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Sweet marjoram is a perennial herb closely related to oregano, though with a slightly sweeter taste. It is evergreen in zones, it is grown either as an annual or as a potted plant that is brought indoors when the weather turns cold. Sweet marjoram is a mound-forming subshrub that grows 30to 60 cms tall with aromatic gray-green leaves. Tiny white or pink flowers bloom from mid to late summer, though they are not especially showy. Sweet marjoram is used in much the same way as oregano, as a flavouring for soups, stews, vegetables, and meat dishes.
The key to growing this herb successfully is to plant it in good well-draining soil. In the garden, space plants about 30cm apart, and give them a normal amount of fertilizer and water. When growing in pots, give a good quality potting mix.
Cut back the stems before the flowers appear to encourage a bushy growth habit. You can dig up and repot garden plants to bring indoors when the weather turns cold but keeping them over winter requires a good amount of sun and fairly stable temperatures.
Sweet marjoram plants love sunlight, so aim to locate your plant somewhere where it can get lots of light throughout the day. If growing indoors, a sunny windowsill that boasts at least six to eight hours of sunlight per day works perfectly, or you can move the plant around your home to "chase" the light and ensure it gets enough rays.
Plant your sweet marjoram in soil that is loose and well-draining, with a pH level that is neutral or slightly acidic. Good drainage is the most important factor, as these plants can be susceptible to root rot. With potted plants, you can aid in drainage by planting your sweet marjoram in a clay or terracotta pot, which can help wick additional moisture from the soil and keep the plant from getting waterlogged.
Keep your sweet marjoram plant well-watered as it's getting established and throughout its first growing season—a cadence of every seven to 10 days is usually fine, as long as the soil dries out nearly completely in between waterings. Once established, your sweet marjoram plant will be drought tolerant, and it's okay to water it only periodically.
A native of mild Mediterranean climates, sweet marjoram plants grow best at temperatures between 18 to 24C. Avoid temperatures below 10C
Sweet marjoram does not need any added humidity—in fact, it really doesn't like it. Assuming you can give it enough sun, sweet marjoram will thrive in the relatively dry indoor air over winter.
While fertilizing your sweet marjoram plant isn't a must, giving it regular feedings can help it to grow more lush and full. If you choose to fertilize your plant, feed it once a month with a liquid blend formulated for herbs. Alternately, you can amend the plant's soil with organic matter to increase the nutrient density.
In addition to the standard species variety, there is also a variegated form of sweet marjoram that has gray-green leaves edged with creamy white. It is a more compact, slower-growing plant that is usually grown as an ornamental plant.
In addition to these forms of sweet marjoram, you may want to consider another type of marjoram for your kitchen garden. French marjoram (Origanum onites) has leaves that turn gold in the summer. It is hardy in most zones and is often grown to attract bees, butterflies, and other pollinators. Its taste is similar to sweet marjoram, and it is also known as Italian marjoram or pot marjoram. Its cultural needs are nearly identical to those of sweet marjoram.
By mid-to-late summer, your plants should be strong enough to be harvested. To do so, cut back the juicy stems and leaves of marjoram as they grow. Sweet marjoram will provide you with multiple cuttings in one season. As with oregano, you can hang sweet marjoram upside down in bundles to air dry. Once dry, remove the leaves from the stems and store them in a glass jar for use throughout the winter.
When it comes to cooking, sweet marjoram is a welcome addition to both Italian and Greek cuisines. Try a sprig of marjoram in your next batch of spaghetti sauce, or pair the herb with some lamb. Keep in mind that the sweeter, more delicate taste of marjoram can get lost in some foods, so if you're using it as a substitute for oregano, use 1/3 more than you would oregano.
Because of its fondness for dry air, sweet marjoram makes a good indoor plant to grow over winter, provided you can give it enough light. Grow it in a 6-inch clay pot filled with a well-draining potting mix. Garden plants can be divided and placed in a container to be brought inside before the first frost hits. If you would like to save the entire marjoram plant, dig it up and pot it in early autumn.
Growing sweet marjoram from seeds can be a bit tricky, since the seeds are slow to germinate and require precise temperature control. It's usually best to sow them indoors about four weeks before last frost in starter trays filled with potting mix. To speed up germination, soak the seeds overnight, then plant them in tray cells, press them into the soil, and lightly cover with 5mm of additional potting mix. Place the tray in a bright location and keep moist until they sprout, which will take about 10 days. For best success, keep temperatures right at 20C until the seedlings develop their true leaves.
Make sure to harden off the seedlings before transplanting them outdoors, at least two weeks after last frost. Seedlings should have at least three pairs of true leaves before transplanting outdoors into the garden. If you plan to grow them as potted plants, transplant them into individual pots filled with potting mix, which can be moved outdoors for the summer or kept growing on a windowsill.
Sweet marjoram appreciates being divided, and a single plant can provide you with sweet marjoram for years to come if given the necessary winter care. Simply dig up the root clump or remove it from the pot, divide it into pieces, and replant the pieces into separate pots or new garden locations.
Sweet marjoram planted in the garden has few serious pest and disease problems, though it can develop root rot in water-logged soils. Like many other houseplants, sweet marjoram has to contend with a few common pests when grown indoors. Aphids, mealybugs, and spider mites can all be an issue for the herb—if you notice signs of an infestation on your plant, move it away from any other herbs as soon as possible. You can try manually removing any pests by either rubbing them off or running the plant under a firm spray of water. If that doesn't work, you can treat the plants with insecticidal soap or Neem oil.
When it comes to diseases that can impact your sweet marjoram plant, most of them come about from too much humidity in the plant's environment. If the air in your home is too damp, your plant may be prone to powdery mildew.