What species of lavender is suitable for Zone 5B?
Answer: Lavandula angustifolia, English lavender, is the most cold-hardy lavender and I would say it is a sure bet in your climate and zone. It overwinters down to zone 5 (there isn’t a lavender that overwinters in zone 4 or below). There are so many varieties within this species, but they typically bloom from late spring through early summer. Tender lavenders (L. dentate, French lavender) and L. stoechas (Spanish lavender), would need to be grown as annuals in your region.
There are some angustifolia varieties that are considered “twice blooming.” If the flowers are cut back shortly after the bloom period is complete, another flush of flowers in September is possible. Here are some of the varieties of L. angustifolia that will likely grow well in your region. Consider planting several varieties to extend the flowering season as much as possible.
• L. angustifolia ‘Hidcote’ grows 12 to 20 inches tall, has silver-gray foliage and boasts deep violet-blue flowers
• L. angustifolia ‘Jean Davis’ is a newer variety that grows 10 to 18 inches tall, with blue-green foliage and pale pink flowers
• L. angustifolia ‘Munstead’ is an early-blooming lavender, more compact at 12 to 15 inches, with true deep lavender flowers and an especially strong fragrance.
• Twice Blooming varieties:
‘Buena Vista’ – a fragrant twice bloomer with nice bi-colored flower spikes
‘Sharon Roberts’ – another twice bloomer with attractive elongated flower spikes
‘Thumbelina Leigh’ – a compact, small grower that blooms for several months beginning in late spring
Lavandula x intermedia, also called Lavandin, is a hybrid cross between L. angustifolia (English Lavender) and Lavandula latifolia (Portuguese Lavender). The Lavandin cultivars are slightly less hardy than L. angustifolia, but tend to grow larger and produce more flower spikes than other lavenders. Sources indicate that it is hardy to zone 5. I would recommend not planting a large amount of the Lavandin, however, until you have tested the overwintering capabilities of a few plants.
Lavender is difficult to grow from seed, but can be propagated by dividing large clumps in the fall or taking stem cuttings in summer. I would suggest buying plants to start out with and then dividing them after at least one full year of establishment. You do not have to buy huge plants, which will be quite expensive. Buying plugs and transplanting them into 4-inch pots would be economical. They will grow substantially over the summer and overwinter. Mature lavender clumps can be left intact throughout the winter to add interest to the winter landscape with their silvery, upright architecture. Gardeners should then cut the clump down to 6 inches in early spring to encourage vigorous new growth.
Lavender requires a very well-drained site in full sun if it is to survive the cold and damp of winter of the Midwest. A sandy loam is ideal with plenty of drip irrigation—the key is not to have the roots saturated, or they will rot. You can add a lot of compost to increase the drainage capabilities of the soil. It is not recommended to add sand. It will turn a clay soil into concrete.
Learn much more about this topic in the ATTRA publication Lavender Production, Markets, and Agritourism. It discusses geographic and climatic considerations for lavender, soil-preparation and cultivation techniques, lavender propagation, and field production. The publication also addresses marketing options for lavender, including essential oils, essential-oil distillation, direct marketing of a variety of lavender products, and information and resources about lavender agritourism and value-added lavender products.