I’m getting antsy. Spring is on its way. The weather lately has been in the 60’s and 70’s, Narcissus and Muscari are in bloom, and dormant perennials are popping out of the ground. Sure, we’ll have a few more frosts (maybe a freeze?), but being just a few weeks away from the first official day of spring, this gardening season is about to get goin’ and growin’.
One goal I have this year is to finalize the design of a few beds near our garage. They’ve been mostly a holding cell for potted plants that right after we bought the house I plopped into the ground to save from incessant August watering.
In my mental iterations of design, I’m not only considering beauty, harmony, and seasonality for these plantings but also management, survival strategies, and the benefits to insects and wildlife. The critters seem to get the short end of the straw when planting versus the elements of design, but that seems to be changing with the increase of the public’s awareness of ecology and our role to make the world a better (or, if we don’t act a worse...) place.
Many people believe that to have a garden good for wildlife your yard has to more closely resemble an unmown field, but what if I told you research shows that making a few small changes to the way you plant could help increase an insect’s survival and even perhaps their numbers?
That’s what the recent paper “Configuration and Location of Small Urban Gardens Affect Colonization by Monarch Butterflies” by Adam Baker and Daniel Potter in Frontiers in Ecology and Evolution indicates. It’s a technical title, but the basic hypothesis they tested was does the way we plant Asclepias (milkweed) species impact how Monarchs can find the plants and subsequently lay eggs on them?
And, yippie! The whole paper is available online for people to read. I really enjoyed diving into this paper. The research was broken down into three parts—investigating Monarch waystation gardens, synthesizing planting configurations, and looking at surrounding vegetation. And, I have used their figures only to help you understand their work. All credit for the following figures goes to these researchers.
MONARCH WAYSTATIONS
For the Monarch waystation gardens, they visited 22 gardens that contained three species of Asclepias (A. incarnata, A. syriaca, and A. tuberosa). They asked two great questions about each garden—were the plants blocked or mixed, and can Monarchs see the plants on a north-south approach.
The former question is interesting from a naturalistic planting perspective because blocking versus mixing are two different approaches for laying out plants. Oudolf and Kingsbury go in greater detail about both approaches in their book Planting: A New Perspective. In my mind, if you had asked me before this study which would be better for insect populations, I would have said mixed. A diverse habitat has been shown to support more species (more on this theory in a minute). But, the research showed that these blocked or as they called them structured plantings had more Monarchs and eggs on them than the mixed plantings.
In these waystations, they also evaluated whether plants could be accessed along a north-south gradient. Monarchs fly north from overwintering in Mexico, and then they fly south at the end of the growing season. And, while the paper does say that they can fly any direction in a garden, planting Asclepias so they are visible in this north-south migration path seems to increase the number of Monarchs encountered and eggs laid on plants.
This figure from from Baker and Potter’s (2019) paper shows that gardens that had structured (aka blocked) Ascelpias had more Monarchs than non-structured (aka mixed) plantings! Additionally, gardens that featured Asclepias that could be viewed on a north-south trajectory had more Monarchs as well. Note: ramet is a fancy word used to describe the number of shoots from a clonal colony. So, if an Asclepias plant has 10 shoots, those are 10 ramets.
PLANTING CONFIGURATIONS
A second step they took in their research was to create three different planting modules for evaluating Monarch counts—Asclepias on the perimeter, Asclepias in the middle, and Asclepias in a mixed planting. All three gardens contained the same number of plants and fillers like nectar-rich Tithonia rotundifolia and Zinnia elegans and the tall ornamental grass Calamagrostis × acutiflora.
Here’s a figure I pulled from Baker and Potter’s (2019) work that helps to illustrate their planting configurations.
Again, if you asked me before reading this, I would have guessed that the mixed planting would be the best. But, their two years of data collection showed that the perimeter plantings had roughly DOUBLE TO QUADRUPLE the number of eggs and larvae as the other two plantings. Wow. I was blown away. They cite a whole plethora of reasons and that having non-host plants (like the Zinnia, Calamagrostis, and Tithonia) might interfere with egg laying by Monarchs onto the host-plant Asclepias—blocking, shading, mixing volatiles, and landing on the wrong plant too many times. And, it appears that if enough of these compound together, the number of eggs and larvae on plants are drastically reduced.
And, here’s Baker and Potter’s (2019) data of Monarch eggs and larvae counts from those planting configurations. Absolutely amazing. Asclepias that were on the perimeter had double to quadruple the number of Monarch youngsters.
I mentioned earlier that increasing diversity (like we see in mixed plantings) can potentially help to support more insects. What if the mixed configuration had more predatory insects? They thought of that by trapping predatory insects and noted they didn’t really see a difference between the perimeter and mixed configurations. Thus, there weren’t insects reducing the numbers of Monarchs in the mixed configuration relative to the perimeter planting.
Basically, they created an unimpeded monoculture for the Monarchs. We talk about how monocultures are bad because a group of plants en masse can have more pests than being mixed in a polyculture, but this research flipped that thinking on its head. That if you want to plant something for a desirable “pest”, then block it and put it where they can see it.
They do make a note in the discussion about the perimeter plantings. Because the between plant distances were greater in the perimeter planting and because Monarchs do prefer to lay eggs on isolated plants, this effect may have had an influence.
ASCLEPIAS HIDE AND SEEK
The last experiment they did was to investigate effects of surrounding vegetation over two weeks. They planted Asclepias incarnata by itself and then hidden by Panicum virgatum ‘Shenandoah’. The two plants didn’t touch (mind your bubble, switchgrass!), but the Pancium were close enough to hide the plants. They observed that unimpeded Asclepias plants had on average a little over three eggs per plant while those screened by the Panicum had nearly zero eggs.
So, the things I took away from this paper about planting for Monarchs:
Plant Asclepias in blocks with adequate spacing between plants.
Plant Asclepias so that Monarchs have north-south access to the plants.
Plant Asclepias on the edges of your garden.
Plant Asclepias so that surrounding vegetation doesn’t hinder access to the plants.
And, that’s how I’m going to do it. I have some locally sourced Asclepias seed, and once I get the plants going, I’m going to plant them in a couple of blocks on the outside of my beds with a few mixed in here and there for harmony.
Now, the question is does this approach also work for other insects? Of course, it would take more research to answer that question. Some insects don’t migrate; therefore, the north-south access might be less important for them. But, I do think that locating host-plant species near the edge, in blocks, and making sure they are accessible could be extrapolated to planting for other species of insects.
A final note. I don’t usually set down and digest a scientific article like this, but I was so impressed by the research and the content that I had to share it. If you like this reflection writing, let me know, and I’ll consider doing more in the future.