Oregano is a Mediterranean herb, but common culinary oregano (Origanum vulgare) is a hardy perennial well-adapted to survive winter in many temperate regions. While light, temporary frost typically only damages the above-ground foliage, a deep, prolonged hard freeze can kill the root crown if the plant is not adequately protected. Understanding the specific type of oregano and providing the right preparation are the deciding factors for overwintering success.
Oregano Variety and Cold Tolerance Levels
The ability of oregano to withstand freezing temperatures depends heavily on its species. The most common variety, Origanum vulgare (including Greek and Italian types), is reliably perennial and survives winters in USDA Hardiness Zones 5 through 9. Established plants can tolerate temperatures as low as -20°F (-29°C) when dormant, provided the soil drainage is excellent. Poorly drained soil is a significant threat, as waterlogged root systems are susceptible to rot and freeze damage.
Not all herbs sold as “oregano” share this cold hardiness. Mexican oregano, which refers to different plants like Poliomintha longiflora or Lippia graveolens, is significantly more tender. These varieties thrive year-round only in frost-free Zones 9 to 11. In colder climates, these non-true oreganos must be treated as annuals or brought indoors, as they cannot withstand sustained freezing temperatures.
Practical Steps for Overwintering Success
Proper preparation in late fall ensures your perennial oregano survives the cold. Before the first hard freeze, reduce watering to encourage dormancy. Overly moist soil in winter can lead to root rot or cause roots to freeze solid, which is often more damaging than the cold air itself. Avoid applying nitrogen-rich fertilizer in the fall, as this encourages tender new growth vulnerable to frost damage.
Pruning reduces the risk of damage from heavy snow or ice accumulation. Cut the woody stems back to four to six inches in late fall; this helps the plant conserve energy and focus on root survival. This light pruning also prevents mold and mildew from developing on dense, decaying foliage. Leave a short structure of stems to mark the plant’s location and provide some natural protection.
The most effective protection for in-ground oregano is a thick layer of organic mulch. Once the ground begins to freeze, apply a two to three-inch layer of straw, shredded leaves, or wood chips around the base of the plant. This mulch insulates the root crown, moderating soil temperature and preventing the damaging cycle of freezing and thawing known as frost heaving. Keep the mulch material a few inches away from the remaining stems to prevent moisture from causing the plant crown to rot.
Indoor Protection
If you live in a climate colder than Zone 5, or if your oregano is in a container, the safest method is to move a portion of the plant indoors. Dig up a small clump of the root ball and transplant it into a pot with well-draining soil before the ground freezes. Place the potted herb in a cool, sunny location, such as an unheated garage or a south-facing windowsill, where it can remain semi-dormant until spring.
Temporary Protection
For unexpected, brief cold snaps, you can temporarily cover in-ground plants. Use a cloche, burlap, or a sheet, ensuring the cover extends to the ground to trap residual heat.
Post-Frost Damage Assessment and Care
Even well-protected oregano may exhibit damage following a severe frost, particularly on exposed tips and leaves. Frost damage manifests as blackened, water-soaked, or mushy foliage, indicating that ice crystals ruptured the cell walls. After the cold event passes, resist the urge to immediately prune away damaged material, as the dead foliage provides insulation to the crown and roots below.
Patience is necessary, as recovery will be slow. Wait until the threat of the last frost has completely passed in early spring before assessing the full extent of the damage. Gently remove the dead, brown, or mushy top growth, cutting the stems back to the point where you see green, healthy tissue. The plant will send out new shoots from the root crown, often appearing as late as May or June in colder regions. Avoid fertilizing until robust new growth is observed, as encouraging premature growth can weaken the recovering plant.