|Most perennial herbs can be made more winter-hardy with a 2- to 3-inch layer of organic mulch.|
Winter Mulch Helps
Organic mulch such as pine straw, hardwood bark or bark-sawdust mixture, is adequate winter protection for herbs such as mint, chives and fennel. It protects them to minus 20 degrees Fahrenheit.
A winter mulch helps maintain uniform soil temperatures around the root system. It provides protection against the heaving caused by frequent freezing and thawing of the soil in colder areas of Georgia.
Some herbs require a thicker layer of mulch to protect their roots during extended freezing weather. Don't mulch heavily before cold weather, since it will keep the soil warmer and may actually decrease winter hardiness.
Mulch After Hard Freeze
After the first hard freeze, apply a 3- to 6-inch layer of organic material such as straw, pine needles or chopped leaves. Remove most of the mulch in the spring as new growth begins.
Rosemary, lemon verbena and a few other perennial herbs are not reliably winter-hardy in areas north of Atlanta. So provide extra winter protection.
Cut plants back to within a couple inches of the ground after the first hard frost. Cover the remaining stub with soil. Then cover the soil with 4 to 5 inches of mulch.
For lemon verbena, using a microfoam ground cover (the packing material used around fragile items) works well, too. This material can be held down with soil and will enable survival in most years.
An alternative is to encircle the plant with a cage of hardware cloth or chicken wire. The cage diameter should be about 12 inches larger than the plant (6 inches on each side). Fill the cage with mulch.
Harsh, drying winds can prove as fatal as cold temperatures to some of the less cold-tolerant herbs. Windbreaks can aid the survival and appearance of herbs such as French tarragon, germander, English lavender, Roman chamomile and winter savory.
Covering with a few evergreen boughs will prevent the drying out of silver and lemon thyme foliage. The more cold-sensitive herbs have a better chance of survival if grown in a protected place.
Other things that influence winter hardiness include fertilizing, pruning, watering and soil drainage.
- Fertilizing. Don't fertilize herbs after early August. Late summer nitrogen applications will promote new growth that may not have time to mature before frost. The herbs will remain actively growing instead of becoming acclimated for cold weather.
- Pruning. Avoid severe pruning in late fall, since winter hardiness is reduced until the cuts have healed. Don't severely prune woody plants within four to six weeks of the first severe freeze. In north Georgia, make the last severe cutting on sage, lavender or oregano before early September. Light pruning after frost is acceptable.
- Watering. Keep plants adequately watered during late summer and fall. Drought-stressed plants are weaker and often less cold-hardy. Water during a dry winter, especially before a severe freeze.
- Soil Drainage. Excessively wet soil or sites with standing water can decrease the winter hardiness of some plants. This is especially true for Mediterranean plants such as rosemary, thyme, lavender and French tarragon, which are adapted to dry climates. Provide adequate drainage by incorporating pine bark mulch or planting in raised beds.