Many gardeners grow herbs primarily for culinary or medicinal uses. Some herbs, however, work equally well as ornamental garden plants and bring a range of blue shades to the garden palette. Many of them bloom in summer, at just the right time to bring a cooling accent to the landscape. In warm climates, some herbs with blue flowers grow as perennials and produce leaves that are available for cooking all year long.
Borage (Borago officinalis) is a sprawling annual herb native to the Mediterranean. Reaching as high as 3 feet, and as wide as 18 inches, borage has large, grayish-green leaves. Their cucumber-like taste makes them a good addition to salads, cold drink or cooked greens. Dried leaves, however, are tasteless.
From June to August, the plant's branches have pedicels (stalks) bearing drooping, star-shaped blue flowers. Borage prefers full sun to partial shade and fertile, well-drained soil. Sow seeds in the spring. Mature plants will self-sow and return each year.
Like borage, hyssop (Hyssopus officinalis) is native to the Mediterranean. This perennial is hardy to winter temperatures as low as minus 30 degrees F. Up to 2 feet high and 18 inches wide, it has an erect, bushy habit and fragrant, narrow, glossy-green leaves. From July to September, hyssop has dense spikes of blue-violet flowers. The lobed, fragrant blooms draw butterflies and bees. Hyssop leaves are traditional flavoring for meat, stews, salads and sauces. Hyssop oil flavors Chartreuse liqueur.
Use this herb in herb or rock gardens, as a specimen plant, grouped in hedges or in containers. It likes a sunny to partly shady location--afternoon shade in hot places--with average, well-drained soil. Rich loam and regular watering are best, but plants can handle dry, sandy, infertile soil. Sow seeds in spring and prune plants back after flowering. Like borage, hyssop will self-sow.
Rosemary (Rosmarinus officinalis) tolerates winter temperatures as low as zero degrees F. In mild winter climates, it can grow 6 feet high and 4 feet wide. It's an annual in colder areas. Dried or fresh, its aromatic, needle-fine green leaves are a culinary staple. They flavor vegetables, meat, fish, stews, vinegar, butter and baked goods. Oil of rosemary is a perfume and toiletry ingredient. Plants have tiny, fragrant white or pale blue flowers on old growth. 'Arp,' a rosemary variety native to Texas, has dark blue booms.
Where it's winter hardy, use rosemary in herb gardens, borders or as a foundation planting or hedge. Shape annual rosemary grown in containers as a topiary. Give plants full sun and light, averagely moist, well-drained soil. They suffer in heavy clay, and seldom survive wet winter roots.