If you've ever wanted to grow your own produce, you may have had this thought pop into your head: "I only want to grow stuff I can eat, and I don't want to grow flowers because I don't care about them/have space for them/want to go through the trouble to raise them with my limited time and/or money."
When I first tried my hand at edible gardening, this was exactly my frame of mind. I also hear this a lot from customers who are starting vegetable gardens. What followed for me, and what generally follows for them, is this: "Crap. Insects have found my plants and are devouring all my precious produce."
Pest insects will find your plants, let me tell you. That is all they spend their whole little lives doing: looking for delicious plants, and then eating them. And there are thousands of them very near to you, wherever you are trying to grow plants. If you want your garden to have a fighting chance, you need a team of allies to help you out.
Integrated pest management (IPM) is about more than fighting insects with other insects, but that is what this instructable is about, because it is easy (and so fun!) to get started inviting insect allies to your garden. I will share a few tips that you can use immediately in your space, no matter what kind of garden you have -- mine is a cramped balcony where all my plants live in containers.
Step 1: If You Grow It, They Will Come
If you grow vegetable plants, pests will come.
If you grow flowers, allies will come.
Here is the example from my garden that drove this point home for me:
My first crop this year was lettuce, which I started (as you do) when it was still cool in early spring. I didn't have much else out there except my succulent collection. As my lettuce began to flourish, aphids soon appeared, even on my second-story balcony. But my sedum happened to be in flower around that time, with dozens of petite yellow blossoms on its dense-yet-delicate foliage. I noticed that hoverflies appreciated these flowers and would visit them often.
Shortly afterward, a few carnivorous hoverfly larvae hatched in the lettuce. After about a week, the lettuce bed was a graveyard of aphid husks. They had eaten every single aphid.
Your allies need flowers, because many of them are nectar-drinking adults who produce carnivorous larvae. They also need safe places to hang out or hide, where they are not exposed to their own predators (such as birds), and where they can have moisture and shade. Many of the insects you want to attract will appreciate profuse small flowers and lots of lacy foliage -- characteristics that our favorite vegetable crops don't have.
Step 2: Start With Flowers
When you plan your vegetable garden, start with flowers before you even get to veggies. Attract your friends first. Choose plants with lots of petite flowers and places for insects to hide; also pay attention to the bloom time for each plant, so that you have flowers all season long. If you live in a mild climate, Sedum angelina (or similar varieties) is a great one to start with. Sweet alyssum has a long bloom season and loads of teeny flowers, but it can be invasive in some areas. Yarrow is naturalized in most of North America, easy to grow, and hardy as all get out. Lots of commonly-grown garden herbs, if allowed to flower, will attract your friends -- dill, thyme, parsley, etc. Marigolds are easy to grow from seed, well-behaved in the garden, and have some capacity to repel soil nematodes. Nasturtiums are famous companion flowers for vegetables.
Many pollinator insects have a preference for native flowers, so it's worth exploring what's native in your area and prioritizing those plants if you can. You want your vegetable plants to grow up in a community that's already thriving.
Step 3: Look for Signs
How do you know it's working? What are you looking for?
It's easy to spot hoverflies, which are pretty, bee-colored flies that have a hummingbird-like flight style. They were the first allies I noticed in my garden, and they've become a kind of indicator for me because they're big enough for me to notice and I know they won't come around if I don't have good flowers. Hoverfly larvae eat aphids and other small, soft-bodied pests that want to suck the life out of your plants.
Lacewings are not so easy to see -- in fact, I've yet to see a single one -- but you might notice their distinctive eggs, which are laid singly on a little stalk wherever they find a spot they like. They also produce carnivorous larvae that will consume your small pests.
You might see ladybugs, and if you have aphids already, they may bless you with their ferocious-looking larvae that consume small pests like little hoovers.
Praying mantises have mixed reviews as allies. They will eat any live prey that they can handle, including your other allies and even, if they get big enough, small birds. But they are really cool, and they can tackle insects that are too big for your carnivorous larvae. Female mantises do not fly, so if your garden is isolated, like mine is, you will need to import mantises if you want them. I ended up with mantises because their egg case was going to be thrown away; my garden is pretty small for them, but I still have one who seems to be doing all right for himself in the alyssum basket.
What if you don't see signs? What if your flowers aren't working?
If you're able to watch for a bit during the day and you're still convinced friends aren't coming after a couple of weeks, try changing your plant varieties. I noticed that hoverflies preferred sedum to alyssum, and didn't visit the alyssum much until the sedum was done flowering. So I might attract more of them if I replaced the alyssum with something else. Also try providing a water source, like a pebble tray with a little water around the pebbles -- not a dish of just water that insects will drown in. If it's hot in your garden, offer more shade, such as a few plants of different heights planted together. Remember that foliage matters, too, not just flowers. Imagine you're two millimeters long, and think about what would make you feel safe and happy.
Step 4: Have a Plan B
Your plants will not only attract small pests like aphids. They will attract caterpillars as well. If you have a large outdoor garden, birds will hunt your caterpillars to some extent. I don't do much to attract birds (other than put out flowers that hummingbirds like) because I have such a small space that I think is too close to human activity for bird comfort, but they are great insect-eaters if you have the space. Offer them some fruiting shrubs like currants, or another native berry bush for your area, to give them safe perches and varied food sources, and they will work for you, too.
Your ladybug, hoverfly, and lacewing larvae are too small to eat caterpillars. Mantises that are large enough will eat them when they can see them, but their biggest enemy is a tiny one: parasitic wasps that lay their eggs on living caterpillars. The larvae hatch and eat the host, sometimes from the inside out.
The invertebrate world is pretty brutal.
You can attract these wasps using the same techniques as for your other allies, but you are not likely to see them. You may notice their eggs on large caterpillars like hornworms, but if you have a small garden with just a few plants, you may not want to let things get to that point, and you may need to resort to a Plan B.
Caterpillar damage is easy to see, because they take bites out of leaves and often will consume almost an entire leaf, leaving just a little bit of vein at the end of the petiole. They may not fly but their camouflage is very good, and it can be hard to find them even when you know they're on your plants. I hand-pick caterpillars when I can, and either feed them to my indoor mantises or toss them into the landscaping. If a plant seems to be in danger, there's a product I will resort to whose active ingredient is spinosad. This chemical is made from a bacterial by-product and only kills insects that ingest it, so it targets leaf-eaters and does not harm the rest of your insect community when used correctly.
I have used this on my tomatoes when their lower leaves started disappearing, and the damage stopped. I think, next time around, it would be better for me to give them more companion plants sooner. In the photo you can see that the marigolds and basil I planted with my tomato are just tiny seedlings, while the tomato is already quite large. Luckily, they grow quickly, so they should fill out soon.
That said, I don't want to imply that using companion plants to attract beneficial insects is an easy solution to all your pest troubles. It is a solid foundation for what will be an ongoing project as long as you are maintaining a garden.
Step 5: Be Willing to Share
Integrated Pest Management is about keeping pest levels tolerable, not eliminating them entirely. Insect predators, if you invite them in, are good at keeping pest populations from reaching infestation levels, but some pests will still be hanging around -- and if they didn't, your allies would leave, too. You'll be more satisfied with your garden results if you prepare ahead of time to lose some of your produce to herbivores. Plant things they like to eat (nasturtiums are famous for this purpose), and they will be more likely to leave alone what you like to eat. If you can, put an extra tomato plant out there. You won't feel quite so angry when some of your crop gets eaten (although it's still hard, at least for me).
Step 6: Additional Resources
IPM is a deep and expanding field. If you're interested in learning more, the excellent UC extension program has a bunch of free online mini-courses that you can find here. They also have books and other materials for sale.
Of course the main idea of attracting insect allies to your garden is to keep more of what your plants produce -- and you will -- but there's an additional benefit that, to me, is almost as satisfying: you'll see your garden, even a small one like mine, become a habitat where tiny wildlife finds refuge and goes about its wild existence. When I see hoverflies stopping by my flowers in the morning, or lacewing eggs on their slender stalks decorating my lavender plant, I know my garden isn't just a source of fresh tomatoes for me -- it's offering something back to the natural world.
I hope I've inspired you to give flowers a try this season. I think you'll find you enjoy them more than you expected.