Butterfly gardening is a way to create, improve, and maintain habitat for lepidopterans including butterflies, skippers, and moths. Butterflies have four distinct life stages—egg, larva, chrysalis, and adult. In order to support and sustain butterfly populations, an ideal butterfly garden contains habitat for each life stage. Butterfly larvae, except the carnivorous harvester (Feniseca tarquinius), consume plant matter and can be generalists or specialists. While butterflies like the painted lady (Vanessa cardui) are known to consume over 200 plants as caterpillars, other species like the monarch (Danaus plexippus), and the regal fritillary (Speyeria idalia) only consume plants in one genus, milkweed and violets, respectively.
As adults, butterflies feed on nectar, but they have also evolved to consume rotting fruit, tree sap, and even carrion. Supporting nectarivorous adult butterflies involves planting nectar plants of different heights, color, and bloom times. Butterfly bait stations can easily be made to provide a food source for species that prefer fruit and sap. In addition to food sources, wind breaks in the form of trees and shrubs shelter butterflies and can provide larval food and overwintering grounds. "Puddling" is a behavior generally done by male butterflies in which they gather to drink nutrients and water and incorporating a puddling ground for butterflies will enhance a butterfly garden. While butterflies are not the only pollinator, creating butterfly habitat also creates habitat for bees, beetles, flies, and other pollinators
Butterfly gardening provides a recreational activity to view butterflies interacting with the environment. Besides anthropocentric values of butterfly gardening, creating habitat reduces the impacts of habitat fragmentation and degradation. Habitat degradation is a multivariate issue; development, increased use of pesticides and herbicides, woody encroachment, and non-native plants are contributing factors to the decline in butterfly and pollinator habitat. Pollination is one ecological service butterflies provide; about 90% of flowering plants and 35% of crops rely on animal pollination. Butterfly gardens, even in urban, developed neighborhoods provide habitat that increases butterfly diversity and also pollinators like bees, flies, and beetles.
Before buying plants and digging into the soil, "ground-truthing" is a necessary first step, Ground-truthing involves surveying a property in order to assess the current resources available. Some aspects to keep in mind are the following:
Butterflies are ectothermic and rely on solar radiation for their metabolism. South-facing slopes are an ideal location for a butterfly garden, as they provide the most solar radiation. Shrubs and trees provide wind breaks for butterflies, and can also be host plants, such as spicebush (Lindera benzoin) or pawpaw (Asimina triloba)
The types of plants used in a butterfly garden will determine which species of butterflies will visit a garden. Lepidoptera societies and the Department of Natural Resources often provide state and county distribution maps of local butterflies. There are lists of butterfly species and their host plants which are informative to the plant species needed in the garden (Larval food plants of Lepidoptera). While non-native plants do provide flora resources later in the season, they have an overall negative effect on butterflies and other pollinators. Therefore, it is recommended to use native plants.
Depending on the zone, some butterfly attracting plants include: purple cone flowers (Echinacea purpurea), yellow cone flowers, sunflowers, marigolds, poppies, cosmos, salvias, some lilies, asters, coreopsis, daisies, verbenas, lantanas, liastris, milkweed (especially for the monarch butterfly, whose caterpillars feed solely on this plant), the butterfly bush (also called buddleia), zinnias, pentas, porterweeds, and others. Avoid cultivars of plants that have "double flowers" (more petals which block the center) as these can be difficult for butterflies to access. Care should also be taken to research a species, to make sure it is not invasive in a given region.
"Puddling" refers to the behavior of male butterflies congregating on soil, dung, and carrion to feed on nutrients, specifically sodium. Nectar is low in sodium, and sodium is a limiting nutrient for Lepidoptera. Male butterflies are able to transfer sodium to females during copulation. The sodium is passed onto offspring and increases reproductive success. To create a simple puddling habitat, fill a shallow dish (like a draining tray for a pot) with sand. To increase the nutrients, mix compost with the sand. Add footholds for butterflies by adding different sized rocks.
There are numerous recipes for creating butterfly bait, but they have common ingredients. Fermentation is the key to a good bait, as it mimics the fermentation of rotting fruit and sap in the natural environment. Recipes include blending rotten fruit (i.e. bananas) with beer, maple syrup, molasses, or sugar. Often yeast is added as well to the mixture and left to ferment for a week. The bait can be laid on stumps, rocks, and tree limbs.
There are diseases that afflict butterflies, such as bacteria in the genus Pseudomonas, the nuclear polyhedrosis virus, and Ophryocystis elektroscirrha, which only infects queen butterflies and monarch butterflies.
In the absence of pesticides, aphids and true bugs may infest plants. Some gardeners may wish to release ladybugs (ladybirds) and other biological pest control agents that do not harm butterflies in order to control aphids. However, the release of ladybugs is not a good idea in places such as the United States where the species that is released is generally the invasive Chinese ladybug. An alternative to this is to wait for local predatory insects to find the aphids. One technique some use to quicken this process if the infestation is particularly high is to spray the bushes with a mix of sugar and water, simulating aphid honeydew. This is known to attract lacewings whose larva eat aphids. Another method of control is by spraying the plants with water, or rinsing plants with a mild dish detergent/water solution (although caterpillars should be relocated before suds are applied). Scented detergents are fine; those containing OxiClean should be avoided. The aphids will turn black within a day, and eventually fall off. One last technique is to plant a variety of different flowers, including ones that attract hoverflies and parasitic Braconid wasps, whose larvae kill pest species. Still, it is not advisable to kill all aphids, just to control them so that they are not detrimental to plants. Aphids still play a role in the environment by providing food for predators. There are even some caterpillars such as the harvester which only eat certain aphid species instead of plants.
With small home butterfly gardens, it is common for the larvae to exhaust the food source before metamorphosis occurs. Gardeners of monarch butterflies can replace the expended milkweed with a slice of pumpkin or cucumber, which can serve as a substitute source of food for monarch caterpillars in their final (fifth) instar. Planting multiple plants in clumps can help lower the chances of running out of leaves.
Efforts to increase butterfly populations by establishing butterfly gardens require particular attention to the target species' food preferences and population cycles, as well to the conditions needed to propagate their food plants. For example, in the Washington, D.C. area and elsewhere in the northeastern United States, monarch butterflies prefer to reproduce on common milkweed (Asclepias syriaca), especially when its foliage is soft and fresh. As monarch reproduction in that area peaks in late summer when most Asclepias syriaca leaves are old and tough, the plant needs to be cut back in June – August to assure that it will be regrowing rapidly when monarch reproduction reaches its peak.
In addition, Asclepias syriaca seed needs a period of cold treatment (cold stratification) before it will germinate. Further, monarch caterpillars do not favor butterfly weed (Asclepias tuberosa) because the leaves of that milkweed species contain little toxin (cardiac glycosides), which monarchs tolerate but which many predators of butterflies do not.