Growing herbs at home is not only easy but also the most effective way to save money on your grocery bill with gardening – think about how much a small bundle of fresh thyme costs and how much thyme even one plant can provide. Oh, and not to mention thyme can be easily propagated into more plants.
But whether you’re keeping your thyme as an investment or as just another addition to your herb garden, you’re here to know about how to protect your thyme over the winter. Fortunately, overwintering thyme is simple and straightforward.
Thyme Temperature Tolerance – Should You Overwinter It?
Most thyme varieties are frost hardy, down to USDA Hardiness Zone 5, which corresponds to an average extreme minimum winter temperature of -10°F to -20°F (-23°C to -29°C). However, overwintering is recommended if you live in Zone 6 or below, unless extra winter protection is provided.
Even if you live in Zone 5, I would overwinter thyme indoors, as depending on the local microclimate and where you’re keeping your thyme, it could be more vulnerable to fatal frost damage even at 0°F (-18°C), especially if you have a freak spring frost like in 2021. Furthermore, if your thyme is in a small pot, the roots will be more vulnerable to frost. If you do decide to keep your thyme outdoors and you live in Zones 5-6, cover with mulch or garden fleece for added protection.
Thyme Light Requirements
Thyme is native to the Mediterranean region, so it thrives in full, direct sun. However, thyme is also a notoriously hardy plant, and can tolerate indirect light, making it ideal for overwintering indoors or even keeping it as a permanent fixture on a windowsill herb garden.
Thyme will easily survive the winter with indirect sunlight. Any window will work, but if you have a north-facing window, it will not only survive but thrive well into spring. Grow lights are not necessary, but you can use them if you want. I would rather save the grow lights for more light-hungry plants such as peppers (which you can also overwinter indoors).
Anecdote time: Last year I kept two thyme plants overwintered in my insulated garage, with very little indirect light. I never got around to bringing them in (they were buried between a bunch of other overwintered plants), however, both managed to survive, although one which was completely shaded ended up dying after taking it outside. If you do keep your thyme in the garage, make sure the garage is insulated or heated if you live in Hardiness Zone 5 and below, and that your thyme is still getting indirect light.
Overwintering Thyme Indoors – Guide
Thyme is a tough, resilient plant. As long as you give it a minimum of indirect light (the more light the better) and don’t overwater it, it should survive and continue to give you fresh thyme to use over the winter.
Where to Keep Your Thyme Indoors
The ideal location for thyme is by a sunny north-facing window. However, thyme can easily tolerate indirect light, so next to any window will suffice.
Watering and Fertilizing Overwintered Thyme
You do not need to water thyme often inside. Water when the top inch or so of soil is dry. Fertilizing is also not necessary, but if you do want to give your thyme a boost over the winter, use quarter strength fertilizer once or twice over the winter.
Thyme is a hardy, Mediterranean herb, so even when grown outside it can tolerate poor soils and dry conditions. In fact, if you’re growing in even moderately fertile soil, you don’t need to fertilize it at all. The only time I fertilize my thyme is after a big harvest early to mid season. When overwintered, thyme will grow more slowly, needing even less fertilizer, and will also require less water because of the more controlled climate and less sunlight indoors.
If you are repotting your thyme before bringing it inside, water it well after repotting and avoid adding any fertilizer for a few weeks.
Do I Need to Prune Thyme Before or After Overwintering?
Unlike overwintered peppers, thyme does not need to be pruned when brought indoors or taken outside.
You can choose to prune thyme or not. I’ve successfully overwintered thyme either way. You can prune down to a few inches before overwintering or you can keep it unpruned and just keep harvesting fresh cuttings for the kitchen over the winter. You also don’t need to prune thyme after taking it outdoors in the spring.
When Should I Take My Overwintered Thyme Outside?
You can take overwintered thyme back outside after the threat of frost has passed. Thyme is frost hardy, but going from a constant room temperature to a sudden frost can shock the plant.
Do I Need to Harden Off Overwintered Thyme?
It’s recommended to harden off overwintered thyme when taking it outside. Hardening off is the process of gradually increasing exposure of an indoor seedling or overwintered plant to outdoor conditions.
Hardening off is important for seedlings started indoors since they’ve only been exposed to artificial light. Even the brightest grow lights pale in comparison to the sun. But even established overwintered plants can get used to the lower light conditions indoors, and taking a thyme plant out in the direct sun can sometimes shock the plant and cause leaf sunburn/sunscald (bleached leaves).
Hardening off can take anywhere from a few days to two weeks, but for overwintered plants, it normally won’t take more than a week. You can keep your thyme in a shaded area outdoors for a week before taking it out into the full sun. Alternatively, you can give your thyme direct sun exposure for an hour before bringing it back indoors, and over the next few days to a week, increase the time outside.
If you’re lucky and have a string of overcast days, you can take your thyme outdoors all day, and it will harden off without having to constantly move it.
Pro-Tip: If you notice the leaves turning white or pale yellow after taking your thyme outdoors, it’s getting sunburned and needs a bit more time to adapt to direct sunlight. Keep it in partial shade for a few more days before bringing it back into full sun.