It depends on where you garden. Marjoram survives the winter outdoors in warm zones 9 and 10, but a hard freeze kills it in colder ground. So overwintering marjoram in most of the country means you pull it out of the cold before the season turns. Once you know your zone, the right move gets clear fast.
Early one fall afternoon I dug a single sweet marjoram out of the raised bed by my south-facing kitchen door. I shook the loose soil off the roots, dropped it into a small pot, and set it on the sunny windowsill above the sink. The first zone 6 marjoram frost hit about a week later, and the plant on the sill never felt it.
The reason comes down to what marjoram is. It grows as a tender perennial from warm Mediterranean hillsides. So it shrugs off a mild winter, but it cannot take a deep cold snap. A light frost may scorch the leaf tips. A hard freeze that locks the soil solid kills the roots, and once the roots go, your plant is gone for good.
Your USDA zone decides your plan. In zones 9 to 10, leave it in the ground and add a thin layer of mulch around the base for a little extra insurance. In zone 8, a heavy mulch blanket gives it a fighting chance, but it is a gamble in a rough year. From zone 7 and colder, your ground will freeze too hard for the roots to make it through. That is the line where you stop trusting mulch and start planning to move the plant.
That is where smart marjoram winter care starts. If you live anywhere the soil freezes solid, the most reliable move is to grow a backup plant in a container so it can come inside. Heavy mulch can work in a mild winter, but you are betting the plant on the weather. A potted plant on a windowsill takes that bet off the table.
Dig up a healthy plant in early fall, before the first hard frost, while it is still actively growing.
Move it into a well-draining pot with fresh potting mix, trimming any leggy or damaged stems.
Place it in a sunny window with at least six hours of light, away from cold drafts.
Water only when the soil surface dries, since growth and water needs both slow indoors over winter.
When you bring marjoram indoors, the brightest window you have is the right spot. A south-facing window with at least six hours of sun keeps the plant compact and green. A dim room makes it stretch, go pale, and drop leaves. Keep it clear of cold drafts and away from a blasting heat vent, since both stress the plant fast.
Go easy on the water. Growth slows to a crawl in winter, so the soil dries much more slowly than it did outside in summer. Water only when the top of the mix feels dry. And never let the pot sit in a saucer of water, since that rots the roots. Watch for pests too. Aphids and spider mites spread fast on indoor plants in dry, warm air. So check the undersides of your leaves once a week and rinse any bugs off in the sink.
Come spring, set your pot back outside once the nights stay above 50°F (10°C) and the danger of frost has passed. So the short version of overwintering marjoram is simple. In zones 9 and 10, you mulch lightly and leave the plant be. Everywhere colder, you pot one up before the first freeze and keep it on a sunny sill until your garden warms again.
Read the full article: Marjoram Plant: Grow, Use, and Benefits
