How to Grow an Antelope Horn Milkweed
Plant Antelope Horn Milkweed in full sun, in lean well-drained or sandy soil, and water sparingly through the first year only. The plant resents rich wet conditions and rewards lean dry ground with sturdy upright stems and clusters of green-and-purple flowers in late spring. Monarch caterpillars feed on the leaves.
Where to plant
Antelope Horn Milkweed is a tough native perennial for USDA zones 4 through 9 across much of the central and southwestern United States. The plant grows 1 to 2 feet tall and a similar spread, dying back to the underground roots each winter and resprouting in spring.
Sun
Full sun is required. At least six hours of direct sun a day, eight or more is better. The plant evolved in open prairie and dry rocky slopes, and any shade leads to floppy weak growth with sparse flowers.
Drainage
Sharp drainage is essential. The deep taproot rots quickly in soil that stays wet. Dig a one-foot test hole and fill with water. If it drains within an hour, the spot is fine. If water sits longer, build a raised mound or plant somewhere else. Sandy, gravelly, and rocky soils all work well.
Soil
Lean soil is best. Plant in the native ground without heavy amendments. Rich garden loam pushes weak growth and increases disease pressure. The plant tolerates poor sandy or rocky soil where many ornamentals struggle.
Space
Give the plant 12 to 18 inches of clear space in every direction. Antelope Horn Milkweed has a deep taproot that resents disturbance once established, so place the plant where you want it to stay long-term. Plant in groups of three or more to support Monarch egg-laying — a single isolated plant attracts fewer butterflies.
How to plant
Plant in spring after the last frost or in early fall at least six weeks before the first hard frost. Young container plants establish best, since the deep taproot resents transplanting once the plant matures.
-
1Dig a deep narrow hole Slightly deeper than the root ball to accommodate the taproot, and only as wide as the root ball plus a couple of inches. The roots go down rather than out, so a deep narrow hole suits the plant's growth pattern.
-
2Loosen the root ball If the roots are circling tightly inside the nursery pot, gently tease them apart or score the outside with a clean knife. The taproot in particular wants to head straight down and a circling pattern slows establishment.
-
3Set the plant level with the soil The top of the root ball should sit right at grade. A buried crown rots faster than one set level, and the new shoots come up from just below the soil surface in spring.
-
4Backfill with native soil Use the soil you dug out, with a small amount of coarse sand or fine gravel mixed in if the native soil is heavy. Avoid heavy compost, peat moss, or potting mix in the planting hole. The plant performs best in lean ground.
-
5Water in once Soak the planting hole once after backfilling, until the top six inches feel uniformly damp. This settles the soil around the roots and is the most important watering of the plant's first season.
-
6Mulch lightly A thin layer of gravel or coarse mulch, no more than an inch deep, conserves moisture without trapping it against the crown. Avoid heavy bark mulch that holds wet conditions against the roots and slow-release rotting wood mulch that promotes fungal problems.
Watering and feeding
Watering
Water deeply once a week through the first growing season to help the plant establish, soaking the root zone rather than wetting the leaves. Once the plant has settled in and the taproot has reached down, stop supplemental watering entirely in most climates.
Antelope Horn Milkweed is highly drought-tolerant and gets by on rainfall in nearly every region. Overwatering is the most common cause of failure on this plant, killing far more new plantings than any other issue.
Feeding
Skip feeding entirely. The plant evolved in lean prairie soil and pushes weak floppy growth with any added fertilizer. Even compost worked into the bed at planting can be too much.
If the soil is genuinely dead, a single light dressing of mineral-rich compost in early spring is fine. Otherwise, leave the plant alone.
Pruning and maintenance
Antelope Horn Milkweed needs almost no pruning. The plant dies back to the ground every winter and resprouts from the taproot in spring, so most pruning is simply cleanup of the previous season's stems.
Annual cleanup
Cut last year's dead stems to the ground in late winter or early spring before the new shoots push. The brown stems are brittle and snap off cleanly. Compost the debris or chop and leave it on the bed as light mulch.
Leave a few seed pods on the plant late in the season if you want to save seed for spreading the planting elsewhere. The pods split open and release silky-tailed seeds on the wind in late fall.
Cutting for arrangements
The clusters of green-and-purple flowers cut well for arrangements. Cut stems early in the morning and dip the cut end immediately in a bowl of warm water for a minute or two to seal the cut and slow the milky sap that the plant exudes. Cut blooms hold for 5 to 7 days in a vase.
Long-term care
The plant resents being moved once established, since the taproot breaks easily. Plant where you want it to stay long-term. Mature plantings spread slowly by seed and rarely become aggressive, but seedlings can be moved as young plants in their first year before the taproot develops.
Blooming and color
Antelope Horn Milkweed is grown for the unusual green-and-purple flower clusters in late spring and the role the plant plays as a host for Monarch butterfly caterpillars. The flowers feed pollinators and the leaves feed the next generation of Monarchs.
Bloom timing
Flowers open in late spring, usually April through June depending on the zone. Each cluster of pale green flowers with maroon centers lasts about two weeks, and the whole plant typically blooms across a 4 to 6 week window. Cooler spring weather extends the bloom and hot dry weather shortens it.
Monarchs and other pollinators
The plant is a critical host for Monarch butterfly caterpillars, who feed only on milkweed species. Monarchs lay eggs on the leaves in spring and summer, the caterpillars feed for two to three weeks, and the leaves grow back after the caterpillars pupate. Tolerate some leaf damage as a normal part of supporting Monarchs.
Native bees, soldier beetles, and small wasps work the flowers heavily for nectar. Plant in groups of three or more for the best butterfly response, since a lone milkweed attracts fewer Monarchs than a small patch.
Seed pods
Distinctive green pods 2 to 4 inches long develop after the flowers fade and look like miniature horns, which gives the plant its common name. The pods turn brown and split open in late fall, releasing flat brown seeds with silky tails that catch the wind. Save a few pods before they split to sow seed elsewhere.
Common problems and pests
Most Antelope Horn Milkweed complaints come from too much water, too much fertilizer, or aphid pressure on the new growth. Leaf damage from Monarch caterpillars is not a problem — it is the point of growing the plant.
Plant rots out the first season
Overwatering or planting in heavy wet clay is the leading cause. The taproot cannot survive in soil that stays wet for more than a few days. Stop supplemental watering after the establishment month and check that drainage is sharp. If the spot consistently drowns, move the planting to a better-drained location or build a raised bed.
Floppy weak growth
Too rich soil or too much fertilizer. The plant evolved on lean prairie ground and pushes elongated weak stems when fed. Stop feeding and let the plant adjust. Next year's growth from the taproot will come in stronger as the soil leans out.
Orange aphids on new growth
Oleander aphids — small bright orange insects that cluster on milkweed stems in summer. Knock them off with a strong spray of water every few days. Avoid insecticides, since they kill the Monarch caterpillars and other beneficial insects that visit the plant. Lady beetles and lacewing larvae eat aphids on their own once they find the colony.
Leaves chewed down to the stem
Monarch caterpillars at work. This is not a problem — it is the reason for growing the plant. The caterpillars feed for two to three weeks and then leave to pupate, after which the plant regrows leaves from the existing stems. Tolerate the damage and watch for the next stage of Monarchs.
Powdery mildew in humid weather
White dusty film on the leaves in late summer, especially in crowded plantings or after a wet spell. Improve airflow by thinning the planting and removing the worst affected stems. Avoid splashing the leaves when you water, soaking the soil directly instead. Heavy infections rarely kill the plant but reduce the look.
Yellow leaves in midsummer
Sometimes a normal response to summer heat and drought, in which case the plant recovers in fall. Persistent yellowing usually indicates root stress from wet soil or fertilizer. Check drainage first and stop any feeding.
Brown rust spots on leaves
Milkweed rust, a fungal disease that produces small brown or orange pustules on the leaves. Remove and discard the worst affected leaves. The disease rarely kills the plant but spreads in crowded humid plantings. Avoid overhead watering and thin out crowded stems to improve airflow.
Milky sap on skin
The plant exudes a milky white latex sap when stems or leaves are cut. The sap can irritate skin and is particularly hard on eyes if rubbed in by accident. Wear gloves when pruning, and rinse skin with soap and water if any sap gets on you. The sap is also toxic to pets if eaten in quantity, though most pets find it bitter and leave it alone.
Plant fails to return in spring
Most often a sign that the taproot rotted during a wet winter or a wet early spring. Check drainage at the spot and consider moving next year's planting to a better-drained location. Occasionally a hard freeze in zone 4 sites kills the crown — wait until late spring before assuming the plant is gone, since the taproot can be slow to push fresh growth after a tough winter.
About This Article
