Agastache ‘Blue Boa’: The 3-Foot Hummingbird Mint That Blooms June Through Frost in Zones 5–10
Agastache ‘Blue Boa’ blooms June to frost on poor soil — it needs just one thing: perfect drainage. Full growing guide for Zones 5–10.
| Feature | Detail |
|---|---|
| Mature height | 30–36 inches (2.5–3 feet) |
| Spread | 20–24 inches |
| USDA Hardiness | Zones 5–9 (Proven Winners lists to Zone 10) |
| Bloom time | June through first frost |
| Sun | Full sun (6+ hours daily) |
| Soil | Well-drained, lean to average, pH 6.0–8.0 |
| Water | Medium first season; low once established |
| Fragrance | Anise/licorice (flowers and foliage) |
| Attracts | Hummingbirds, butterflies, bees, hummingbird moths |
| Deer resistant | Yes |
Most perennials give you 6–8 weeks of peak bloom. Agastache ‘Blue Boa’ gives you 4–5 months — from June until your first killing frost — on soil so lean that most plants would refuse to grow. That makes it one of the longest-blooming perennials available for a sunny border, and explains why hummingbirds arrive before you’ve finished planting it.
‘Blue Boa’ is a patented hybrid released in 2013, bred for denser flower spikes, more uniform height, and longer bloom than straight-species agastache. It grows 30–36 inches tall with deep violet-blue spikes — tubular, nectar-rich, and fragrant — that open progressively from the base of each spike to the tip, stretching a single stem’s performance across weeks rather than days.
There is one non-negotiable requirement: drainage. Get that right and almost everything else takes care of itself.
What Makes ‘Blue Boa’ Different from Other Agastache
Agastache is a genus of 22–29 native North American perennials in the mint family (Lamiaceae). Most species are excellent garden plants, but ‘Blue Boa’ is not a straight species — it’s a patented hybrid (US Plant Patent PP24,050, issued November 2013) developed specifically for ornamental performance.
That distinction matters for three reasons.
Flower structure: Each spike contains 8–12 false whorls — tiers of tiny 2-lipped tubular flowers arranged around the stem, with spikes reaching 6 inches long. The tubular shape is functionally precise: nectar sits deep inside, accessible to hummingbirds and long-tongued native bees but not to short-tongued insects that would consume nectar without contributing to pollination.
Fragrance chemistry: The leaves smell of anise and licorice — not from the flowers, but from glandular trichomes (microscopic hair-like structures) on the leaf surface that store volatile compounds, primarily estragole. Research published in PMC on Agastache phytochemistry confirms that estragole makes up 18–98% of the genus’s essential oil profile depending on species and growing conditions, with menthone, limonene, and β-caryophyllene as supporting compounds. When you brush a leaf, you rupture those trichomes and release the oil. This chemistry is also consistent with the plant’s drought tolerance: volatile oil layers on leaf surfaces reduce the temperature differential between leaf and surrounding air, which lowers transpiration demand in hot, dry conditions. Direct controlled studies on this mechanism in agastache are limited, but the phytochemical profile is consistent with the pattern seen in other aromatic Lamiaceae adapted to dry habitats.
Seedling behavior: Because ‘Blue Boa’ is a patented hybrid, seeds harvested from it won’t produce plants identical to the parent. Self-sown seedlings are still worth keeping for garden interest, but expect variation in flower color, height, and bloom density rather than the specific deep violet-blue of the named cultivar.
Choosing the Right Site
Two variables determine whether Blue Boa thrives or struggles: sun and drainage. Get both right and the plant essentially manages itself for the rest of the growing season.
Sun: Blue Boa requires full sun — a minimum of 6 hours of direct sunlight daily. Below that threshold, flower production drops and stems tend to flop. In the hottest zones (8–10), a brief break from afternoon sun is tolerated, but consistent partial shade will noticeably reduce bloom count.
Drainage — the non-negotiable: Perfect drainage matters more than soil type, fertility, or pH. NC State Extension and Missouri Botanical Garden both identify crown rot in waterlogged soil as the primary killer of agastache, particularly in winter when cold, wet soil is lethal to the crown. Blue Boa evolved from dry-prairie and rocky-hillside ancestors; saturated roots are not part of its biology.
If your garden soil stays wet through winter or drains slowly after rain, you have two practical solutions: raise the bed by 6–8 inches to lift the crown above the waterline, or incorporate horticultural grit or coarse gravel throughout the planting area and at the base of the planting hole. Proven Winners specifically recommends gravel at the hole’s base to prevent water pooling at root level. Containers are an excellent alternative in Zone 5–6 clay soils — they give you complete drainage control and let you overwinter the plant in a sheltered spot if needed.
Soil fertility: Average to poor soil is ideal. Blue Boa is native to lean prairie habitats and responds to high fertility by producing dense, floppy growth with fewer flowers. There is no need to amend the planting site with compost unless the soil is genuinely impoverished sand.
pH: 6.0–8.0, with a slight preference for neutral to alkaline conditions. BBC Gardeners World notes it even tolerates chalky soils well — a useful data point for gardeners in limestone regions.
How to Plant Blue Boa
The best planting time depends on your zone:
- Zones 5–7: Plant in spring after your last frost date, once soil is consistently above 50°F. This gives roots a full growing season to establish before the first winter.
- Zones 8–10: Both spring and fall planting work. Fall planting (September through October) lets roots establish during mild temperatures before the following summer’s heat arrives, giving you a more floriferous first year.
At planting:
- Dig a hole to the depth of the nursery container — no deeper.
- If drainage is questionable, place a 2-inch layer of coarse gravel or grit at the base of the hole.
- Set the plant at the original soil line, backfill, and firm gently around the rootball.
- Space plants 20–24 inches apart center-to-center; this air circulation reduces fungal pressure.
- Water thoroughly at planting.
- Do not fertilize at planting — Blue Boa establishes best in lean conditions.
First-season care: Water consistently through the first growing season. Once the plant shows vigorous new growth — typically 4–6 weeks in — begin reducing watering frequency toward the established plant’s low water regime.
Watering: Why Blue Boa Thrives on Neglect
Blue Boa’s water needs shift fundamentally between its first season and every season after.
Year 1: Water regularly — every 1–2 days in hot weather — until the root system establishes. A reliable indicator: the plant shows consistent new growth and stops wilting between waterings.
Year 2 and beyond: Water deeply and infrequently. Allow the top inch of soil to dry completely before the next irrigation. In most US climates, once-weekly deep watering through summer is sufficient; in Zones 5–6 with normal summer rainfall, established plants may not need supplemental water at all.
Why does it tolerate drought so well? Blue Boa’s ancestors come from North American prairies and dry upland forests where summer droughts are a normal feature of the growing season. At the leaf level, the glandular trichomes that produce the aromatic volatile oils (estragole, menthone, β-caryophyllene) are consistent with an adaptation that reduces heat load and slows transpiration — the aromatic compound layer on the leaf surface acts as a kind of thermal buffer. While the evidence for this specific mechanism in Agastache is largely inferential from phytochemical data rather than direct physiological studies, it aligns with patterns documented in other aromatic Lamiaceae from dry habitats.
The practical implication: a mild afternoon droop in August heat is normal. The plant recovers overnight. True water stress looks like persistent wilting that doesn’t resolve by morning, combined with bone-dry soil 3–4 inches deep.
The overwatering risk: Crown rot caused by waterlogged roots is the most common way Blue Boa dies. Symptoms — a sudden collapse of stems at the soil line with a soft, brown crown — are usually irreversible. If the soil is constantly moist, the plant is already at risk before any visible symptoms appear.
Fertilizing: Why Less Is More
Do not fertilize Blue Boa, or do so once and lightly. This runs counter to the instinct to feed flowering perennials, but agastache evolved in lean soils and responds to excess nutrients — especially nitrogen — by producing rank, floppy growth with noticeably fewer flower spikes. BBC Gardeners World states this directly: fertilizer causes stem flopping and reduced flowering.
Stop missing your zone's planting windows.
Select your US zone and month — get a complete checklist of what to plant, prune, feed, and protect right now.
→ View My Garden Calendar
In my experience growing agastache alongside lavender and ornamental salvias, treating them all identically — ignoring the fertilizer drawer entirely — produces the best results for all three. Blue Boa sits in the same category: a plant that flowers best when pushed toward lean conditions.
If your soil is genuinely impoverished (pure sand with no organic matter), a single application of a balanced, slow-release fertilizer in early spring is the maximum. High-nitrogen formulas — lawn fertilizers, liquid feeds — will actively reduce flowering. Compost worked in at planting is the safer amendment if you want to add any organic matter to the bed.
Month-by-Month Care Calendar
| Month | Zones 5–6 | Zones 7–10 |
|---|---|---|
| January–February | Leave stems standing; they insulate the crown and provide finch seeds | Watch drainage; cut back in February once new basal growth emerges |
| March–April | Wait for new growth at the base before cutting back — Blue Boa is a late riser | Cut stems to 4–6 in above soil; divide large clumps now if needed |
| May | Plant after last frost; pinch growing tips at 4–6 in for bushy habit | Plant or establish fall divisions; pinch tips for bushiness |
| June | Bloom begins; reduce watering for established plants | Full bloom underway; water deeply but infrequently |
| July–August | Peak bloom; deadhead every 2–3 weeks for continuous display | Peak bloom; watch for spider mites in prolonged dry heat |
| September–October | Bloom continues to frost; reduce watering as temperatures drop | Bloom continues; fall planting window opens in Zones 8–10 |
| November–December | Leave stems standing — they protect the crown and hold ornamental seedheads | Trim to a few inches; light mulch optional in Zone 7 |
Critical timing note for Zones 5–7: Don’t cut back in early spring until you see new growth emerging at the base. Blue Boa looks completely dead longer than most perennials, but the crown is alive below. Cutting too early removes the insulating stems before new growth has anything to protect it from late frosts.
Pruning and Deadheading
Blue Boa responds well to deadheading but won’t shut down without it. Individual spikes bloom progressively from the base upward, so a single stem delivers weeks of flowers — a useful trait that reduces the urgency of deadheading compared to plants that bloom all at once.
Deadheading: Cut spent spikes back to the nearest visible side bud or the next pair of leaves. Don’t cut to ground level when removing spent blooms — this removes the structural framework and triggers slow regrowth. If you allow a portion of your planting to go to seed, the dried calyxes remain ornamentally attractive through winter and provide food for goldfinches.
Pinching in spring: When new growth reaches 4–6 inches tall in spring, pinch the growing tips to encourage branching. This produces a denser, wider plant with more flowering stems and better wind resistance — the most reliable fix for floppy Blue Boa in fertile soils.
The fall pruning mistake: Do not cut Blue Boa back in autumn. According to BBC Gardeners World, pruning in fall stimulates new growth that won’t survive freezing temperatures. The old stems serve two purposes: they insulate the crown marginally from cold, and their upright structure catches snow and leaf litter that adds further insulation. In Zones 5–6, this distinction can determine whether the plant survives winter.
Spring cutback timing: Cut old stems to 4–6 inches above the soil line in early spring — but only after you can see new growth emerging from the base. That visible green growth is your safe cue.
How to Propagate Blue Boa
Because ‘Blue Boa’ is a patented hybrid, propagating it for commercial sale requires a license from the breeder. Home gardeners can freely divide established plants and take cuttings for personal use.
Division (most reliable): Divide every 3–5 years in spring, when the crown has grown large enough to split productively. Dig around the full clump with a sharp spade, lift the root ball, and use a clean knife to cut it into sections — each section needs both healthy roots and several growing shoots. Replant immediately at the original depth and water in well.
A note on timing: Missouri Botanical Garden recommends spring division; BBC Gardeners World suggests autumn. In Zones 5–7, spring is the safer choice — fall-divided plants in cold climates may not establish root growth before winter arrives. In Zones 8–10, either season works.
Stem cuttings: Take 4–6 inch cuttings from non-flowering stems in late spring to early summer. Remove lower leaves, dip the cut end in rooting hormone, and insert into a well-draining propagation mix. Maintain at approximately 70°F with consistent moisture but not saturation. Roots typically develop within 3–5 weeks.
Seeds: Sow seeds indoors 6–8 weeks before your last frost date. Seeds need light to germinate — press them onto the surface of a damp seed-starting mix without covering. At 70°F, germination takes 14–21 days. However, seeds from a patented hybrid won’t produce plants identical to ‘Blue Boa.’ Seedlings may show the general agastache habit but will vary in flower color, height, and uniformity. The UC Master Gardener Program of Sonoma County recommends deadheading if you’re growing multiple agastache cultivars nearby — it prevents unwanted cross-pollination that would further confound seed outcomes.
‘Blue Boa’ vs. Other Agastache Cultivars
‘Blue Boa’ holds its place as the deepest violet-blue in the genus and one of the longest-blooming. But other cultivars suit specific situations better. Use this table to match the right agastache to your garden goals:
| Cultivar | Height | Zones | Color | Best for | Avoid if |
|---|---|---|---|---|---|
| ‘Blue Boa’ | 30–36 in | 5–9 | Deep violet-blue | Back border, cut flowers, long bloom season | Zone 5 with heavy clay or wet winters |
| ‘Blue Fortune’ | 36 in | 5–9 | Powder blue | Cold climates; tolerates -15°C (-5°F) | Hot Zone 9–10 summers without irrigation |
| Kudos Coral | 16–20 in | 6–9 | Coral-pink | Containers, border front, small gardens | Zones 5–6 without reliable winter protection |
| Desert Solstice | 36 in | 5–9 | Mixed orange/pink calyxes | Unique warm-toned pollinator meadow | Formal or cool-palette gardens |
| ‘Glowing Embers’ | 24–30 in | 5–9 | Orange-red | Warm-toned borders; hummingbird focus | Blue or purple planting schemes |
| Acapulco Orange | 18 in | 6–9 | Orange | Container centerpiece; Zone 6 borders | Zone 5 without protection; cold wet winters |
If you’re in a borderline Zone 5 with heavy soil, ‘Blue Fortune’ is the safer bet — it tolerates significantly colder temperatures and wetter conditions. Choose ‘Blue Boa’ when you want the deepest violet-blue available in the genus and a proven bloom season running from early summer to frost.
Garden Design and Companion Plants
Blue Boa’s upright, spiky form provides strong vertical contrast to mound-forming perennials. The deep violet-blue registers clearly from a distance, so it earns its place in border mid-ground or back, where shorter plants don’t obscure it. Plant in groups of 3–5 for the most visual impact; a single specimen disappears in a mixed border but a drift stops traffic.
Drought-tolerant borders: Blue Boa pairs naturally with lavender, catmint, and ornamental salvias — all share the same full-sun, lean-soil, minimal-water requirements. This combination delivers continuous bloom from May through October. See our drought-tolerant flower guide for complementary plants that complete the palette.
Pollinator gardens: Few perennials rival Blue Boa for hummingbird traffic in high summer. Combine it with native Echinacea and Rudbeckia ‘Prairie Sun’ for a season-long pollinator buffet from June through October. Our full pollinator garden guide has plant-by-bloom-month combinations to extend the feeding window across the whole season.
Prairie and meadow plantings: Blue Boa is at home in naturalistic designs with ornamental grasses, rudbeckia, and echinacea — its prairie ancestry makes it a genuine fit rather than a design imitation. For more native perennials that share Blue Boa’s lean-soil tolerance, see our native plants guide.
Containers: Use a pot with at least one large drainage hole, a well-draining mix (add 20–30% perlite to standard potting soil), and a container of at least 3 gallons. In Zones 9–10, containers allow you to move the plant to shelter if a rare cold snap threatens. Blue Boa performs exceptionally as a container plant and serves as a strong thriller in mixed patio arrangements paired with trailing verbena or calibrachoa.
Troubleshooting: Diagnostic Table
Most Blue Boa problems trace back to moisture — either too much (root and crown rot) or, less commonly, to insufficient sun or soil that’s too fertile. The table below covers the most common issues:
| Symptom | Likely Cause | Fix |
|---|---|---|
| Stems collapse suddenly at soil level; crown soft and brown | Crown rot from waterlogged soil | Remove plant; improve drainage before replanting. Recovery unlikely once crown is mushy. |
| White powdery coating on leaf surfaces | Powdery mildew (high humidity, poor air circulation) | Improve spacing for airflow; apply sulfur fungicide if spreading. Rarely fatal — mostly cosmetic. |
| Orange or rust-brown spots on leaf undersides | Rust fungus | Remove affected leaves; avoid overhead watering; apply copper fungicide if spreading rapidly. |
| Distorted new growth; sticky honeydew on leaves | Aphids | Blast with a strong jet of water; insecticidal soap for heavy infestations. Rarely causes serious damage. |
| Leaves stippled bronze or silver; fine webbing underneath | Spider mites (hot, dry conditions in Zones 8–10) | Increase humidity around plant; insecticidal soap or miticide. Most common in prolonged summer heat. |
| No flowers by late July despite full sun | Insufficient sun; soil too fertile | Relocate to a sunnier position; stop fertilizing. Blue Boa needs 6+ hours to bloom reliably. |
| Tall stems flopping and falling over | Soil too rich; insufficient sun; not pinched in spring | Plant in lean soil and full sun; pinch growing tips when new spring growth reaches 4–6 inches. |
| Plant fails to return in spring | Crown rot from winter wet; zone too marginal; stems cut back in fall | Improve drainage; leave stems standing through winter; mulch after ground freezes in Zone 5. |
When not to treat: Aphid and spider mite pressure in mid-summer is common on many perennials and rarely reaches levels that threaten Blue Boa’s health. A strong hose blast every few days is often sufficient. Applying systemic insecticides to a plant grown specifically for pollinators defeats the purpose — reserve those treatments for infestations that are genuinely overwhelming.
Sources
- NC State Extension Gardener Plant Toolbox — Agastache ‘Blue Boa’
- Phytochemistry and bioactivity of aromatic and medicinal plants from the genus Agastache (Lamiaceae) — PMC
- Missouri Botanical Garden Plant Finder — Agastache ‘Blue Boa’
- How to Grow Agastache — BBC Gardeners World Magazine
- Agastache ‘Blue Boa’ Hummingbird Mint — Proven Winners
- Agastache — Hummingbird Mint — UC Master Gardener Program of Sonoma County
- Hummingbird Mint Creating a Buzz — Illinois Extension, University of Illinois
- Agastache: A Growing Guide — Garden Design
