Milkweeds are perennials that attract a variety of butterflies, including the monarch, whose caterpillars consume the plant's leaves. Milkweeds bloom with clusters of red, pink, white, orange, or yellow flowers in the summer. Later in the season they develop feathery seed capsules that can be dried and used in craft projects. Most milkweeds bear a white, milky sap in their leaves and stems.
- Common name: Milkweed
- Botanical name: Asclepias spp.
- Zones: 3 to 10, depending on species
- Size: To 6 feet tall, depending on species
- From: Areas of North and South America
- Family: Asclepiadaceae (milkweed family)
- Sun: Full sun is best; plants tolerate partial shade.
- Soil: Moist, well-drained soil for best results.
- Moisture: Some species are drought-tolerant; others prefer moist soils and will grow well along ponds or streams. A layer of mulch in the summer is beneficial, especially in hot summer areas. The mulch helps retain moisture and keep soil temperatures cool.
- Mulch: Lay a 2- to 3-inch-deep layer of mulch over the soil to conserve moisture and reduce weeds.
- Pruning: Cut the plants to the ground after they freeze in autumn or before growth in spring.
- Fertilizer: Fertilizer is unnecessary in soils rich in organic matter.
- Staking: To stake the tall plants, sink a tall stick or stake into the ground a short distance from the plant (that way, you'll avoid harming the root system). Tie the plant stem to the support using a figure-eight pattern with the stem in one loop and the stake in the other. This helps prevent excessive rubbing, which can cause disease.
- Seed: Sow seeds in a cold frame or a sheltered spot in the garden in early spring. Seeds can take several months to germinate.
- Division: Because the plants have large taproots, division can be difficult.
- Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil spray for severe infestations.
- Fungal diseases: To avoid fungal diseases, prune plants to encourage good air flow, water at the base of the plant to keep the foliage dry, and mulch the soil around the plants.
- Leaf spot: In summer or autumn, leaves develop yellowish or dark-colored spots. Each spot often has concentric rings around it, forming a bull's-eye pattern.
- Powdery mildew: This disease tends to appear in mid- to late summer. Affected leaves are covered with a grayish powder. When heavily infected, leaves drop off.
- Rust: It usually looks like leaf spotting that's followed by small masses of rust-colored powder on the leaves. Infected leaves die by the end of the season.
- Milkweeds are attractive as cut flowers. Before placing the stems in water, sear stems in a small candle flame for several seconds to stop the flow of milky sap, which can irritate a gardener's skin.
- Because the plants have tap roots and are difficult to transplant, site them carefully.
- Many milkweeds emerge later than other perennials, so mark them well to avoid accidentally planting over them.
- Monarch caterpillars may cause a great deal of leaf damage as they feed on the leaves. Keep milkweeds near the back of the border so the damage is less noticeable.
- Asclepias curassavica: Tropical species to 3 feet tall with striking red or orange flowers. Zone 10. Often grown as an annual outside of the tropics.
- Asclepias incarnata: Grows to 4 feet tall and bears clusters of pinkish or reddish flowers in summer. There are several named selections with various flower colors. Zones 3 to 8. Native to areas of North America.
- Asclepias incarnata ‘Ice Ballet': Grows to 4 feet tall and bears clusters of white flowers in summer. Zones 3 to 8. Native to areas of North America.
- Asclepias syriaca: Grows to 6 feet tall and bears clusters of dusty-pink flowers in summer. Zones 4 to 9. Native to areas of North America; considered an agricultural weed.
- Asclepias tuberosa: Grows to 3 feet tall and bears clusters of bright orange flowers in summer. Zones 4 to 9. Native to areas of North America.