Some of the most commonly used aromatic herbs in a garden originate in the Mediterranean. Thyme, basil, and oregano are excellent additions to marinades, sauces, and even medicinal teas. But rosemary might be the most well-known among these. This summer-loving woody perennial has so much use in cooking and the apothecary, but what if you don’t have the space to grow outdoors? Maybe you have grown rosemary in your garden through spring and summer, and need to switch to growing rosemary indoors for the winter.
No worries there. Rosemary’s versatility in the home is parallel with its ability to be grown in different settings. Are you a person who struggles with mobility? Are you living in an apartment? Maybe you’d like to try to grow rosemary year-round, but you live in far North America in a zone where arctic winters knock any living thing out. Try growing rosemary inside!
Rosemary plants do have a reputation for getting rather large in certain USDA hardiness zones, but that doesn’t mean the right conditions can’t be crafted to contain them. With the help of grow lights, a grow tent or a hydroponic system, you’ll have fresh herbs for cooking, teas, medicines, or simply aromatics in every season — spring, summer, fall, and even winter.
Methods For Growing Rosemary Indoors
Rosemary plants grow in any kind of indoor growing setting as long as proper conditions are met. A large pot in a well-lit window with good soil will host a healthy plant. Keep the plant in your kitchen for easy access, or in a bedroom to waft in its lovely lemony smell while you relax. A potted rosemary plant in a south-facing window is not difficult to care for. An indoor grow also means there is less likelihood for pests.
If there is not enough sun flowing into your home to host a potted rosemary plant, grow lights can help. Each type of grow light provides a different condition. For rosemary, a sun-loving herb, fluorescent light is best. Find a space in your home that can fit your potted plant and light, and set it up. You may find yourself hanging out in that area often. Any area that is large enough for your potted plant will most likely fit a small grow light as well.
Grow tents are another option for rosemary and may be even better than lights as rosemary prefers high humidity. A grow tent keeps light and humidity in, giving you conditions that mimic rosemary’s favorite place to be: the Mediterranean coast. The reflective interior of the tent allows light and humidity within to bounce around. There are different types of grow tents, but all require a little more space than just a potted plant and a grow light. If you have a lot of counter space with little overhang, a full grow tent setup could be the indoor rosemary solution for you.
Even though woody perennials like rosemary plants are prone to root rot in settings with too much moisture, hydroponics are another option that allows you to harvest these herbs with much efficacy. There are lots of different types of hydroponic systems, but a full setup that uses Nutrient Film Technology is best. The only drawback to a hydroponic system is the amount of room you’ll need (at least a few feet wide, and tall).
Caring For Indoor Rosemary
So what are the requirements to grow rosemary indoors in each of the above settings? Follow these tips to learn about the essential conditions for cultivating rosemary plants.
Lighting & Temperature
Rosemary plants love a full sun zone or 6 hours of sunlight or more per day. For growing potted rosemary in a window, ensure you access the full spectrum of sunlight available. For people in the Northern hemisphere, a south-facing window is best. The opposite goes for those in the Southern hemisphere; a north-facing window is best in this regard.
Rotate the rosemary plant container or external light for full sun coverage. Lights often come with a timer that allows you to set the amount of light per day. Start at six hours a day, and if you notice the plant yellows or wilts, scale it back. If your rosemary plant looks stunted with just six hours, try to scale up from there. If you have a light with no timer setting, turn it on and off manually.
Room temperature (72 degrees Fahrenheit) is perfect for a rosemary plant that thrives in temperate coastal regions. Anywhere from high heat to low 30s is acceptable, too, although this likely won’t be something you’ll run into indoors. Rosemary is very hardy but appreciates higher humidity. Avoid if at all possible the dry heat of an air conditioning system. Water your plant more if there is no way to keep it away from a vent. Grow tents and hydroponic systems are great for maintaining the high humidity needed for a thriving rosemary plant.
Water & Humidity
Rosemary needs good drainage and not a lot of water when in the proper humidity. Indoors in a pot or planter, water your rosemary plant regularly when potting soil is dry. In winter, water rosemary less. Like all flora, rosemary goes into dormancy in colder months.
Rosemary is drought tolerant and doesn’t require a lot of water to grow well. Let the soil dry out between watering to prevent powdery mildew and other issues. Rosemary needs good air circulation, which will prevent problems like mildews that commonly affect rosemary, especially indoors.
For hydroponic systems, change the nutrient solution every three weeks. Some NFT systems come with small domes you can place over the rosemary plant after it has been transplanted into the system for humidity control. Test the dome for a trial period, and remove it if necessary. Ambient humidity is easily kept up in grow tents and hydroponics. As long as enough water is present, rosemary plants absorb enough to grow, and air circulation allows evaporation to wick away excess water that can damage the plant.
Growing Medium & Container
Since this plant prefers sandy well-draining soil, you can use a soilless medium to host your rosemary. Soilless media are a combination of perlite, vermiculite, and peat moss that simulate the coastal ecology of the Mediterranean. Rosemary roots don’t need loam and prefer well-drained sandy soil to stay alive.
For propagation, a small container or pot is fine. But when it is time to transplant your rosemary plant will need at least 12 inches of depth to accommodate roots. Even though rosemary prefers sandy soil, it’s totally fine to grow this plant in a basic potting mix in a windowsill or under a light. A terra-cotta pot is great for rosemary because it draws moisture out of the soil and prevents root rot. Plastic containers are also suitable, but the soil will need lots of attention in this case as plastic pots retain moisture.
Plants growing indoors in a hydroponic setting need to be checked frequently to ensure roots are healthy. As we will cover in the propagation section of this article, root rot strikes rosemary quickly in water. Keep the water fresh, in this case, and follow the guidelines that come with the system to keep roots from rotting.
Self-watering pots tend to hold too much water for rosemary plants. Since rosemary needs to dry out between watering, plants growing in a self-watering container can cause root rot and mildew. As long as drainage is substantial, growing rosemary indoors is a sinch.
Fertilizing too much could damage rosemary. This herb doesn’t need much more than good drainage and the right medium to stay alive. No fertilizer is needed unless a significant nutrient loss is evident from yellowed leaves. In that case, a full-spectrum, balanced liquid fertilizer is ok. Change the nutrient solution every three weeks in hydroponic systems.
Rosemary likes pruning, like many aromatic herbs. Since it’s a woody herb, prune the green tips on each branch to help it grow. You can do this all at once, or as needed. In spring and summer, more growth will accompany pruning. In winter when it’s cold, reduce pruning frequency. Prune between growth points right at the bottom of new growth after the plant is established to encourage growth and keep the shape of the plant to your liking.
If your rosemary plant grows flowers, deadhead them at the stem for higher herb potency.
To start rosemary from seed, plant several seeds in a pot or starting container with a well-draining medium a few months before warm weather arrives. Although your goal is to grow indoors rather than outdoors, these plants have cycles that they can sense in any place. Rosemary has a very low germination rate (about 30%), so sow several seeds at once. It also grows very slowly — many herbs have a very prolonged maturation process. So sowing in early winter is best. When seedlings have matured to a height of 3 inches transplant them in a larger container or your hydroponic system.
It’s easiest to propagate rosemary from cuttings. Just as you wouldn’t prune past the new green growth of a rosemary plant, use this same method to select cuttings. A rooting hormone helps roots develop. Remove the bottom leaves, and dip tips in rooting hormone before planting in either starting containers or the container where your mature rosemary will live. You can plant several rooted rosemary starts in one container to create what are known as topiaries, where you painstakingly shape the plant by winding it around other plants and pruning as it grows.
Start hydroponic seeds in a growing medium like coconut coir or rockwool, and transplant starts into your system with fresh water and nutrients when roots begin to move through the medium. This takes about 1-2 weeks. When you transplant, space seedlings about six inches apart to provide enough room for a frequent harvest. Because the water in a hydroponic system is flowing and clean, it will not cause rosemary to suffer root rot as a traditional water propagation would.
Since rosemary is so hardy and likes dry conditions outdoors and indoors, most problems stem from ground that remains wet for too long. It’s not often your rosemary plant will get upset in dry conditions or even from a lack of sunlight once it’s established.
Powdery mildew can arise on needles if rosemary is watered from above. This mildew looks like yellowish to white powdery dust. To prevent powdery mildew, always water at the base of your plant. Overwatering can cause mildew in the soil, or an overabundance of moisture retained in media can give fungus and bacteria the conditions they need to proliferate. A little bit of fungus or mold in the soil is normal. But the result of too much water in the soil is root rot. Rosemary needs soil to dry out. If you keep it in a sunny or well-lit area, it should have no problem soaking up moisture in between watering. If bacteria or fungus become an issue, remove the rosemary and transplant it into a dry medium in a sanitized pot.
Spider mites are an insect pest that appears indoors on plants that have been brought in from outdoors. If you have decided to bring your rosemary plant in from your garden for the winter, check for spider mites before bringing it in. Spider mites weave a light web around needles. Look closely at the web before determining whether or not to treat with a commercial insecticidal soap. If multiple small bugs are crawling in the web, it’s spider mites. Always pick treatments that are safe for human contact for indoor grows. Applications may need to occur once per week over several weeks. Damaged branches should be removed and discarded.
Fungus gnats may hang around soil that’s too wet. These are small fly-like insects, and although they don’t hurt rosemary plants at first, they can reproduce in your growing medium and cause more damage as time goes on. For fungus gnats, hang a sticky trap, or create a homemade trap in a small cup capped with plastic wrap that has holes in it. In the cup, put things that gnats like to eat, like fruit, or vegetable matter. Add a liquid solution of vinegar and dish soap. When gnats go to eat the veggies or fruit, they’ll fall into the solution and will be unable to leave the trap.