Giant hyssop (Agastache 'Blue Boa')

Overview

Agastache ‘Blue Boa’, a popular cultivar of Giant hyssop, distinguishes itself with a vigorous, stiffly upright habit and stunning, long-lasting flower color. This selection explodes with deep, violet-blue flower spikes, making it a dynamic focal point in the summer garden from early June well into September. As an herbaceous perennial, it provides reliable structure and reliable performance across multiple seasons.

The appeal of Agastache ‘Blue Boa’ extends beyond its aesthetics; it is highly functional in warm climates. This plant requires relatively little attention once established, tolerating heat and dry conditions well, provided its basic soil drainage needs are met. Furthermore, its fragrant foliage and nectar-rich flowers provide significant ecological benefits, drawing in essential pollinators like hummingbirds and butterflies.

Gardeners appreciate the long blooming window and low maintenance associated with this Giant hyssop hybrid. Whether used as a bold statement plant along a walkway or mixed into cottage garden borders, Agastache ‘Blue Boa’ delivers significant visual impact without demanding constant fuss. Ensure optimal conditions—full sun and excellent drainage—to guarantee this plant returns successfully year after year.

Fast Facts

• Plant Family: Lamiaceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 5-9
• Size at Maturity:
  • Height: 2-3 ft
  • Spread: 1-1.5 ft
• Bloom Time: June to September
• Bloom Description: Violet blue
• Sun Exposure: Full sun
• Water Needs: Medium
• Maintenance Level: Low

How to Grow

Planting Agastache ‘Blue Boa’ should ideally occur in the spring after the danger of hard frost has passed. The most critical factor for success is soil quality; this Giant hyssop demands very well-drained soil. Choose a location receiving full sun for the best flowering display, though some light afternoon shade is tolerated in the hottest climates.

Ongoing care for this herbaceous perennial is straightforward. Maintain medium moisture levels, especially during establishment. Fertilizing is rarely necessary due to its low maintenance requirements. The chief maintenance task is deadheading spent flowers occasionally to encourage a continuous succession of blooms throughout the summer season.

Winter preparation involves careful siting. In the northern reaches of its range, ensure plants are not situated in low spots where water pools, as poor drainage leads to crown or root rot over winter. In colder zones nearing the minimum, leaving the dead flower stems intact over winter offers protection; prune back fully in early spring before new growth emerges.

Landscape Uses

The bold structure and vibrant color of Agastache ‘Blue Boa’ make it indispensable for designs needing vertical accentuation. These aromatic, long-blooming perennials are perfectly suited for sunny borders, providing crucial mid-summer color when other spring bloomers fade. They look particularly effective planted near patios or along frequently viewed walkways where their anise-scented foliage can be accidentally brushed.

Consider incorporating Agastache ‘Blue Boa’ into cottage gardens, where its strong vertical lines contrast beautifully with looser, mounding perennials. Due to their attractiveness to pollinators, they pair well with Salvia, Echinacea, and ornamental grasses. Since the flowers hold their color well, they are also excellent candidates for cutting gardens, providing vibrant texture in fresh arrangements.

Standout Features

Flower Qualities

• Showy

Noteworthy Characteristics

Agastache, commonly called giant hyssop, is a genus containing about 30 species of upright herbaceous perennials, most of which are native to North America. Agastache hybrids often have showier flowers and better winter hardiness than species plants. Hybrids typically feature dense terminal spikes of tiny 2-lipped tubular flowers which bloom mid-summer to fall in many-flowered verticillasters atop stiff square stems clad with opposite pairs of serrate, fragrant gray-green to medium green leaves. Specifically, ‘Blue Boa’ is a vigorous hybrid cultivar with showy, deep, violet-blue flowers blooming from June to September in large terminal spikes rising above the clumping foliage.

Tolerances

• Deer

Potential Problems

The primary concern when growing Agastache ‘Blue Boa’ is excessive moisture, particularly during winter dormancy. Crown or root rot is a serious threat if the soil is heavy clay or poorly draining. Always amend heavy soils heavily with grit or compost to ensure sharp drainage. While generally resistant to pests, gardeners should monitor for fungal issues like rust, powdery mildew, or leaf spots, which thrive in humid, poor-airflow conditions.

Management of these potential problems is preventative. Proper site selection—full sun and excellent drainage—is the best defense. If fungal leaf spots appear, ensure good air circulation around the clumps and focus watering at the base of the plant rather than overhead. Deer fortunately tend to leave this aromatic Giant hyssop alone.

Frequently Asked Questions

What hardiness zones is Giant hyssop suitable for?

Agastache ‘Blue Boa’ is generally hardy in USDA Zones 5 through 9, offering reliable perennial performance across a wide range of climates.

How large does Agastache ‘Blue Boa’ grow?

This cultivar typically reaches a height of 2 to 3 feet with a spread between 1 and 1.5 feet, forming a neat, upright clump perfect for intermediate garden layers.

When does Giant hyssop bloom?

Agastache ‘Blue Boa’ provides consistent color from June through September, featuring dense spikes of vibrant violet-blue flowers.

What sun exposure does Agastache ‘Blue Boa’ need?

For the most vigorous growth and best violet-blue floral display, Agastache ‘Blue Boa’ requires a location providing full sun exposure daily.

Conclusion

The striking, long-lasting violet-blue flower spikes and inherent drought tolerance make Agastache ‘Blue Boa’ a superb, low-effort addition to any sunny perennial border. This variety of Giant hyssop reliably supports pollinators while resisting deer browsing, offering beauty and function. Before planting, confirm your site has the excellent drainage required for this aromatic beauty to thrive across its USDA Zones 5–9 range.

Companion Planting

Choosing companions for Agastache ‘Blue Boa’ should focus on plants that share its preference for full sun and well-drained soil, while offering complementary textures or bloom times. Think about pairing the vertical spikes of this Giant hyssop with mounding plants like shorter ornamental grasses or sturdy coneflowers (Echinacea) for textural contrast. Lavender and Russian Sage are excellent neighbors, as they also demand sharp drainage and thrive in similar hot, sunny conditions.

To extend the season of interest, consider placing early-season bloomers like Siberian Iris or later-season Sedum varieties near the Agastache. This strategic grouping ensures that as the early flowers fade, the deep blue plumes of the hummingbird mint take over center stage. Always ensure adequate spacing to promote the air circulation needed to protect the leaves from potential mildew.

Wildlife Benefits

The genus Agastache is renowned for its exceptional value in wildlife gardening, and the hybrid ‘Blue Boa’ is no exception. The small, tubular, two-lipped flowers are perfectly structured to provide easy access to nectar for hummingbirds, which are strongly attracted to the blue and purple hues. Furthermore, the high nectar content makes this a favorite foraging spot for beneficial native bees and numerous butterfly species throughout the summer months.

Attracting beneficial insects is as important as attracting pollinators. While the flowers bring in the fliers, the anise-scented foliage, typical of many Mexican hyssop varieties, often deters unwanted browsing by deer and rabbits. Planting a collective grouping of Agastache ‘Blue Boa’ helps create a vibrant, low-impact ecosystem hub right in your sunny border.