There are only a few critical guidelines to keep in mind.
To provide us with another glorious purple performance next summer, our lavender plants must survive the challenges of the cold, wet winter. The main winter threats to lavender plants growing in the Pacific Northwest (PNW) are centered around excess moisture and the combination of cold temperatures and harsh conditions, which can be particularly damaging when coupled with the region’s wet climate. Let’s take a look at the primary threats.
1. Root Rot (The Biggest Killer)
This is the most common cause of lavender death in the PNW. Lavender is native to the dry, rocky Mediterranean and really cannot tolerate “wet feet,” especially in cold weather.
- Cause: Poor soil drainage combined with heavy winter rains or snowmelt leads to waterlogged soil. This suffocates the roots and encourages various fungal-like pathogens (like Phytophthora and Pythium species) that cause the roots to rot.
- Symptoms: Blackened, mushy roots, and above-ground signs like wilting, yellowing, or browning foliage, and overall plant decline.
2. Freeze/Thaw Cycles and Winterkill
Unpredictable temperature swings are a major hazard.
- Sudden Freezing: While Lavandula angustifolia cultivars are relatively cold-hardy (some to USDA Zone 5), sudden, hard frosts can still kill branches or entire plants, especially less hardy lavandins and L. stoechas cultivars.
- Heaving: Repeated cycles of freezing and thawing can cause the soil to expand and contract, pushing plants right out of the ground (known as “heaving”). This damages the delicate root system, exposing it to air and cold.
- Windburn/Winter Desiccation: Harsh, cold winds can dry out the plant’s evergreen foliage, especially when the ground is frozen and the roots can’t take up water. The leaves may turn silvery, brittle, or brown, which is often mistaken for disease.
3. Snow and Ice Damage
Heavy, wet snow or ice accumulation can physically harm the plant.
- Breaking Stems: The weight of snow or ice can cause the woody stems and branches to split or break off, creating open wounds susceptible to disease.
- Flattening: Plants can be flattened under heavy loads, which restricts airflow and creates moist pockets, increasing the risk of rot and fungal issues.
4. Fungal Diseases
The cool, damp, and often low-airflow conditions of a PNW winter can encourage various fungal problems:
- Botrytis: A fungal disease that can show up as gray, moldy growth and cause leaves to yellow and wilt.
- Septoria Leaf Spot: Thrives in high humidity and causes discolored spots on the leaves.
To give your lavender the best chance of survival, the most crucial steps are excellent drainage and choosing the right cultivars. Preparing lavender for a Pacific Northwest winter is all about mitigating the risks of root rot and excess moisture. Here are the three golden rules for lavender survival in the PNW’s cool, wet climate:
1. Prioritize Drainage (The Most Crucial Step)
In the PNW, lavender usually dies from being too wet, not too cold.
- On a small scale, amend the soil: If your lavender is planted in heavy clay soil, winter may be too late to fully amend the beds, but you can prepare now for next year. For existing plants, make sure the surrounding soil is well-draining. You can mound up the soil around the plant base to raise the root crown slightly above the surrounding grade, encouraging water to run off.
- Choose the right mulch: Avoid traditional, moisture-retaining mulches like wood chips or shredded bark right against the plant. Instead, use a layer of gravel, pea gravel, or small stones (about 2 inches deep) around the base. This insulates the roots from cold and reflects light, but, most importantly, it prevents rain from splashing soil onto the foliage and keeps the plant crown dry.
2. Avoid Heavy Fall Pruning
While pruning is essential for lavender health, the timing is critical in a climate with cold snaps. The best time for the main, heavy pruning is in the early spring when you see the first signs of new green growth. If done too early in the fall, a hard pruning encourages new, tender growth that won’t have time to harden before the first frost, making it highly susceptible to winterkill and disease. If you must prune for shaping in the autumn, do a very light trim in early autumn (at least 6-8 weeks before the first hard frost) and only cut into the green growth, not the woody base.
3. Minimize or Stop Watering
As the rainy season begins, your lavender will naturally go dormant and will not need supplemental water. If you have an irrigation system, make sure the lavender is off the circuit for the winter. The heavy PNW rain will provide all the moisture it needs. If your lavender (especially a tender lavender plant) is in a pot, move it to a sheltered area like a covered porch, unheated garage, or under a wide eave. Only water container plants once a month, if the soil is bone-dry.
Extra Protection Tips
1. Problem: Wind and frost
If your plants are in an exposed location, use a few stakes and a piece of burlap or frost cloth to create a loose screen on the side facing the prevailing winter wind.
2. Problem: Heavy snow
If heavy, wet snow piles up, the weight can split the woody stems. Wait until the temperature rises slightly and gently brush the snow off upward with a broom. Do not try to knock off frozen ice.
3. Problem: Young, tender plant
For first-year plants or those you’re particularly worried about, you can place evergreen boughs (like from a Christmas tree) over the plant crown after the first hard frost. This provides insulation without holding excessive moisture.
4. Problem: Wrong cultivars for your risky location
If you find yourself in a particularly challenging location for lavender survival, try to find Lavandula angustifolia cultivars that are known to be especially hardy, for example: ‘Croxton’s Wild’, ‘Cynthia Johnson’, ‘Fiona English’, ‘Frances’, ‘Graves’, ‘Hidcote’, ‘Imperial Gem’, ‘Jean Davis (Pink)’, Loddon Blue’, ‘Mitcham Grey’ , ‘Munstead’, ‘New Zealand Blue’, ‘Royal Velvet’, ‘Violet Intrigue’. Among the lavandins, L. x intermedia ‘Grosso’, ‘Phenomenal’ and ‘Sensational’ may be successful under adverse conditions.
The Bottom Line: By focusing on keeping the roots dry and protected from heavy moisture and wind, you can significantly increase your lavenders’ chances of thriving again in the spring!
Contributed, edited & formatted by
Michael Lemmers & Christine Mulder
RavenCroft & Barn Owl Nursery
