between pruning by 2 to 3 years – which is a big deal to utility arborists.  More recently, I’ve been observing shrubs here on campus that our landscape service group has been treating with paclobutrazol after pruning.  Typically many shrubs are rejuvenated after pruning and put on a big flush of growth.  The PGR application was effective in keeping this in check.  (Some examples with burning bush appear below). Even to my highly skeptical eye, the treated plants just looked a heck of lot better than the untreated.

Do I believe all the marketing claims made about PGR’s for landscape plants?  No. But for extending pruning cycles and keeping plants in check, I have to admit I was not exactly right. 

Burning bush with PGR app.

Burning bush without PGR app. (Note treated and untreated were growing in same bed)

By controlling growth after pruning PGR application can help keep these shrubs in line and lengthen the time between pruning cycles.

Are Goodies Bad?

I can’t decide if I like the fact that various companies read what I write or not. On the one hand, it’s kind of nice to know they care, but on the other, I kind of like to think that I can talk to people without them hanging over my shoulder.

How do I know they’re there over my shoulder?

They send me stuff.  Sometimes it’s a nasty or "educational" e-mail after I’ve published something about their product that they don’t like, and sometimes it’s a gift bag (or an offer of a gift bag) if I mention that I like something.

I never respond, with one notable exception.  Once I wrote a little something on bees for a newspaper and a small honey operation went out of their way to drop off some honey for me at the front desk.  I thought that was really nice so I wrote them a quick thank-you. 

I wrote something nice about Milorganite recently and they sent me a ballcap, some pens, and samples — along with some literature.  That was nice, but I feel like it wouldn’t be appropriate for me to write back.  I do like Milorganite, but if I start to think of them as my "friends" I don’t know how impartial I’ll be able to be if I find something out that changes my opinion.  I will use the free sample though.

On the boo-hiss side I had the lawyer from company in town call a newspaper where I published a story recently to tell them I got my facts wrong and that they needed to publish a retraction.  The company was wrong though — so no retraction was published, but it was still odd to have a lawyer get involved like that.  Will I think twice about talking about that company’s product in the future?  Not consciously.  But subconsciously?  Who knows (shoot — subconsciously it might make me talk about them more — I don’t know).