Houstonia spp.
flowering bluets
Eastern and central North America to Central America
Overview
Houstonia spp. is a genus of about 20 species of small herbaceous annuals and perennials in the coffee family (Rubiaceae), native to North and Central America. Plants are low and tufted or mat-forming, generally 5-20 cm (2-8 in) tall, with slender stems and small, opposite, often spoon-shaped leaves. The flowers are small, 5-12 mm across, with four spreading petal lobes fused into a short tube; colour ranges through pale blue, lilac, violet, and white, usually with a yellow or greenish eye. H. caerulea, the azure bluet, carpets spring meadows and lawns with pale blue flowers, while H. purpurea and H. longifolia are taller, clump-forming woodland species. Flowering is heaviest in spring, with some species continuing into summer. The fruit is a small two-lobed capsule. Houstonia spp. grows in moist meadows, open woodland, rock outcrops, and acidic, gravelly soils. The low-growing species are short-lived and depend on regular self-seeding to persist, and they are easily crowded out by taller, more vigorous plants.
Native Range
Native to eastern and central North America, extending into Mexico and Central America. The genus is most diverse in the eastern United States, where species grow from open woodlands to rocky glades.Suggested Uses
Grown in rock gardens, woodland edges, native-plant meadows, and as a flowering groundcover in lawns left unmown in spring. The clump-forming woodland species suit shaded native borders and naturalistic plantings.How to Identify
Appearance
Size & Dimensions
Height2" - 8"
Width/Spread2" - 8"
Bloom Information
Most species flower in spring, roughly April to June, with H. caerulea sometimes reblooming sparsely into autumn in cool, moist sites. Woodland clump-forming species such as H. purpurea bloom from late spring into early summer. The small flowers are pollinated by bees, flies, and small butterflies.
Detailed Descriptions
Flower Description
pale blue, lilac, violet, or white with a yellow eyeFoliage Description
greenGrowing Conditions
Sun Requirements
Requires 3-8 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Houstonia spp. grows in full sun to partial shade in moist, acidic, gravelly or sandy soil that drains freely. The mat-forming species need consistent spring moisture and resent both drought and dense competition. Most species are short-lived and rely on self-sown seedlings, so disturbed, open ground favours their persistence. Little or no fertiliser is needed, and rich soil encourages taller neighbours that shade them out. Propagation is from seed sown fresh or by division of the clumping woodland species. Plants are otherwise undemanding where soil and moisture suit them.Pruning
Formal pruning is not required. Spent flowering stems can be sheared after bloom to tidy mat-forming species and may encourage a light second flush. Clump-forming woodland species are cut back as foliage dies down in autumn.Container Growing
✓ Suitable for container growing
Minimum container size: 1 gallons