Clematis

 Jackmanii Clematis

Clematis ‘Jackmanii’ remains one of the best choices for Texas gardeners who want a classic, large-flowered clematis, provided it receives protection from afternoon heat, benefits from cool, moist, but well-drained soil, and is monitored for common vine diseases. With proper care, ‘Jackmanii’ rewards with two strong bloom seasons each year and maintains its reputation as one of the most enduring and admired clematis varieties.

Clematis ‘Jackmanii’ is one of the oldest and most recognized large-flowered clematis hybrids, introduced in 1862 by George Jackman. It produces rich deep purple to violet blooms that are 4 to 6 inches wide, with four broad petals. In Texas, ‘Jackmanii’ typically blooms first in mid-spring, around April to May, with a strong second flush of blooms in late summer, usually August through September, particularly if the plant is deadheaded after the initial bloom cycle. The vine performs best during the cooler parts of the growing season; extreme summer heat can cause a temporary slowdown in flowering.

For success in Texas, ‘Jackmanii’ requires full morning sun but must be protected from the intense afternoon sun, especially in Central, South, and West Texas. It grows best in well-draining, organic-rich soil that is neutral to slightly alkaline, and consistent deep watering is necessary. Mulching the base heavily is critical to keep the root zone cool while allowing the vine to grow upward into the sun. This variety needs a strong support structure such as a trellis, arbor, or fence because its stems are thin and twining.

‘Jackmanii’ has earned the prestigious Royal Horticultural Society’s Award of Garden Merit, highlighting its reliable flowering, resilience, and overall garden performance. However, it is moderately susceptible to clematis wilt, a fungal issue that can cause sudden stem collapse. If this occurs, immediate pruning down to healthy wood at the base is necessary, and the plant typically recovers by pushing out new shoots. In humid areas like East Texas, powdery mildew can occasionally be a problem, but ensuring good air circulation and avoiding overhead watering helps reduce risk. Root rot is a more serious threat in poorly draining soils, making proper site preparation essential, especially in heavy clay regions.

Henry I Clematis

Clematis ‘Henryi’ is a large-flowered hybrid introduced in 1858 by Henry Stevens. It is well-known for its striking, pure white blooms that can reach 6 to 8 inches across, with creamy white sepals and a contrasting dark center of stamens. In Texas, ‘Henryi’ blooms in two major cycles: the first flush appears in mid to late spring, typically April through May, and a second, lighter bloom can occur in late summer to early fall, especially if the plant is lightly pruned and deadheaded after the first flowering. Like most large-flowered clematis, ‘Henryi’ performs best outside the peak heat of summer, with cooler spring and fall periods producing the showiest flowers.

Growing ‘Henryi’ successfully in Texas requires careful placement. It needs full sun on its upper growth but greatly benefits from shade at its roots to keep them cool, especially in the harsh summer conditions of Central and South Texas. Morning sun with afternoon shade is ideal. It prefers rich, well-drained soil with a slightly neutral to alkaline pH and consistent watering without waterlogging the roots. Heavy mulching around the base is recommended to maintain cooler soil temperatures. Like other clematis, ‘Henryi’ needs strong vertical support such as a trellis or arbor and benefits from good air circulation to reduce fungal disease pressure.

Best Clematis Varieties for Texas

You need varieties that can handle strong sun, intense summer heat, and alkaline soils, especially in Central and North Texas.

• ‘Duchess of Edinburgh’ (double white flowers)
  Tolerates some heat, prefers afternoon shade.

• ‘Nelly Moser’ (pink with red center stripe)
  Blooms early, benefits from protection from intense afternoon sun.

• ‘Henryi’ (pure white, large flowers)
  Strong bloomer, performs well with morning sun and afternoon shade.

• ‘General Sikorski’ (lavender-blue flowers)
  Highly adaptable; tolerates more heat if roots stay cool.

• ‘Etoile Violette’ (small deep purple flowers, vigorous)
  A viticella type — viticellas are generally the best clematis group for Texas because they tolerate heat and recover well from stress.

• ‘Madame Julia Correvon’ (crimson red viticella)
  Reliable rebloomer, heat tolerant, disease resistant.

Key Tip: In Central and South Texas, favor viticella hybrids and texensis hybrids (like ‘Duchess of Albany’), which are more heat-adapted than large-flowered types.

Clematis Varieties with Notable Awards

• ‘Etoile Violette’: RHS Award of Garden Merit (Royal Horticultural Society, UK)

• ‘Nelly Moser’: RHS Award of Garden Merit

• ‘Henryi’: RHS Award of Garden Merit

• ‘General Sikorski’: RHS Award of Garden Merit

1. Q: Can clematis be successfully grown in Texas?
A: Yes, but success depends on choosing the right varieties, providing protection from extreme heat, and planting them with cool, moist roots and good drainage. Viticella and texensis hybrids are the most reliable for Texas conditions.

2. Q: What are the best clematis varieties for Texas gardeners?
A: The best clematis for Texas include viticella types like ‘Etoile Violette’ and ‘Madame Julia Correvon’, texensis hybrids like ‘Duchess of Albany’, and heat-tolerant large-flowered varieties like ‘Nelly Moser’, ‘General Sikorski’, and ‘Henryi’ if they receive afternoon shade.

3. Q: When does clematis bloom in Texas?
A: Most clematis bloom heavily in spring (March to May) with a potential second, lighter bloom period in late summer or early fall (August to September) if deadheaded and properly watered during the summer heat.

4. Q: What are common problems clematis face in Texas gardens?
A: The biggest problems are clematis wilt (sudden stem collapse), root rot in poorly drained soils, powdery mildew during humid periods, and heat stress if planted in full afternoon sun without protection.

5. Q: What are the keys to successfully growing clematis in Texas?
A: Plant in morning sun with afternoon shade, heavily mulch the root zone to keep it cool, ensure excellent soil drainage, water deeply but not constantly, and choose heat-adapted varieties suited for Texas conditions.