Growing Guide: Swallowtail Butterfly Host Plant Herb Collection
Or How to Grow Dill, Parsley, Fennel, and Rue
Mature caterpillar crawls up a fennel about to flower.
This guide will help you successfully grow each plant in your collection to create a welcoming habitat for swallowtail butterflies at every stage of their lifecycle. To learn more about raising caterpillars, read my guide here.
Getting Started
Timing
When to plant: Most herbs in this collection can be started indoors 6-8 weeks before the last frost date in your area, or directly sown outdoors after all danger of frost has passed. I direct sow parsley in December, at the same time I sow cilantro with great success.
Growing season: Spring through fall, with some plants persisting as perennials in certain zones.
Basic Supplies
Seed-starting containers or seed trays
Well-draining potting soil or seed-starting mix
Spray bottle for gentle watering
Sunny location or grow lights
Garden space or large containers for transplanting or direct sowing
Plant-Specific Growing Instructions
Bouquet Dill
Anethum graveolens
Planting depth: 1/4 - 1/2 inch deep
Days to germination: 7-21 days (direct sowing is best)
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1/8 to 1/4 inch deep spaced 2-4 inches apart. If planting in rows, space the rows about a foot apart. Dill can also be successfully grown in containers, provided they are at least 18 inches deep to accommodate the plant’s long taproot. Direct sowing is easiest but if starting seeds indoors, transplant early before roots get long and baby with seaweed waterings until the seedling recovers. Eventually thin to 4-10 inches apart depending on how much leaf harvesting you plan to do.
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It prefers full sunlight, even full Texas sun, though it can tolerate partial shade. Protect from strong winds.
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Prefers a rich, light soil, though dill isn’t picky about soil quality and will grow in most anything that drains.Moderate water needs, keep soil evenly moist until sprouting and water regularly after established for best results. It likes to be moist but not wet.
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Basil, broccoli, marigolds, corn, lettuce, onions, nasturtiums, chives, squash and zucchini
AVOID: Peppers (will compete for same nutrients), carrots (potential for cross-pollination).
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Dill is an annual that self-seeds readily. Allow some plants to flower and set seed for continuous growth. Dill does not transplant well, so direct sowing is recommended. If you do transplant, water with seaweed water until they perk up.
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Harvest when flower heads are fully developed and bright yellow. Seed heads can also be dried and used indefinitely. Expect a vase life of 7 to 10 days. Dry foliage in the dark to preserve flavor and color for cooking.
Read more on Dill’s product page
Swallowtail eggs on dill
Fennel (Foeniculum vulgare)
Swallowtail caterpillar on fennel leaves
Planting depth: 1/4 inch deep
Spacing: 12-18 inches apart
Days to germination: 7-14 days
Light requirements: Full sun/part shade
Water needs: Moderate, tolerates some drought once established. Fennel bulbs are tastiest when they are kept
Special notes: Fennel is a perennial in zones 4-9. Fennel can reach 3-5 feet tall, so place it toward the back of garden beds.
Warning: Fennel produces allelochemicals which suppress the growth of plants around it and inhibit germination of rival seeds. For that reason, do not plant near other crops, especially near nightshades– tomatoes, peppers, potatoes, and eggplants. Planting it where you have a lot of unwanted weeds can help repel them.
Rue (Ruta graveolens)
Rue is also a host plant for Giant Swallowtail Butterflies
Planting depth: 1/8 inch deep
Spacing: 18-24 inches apart
Days to germination: 14-21 days
Light requirements: Full sun to partial shade
Water needs: Low, drought tolerant once established
Special notes: Rue is a woody perennial in zones 4-9. Some people experience skin irritation when handling rue, so wear gloves. Rue has beautiful blue-green foliage and yellow flowers.
Parsley (Petroselinum crispum)
Young Swallowtail instars on parsley
Planting depth: Surface
Spacing: Thin strong seedlings to 6-8 inches apart
Days to germination: 14-60 days (soaking seeds overnight speeds germination)
Light requirements: Full sun to partial shade. Afternoon shade is best.
Water needs: Moderate, keep soil consistently moist but never soggy.
Special notes: Parsley is a biennial, producing leaves the first year and flowers the second. Both flat-leaf and curly varieties attract swallowtail.
Planting Tips for Creating a Butterfly Habitat
Plant herbs en masse rather than individually to make it easier for female butterflies to find them.
Include nectar plants for adult butterflies alongside host plants.
Do not use inorganic pesticides in your butterfly garden. If you use a product like BT on your brassicas, make sure a breeze isn’t going to carry it to your host plants.
CATERPILLAR & BUTTERFLY LIFE CYCLE SUPPORT
Eggs: Female butterflies lay eggs on host plants. Be careful when harvesting herbs to check for tiny eggs on leaf undersides. If you find them, you can just collect a few of those leaves and put the eggs and foliage in an old berry container until they hatch and you transfer them to your enclosure or back outdoors on the host plant.
Caterpillars: Create undisturbed areas where caterpillars can feed and you aren’t actively harvesting.
Chrysalis: Provide structures like trellises and bamboo stakes or plant near fences or tall plants where caterpillars can form their chrysalides. They will leave the host plants when they are ready to pupate. You can also set up an enclosure to raise your caterpillars with more attention.
Adult butterflies: Plant nectar-rich flowers nearby to feed adult butterflies.