This column resumes the development of a butterfly garden to fill a 270-square-foot open space resulting from the removal of a large invasive shrub.

The National Gardening Association’s recent newsletter (garden.org/newsletter/) provided the basic components of a butterfly garden: a large flat rock for basking, a puddle for drinking, and nectar plants for feeding. The site should be sunny and sheltered, with a few trees and shrubs on which butterflies could perch.

Creating a butterfly garden that satisfies these conditions is a straightforward task: There is a vast number of flowering plants from which to choose and butterflies can be expected to feed on the nectar of almost any flowers they encounter.

From an ecological perspective, however, drawing upon the science of Entomologist Douglas Tallamy, the priorities for the design of a butterfly garden focus on the butterflies and moths (Lepidoptera) that live within the garden’s region, and the plants that are native to the same region, and favored by the Lepidoptera.

The Lepidoptera decide on their own to inhabit the garden’s region, so our design focus is on plant selection.

The California Native Plant Society’s CalScape database (calscpe.org) is a powerful planning tool for designing a California native garden. There are no comparable garden design tools for other summer-dry (or Mediterranean) climate regions.

Accordingly, our design process constitutes an exercise in the use of this tool.

The CalScape database includes 7,934 plants that are native to California. Given the state’s varied habitats (coastal, desert, mountains, etc.), we should select plants that are compatible with our garden’s environment. Our first screening narrows the list to plants that are native to the Santa Cruz area. There are 599 plants in that category, just 7.5% of the statewide total.

Our next screening identifies plants that are butterfly hosts. CalScape does not identify plants that are hosts to moths, but we can assume that butterfly hosts have characteristics that also appeal to moths. This screening reduces the list to 492 plants, 82% of the plants native to the Santa Cruz area.

The CalScape database includes several categories of plants: trees, shrubs, vines, perennials, succulents, etc. For this butterfly garden design project, we have decided to focus on annual herbs for several reasons. First, because annuals grow quickly, we could create a resource for the butterflies in the spring. Second, if we get started soon, we could grow plants from seed, which would greatly reduce the cost of this project. (Buying seedlings from a garden center is certainly convenient but more costly than buying and planting seeds.) Third, we would have a greater variety of plants from which to choose, compared to the availabilities in local or mail-order sources. By limiting our plant selection to annual herbs, we reduced the list from 492 plants to 170 plants (35.5%).

Our next screening identified (a) annual herbs that are (b) native to the Santa Cruz area, (c) commonly used for butterfly gardens and butterfly hosts, and (d) grow in full sun. This screening reduced our target list to 69 plants, a manageable 40.5% of the annual herb list.

Our final screening eliminated hard-to-find plants. CalScape allows screening of plants in terms of availability in nurseries: Commonly Available, Sometimes Available, Rarely Available, Never or Almost Never Available, and Available Through Seed Stores. By selecting “commonly available” plants, we reduced our list to 19 plants.

It could be an interesting project to develop a butterfly garden with uncommon or even rare plants. It could be enjoyable to surprise garden visitors with plants they have rarely or never seen, but that’s a more challenging task than would be appealing for this project.

We then dropped two plants from the list: California Poppy (Eschscholzia californica), which is already spreading in other areas of my garden, and Seep Monkey Flower (Erythranthe guttat), which grows in moist soil or even in water. Those deletions reduced the list to 17 plants.

CalScape has a page of information on each of the plants in the database, based on the plant’s botanical name. We examined each of the 17 plants to decide which ones we would want in this new butterfly garden.

The first variable of interest is the mature size of each of these plants. I have often mentioned my first rule of landscape design: taller plants in the back. With this in mind, I sorted the list into three size categories: four large (3 feet high and wide), three mid-size (about 2.5 feet high), and nine small (under 2 feet high). The bed under development is 30 feet wide, with a picket fence across the back side and a seating wall along the front side. My simple landscape design consists of three rows: tall, mid-size and small.

I also made note of each plant’s blossom color and bloom period, for reference while making the final selections.

This column’s photo gallery shows examples of several specimens in the list of 17 plants. We drew these examples from Wikimedia Commons (commons.wikimedia.org), a useful online resource when learning about unfamiliar plants. The captions are brief excerpts from CalScape’s plant descriptions.

The next stages in this butterfly garden design project are to select enough annual herbs to fill this 270-square-foot garden bed (taking mature sizes into account) and locate sources. The clock is ticking, so I might decide to purchase seedlings to have a resource in the spring for the butterflies.

My next column will describe the search for seeds or plants.

Enjoy the development of your butterfly garden!

Tom Karwin is a past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a past president and Lifetime Member of the Monterey Bay Area Cactus & Succulent Society, and a Lifetime UC Master Gardener (Certified 1999—2009). He is now a board member of the Santa Cruz Hostel Society, and active with the Pacific Horticultural Society. To view photos from his garden, https://www.facebook.com/ongardeningcom- 566511763375123/ . For garden coaching info and an archive of On Gardening columns, visit ongardening.com for earlier columns or visit www.santacruzsentinel.com/ and search for “Karwin” for more recent columns. Email comments or questions to gardening@karwin.com.