Important Lavender Temperature Tolerance Tips (Plus Info for USDA Zones)

Lavender plants bring old-world elegance to modern gardens; their silvery-grey leaves provide a subtle contrast to their deep purple, pale pink, and gossamer white flowers. Lavender’s aroma is scientifically proven to have a calming effect; however, the soothing effects of Lavender are somewhat lost if gardeners are struggling to keep them alive in hot or cold conditions!

There are some important lavender temperature tolerance requirements for gardeners to be aware of. Most Lavender cultivars are tolerant of winter temperatures found in USDA Zones 6 to 9. Cold hardy species like the Munstead, Hidcote Blue, and Melissa are classified as hardy for USDA Zone 5. Lavender grows best in temperatures between -10 °F and 72 °F (- 23.3 °C to 22 °C).

Lavender is frequently marketed as “hardy and easy to grow”; however, this does not mean that Lavender will thrive in all environments. Understanding what Lavender species tolerate which temperatures is essential to successfully growing Lavender.

What Are The USDA Hardiness Zones?

The USA Department of Agriculture (USDA) has created a map of the USA that divides the country into 11 different growing regions based on the average winter temperature.

These zones provide a classification system describing the hardiness of plants that can survive in these regions; each successive zone represents a region that is 10°F warmer than the previous region. For example, Zone 1 regions have an average annual winter temperature of -60 °F to -50 °F (-51.1 °C to -45.6 °C) whereas zone 2 regions have winter temperatures between -50 °F to – 40 °F (-34.4 °C to -23.3°C).

Each zone is divided into two halves: a and b. “a” represents the lower 5 °F, and “b” represents the higher 5 °F of each zone. For example, Zone 1a has annual winter temperatures between -60 °F to -55 °F (-34.4 °C to -48.3°C), whereas Zone 1b has an average winter temperature between -55 °F to -60 °F (-48.3 °C to -45.6°C).

Every few years, the USDA revises the map based on variances in winter temperature due to climate changes. The 2012 map showed an average increase of 5 °F in all USA regions compared to previous maps.

Gardeners can check whether a particular Lavender species will survive in their area by comparing a specific Lavender’s temperature tolerance with the hardiness zone they live in.

Lavender in snow

Issues With The USDA Hardiness Zone Map

While the map remains a valuable resource for USA gardeners, it is not a full-proof system. Successfully growing Lavender is not exclusively dependent on regional temperatures.

The USDA Zone map only reflects temperature variances and not humidity, snowfall, or any other factors that affect Lavender’s ability to grow. The ideal growth conditions for any plant are the cumulative effects of:

  1. Soil quality
  2. Snow, rain, and hail
  3. Wind and air humidity
  4. Temperature fluctuations
  5. Hours of daylight

For example, Lavender is easier to grow in places like Tucson, Arizona (dry conditions) than Seattle (humid conditions). Yet, both areas are listed as Zone 8 with no differences in growing conditions!

Where Can Gardeners Find The USDA Hardiness Map?

Gardeners can access the 2012 USDA hardiness zone map here.

Gardeners can either enter their zip code or manually scroll through the map to their region. The region will be color-coded, and the corresponding temperatures can be accessed via a map key located next to the map.

Lavender Species Which Can Survive USDA Zones 1 – 3?

There are no Lavender species that can survive temperatures of -60 °F to -30 °F (-51.1 °C to -34.4 °C). The only Lavender species that can survive in zones 1 to 3 are those kept in controlled growing conditions, e.g., a hothouse.

Read more: Is My Lavender Plant Dying? 8 Likely Factors and Effective Solutions

Which Lavender Species Are Hardy In USDA Zones 4 And 5

Wild Lavender species originated in Mediterranean countries, where warm, languid weather is the norm. Based on its place of origin, people are often surprised to find Lavender growing in USDA Zone 4 and 5.

The annual average winter temperature for Zones 4 and 5 are -30 °F to -10 °F (-34.4 °C to -23.3°C). That is “lose your toes” level of cold!

Lavender’s adaptability and ease of cultivation have allowed horticulturists to create more than 400 different Lavender cultivars. Naturally, some of these horticulturists lived in cold environments unsuitable for Lavender.

However, the harsh temperatures did not deter these determined souls, and they created 3 cold-hardy Lavender cultivars:

  1. Munstead
  2. Hidcote Blue
  3. Melissa

Munstead

Munstead is a cultivar of Lavandula angustifolia (Common name: English Lavender), listed as hardy for zones 5 to 9; it can still survive in zone 4 if potted and kept indoors during the winter months.

Munstead has more than earned its popularity as a compact lavender as it grows to a maximum size of 1.5ft (0.48m) high and 1.5ft (0.48m) across, making it a perfect size for potting or planting in small gardens.

Like most English Lavender cultivars, Munstead has a sweet scent; Munstead is a good Lavender to dry and use in pot potpourris, sachets, or other scented items. This Lavender species may also be safely used as a flavoring in cooking.

Hidcote Blue

Hidcote Blue Lavender shares many characteristics with Munstead Lavender. Like, Munstead, Hidcote is a cultivar of Lavandula angustifolia and is also known for its gorgeously rich scent.

Hidcote Blue differs from Munstead in 3 aspects:

  1. Its heat tolerance
  2. The color and density of its flower clusters
  3. The size of the plant

Hidcote Blue is hardy for Zones 5 to 8, whereas Munstead is hardy for Zones 5 to 9; this English Lavender cultivar is less heat tolerant than Munstead. Created in Britain by Lawrence Johnson in the early 20th century, this Lavender species was designed to survive cold seasons and may be able to tolerate marginally colder conditions than Munstead. 

Where Munstead sports widely dispersed pink-purple flowers, Hidcote Blue can be pruned to increase its density, allowing it dramatically showcase its vibrant blue-purple flowers.

The last significant difference between Munstead and Hidcote Blue is the size of the plant. Hidcote Blue is almost twice the size of Munstead and grows to a maximum height of 20” (50cm) and width of 24” (60cm).

Melissa

The Melissa Lavender is yet another cultivar of Lavandula angustifolia; Although it is hardly surprising that the English Lavender was used to create cultivars that could thrive in chilly England!

Melissa’s most distinctive feature is its pale pink flowers. Upon first bloom, the newly revealed flowers are pure white and gradually change color as they age until they reach the silvery pink of the mature flower.

The Melissa is hardy for Zones 5 to 8 and grows to a height of 2 ft (60cm) and a width of 2 ft (60cm). This Lavender species will tend to develop woody stems unless pruned frequently.

Planting Hidcote Blue and Melissa side by side creates a stunning visual effect. Alternatively, the Melissa makes a beautiful accent plant in rockeries, along pathways and interspersed between other flowering plants.

Dry lavender in snow

USDA Zone 6 to 9 Hardy Lavender Species

USDA Zones 6 to 8 are the sweet spot for most Lavender species, English, Spanish and French Lavender species all do well when grown in temperatures between -10 °F and 72 °F (- 23.3 °C to 22 °C).

The USDA zones 6 to 9 have an average winter temperature of -10 °F to 30 °F (- 23.3 °C to -1.1 °C).

Although most Lavender grows well in zone 6 to 8 regions, it will be easier to grow in dryer regions. Humid conditions provide the perfect opportunity for the growth of root rot, particularly black root rot caused by the pathogen, Thielaviopsis basicola.

Unless addressed during the early stages of root rot, root rot will result in the death of the lavender plant. Always plant Lavender in dry, well-drained soil to avoid the roots sitting in persistently damp conditions.

Examples of Lavender cultivars that grow in Zones 6 to 9 are:

  1. Nana alba – white flower, English Lavender cultivar
  2. Little Lotti – pink and white flowers, English Lavender cultivar
  3. Thumbelina Leigh – pale purple, English Lavender cultivar
  4. Regal Splendor – vibrantly pink flower, French Lavender cultivar
  5. Ballerina – white and purple flower, French Lavender cultivar

Users Also Read: Growing Lavender Plant in Colorado – Detailed Guide

Lavender’s Role In Fire-Resistant Landscaping

Ideally, fire-proofing a home would include clearing all vegetation within a 100 ft radius of the house. However, not only would this be unsightly, but it would cause other problems, e.g., dust, erosion, loss of property value, etc.

Property owners are encouraged to use fire-resistant plants when landscaping the immediate area surrounding their homes. These plants are FIRE-RESISTANT, not FIRE-PROOF, so while they limit the risk of a wildfire spreading to the buildings, they cannot nullify it.

Some lavender species, especially French Lavender species, are listed as fire-resistant plants, i.e., they are legally allowed to be included in landscape designs falling within 30ft to 100 ft of the building depending on the state and municipal laws.

Conclusion: Lavender Temperature Tolerance

Lavender shows a range of temperature tolerances and can be successfully grown in USDA Zones 5 to 11; most Lavender cultivars easily tolerate temperatures between -10 °F and 72 °F (- 23.3 °C to 22 °C).

Excess humidity, not temperature, is the most common reason gardeners lose established Lavender plants or fail to grow new Lavender successfully.

Source

https://garden.org/nga/zipzone/

https://planthardiness.ars.usda.gov/

https://pss.uvm.edu/ppp/articles/lavender.html

https://www.britannica.com/place/Mediterranean-Sea/Hydrologic-features-and-climate

https://www.fs.fed.us/psw/publications/documents/gtr-050/landscaping.html

https://s3.wp.wsu.edu/uploads/sites/2086/2018/01/fireresistantplants2017.pdf