How To Winterize Herb Garden

Autumn has arrived: temperatures are dropping and so are the leaves, and herb gardeners are harvesting their last big hauls of the year. If you fear this is the end for your herb plants, take heart. Woody perennial herbs, as well as tender perennials, can overwinter in most climates if you play your cards right.

Regardless of your climate, with a little effort, you can ensure that your herb garden survives to produce for another year–even in very cold climates.

How to prepare your herbs for winter

Regardless of classification (annual, biennial, perennial), there are a few actions you can take to prepare all of your herbs for the upcoming winter.

Fertilizer cutoff period

Once the high temperatures of summer have passed–generally in late August to Early September–stop applying any fertilizer to your herb plants (1). Once the days grow short and cool, any new growth is vulnerable to frost, so you want to discourage vigorous growth for now. On the other hand, mature growth that is allowed to respond naturally to the season will develop more winter hardiness.

Don't-Prune-Past Date

Depending on your local climate, you'll want to stop doing any major pruning between early August and early September. This helps you to avoid stimulating new, vulnerable growth. Avoid doing any heavy pruning in late fall because if your herbs plants are unable to heal before a freeze it can severely damage them.

Mulch Generously

Applying a three to four inches deep layer of mulch to outdoor herbs after the first freeze will help them overwinter. This extra bit of insulation will protect roots from freezing temperatures by providing a little insulation to keep soil warmer. Just be sure to leave a little space around the stem (one to two inches) where the mulch doesn't touch it.

Maintain health through fall

The most important thing you can do to prepare your herbs for winter is to maintain their health throughout the year. Monitor for pests, fertilize, water regularly and prune to promote dense, bushy growth. A healthy plant is a hardy plant.

Can herbs survive without preparations?

Some herbs can survive winter without any preparations at all. Unfortunately, this can be difficult to predict. The hardiness of an herb will depend on the soil, the specific species variety, the planting location, and rainfall and drainage. The best way to predict a plant's ability to survive the winter is to act in accordance with its hardiness zone and observe it over the course of a winter. If it survives, you'll know it's hardy.

Overwintering Herbs

Leaving plants outdoors to (hopefully) survive winter is called "overwintering." This is only advisable if you live above zone 6. Many culinary herbs are Mediterranean and are simply not cut out for hard freezes.

Tips for protecting outdoor herbs

in addition to the above guidelines, outdoor hardy perennials will benefit tremendously from a little TLC as winter sets in. Chives, lavender, oregano, and thyme can all take the cold–especially with a little extra help.

Put a sweater on your herbs

If you happen to live in zone 7 or higher, you may be able to get away with covering your woody perennial herbs to protect them from freezes. If you aren't familiar with hardiness zones, you should definitely get with the program. There are 13 hardiness zones in all, used to determine the suitability of certain plants for different parts of the country. Check out the USDA Plant Hardiness Zone map to get a better feel for your seasonal highs and lows.

Using horticultural fleece or other fabric designed for plants, cover before a freeze, weighing or pinning the fabric to the ground securely. Once the freeze has passed, uncover the plant and repeat as needed.

Cut after the first hard freeze

A freeze that gets down to 28 degrees is considered a hard freeze. Once you've had the first hard frost, cut hardy perennials back to between four and six inches from the ground.

Pot up and bring inside

While time-consuming and labor-intensive, you may want to consider digging up herb plants and keeping indoors as potted plants in the winter. If you have herbs that you are super-attached to, this is a good option. Rosemary is a little on the fussy side (2), so be very careful if you choose to do this with your outdoor rosemary plants. However, there is always some risk of killing a plant by doing this, so take your time and be gentle with them.

Mint, oregano, and thyme will survive winter, but if you bring them inside in pots you can enjoy fresh herbs for cooking with all winter long.

Winter care for different classes of herbs

If you're not sure which plants fall under which category, see the handy list at the end of this article for a clear explanation of which plants can survive winter temperatures.

Annuals and Biennials

Basil and parsley are unable to take a freeze but will produce happily indoors all winter long under the right conditions. If you dig parsley up to put in a pot, make sure you get as much of the long taproot as possible. Your parsley and basil will definitely want supplemental light through winter, and in its second year parsley will begin to fade out as it prepares to produce a seed stalk.

Tender Perennials

Certain herb garden favorites like curry plants, lemon verbena, marjoram, pineapple sage, rosemary, and sweet bay laurel are considered tender perennial herbs. These tender herbs need a little extra love when the temperatures drop down to freezing if you want them to continue producing over time.

For lemon verbena and pineapple sage, you can dig plants out of the ground and pot them up to take inside for the winter. In temperate climates, sweet bay is best as a container plant moved from outdoors to a sunny indoor spot in the winter. Some rosemary is winter-hardy (to a limited extent), but it's always a good idea to propagate extra plants in the spring to keep in containers just in case you have to replace a plant that succumbs to cold temperatures outdoors.

Hardy Perennials

For hardy perennial herbs, follow instructions for overwintering plants and you can't go wrong. If you overwinter plants outdoors, always be prepared for failure, because the weather is unpredictable. Read the farmer's almanac and see if a cold winter is predicted.

Herbs that CAN survive winter and cold weather:

Chives- are fine overwintering and will benefit from a period of dormancy
Lavender- Consider covering and/or cutting back and mulching over
Lemon verbena- Plan on cutting back to 6 inches and mulching over
Mint- Dormant in winter, consider covering, cutting back or potting up for indoor use
Oregano- Check growing guides for winter hardiness, consider covering or cutting back
Rosemary- Check growing guides for winter hardiness, consider covering or cutting back
Sage- Check growing guides for winter hardiness, consider covering or cutting back
Thyme- Check growing guides for winter hardiness, consider covering or cutting back

Herbs that CAN NOT survive winter and cold weather:

Basil- will do well over winter indoors with supplemental light (do not place too close to a window if it is freezing outside)
Cilantro- Let it go to seed and collect seed for planting next spring or for cooking with
Parsley- will produce for 2 years straight including winter indoors with supplemental light
Lemongrass- must be brought inside during the winter to survive

Gardening tips for pre-winter

Take an inventory of your herbs in early fall and make a winter plan for them.
Harvest fresh leaves and preserve them for winter use by drying and storing in airtight containers or using other preservation methods.
Take cuttings of plants you plan to overwinter, just in case any of them don't survive.
Clear off your sunny windowsills to make room for potted herbs that you will bring indoors.
Collect seeds from annual herbs to plant next spring when the cold weather is over.

Much of herb gardening is trial and error, so don't be discouraged if you lose a plant or two to a cold snap. If you take your time and do a bit of planning, you can still enjoy many herbs year-round, and you can replace your plants in the spring.

Resources:

https://extension.psu.edu/growing-herbs-outdoors
https://blog-yard-garden-news.extension.umn.edu/2018/12/the-challenges-of-overwintering-rosemary.html