Every spring we fill one compartment of the shop kitchen garden with dill. The garden lives in an old kitchen sink, and the dill gets its own basin. Not for us. We are never going to eat it. We grow it so that some evening in June I can walk out back, part the feathery tops, and find a fat green caterpillar banded in black and gold working its way down a stem. That is a black swallowtail in progress. The dill is not a crop. It is a nursery.
That one basin of dill is the whole idea of this post, so let me hand it to you straight: you do not have to rewild your yard to help butterflies. You have to pick one plant, on purpose, and let something eat it.
Nectar plants vs. host plants: the difference nobody explains
When people say they are planting "for pollinators," they almost always mean nectar, not host plants. Flowers for the grown butterflies to sip from. That is lovely, and it matters, but it only feeds the adults passing through. It is a diner with no kitchen.
Host plants are the kitchen. They are what the caterpillars eat, and the catch that makes the whole thing work is this: most butterflies and moths can only eat one specific plant, or one small family of them. A monarch caterpillar will starve on a bed of the finest zinnias, because the only thing it can digest is milkweed. Nectar keeps the adults fed for a few weeks. A host plant is how you get a next generation at all.
You have to let it get eaten
I will not pretend this part away. A host plant is a plant you are inviting something to eat. It will get holes in it. It will sometimes look, for a week or two, frankly rough.
That is not your garden failing. That is your garden working. A leaf with no bite marks is a leaf that is feeding nothing. Once you have watched a caterpillar you have been rooting for turn a ragged plant into a butterfly, the holes stop reading as damage and start reading as proof.
At the shop we make it a team thing. Once the caterpillars show up, we trade daily updates on how everyone is doing. When they are ready to pupate we drape the basin in netting so the birds cannot get them, and when the butterflies finally emerge we release them together. It is one of the better things we do all summer, and it costs us nothing but a sink full of dill. By the time those caterpillars have wrapped up to change, our dill is stripped down to bare stalks. That is not a bad year for the dill. That is a good year for the dill.
Two things make this easy to live with. First, put your host plant where a little mess is fine. The middle of a border, the back of a bed, a corner by the shed, not the pot flanking your front step. Second, plant one nectar-rich flower nearby so the spot still reads as intentional rather than neglected. The nectar feeds the adults, the host plant feeds the young, and the two together look like a plan.
If you want the overwintering piece too, the single most helpful thing you can do costs nothing: leave some leaf litter and standing stems through the winter. That is where a lot of these insects actually spend the cold months. It is the same argument I keep making about not bagging up everything in fall, and it applies double here.
Pick one. That is the whole assignment.
This is the part I give clients, especially the ones with kids. Do not try to build a butterfly sanctuary in one season. Choose a single host plant. Learn the one insect it feeds. Then go outside and watch. Children who will not look up from a screen will absolutely check on a caterpillar every single day, because it is theirs and it is changing.
So, the short list, easiest first. Read until you find your one, then you can stop.
Black swallowtail → dill or parsley
Start here. This is our dill-bed trick, the lowest bar there is. Dill, parsley, and carrot tops all work, and you may already grow them. The caterpillars are gorgeous, green with black bands and yellow dots, and big enough for small hands to spot. You get dill and parsley seedlings from our spring seedling sale with Mad Meadow Farms, so this one is genuinely a this-weekend project. If you would rather it be permanent, golden alexanders is the native cousin that does the same job and comes back every year.
Monarch → native milkweed
The famous one. Milkweed is the only thing a monarch caterpillar can eat, full stop. Swamp milkweed is the well-behaved garden pick and takes ordinary beds happily; butterfly weed is the one for a hot, dry, sunny spot and throws bright orange flowers as a bonus. The caterpillars are the showy striped ones, easy to find and easy to love. One thing I will be firm on: plant native milkweed, not the tropical kind sometimes sold in big-box stores, which does not belong in our zone and can do migrating monarchs more harm than good. Northland in Millgrove is your source for the native species.
Pearl crescent → native asters
The double-duty pick. Asters earn their space twice. In late summer and fall they are one of the best nectar sources going, humming with everything. They are also the host for the little orange pearl crescent, so the same plant feeds the adults of a dozen species and raises the young of one. Hard to beat that ratio. Northland again.
Great spangled fritillary → native violets
The permission gem. The violets you have been pulling out of your lawn as weeds are a butterfly nursery. Fritillary caterpillars feed on them at night, so you will not catch them in the act the way you will a swallowtail, which makes this the plant-it-and-trust option. But if you have violets, you already have habitat. Consider not weeding.
Spicebush swallowtail → spicebush
Ready to plant a shrub. If you want to graduate from a pot of parsley to a real shrub, spicebush is a native that takes part shade and slightly damp ground. The payoff is the best caterpillar on this whole list: two huge fake eyespots that make it look exactly like a tiny green snake, and it folds itself up inside a leaf like a sleeping bag. Children lose their minds over it, in the good way. Connons carries native shrubs like this.
Baltimore checkerspot → turtlehead
For the damp corner. If you have a low, wet spot, or you are one of the folks eyeing a rain-garden-adjacent bed, turtlehead is a native perennial that thrives where other things sulk, and it hosts the Baltimore checkerspot. It solves a drainage headache and feeds a butterfly in one move. Northland for the plant.
Giant swallowtail → hoptree
A little tree, if you have room. The giant swallowtail is our largest butterfly and its range has been creeping our way. Its caterpillar is a masterpiece of disguise: it looks precisely like a fresh bird dropping, which no predator wants and every eight-year-old finds hilarious. It needs a plant in the citrus family, and our native option is hoptree, a small understory tree. Connons for this one.
Giant silk moths (cecropia, luna) → native cherry or birch
The showstopper you might already have. This last one you do not really plant for, you get. If you have a native cherry or a birch in your yard, you may already be hosting a cecropia or a luna moth without knowing it. The caterpillars are palm-sized and green and honestly a little unbelievable. The adult moths are as big as your hand, live only about a week, and do not even have mouths, because their entire adulthood is one long date. Finding one of these is the thing that turns a kid into a lifelong bug person. You cannot buy that. You can only leave the tree standing and get lucky.
A quick word about butterfly bush
You are going to see butterfly bush at garden centres with butterflies photographed all over it, and you are going to think it belongs in this post. It does not. Butterfly bush is a nectar bar and nothing more. Not a single native caterpillar can eat it, so it feeds the adults and raises none of the young. It is a diner with no kitchen, wearing a sign that says kitchen.
It is also on Ontario's invasive watch list. The provincial ranking flags it as a species to watch and advises against planting it, cultivars included, because it spreads where it is not wanted. If you love the idea of a shrub that pulls butterflies in, plant a native one that actually pulls its weight. Buttonbush and ninebark are both on the province's recommended list, both feed adult butterflies, and unlike butterfly bush they host caterpillars too.
Back to the dill
You do not need any of the big ones to start. You need a pot of dill, a spot where you will not mind some holes, and the patience to check it on summer evenings. The first time you find a caterpillar you were hoping for, something shifts. The chewed leaf stops being a problem to fix and becomes the thing you are quietly proud of.
Pick one plant. Learn its one butterfly. Then go outside and watch.