How to Grow Potomac Royal
Antirrhinum majus
Antirrhinum majus, commonly known as Potomac Royal snapdragons, offers vibrant vertical interest for gardens during warm months. Gardeners prize these easy-to-grow annuals for their long bloom period and ability to thrive in full sun or partial shade.
📷 Wikipedia: Antirrhinum majusStarting Potomac Royal: indoors or direct sow?
🏠 Start indoors 3 weeks before your last spring frost, then move the seedlings outside.
Move sturdy seedlings outdoors after all danger of frost has passed and soil temperatures have warmed sufficiently for this warm-season annual.
Soil, care & harvest
Prepare well-draining soil with a pH between 6.0 and 7.5. As a warm-season crop, start seeds indoors 2 to 3 weeks before the last frost date. Sow seeds about 1/4 inch deep; they typically germinate within 7 to 14 days once warmth is established.
Space plants 12 to 18 inches apart to ensure good air circulation. Provide consistent moisture without waterlogging, as snapdragons prefer regular watering. Apply a light layer of mulch to retain soil moisture and feed with balanced fertilizer every few weeks during active growth.
Watch for aphids, spider mites, whiteflies, powdery mildew, rust, and damping off. Prevent issues by ensuring good airflow, avoiding overhead watering, and removing infected leaves promptly. These flowers bloom continuously; enjoy the display over their 110 to 120-day growing season rather than harvesting individual blooms.
When to Plant Potomac Royal
Planting windows vary by USDA hardiness zone. Look up yours by ZIP code.
| Zone | Start Indoors | Direct Sow | Harvest |
|---|---|---|---|
| Zone 1 | May – June | July – September | — |
| Zone 2 | April – May | June – August | — |
| Zone 3 | April – May | June – August | — |
| Zone 4 | March – April | June – July | — |
| Zone 5 | March – April | May – July | — |
| Zone 6 | March – April | May – July | — |
| Zone 7 | February – March | April – June | — |
| Zone 8 | February – March | April – June | — |
| Zone 9 | January – February | March – May | — |
| Zone 10 | January | February – April | — |
| Zone 11 | January | January – March | — |
| Zone 12 | January | January – March | — |
| Zone 13 | January | January – March | — |
Companion Plants for Potomac Royal
✓ Good companions
Attracts beneficial insects like hoverflies and provides ground cover
Attracts beneficial insects and provides habitat for predatory insects
Deters pests with fragrance and attracts pollinators and beneficial insects
Repels nematodes, aphids, and whiteflies while attracting beneficial insects
Acts as trap crop for aphids and cucumber beetles, repels squash bugs
Repels aphids, tomato hornworms, and other garden pests
Repels cabbage moths, carrot flies, and other pests with aromatic oils
Attracts beneficial insects and pollinators, provides companion blooming
✗ Keep away from
Produces juglone toxin that inhibits growth and can kill many flowers
Allelopathic compounds suppress growth of nearby plants
Allelopathic effects can inhibit germination and growth of other flowers
