By Susan Martin – Piedmont Master Gardeners
At this time of year, starting an indoor herb garden is an inspiring idea. Add a handful of fresh parsley to the turkey stuffing. Dress up boiled potatoes with fresh rosemary. Snip some fresh chives into eggs and hash browns. Sprinkle fresh oregano in soups and pasta dishes. Cooking with fresh herbs makes me feel like a chef, not just the person whose turn it is to make dinner. Plus, it’s so convenient to have everything on hand. No checking of expiration dates on the windowsill basil!
I used the term “indoor herb garden,” but that may be too intimidating. Although it looks magazine-beautiful to have a basket of several different herbs of various green hues and textures, a multiple-plant grouping presents challenges. While most herbs share the same general needs, some herbs have specific preferences. Using individual potting containers makes it easier to cater to specific needs, promote air circulation, and provide ample space for each plant as it matures. If you like the look of containers with multiple herbs, or if space is a constraint, group herbs with similar light, water, temperature, and humidity requirements.
This article will focus on growing indoor herbs to use in everyday cooking. We’ll look at a few basic herbs and their requirements. You can then add your personal favorites based on these general guidelines, plus your own additional research.
GENERAL REQUIREMENTS
LIGHT
Light is the most important variable for growing herbs indoors. Herbs that are not exposed to their preferred light conditions will become thin and spindly, produce smaller leaves, and have a reduced aroma. Be sure your herbs get at least six hours of sunlight a day. An easy way to judge this beforehand is to put an empty pot where you plan to place your herbs and watch how the sun changes throughout the day. Southern exposure is best, western exposure is next best. If plants are grown on windowsills, it will be necessary to rotate pots often so that each side gets enough light for uniform growth. Depending on your home’s sun exposure, you may need to use supplemental lighting. Or, you can choose herbs that can thrive with the light you naturally have and eliminate the “sun-hogs” that won’t be at their best.
SUPPLEMENTAL LIGHTING
General advice is to place herbs 6-12″ from two 40-watt, cool white fluorescent bulbs for 14-16 hours. There are many sources for very handy, counter-top herb gardens with lights. You may also build your own fluorescent-enhanced herb garden; a google search will reveal many DIY plans, although these tend to be for “operations” larger than kitchen counters. Or, you can use an easy clip-on light that works on one small area at a time (presumably not close to cooking activity), or tube-style lights that can hang from underneath kitchen cabinets. You’ll need to weigh the pros and cons of taking these extra steps.
SOIL
Most herbs like loose soil that drains easily. Most do well in a soilless potting mix. For even more drainage, mix two parts good-quality, soilless potting mixture, and one part perlite. Straight potting soil is too compact and heavy for good drainage. You can make a customized soil mix by using 1/3 potting soil, 1/3 organic matter (peat moss, compost, or leaf mold), and 1/3 perlite. (See this link for a description of the differences between perlite and vermiculite, and when to use each.)
WATER
Water each herb as needed; many herbs like to be on the slightly dry side. Separate pots allow you to monitor water needs for each plant. Bay, marjoram, oregano, sage, and thyme need to dry out between watering. Never allow rosemary or chives to dry out completely. Basil likes moist, but not wet soil, with excellent drainage to avoid root rot. Generally, more indoor herbs die from overwatering than from underwatering. If the plant is limp or has yellow leaves, test the soil with your finger before watering.
HUMIDITY
Herbs also require a proper balance between a humid environment and adequate air circulation. When grouped together, containers create a humid environment. However, the closely-grouped containers may not allow sufficient air circulation. Basil and rosemary are susceptible to powdery mildew. This again highlights the advantage of using separate pots. You can rearrange group containers to allow space for more air circulation. For herbs that like humidity, such as rosemary and parsley, pots can be placed in a pan of moist pebbles, or misted twice weekly with a water sprayer.
FERTILIZATION
Fertilize herbs with a low dose of liquid fertilizer, such as fish emulsion, seaweed, or a general-purpose, water-soluble fertilizer used at half the label-recommended strength. Some herbs require very little fertilizer, some can benefit from applications every 4-6 weeks. Over-fertilizing may negatively affect an herb’s aroma and taste.
TEMPERATURE
Ideally, herbs prefer room temperatures of at least a 65-70°F during the day and 55-60°F at night. You and your plants may have different opinions on what temperatures are most comfortable! Some herbs like indoor temperatures warmer, some like them cooler. You should definitely avoid placing herbs by a fireplace or a heat vent. Also, avoid drafty windows, or placing the pot right next to the glass on a freezing night. A sunny windowsill can become a chilly spot for basil after the sun goes down. You may need to shift plants around to keep them happy. But that’s what we do for our plants!
CONTAINERS
Choose pots that have drainage holes. All herbs need good drainage. There are pros and cons to using clay pots. Clay pots are porous which allows air and water to flow through them. This helps prevent root rot. Clay tends to dry out quickly, however, so watering is needed more frequently. A glazed or plastic container won’t dry out as quickly. This advantage can turn into a con if you tend to overwater. Take care with the saucers you choose. Clay saucers can leave wet marks on window sills and furniture. Plastic saucers are less likely to leave water stains, but placing protection under any type of saucer will help reduce the risk of water stains. If herbs are placed on a non-porous kitchen countertop, staining will be less of a problem. If you’re tight on counter space and don’t have a convenient area in proximity, combining herbs in a hanging basket might be a good alternative. In this case, group herbs that have similar requirements. For example, don’t put basil with oregano and thyme. Be on the lookout throughout the year for fun and attractive pots for giving herbs as gifts. Just make sure to select pots with drainage holes.
PROPAGATION
The easiest and quickest way to get started is to purchase healthy starter plants. But, if you want to start from seed, see this article from the University of Illinois Extension. Many herbs can be easily started from stem cuttings of existing plants. See this article from The Garden Shed on starting plants from stem cuttings. It’s too late this year for taking cuttings from outdoor plants, but perhaps you’re overwintering a large, containerized herb in the house – you could start a little stem cutting plant to keep in the kitchen. Or, you could simply tuck this idea away for next year.
POPULAR HERBS FOR INDOOR GROWING
Virginia Tech recommends that most of the herbs that have a mature height shorter than 12″ may be grown in 6″ pots as indoor plants. Many dwarf varieties of larger herbs are appropriate indoors, as well, including, spicy globe basil, dwarf sage, winter savory, parsley, chives, and varieties of oregano and thyme. Any herbs with a taproot, such as dill (Anethium graveolens), require deep pots. Consider the size of plants your space can accommodate.
SUGGESTED HERBS
The following herbs are frequently used for cooking, and appropriate to growing indoors:
Basil (Ocimum basilicum)
The leaves of basil have numerous oil glands with aromatic volatile oil, which makes it such a pleasure to have in the house. Just as with outside plants, basil should be pinched back to promote bushiness, and to prevent flower heads from forming. This plant likes a sunny southern exposure and consistently warm room temperatures, both day and evening. Basil leaves will droop and fade after a short time in cool air, so avoid putting basil in a drafty spot, or next to a window on cold nights. While the soil should be kept somewhat moist, it should never be soggy, which could cause root rot. General houseplant fertilizer can be used at half the label-recommended strength every 4-6 weeks; apply to the soil, avoid getting it on stems or leaves. Spicy globe basil is a compact variety suitable for indoors. Don’t be dismayed if you need to replace the basil and start again. It’s a small price to pay for something that works in so many recipes! Or, you may decide to label basil as a “sun hog” and move on to something else.
Chives (Allium schoenoprasum)
Chives are much less finicky about indoor conditions. They tolerate the lower light of the winter sun, as well as temperature fluctuations characteristic of a kitchen windowsill that can range from 55-75⁰ F. Chives grow best when watered frequently, as long as there is proper soil drainage. Soil should be moist but not wet. Tips of foliage will turn yellow if the plant is too dry. Use liquid fertilizer at half the label-recommended strength every four to six weeks. Once the plant is 6” tall, cut leaves with scissors as needed, leaving at least 2” of growth above the soil. The plant will continue to grow. The Grolau variety, appropriately called Windowsill Chives, was bred for growing indoors. It has an extra strong flavor, thick, dark leaves, and is less susceptible to becoming leggy.
Oregano (Origanum vulgare)
This perennial herb from the Mediterranean likes it hot and bright. If there’s no spot in your home that receives six hours of sun per day, you may have to supplement with fluorescent lights or grow lights. Water only when the soil feels completely dry. Poke your finger about ½” into the dirt. You can fertilize occasionally with liquid fertilizer at half the label-recommended strength, but fertilization is generally unnecessary. Oregano can be grown from seed, or from cuttings of high-flavor plants. Do not allow the plant to flower; this will reduce growth or stop growth completely. Flowering also reduces the flavor of the leaves. When harvesting, remove the stem tips, leaving 4-6 pairs of leaves on the plant in order for it to produce side shoots for additional harvesting. Leaves should be stripped from the stems by running your fingers down the stems. Chop the leaves before use. Greek oregano, or true oregano, has an excellent flavor. Another popular variety with an intense flavor is “Profusion®” oregano.
Parsley (Petroselinum crispum)
The most common variety is common or curly parsley, Petroselinum crispum. Curly parsley typically grows 8-14″ tall and is a good candidate for growing indoors. Italian flat-leaf parsley, P. neapolitanum, is another popular variety. The flat, serrated leaves have a much stronger and sweeter flavor than the other varieties, making it more desirable for cooking.
Set parsley in a sunny, preferably south-facing window where it will receive 6-8 hours of direct sunlight every day. If your window doesn’t provide that much light, supplement it with fluorescent lighting. Turn the pot every 3-4 days so that the plant doesn’t lean into the sun. Parsley also needs humidity, and you may need to mist the plants from time to time. If the leaves look dry and brittle, set the plant on top of a tray of pebbles and add water to the tray, leaving the tops of the pebbles exposed. The plants may be a bit spindly when grown indoors because of lower light levels. Use liquid fertilizer at half the label-recommended strength every 4-6 weeks. Harvest parsley by snipping off the stalks close to the soil, beginning with the outside stalks. If you just cut the tops off and the leaf stalks remain, the plant will be less productive.
Rosemary (Rosemarinus officinalis)
Rosemary prefers a cool, sunny location where the humidity is high. The herb dries out quickly in an indoor growing environment and may exhibit brown leaf tips and die-back. Do not react to these signs by watering the plant more; this could lead to root rot and loss of the plant. Rosemary likes dry roots and prefers to absorb moisture from the air through its foliage. Keep the plant cool, and place it on pebble-filled saucers. Make sure there is always some water in the saucer, but not above the level of the pebbles. This helps to increase humidity around the plant and reduce foliage damage. Frequent misting, twice weekly, is also helpful. Rosemary doesn’t require much fertilizing outdoors or indoors. When the plant is 6” tall, cut leaves as needed leaving at least 2” of growth above the soil. Don’t let the branches get too spiky – trim them back to keep the plant bushy. You can use any R. officinalis for cooking, but upright kinds with broader leaves contain more aromatic oil.
“Spice Island” is a variety normally sold in the herb section of the nursery. ‘Tuscan Blue’ is the favorite of many chefs; “Blue Spires” and “Miss Jessup’s Upright” are also good. Rosemary is easily propagated from cuttings.
Thyme (Thymus vulgaris)
Common thyme is native to the western Mediterranean region and prefers full sun. It can, however, tolerate indirect light if you are running out of prime sun spots for other needy herbs. The most popular thyme is English thyme (Thymus vulgaris), which is not native to England, but was introduced by the Romans. Its strong, distinctive flavor is what most of us associate with the herb. Another good culinary option is French thyme (Thymus vulgaris), a variety of English thyme that has narrower, grey-green leaves and a slightly sweeter flavor. It is often preferred by chefs and is excellent for seasoning meat, fish, soup, and vegetables. Another option is lemon thyme (Thymus x citriodorus). Its lemony taste and scent are a great addition to chicken, fish, and salads that can use a citrusy overlay.
Thyme is a hardy plant and will do very well when kept trimmed and in good light. Water the thyme only when the soil feels dry. Poke your finger about ½” into the soil. If it’s dry, give the plant a good soaking, pouring in enough water so that it drains into the saucer. Thyme has small, wiry stems; to harvest, strip the leaves from the stems by running your fingers down the stems. Thyme’s primary oil, thymol, is considered an antiseptic.
HARVESTING
Clipping your herbs to use for cooking is the biggest reason to grow them. This “pruning” is beneficial to the plants as well, as long as you clip less than one-third of the plant at one time.
INSECTS
The high concentration of essential oils in healthy, actively growing herbs repels most insects. However, aphids and spider mites can be a problem. If aphids are a problem, wash the leaves with water. Aphids seem to be more prevalent in crowded conditions. Spider mites thrive in dry conditions and can be controlled by spraying the plants with plain water at regular intervals. You can also use a soapy solution of 1-2 tablespoons of mild soap, such as dishwashing soap, to one gallon of warm water. Spray infested plants with the solution once a week while pests are visible.
COOKING WITH HERBS
When using fresh herbs in a recipe, a general guideline is to use three times as much as you would use of a dried herb. When substituting, you’ll often be more successful substituting fresh herbs for dried herbs, rather than the other way around. If you pick more than you need, store the extra in an open or perforated plastic bag (use a sharp object to make several small holes) in the crisper drawer of the refrigerator for a few days. After picking, wash smaller amounts of herbs thoroughly under running water, shake off the moisture, and pat off any remaining moisture with clean paper towels. For a larger amount of herbs, you could use a salad spinner. Unlike dried herbs, fresh herbs are usually added toward the end in cooked dishes to preserve their flavor. Add the more delicate herbs – basil, chives, cilantro, dill leaves, parsley, marjoram, and mint – a minute or two before the end of cooking, or sprinkle them on the food before it’s served. The less delicate herbs, such as oregano, rosemary, tarragon, and thyme, can be added about the last 20 minutes of cooking. Add fresh herbs to refrigerated cold foods several hours before serving; this helps the flavors to blend.
An indoor herb garden is a sensory experience, adding fragrance to the kitchen, beauty to the eye, and flavor to food – flavor that can help reduce the need for salt, fat, and sugar. Researchers are finding that many culinary herbs (both fresh and dried) have antioxidants that may help protect against diseases such as cancer and heart disease. Providing sufficient light is the most challenging part of growing herbs indoors. When herbs are grouped in containers, make sure the selections have compatible light, water, temperature, and humidity requirements. An herb garden can be a selection of plants, or just one or two favorites in single pots. Extend the growing season, and have some fun!
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