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Portland Nursery

Indoor Herb Gardening

Imagine harvesting fresh basil, rosemary, or lemongrass right from your kitchen all winter long! Herb gardening kits make popular gifts and can provide years of enjoyment if properly cared for. Here are some tips on how to keep your indoor herbs happy and healthy.

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Before selecting herbs for your indoor garden, consider whether you have an outdoor space available to grow hardy herbs in pots or in the ground. Many culinary herbs are evergreen in the Pacific Northwest, and are generally happier and live longer outside. There are also many culinary herbs that get far too big to grow inside, unless you happen to have a sunroom!

Herbs that can be grown indoors:


Evergreen hardy herbs: bay, rosemary, garden sage, thyme, and winter savory.

These keep their leaves and can be harvested all year.


Hardy perennial herbs: chives, mint, marjoram, oregano, parsley (technically a biennial), and sorrel.

These are deciduous perennials that naturally die back in winter outdoors. They can be kept from going dormant if they are grown inside all winter. Outside they may keep their leaves if the weather is mild or if they are grown in a protected spot. They do appreciate a winter rest, so if grown exclusively indoors they may be considered somewhat short-lived.


Annual herbs: basil, chamomile, chervil, cilantro, dill, epazote, shiso, summer savory, and wheatgrass.

Leafy greens that can grow indoors also fall into this category: lettuce, arugula, mesclun mixes, micro greens, and spinach.

Annuals usually complete their life cycles in the course of a single season, and will die sometime after setting seed.


Tropical and tender herbs: lemongrass, lemon verbena, scented geraniums, ginger, stevia, tarragon.

Tropical herbs need constant moderate temperatures to do well.


You can buy small herb plants from the nursery, start seeds inside, or take cuttings of or make divisions from mature plants.

Buying plants is the easiest way to start your herb garden. Portland Nursery usually has a good selection of evergreen herbs through the winter. Deciduous perennial herbs are generally available through early autumn. Annual and tropical herbs are generally available until late summer.

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If your herbs have been growing outside, you’ll want to slowly transition them to an indoor environment. Place your plants in a sheltered location outside, in a spot that is warmer and gets less light, such as a covered porch, for a week or so before bringing them in. The following week, bring your plants inside at night, but move them back to their protected spot in the daytime. After this, the plants will be less susceptible to shock when they are permanently moved inside. Reverse this process if you want to move your plants outside after they have been indoors.

Starting seeds inside is a great way to grow all annual herbs, and some perennials. This way they are already acclimated to indoor conditions. All of the annual herbs tend to be easy to start from seed. Perennials are generally somewhat easy to grow from seed. Evergreen or shrubby herbs tend to be fairly difficult to start from seed, but are usually easier to propagate from cuttings.

For detailed information about starting seeds or cuttings, please give us a call at Portland Nursery!

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Lighting

Lighting is the most important factor in the success of your indoor herb garden! While you can try to grow herbs in an unobstructed south-facing window, we really do not have enough light in our area to support healthy plant growth for sun-loving herbs indoors. Plants suffering from lack of light often have long, leggy stems and pale leaves. Fortunately, setting up a grow light system is easy and doesn’t have to be expensive. You can buy full-spectrum fluorescent lights that fit into 2’, 3’, or 4’ fixtures (a hooded “shop light” setup). You can also use a single full-spectrum grow light in a lamp or spotlight. The key is keeping the lights very close to the plants: no more than 1 foot away from them. The lights should be on for about 12 hours in summer, and 8 hours in winter.

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Culture and Maintenance

You can grow herbs in any kind of pot, as long it is big enough to support root growth and has a hole in the bottom for drainage. Plastic or ceramic are good choices for indoor plants. Terracotta looks pretty but is porous, and therefore loses moisture more quickly, and mold can develop on the pots.

Transplant herbs into pots that are at least 2” larger than the root ball on all sides. It is fine to put multiple plants in one pot, as long as they have ample space to grow in to. It is also a good idea to give mints their own pot, as they are very vigorous and easily overtake slower-growing plants!

When up-potting, use a good-quality potting soil such as Black Gold or Edna’s Best brands. Mix in an organic, all-purpose fertilizer such as E.B. Stone’s Sure Start.

Let the soil dry out very slightly between waterings. Indoor plants generally need less water in winter, and most herbs don’t like constantly wet soil.

The occasional feeding is beneficial to all indoor plants. Fertilize herbs with an organic liquid fertilizer such as fish emulsion monthly from spring through late summer. You can also use granular amendments such as blood meal and seed meals a few times during the growing season, or a dry all-purpose fertilizer. Herbs are not heavy feeders, and do not need intense synthetic fertilizers.

Herbs tend to be happiest in average indoor temperatures, between 65°-75°F in the daytime, and cooler at night. Lowering the temperature by about 10° at night helps mimic natural growing conditions.

Pests and Diseases

Indoor plants are often susceptible to fungal problems such as powdery mildew, botrytis, or root rot.

White, slightly fuzzy spots on leaves indicate powdery mildew, which is often exacerbated by dry conditions and poor air circulation. Use a small fan to keep air moving, maintain fairly consistent soil moisture, and use an organic fungicide such as neem oil if the problem persists.

Fuzzy gray mold on soil, around stems, or on leaves, sometimes with dieback on stems, indicates botrytis. Remove any infected plant parts and clean up dead plant material on the surface of the soil. Decrease watering, and avoid wetting leaves. Use a small fan to promote air circulation. Use neem if necessary.

Root rot is an often-fatal issue. It can be caused by overwatering, and is exacerbated by crowded roots and inadequate light. Leaves may wilt, turn yellow and drop off. Unfortunately, the most common reaction to these symptoms is to water more, which often kills the plant. Let the soil dry slightly between watering, and feel the roots to make sure that plant is not pot-bound. Repot the plant in fresh soil if it seems snug.

There are a few pests common to indoor gardens. Aphids, whiteflies, scale, fungus gnats, and spider mites can occur. Insecticidal soaps are the most common pesticides to use on edibles, but if you suspect an infestation, call Portland Nursery to find out the best treatment options.

Resources: The Bountiful Container by Rose Marie Nichols McGee and Maggie Stuckey is a great resource for edible and herbal container gardening!

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Basil ’Queen of Sheba’

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Lemon Thyme

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Parsley ’Extra Curled’

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Lemon Verbena

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Chives - Bronze Fennel

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Mint

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Lemon Grass

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Cilantro - Coriander