Solving the bagworm problem without chemicals

Sooner or later, most landscapes have to deal with a bagworm problem. Sometimes the hungry pests only threaten one or two trees in a landscape. But they can really ruin the party when it comes to the classic, evergreen  privacy buffer. A long line of Arborvitae, Leland cypress, or cryptomeria are the perfect home for bagworms, because of the way the bagworms spread.

Eggs hatch out and the tiny larvae begin feeding or climb to higher parts of the tree, then “balloon” on a thread of silk, hoping to land on a neighboring tree (which is why those lines of screening trees make such a perfect place to keep feeding, generation after generation). Then they spin a protective bag composed of silk and the fine-textured needles or bits of leaves of whatever tree they are eating. Female bagworms never leave their bag, even in the adult stage.

Adult male bagworms can fly, and tend to hang out toward the bottom of the tree, and this important fact highlights a major vulnerability that the eco-conscientious gardener can exploit: Because of their location, these male bagworms are particularly susceptible to attack by two predatory insects.

These tiny predatory insects, Chirotic thyridopteryx and Itoplectis conquisitor, are among the most common of a group of insects called predatory wasps. These predatory wasps generally do not sting humans and do not protect or even form social hives of any kind.

You can attract and support predatory wasps by making sure that your landscape provides a steady supply of nectar throughout the growing season. Try planting a 3’ meadow strip along the sunny side of your privacy buffer that includes long-blooming, nectar-rich perennials like Agastache or Pycnanthemum.

I do not recommend the use of Bacillus thuringiensis (B.t.) in the landscape because even though it is a naturally occurring, organic insecticide, it kills ALL SMALL CATERPILLAR LARVAE. If you are gardening to promote butterflies, this is a no-brainer decision.

The other, even less attractive alternative--using chemical spray or soil drench--is not only harmful to the environment but over time less and less effective because the trees become very dense and tall. The chemicals are not effective unless you can reach the crown of the tree early in June, where the larvae that are most vulnerable to the sprays will be.  Those tough, water-proof bags later in the season effectively protect the bagworms from the spray.

Another environmentally sound way to avoid the bagworm problem is to plant less susceptible trees and shrubs. Although bagworms in captivity have been shown to be able to survive on the leaves of just about any tree or shrub, out in the jungle of real-world landscapes, broadleaf evergreens show much less damage. This might be due to their leaves being not quite as ideal for weaving into a bag to provide camouflage protection for the bagworms, compared to needle evergreens.

Also, deciduous trees, while still edible to bagworms, are both less of a first-choice target and also more likely to bounce back with fresh growth after being defoliated by bagworms. Plus, if you plant trees that provide direct food and shelter for birds, you will attract another bagworm larva predator: birds who have young to feed in June.

So if you can, plant a mixed buffer that includes deciduous trees and broadleaf evergreens (Magnolia virginiana, Morella pensylvanica and Ilex opaca ‘Satyr Hill’ are some of my broadleaf evergreen favorites). Doing this should help to slow the bagworms down to the point that they don’t decimate your privacy buffer.

There are also three common birdfeeder birds that are known to scavenge bagworm eggs from twigs and branches during the winter months: chickadees, nuthatches, and titmice. So keeping that birdfeeder going through the winter months might have some secondary benefits in addition to being something fun to watch.

Since the goal is balance, and not total eradication, this multi-pronged approach of planting resistant species combined with attracting predatory beneficial insects and birds in June and over the winter, can really help.

Summary: 4 steps that can reduce bagworm populations:

1. First, plant a long-season, nectar-producing strip of perennials and/or shrubs near your bagworm hangout, to attract beneficial parasitic wasps.

2. Consider replacing the bagworm-magnet trees with trees that are less attractive but still provide evergreen cover (such as magnolias, hollies, and morellas).

3. Mix some deciduous trees and shrubs into the buffer to provide food and cover for birds that nest in June, which will encourage predation of the bagworm larvae in June when they are most vulnerable.

4. Attract winter birds to your landscape to hunt the bagworm eggs from trunks and branches.

And it surely doesn't hurt that all of these recommendations are also good practices for strengthening any environmentally friendly landscape!

Have you had any battles with bagworms and tried these methods? What were your results?--I'd love to hear about it!


Chris Pax

P.S. The Native Plants for the Landscape COURSE is full (yay!) and started last week. But there will be another one in February, on Saturdays. If you're interested, let me know.

Should you plan your garden the way a chef plans a menu?

Hello Gardeners!

Our recent, amazing warm spell got me thinking about what it takes to transform a landscape. I was driving with the windows down, and the warm breezes, cheery sunshine, and sounds of birds all juxtaposed with the winter-weary landscapes I was driving through... It got me thinking about how sometimes, in spite of best efforts, landscapes just feel... tired and uninspired.  Late winter and early spring is a time when you can really feel the rub!

The gorgeous spring weather can really bring on the itch to do more! But what does it take to get past that blank panel of lawn, or those giant old, foundation shrubs that are now blocking the windows, toward creating a landscape that is authentically beautiful and supports vitality for us and other creatures?

I have been through this process a number of times, and I feel there are 3 key things that make it work:

Create bite-size, manageable projects.

It helps to break the whole, big, desired change down into tasks that can be accomplished in a day, or at most a weekend. Projects that do not ruin the budget for the year, but are part of a gradual, sustainable series of improvements.

Some people will hire help to get these things done, while others will enjoy the challenge and exercise of doing it themselves. But either way, when the projects are small and manageable, they get done and they tend to be easier to maintain, especially during their first, most vulnerable season.

Know Your Big Picture.

In order to prioritize the projects and make sure that they all contribute to your overall goals, you need to have a clear, detailed idea of where you're headed. Progress on smaller projects can come to a complete halt if you are struggling with doubts or conflicts as you try to move forward.

Take the time to plan. It doesn't have to be a beautiful drawing, but it does need to be well-considered. If you will need to move a downspout, for example,  you don't want to find out after you've already planted a tree at that corner.

When you go shopping for your plants, you want to have a specific, well-thought-out list in hand so that you are less tempted to buy beautiful plants that love a sunny, wet area while you are actually shopping for your dry, shaded slope.

Don't plan your garden the way a chef plans a menu! You know how in the movies a great chef goes to the market to see what inspires him or her? It sounds wonderfully spontaneous, but unfortunately that approach just doesn't work for planning your landscape...

Why not? There are too many things to consider: the plants' preferred conditions, the height, growth pattern,  color, and bloom sequence--all the details of how each plant fits into the plant community that you're creating. It's hard, if not impossible, to think all this through while you're shopping.  Having the pre-planned list firmly in hand will help you stay on track!

Blend Outsider with Insider Perspectives.

A good Big Picture requires thinking from several angles. Outside perspective is crucial. I'm not sure why this is, but we have a very hard time bringing fresh perspective to a landscape while we are living in it. Even a designer like me needs to bounce ideas off other gardeners and designers when it comes to my own landscape, to hear a fresh perspective on what might be possible, or to talk through a potential solution to a tricky problem.

I don't mean to imply that you absolutely have to hire a designer, although of course that is one way to do it. There are many ways to get that outside perspective. You might invite a friend or two from the garden club over for lunch and pick their brains. Scour blogs and magazines for ideas. Visit gardens on a local tour, or go to public gardens, especially those that feature creative uses of native plants.

But then--and this is really crucial--that outside perspective needs to be blended with the perspective of the ones who actually live in this landscape. Those who will be watching it evolve and taking care of it. Those who will be walking the pathways, eating on the porch, running the dog, bringing in groceries, grilling outdoors, or looking out the kitchen window. Insider perspectives are the lifeblood of an excellent design.

If you don't successfully blend these two perspectives, you get a disaster in one of several flavors. One kind of disaster is where a lot of money is spent on a garden with strong visual appeal, perhaps a look that was featured in one of those magazines, or from a public garden, but that wasn't adapted or modified for the family that lives there.

So then the kids, who need to get to the neighbor's playground, blaze a path over the roots of some delicate shrubs. Or the lawnmower, not able to turn around a sharp corner, wrecks the groundcover before it can get established.

Another sad kind of disaster is where one or the other half of a partnership feels left out, and the garden brings resentment instead of joy. That's really unfortunate, and unnecessary, I think. It's not their fault! Gardens are for living in. If a garden is planned with insiders all having a say, the process can take a little longer, but the results are more rewarding.

I also don't mean to imply that this Big Picture is carved in stone and dictates all future decisions, forever. It can and should be flexible. It can be the place from whence changes are considered. What I mean is that when you can return to the Big Picture and make your change from there, you can see where the other impacts will be. It makes gardening less capricious, less wasteful, less overwhelming, and more sustainable.

Speaking of Native Garden Tours, I have a heads-up for you! Adkins Arboretum will host this year's Native Garden Tour this fall, on Saturday, October 6th. Save the date!

Chris Pax

Which phlox is best for you?

Hello Everyone,

Last summer I did the wrong thing. I bought a plant on impulse, in spite of what I knew would happen. But there they were, in spectacular bloom at the nursery, just LOADED with swallowtail butterflies!

I was, after all, shopping for plants for a butterfly mini-meadow. What stronger sales pitch could there be? I stood still for a moment and asked myself to imagine these beautiful plants the way I knew they would look, if not by the end of this season, perhaps early the next…leaves sagging under a heavy coating of white powdery mildew.

But even that didn’t work…the butterflies won. I ended up finding room on my crowded cart for five more plants--some of the most beautiful phlox paniculata I’d ever seen.

I planted the mini-meadow within a few days, and the phlox did not disappoint. For the next several weeks they continued to look amazing, and I saw an impressive number of butterflies on those phlox. And, surprisingly… no mildew! (Not yet, but probably next year, I thought).

Well, it turns out they may not have been as big a mistake as I thought at the time. Because the Mt Cuba Phlox Trial Results have just come out, and that particular variety of phlox—‘Jeana’—actually did quite well.

Phlox paniculata ‘Jeana’ not only managed to remain completely disease free in trial gardens that were chock full of powdery mildew by the end of three years of phlox trials (talk about a tough test!), but also attracted many more butterflies with her abundant, delicate, rosy-pink blooms. ‘Jeana’ brought in an average of 539 butterfly visits per plant, while her nearest competitor, ‘Lavelle’ had only 117 visits per plant. (Data was collected over two years' time).

The results of the butterfly count were enough to attract the attention of University of Delaware grad student, Keith Nevison, who measured the quantity of nectar and concentration of sugar in the nectar of ‘Jeana’ and other phlox, attempting to find out what the butterflies were so excited about. But he found that ‘Jeana’ is not making more or better nectar. It had to be something else. 

Nevison’s current theory—yet to be proven—is that the smaller flower size of ‘Jeana’ and particularly the narrower and shallower flower tubes, make for a preferable nectar harvest environment—allowing the butterfly to quickly slurp more nectar without moving as frequently. Fascinating, isn't it?

The phlox varieties were evaluated based on mildew resistance, length and quality of bloom, visitor ratings, neatness of foliage, and popularity with pollinators.

You might want to read the report, there’s a lot of great stuff in there. But if you want just a little more, here are some takeaway points:

  (Table here--see subscriber version, for some reason it didn't come through for the archives!)

Looking ahead to this fall: Adkins Arboretum is talking to Co-design Graduates about gardens to put on the Native Garden Tour for early October. If your garden is chosen, you can order all your native plants from the Arboretum at a generous 35% off. So this is a GREAT way to finally finish installing your garden! (If you are interested or even just curious about the details, please send me an email!)

Chris Pax

Good groundcovers reduce mulching & weeding

Hello Gardeners,

First, a little diversion about hummingbirds. Usually we think of attracting them with nectar-rich, tubular-shaped, deep red- and blue-colored flowers, right? Well...apparently there are other ways to attract them, as well.

My husband and I recently planted two, 10' tall, river birch trees (Betula nigra 'Heritage') We wanted a couple of fast-growing, medium sized trees to screen the view of a nearby house. We were surprised to be almost immediately rewarded with our first hummingbird visit. She sat quietly in the birch tree for a tiny moment, then seemed to pick at something on the branches. We used to see lots of them, nectaring on flowers at our previous home, but in three years of living here in Annapolis, nada-zip in the hummingbird department. So this first sighting feels special.

Hummingbirds, with their delicate little feet, love to perch on the numerous, slender branches of birch trees. And there seems to be something that interests them, within the peeling bark of these trees. I've read that although people often put out sugar water for hummingbirds, insects are actually a very important source of nutrition for these high-metabolism birds, with aphids and spiders among their favorite foods. So maybe there are little insect treats hiding in those crevices in the birch bark...

On to today's promised topic: how to reduce mulching by using carefully selected groundcover plants. You've probably heard why mulch is "necessary": it prevents weeds, retains moisture, and helps keep erosion in check. But if you can get a good, thick groundcover established, the benefits are the same as or better than mulch.

The leafiness and roots naturally help keep soil from eroding away and reduce evaporation, helping retain moisture for the other plants in the bed. It greatly reduces the need for weeding, since the weeds find a harder time getting a foothold where the groundcover has already declared victory. And finally, there is less work, because you don't have to replace with new mulch every year--you plant once, and except for adjustments and tweaking, you are done!

There is a trick to it, though. In order to get quick, lush, weed-suppressing growth that doesn't have a lot of bare spots, you have to match the groundcover's preferences to the type of soil, sun and moisture that you have. Yet you can't have a plant that is so aggressive it will overwhelm whatever else you want to have in the bed. 

I have a long, slightly nerdy list of about 14 groundcovers that I use often--some fiercely aggressive, some that need a little coaxing at first. My list shows the preferred growing conditions, bloom time and color, and notes about the wildlife each plant supports. But today I just want to share the several plants I probably use the most often.

There are three, relatively-adaptable favorites---groundcover plants I've been using for some time, that have performed well for reducing weeding and mulching. If you've worked with me on your landscape design, you more than likely have at least one of these in your landscape.

1. Iris cristata, Crested iris. The beauty of this plant is that the slender leaves spread into a pretty thick mat of graceful arches within a year or two. Once established, I rarely have to pull weeds among them. Good for either clay or sandy soil. Best in part sun or shade, unless the area is consistently moist (avoid dry, hot, and sunny). This has a short-but-lovely bloom time (blue). You can divide every 3 years to spread the area out (free plants!). Best time to divide is in August just after the plant has died back for the fall.

2. Chrysogonum virginianum, Green and gold. Prefers moist, alkaline soil but is remarkably adaptable as long as you take good care of it during establishment. There are several good cultivars. Most are selected for their shorter inter-nodal growth, which will make them more likely to form a mat that prevents weeds from weaving in to your garden. (In a later post I'll talk about how author/designer Larry Weaner uses the straight species, with its longer internodal growth, to creatively fill bare spots without making a solid mat--kind of an advanced technique that can be used in an already established bed). This plant is also semi-evergreen, so there is some presence protecting the bed even through the winter months.

3. Heuchera villosa 'Autumn Bride'. This plant amazes me with its sturdy resilience in the face of drought and poor soil. In the Mt. Cuba trial gardens, this cultivar got winning scores in all categories. 'Autumn Bride' tolerates full shade or (with a little more moisture) full sun. It is quite drought tolerant except in super hot sun, and rebounds pretty well from early season deer browsing (later in the season it gets hairy and tough, and the deer leave it alone). I use it to give a big, leafy texture in areas where I'm concerned about erosion and dry soil. It has a small-flowered, white bloom stalk in July, and the leaves turn blush-burgundy in autumn. Although a perennial, this plant usually persists through the winter (semi-evergreen).
So those are a few good ones. Do you have any favorite native groundcovers that have done well in your landscape? Send me a note--I'd love to hear about them!

Also, if you know anyone else who is interested in natives and might like to receive this newsletter, please forward to them. Thank you!

Chris Pax

Annapolis Native Landscape Design has a newsletter!

I've been publishing this newsletter much more regularly lately--generally every two weeks or so. Topics include planting, maintaining, and designing with native plants.

This is the continuation of the Pax Garden Design newsletter. The business name has changed to make it easier for people to find me and to encourage more local business.

Within a few months I hope to have the newsletter archives available here. 

Come and join us--we'd love to have you along! All you have to do is sign up--you can unsubscribe and/or re-subscribe any time you like.