Iron Purple
Matthiola incana
Photo: Robert Flogaus-Faust · Wikimedia Commons · (CC BY 4.0)
Early single-stem, or column-type stock in a highly uniform series for one-cut harvest. Aptly named for strong, straight, rigid stems. Iron performed well in our spring, early summer, and fall trials. Selectable for doubles and 55% double without selection. Compared to Katz, Iron is slightly later to flower, and has somewhat shorter and thicker stems. Tightly spaced florets on the flower spike make for compact 1 1/2-2", deep plum-colored blooms with a full appearance. NOTE: This variety produces one flowering stem per plant. Pinching is not advisable as it will terminate flowering.Edible Flowers: The peppery, clove-like flavor of the flowers lends itself well to use as a garnish on salads, desserts, and drinks.
Harvest
90-105d
Days to harvest
Sun
Full sun to partial shade
Zones
6–10
USDA hardiness
Height
1-3 feet
Planting Timeline
Showing dates for Iron Purple in USDA Zone 7
All Zone 7 flower →Zone Map
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Iron Purple · Zones 6–10
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 1 | May – June | July – August | July – September | — |
| Zone 2 | April – May | June – July | June – August | — |
| Zone 11 | January – January | January – February | January – March | — |
| Zone 12 | January – January | January – February | January – March | — |
| Zone 13 | January – January | January – February | January – March | — |
| Zone 3 | April – May | June – July | June – August | — |
| Zone 4 | March – April | June – June | June – July | — |
| Zone 5 | March – April | May – June | May – July | — |
| Zone 6 | March – April | May – June | May – July | — |
| Zone 7 | February – March | April – May | April – June | — |
| Zone 8 | February – March | April – May | April – June | — |
| Zone 9 | January – February | March – April | March – May | — |
| Zone 10 | January – January | February – March | February – April | — |
Succession Planting
Stock is a one-and-done crop per plant — each spike blooms once, so succession planting is the only way to keep cut stems coming. In zone 7, sow indoors every 3 weeks from early February through mid-March, then start another round of direct sowing in late July or August for a fall flush. That fall window is often the better one: nights dropping back into the 50s°F improve flower color and the plants aren't racing summer heat to finish.
Stop succession sowing once daytime highs are reliably above 80°F — stock pushed into that heat will stall or produce weak, abbreviated spikes. Pick back up with fresh seed in late July and count forward 90-105 days to confirm your transplants will hit maturity when conditions have cooled back down.
Complete Growing Guide
Early single-stem, or column-type stock in a highly uniform series for one-cut harvest. Aptly named for strong, straight, rigid stems. Iron performed well in our spring, early summer, and fall trials. Selectable for doubles and 55% double without selection. Compared to Katz, Iron is slightly later to flower, and has somewhat shorter and thicker stems. Tightly spaced florets on the flower spike make for compact 1 1/2-2", deep plum-colored blooms with a full appearance. NOTE: This variety produces one flowering stem per plant. Pinching is not advisable as it will terminate flowering.Edible Flowers: The peppery, clove-like flavor of the flowers lends itself well to use as a garnish on salads, desserts, and drinks. According to Johnny's Selected Seeds, Iron Purple is 90 - 105 days to maturity, annual, open pollinated. Notable features: Use for Cut Flowers and Bouquets, Edible Flowers, Fragrant.
Light: Full sun (6 or more hours of direct sunlight a day), Partial Shade (Direct sunlight only part of the day, 2-6 hours). Soil: Clay, High Organic Matter, Loam (Silt), Sand. Soil pH: Alkaline (>8.0), Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 1 ft. 0 in. - 3 ft. 0 in.. Spread: 0 ft. 9 in. - 1 ft. 6 in.. Spacing: Less than 12 inches, 12 inches-3 feet. Growth rate: Rapid. Maintenance: Low. Propagation: Seed. Regions: Coastal, Mountains.
Harvesting
Iron Purple reaches harvest at 90 - 105 days from sowing per Johnny's Selected Seeds. Expect 1 1/2-2" at peak. As an annual, harvest continues until frost ends the season.
Seeds will ripen in August and September.
Harvest time: Fall
Storage & Preservation
Cut Iron Purple stock flowers last longest when placed in cool water immediately after harvest. Store in the refrigerator at 34-40°F with 90% humidity for maximum vase life of 7-10 days. For short-term counter display, keep in cool conditions away from direct sunlight and ethylene-producing fruits. For preservation, hang-dry flowers upside down in a warm, dark, well-ventilated space for 1-2 weeks to create dried arrangements. Alternatively, press flowers between parchment paper under weight for 2-3 weeks for botanical crafts and herbal use.
History & Origin
Iron Purple is open-pollinated, meaning seed saved from healthy plants will produce true-to-type offspring. Listed in the Johnny's Selected Seeds catalog.
Origin: The Coast of Europe from Spain to Greece.
Advantages
- +Strong, rigid stems ideal for professional floral arrangements and cut flowers
- +Highly uniform series ensures consistent quality for one-cut harvest operations
- +Compact, full 1.5-2" deep plum blooms with tightly spaced florets
- +Selectable for doubles with 55% double rate without additional selection
- +Edible flowers offer unique peppery, clove-like flavor for culinary garnish
Considerations
- -Single flowering stem per plant limits yield compared to pinchable varieties
- -Slightly later to flower than Katz variety may delay harvest scheduling
- -No pinching option available makes plant management inflexible for growers
- -Shorter stems than some competitors may limit arrangement design options
Companion Plants
Marigolds and nasturtiums do real work near stock. French marigold varieties like 'Petite Gold' deter aphids through scent and draw in predatory wasps that keep soft-bodied pest pressure down. Nasturtiums pull double duty as a trap crop — aphids pile onto them first, which makes scouting simple: check the nasturtiums, not your Matthiola spikes, and you'll know immediately what's building. Sweet alyssum fills in low around the base without competing with stock's 1-3 foot height, and its flowers recruit hoverflies whose larvae are effective aphid predators at the larval stage.
Black walnut, eucalyptus, and fennel all release allelopathic compounds that can suppress neighboring plants. Black walnut produces juglone through its roots and leaf litter; Matthiola is sensitive enough that it's not worth planting anywhere near one. Eucalyptus puts out cineole and other volatile compounds that inhibit germination and root development in close neighbors. Fennel is a chronic problem in mixed plantings regardless of species — it suppresses almost everything around it and belongs in its own isolated bed.
Plant Together
Marigolds
Repel nematodes and aphids while attracting beneficial insects
Nasturtiums
Act as trap crops for aphids and cucumber beetles
Sweet Alyssum
Attracts beneficial predatory insects and provides ground cover
Zinnia
Attracts pollinators and beneficial predatory insects
Petunias
Repel aphids, tomato hornworms, and other garden pests
Lavender
Repels moths, fleas, and mosquitoes while attracting pollinators
Catnip
Repels ants, aphids, and mosquitoes effectively
Cosmos
Attracts beneficial insects and provides vertical interest
Keep Apart
Black Walnut
Produces juglone toxin that inhibits growth of many flowering plants
Eucalyptus
Releases allelopathic compounds that suppress nearby plant growth
Fennel
Inhibits growth of most garden plants through allelopathy
Troubleshooting Iron Purple
What you'll see, why it happens, and what to do about it.
Seedlings collapse at the soil line, stems pinched and darkened, within the first 2-3 weeks after germination
Likely Causes
- Damping off (Pythium or Rhizoctonia solani) — fungal rot triggered by overwatering and poor airflow around the stem base
- Sowing too deep in heavy, slow-draining starting mix
What to Do
- 1.Water from the bottom only, and let the top inch of mix dry out between waterings
- 2.Run a small fan near your seedling trays for 30-60 minutes a day to keep air moving
- 3.If a whole flat is affected, start fresh — the fungus spreads fast and there's no saving a collapsed flat
Leaves show irregular yellow patches turning bronze or silvery, with tiny dark specks on the undersides
Likely Causes
- Two-spotted spider mite (Tetranychus urticae) — shows up fast in hot, dry conditions above 85°F
- Thrips (Frankliniella occidentalis) — rasping damage looks similar but you'll see tiny insects moving if you tap a stem over white paper
What to Do
- 1.Blast the undersides of leaves with a hard spray of water every 2-3 days to knock mite populations down
- 2.Apply insecticidal soap or neem oil in the evening, coating the undersides thoroughly — repeat every 5-7 days for 3 applications
- 3.Keep plants well-watered; drought-stressed stock draws mites in faster than healthy ones
Buds form but flowers never fully open, or the spike stalls out around 60-70 days and just sits there
Likely Causes
- Heat stress — Matthiola incana blooms poorly once daytime highs consistently exceed 80°F
- Skipped vernalization: stock benefits from cool exposure around 50°F for 1-2 weeks at the seedling stage to trigger proper budset
What to Do
- 1.Start seeds indoors in February so transplants go out in early April and finish blooming before summer heat arrives
- 2.If you're already mid-season and temps are climbing, cut any open spikes now, then plan a late-July direct sow for a fall flush instead
- 3.During hardening off, don't rush the cool-night exposure — 2 weeks at 50°F before transplanting makes a measurable difference in spike quality
Frequently Asked Questions
How long do Iron Purple stock flowers last in a vase?▼
Is Iron Purple stock good for beginners?▼
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Growing Guides from Wind River Greens
Where to Buy Seeds
Sources & References
External authority sources used in compiling this guide.
- BreederJohnny's Selected Seeds
See the Methodology page for how this data is sourced, what's AI-assisted, and known limitations.