Your Herb Garden Needs Special Care in Winter—These Expert Tips Will Keep It Healthy

No one wants to see months of diligent work destroyed at the first sign of frost; preparing your herb garden for the winter will ensure your plants are strong enough to rebound in the spring. The colder months, after all, are tough on greenery: Reduced sunlight can stifle vegetative growth, and freezing temperatures can wreak havoc on both plants and their roots. Here, we spoke with experts to get the scoop on how to best protect your herb garden against these chilly risk factors.

Know Your Herbs

The great thing about perennial herbs, according to Luay Ghafari, creator and recipe developer at Urban Farm and Kitchen, is that they can often withstand a little frost and even snow. "This means you can continue harvesting well into late fall and even early winter," he says. "You might even be able to harvest some sage and rosemary for your holiday dinner."

If other perennial herbs, such as thyme and oregano, are still quite large in the fall, then Ghafari suggests harvesting in large bunches for drying and preserving. "Once dry, you can crumble the herbs and store them in spice jars," he says. "Or if you're feeling creative, mix and match to make your own custom spice blends."

When it comes to annual herbs such as cilantro, consider letting any remaining plants flower and go to seed. "The seeds can be saved and replanted next spring, or they can be used in the kitchen as coriander spice," he says. 

Mulch, Mulch, Mulch

If an herb is a perennial in your particular growing zone, then it won’t need much in terms of winter protection, according to Ghafari. "Applying a layer of mulch—such as straw, leaf, or compost—around the base of the herb will help regulate the soil temperature," he says. "The mulch will also break down and give the soil a nutrient boost." 

In growing zones that experience deep freezes, It's vital to provide more mulch to protect the roots. Jonas Portillo, a food program associate at the Case Western Reserve University Farm, recommends using organic black or brown wood chip mulch for perennial herbs. "The darker mulch will help to absorb and retain heat from the sun," he says. 

Cover Up

In terms of cover, Thewlis recommends a frost blanket—a synthetic fabric that retains heat and acts as a windbreaker. "Fabric row covers are permeable and allow for light, water, and air to reach plants," he says. 

Depending on the degree of coverage needed, an array of fabric weights are available. Thewlis says lightweight cover allows for maximum light penetration, but provides minimal temperature protection. Often, it doesn't require physical support, and can be laid directly over low growing crops. 

"For frostier conditions, fortify your herb garden with a heavyweight cover, which can provide protection up to four to eight degrees Fahrenheit," Thewlis says. "Heavyweight cover necessitates the use of hoops to support the fabric. PVC pipes are a breeze to bend and can be stuck in the soil to build an arching framework for the fabric to drape over. Space hoops every four to five feet." 

When looking ahead to next year, Thewlis recommends cover cropping. "Cover crops are plants grown to cover the soil for the purpose of supporting soil health," he says. "They protect soil from erosion, suppress cool season weeds, build organic matter, enhance tilth and drainage, and bolster biodiversity above and below the soil. Winter-hardy cover crops include winter rye, winter wheat, hairy vetch, and white clover." 

Move It Indoors

While some herbs may be fine under a nice layer of mulch, those that are particularly vulnerable to cold will need to be moved indoors. "Herbs such as basil, parsley, or cilantro will need to be placed inside in a location that receives ample sunlight throughout the winter," Portillo says.

If your herb garden is already under the cover of a greenhouse or polytunnel, lengthen winter’s limited light with the use of supplement grow lights. "Use a timer to automatically turn lights on and off at specific intervals prior to dawn and after dusk," Thewlis says. "A continuous light cycle of 18 hours promotes vigorous vegetative growth." 

Cut Back 

"Perennial herbs like oregano, chives, thyme, and lemon balm can be cut back to about four to six inches above the ground after the first frost or in late fall," says Ghafari. "Cutting perennial herbs back in the fall will help them grow strong the following year." 

For other perennials like lavender, Portillo recommends pruning back the plant while making sure not to cut off the woody stems. "For mint, you want to leave the parts of the plant that die off until the springtime when you can prune them," he says.

While pruning may be an important step to prepare your herbs for winter, Tammy Sons, founder and CEO at TN Nursery, advises against cutting too late into the fall. "It’s imperative that your plants have enough time to heal before the first frost," she says. "Exposing the soft inner tissues to freezing temperatures causes plant death." 

Hold the Fertilizer

Sons cautions against fertilizing plants in the fall or winter, as this may stimulate them to grow and cause winter kill and shock. Thewlis, meanwhile, encourages gardeners to work on building their soil during the winter months in order to optimize the opulence and grandeur of their space. "A proper soil test is worth its weight in gold," he says. "Macro and micro mineral ratios, organic matter content, and pH levels are of paramount importance. By balancing your soil now, plants will be poised for success in the spring."