That is a question we should all be asking when planning our butterfly gardens. Lately there is a trend among commercial plant growers to claim just about any flowering plant will attract butterflies.
One Florida grower that sells to the big box retailers actually prints a big butterfly on the side of their pots and a whole ring of little butterflies all the way around! It doesn't actually say this is a butterfly plant, but who could blame a novice gardener for being misled?
Another question we should be asking is "WHAT butterflies does the plant attract?" Many common garden plants are native to other parts of the world, and have been propagated and moved around by avid gardeners. The butterflies that were attracted to the plant in their native habitat may not even exist in your garden.
Some butterflies prefer to feed on the nectar of specific plants. They are even more specific about where they lay their eggs. Some caterpillars are only able to feed on a single species of plant!
So, ask lots of questions before you make your purchase. Unfortunately, the largest plant retailers rarely have knowledgeable people on their staff.
So what's a butterfly lover to do? You could do some research online, but here again lots of misinformation is circulating, getting copied and pasted from one website to another.
The best solution is to zero in on your local community. Visit a neighbor who has a butterfly garden. Go to a local park or botanical garden and watch where the butterflies spend their time. Make your observations at various times during the day; some flowers release their nectar at specific times. Also be aware of which butterflies you already see in your yard. Planting the right flowers could bring more of them. Above all don't forget to include some larval food plants. Your butterfly population can multiply exponentially if they can live out their entire life cycle without leaving your yard!