In parts I and II of this series on gardening for good bugs, I've discussed the kinds of plants that nourish good bugs, attracting them to our gardens. For part III, I will discuss the gardening practices that encourage good bugs to take up permanent residence. Since this will be a "do this, not that" kind of discussion, I want to say up front that this is not a guilt trip, this is an invitation to make better choices for the future. I will be discussing the evolution of my own gardening practices as well as the evidence that has changed my thinking.
Bug-protective Gardening Practice 1: Go Pesticide-Free
First, chemical pesticide use leads to pesticide-resistance. Sure, when we spray for pests, we are successful in killing most of our desired target, but some pests survive nonetheless. Those survivors breed and pass on their resistance to the next generation, creating a resistant population over time. This spurs the need to use even more toxic pesticides in a pest versus pesticide arms race.
Second, many pesticides are not specific to the targeted pest, so any beneficial insects that are present at the time of pesticide application are just as likely to be killed. So now, we not only have a pesticide-resistant pest population, but a diminished population of predators, leading to opportunistic pest outbreaks. And the point about specificity is true of even natural and organic pesticides. Oils and soaps may be non-toxic, but they are also non-specific. They kill by physical means, smothering bugs so that they cannot breathe, affecting pest and predator alike. Diatomaceous earth is also a non-specific physical pesticide.
What do you do when you notice a pest outbreak in your garden? Identify which plants are affected, which pests are causing the damage, and which predators that are likely to come to your aid before deciding if you need to intervene. True story: last summer, I noticed aphids on the leaves of one of my melon vines. But on another leaf on the same plant, I found green lacewing larvae (aka "aphid lions") already chowing down on aphids. The aphids and aphid lions were gone the next day, but I did spot some lacewing eggs, reinforcements on the ready.
Many beneficial bugs undergo metamorphosis, so it is important to recognize our friends in all of their forms. This image represents the green lacewing life cycle. Source: University of California.
I used to spray Btk to defend my Brassicas against cabbage worms. Even the crunchiest, granola-iest organic gardeners recommend it. Bacillus thuringiensis is a naturally-occurring bacteria that infects larvae. The kurstaki strain (the 'k' in Btk) specifically infects caterpillars, making it an effective pesticide against cabbage worms, the larval stage of cabbage white butterflies. But wait a minute, I'm now talking about killing butterflies, after posting last week about butterfly conservation?! Yes, well, it's a bit more complicated than that. See, cabbage worms are an introduced pest and they have an abundance of larval hosts outside of our gardens in the form of invasive weeds like garlic mustard. So I really don't feel bad about killing cabbage worms in my garden. ...except that Btk affects all caterpillars, pests and desirable species alike, and sprays aren't easy to control with exacting precision. What if, while spraying kale with Btk for cabbage worms, I unintentionally spray the parsley (host plant of desirable Black Swallowtail caterpillar) that's growing next to the kale?
Here's what I do now. Before planting Brassica seedlings in the garden, I now meticulously scan the leaves, paying close attention to the undersides for singly-laid cabbage worm eggs, and I rub off any eggs that I find. After planting, I keep Brassicas covered with a physical barrier of floating row cover, preventing adult cabbage white butterflies from laying eggs on my plants. As my plants grow, I continue to scan them (those eggs are tiny and tough to spot) and I pluck off any caterpillars I find. For more about row cover as protection from cabbage worms, check out this post.
Bug-protective Gardening Practice 2: Save Garden Clean-up for Spring
Not only do the native perennials I've planted in my garden provide nectar, pollen, and food for butterfly larvae, they also provide shelter for good bugs. Eggs and pupae overwinter in a state of diapause, protected by egg sacs and cocoons attached to perennials and other permanent garden structures. Meanwhile, adult bugs tend to get cozy in the warmth of decomposing plant matter like leaf litter, brush, and fallen logs. That is, until I come around to tidy up, cutting back perennials and raking up the leaves, effectively serving eviction notices to all the sleeping good bugs. I'm a little embarrassed that it took me so long to figure that one out.
This egg sac was left by a yellow garden spider that spent the late summer and early fall next to my compost bin.
Here's an important traditional gardener reason to save cutting back or pruning for the spring. Pruning plants stimulates their growth. To prune in the fall, when perennials are entering dormancy for winter survival, is therefore potentially damaging to plants. (Yes, I only realized this after I had pruned my grape vine this fall.) Instead, if we wait for spring to prune, we protect both plants and bugs alike.
Of course, any fallen leaves on paved surfaces such as sidewalks and driveways should be removed so that they don't pose a slipping hazard or end up clogging storm drains. Instead of bagging them and setting them on the curb for collection, spread fallen leaves as mulch in garden beds. Your plants will benefit from the added nutrients as the leaves decompose and the good bugs will remain in your garden. You can also add fallen leaves to your compost bin (I'll discuss compost and soil bugs in my final post of this series).
Bug-protective Gardening Practice 3: Become a Bug Hotelier
I'm fascinated by bug hotels, the clever, artful way to disguise an unsightly brush pile and provide overwintering shelter. By including a variety of natural materials in the construction of your bug hotel, you'll encourage the widest variety of good bugs to stay for the winter. Solitary bees nest in holes drilled into wood or inside of hollow stems. Some species of adult butterflies overwinter in tight enclosed spaces. Ladybugs seem to prefer to nap among sticks or dried grass.
And what luxury bug hotel doesn't have a bug spa? Add a large stone (or several) to a bird bath, so that bugs may land, sunbathe, and take a drink. Birds will use it too, of course. Just be sure to empty and refill your birdbath twice a week to control mosquitoes.