Aside from adequate lighting, herbs require only water and fertilizer to thrive. It sounds simple, but applying them at the right time and in the right amounts is the key to happy, healthy plants.
One of the most important considerations when watering container herbs is drainage. Herbs thrive best in well-drained soil and both the pot and the soil should facilitate this process. Using coarse potting mixes and lining the bottom of the pot with gravel both help drainage. Excess water in the soil can cause molds, mildews and fungal growth, rendering the herbs inedible or killing them altogether.
The most effective way to water container herbs is to drench the soil until it begins to drain at the bottom, and then completely drain and remove excess water. This gives herbs the water they need without drowning the roots. Watering in small frequent amounts may not allow water to reach roots at the bottom, causing them to grow toward the surface of the soil.
After drenching and draining container herbs, it is best to allow the top 1-inch of the soil to dry before watering again. You can test with a moisture gauge or meter to see if your herb requires water, but you can just as easily use your thumb. If you feel moist soil before you reach the first joint of the thumb, wait another day or so to water.
Fertilizers, both organic and synthetic, provide vital nutrients and organic chemicals that herbs cannot get from the soil, with some needed in large amounts (primary) and others needed in smaller or trace amounts (secondary). Primary nutrients include nitrogen (N), phosphorous (P) and potassium (K), and their content in fertilizers is represented by three numbers separated by hyphens, such as 10-6-4 (N-P-K). Nitrogen supports color and growth, phosphorous aids root system development and potassium stimulates the immune system. Fertilizers containing nearly equal parts of primary nutrients are considered to be balanced. Secondary nutrients found in fertilizer are calcium, magnesium, sulfur, boron, iron and zinc.
When potting new herbs, both starter fertilizers, and compost can help to grow a healthy herb. Because phosphorous supports root systems, starter fertilizers rich in phosphorous can aid in establishing the herb. Also added to the soil during potting, compost is not only organic and healthy but is actually quite easy to create and is an excellent way to recycle organic kitchen waste, such as fruit and vegetable cores and peels.
Use a plastic bin or container with a tightly fitting lid at least 24 inches tall and drill small holes both in the lid and bottom. Line the bottom of the container with shredded newspaper, pine straw or dead leaves, and then add soil until the container is half full. Add waste scraps, stir to cover the waste with soil, and spray with water. Secure the lid and let nature turn waste into nutrient-dense compost, stirring every couple of days.
Synthetic vs. Organic Fertilizers
Although synthetic fertilizers are generally cheaper, many gardeners suggest using organic fertilizers because synthetics do not provide secondary nutrients and can contain salt that can eventually build up and leach moisture from the plant. Some organic fertilizers are fish emulsions, bone meal (1-11-0 or 5-12-0) and cottonseed meal (6-4-1.5 or 6-2-1).
Water-Soluble vs. Slow-Release Fertilizers
Two main types of fertilizers are water-soluble and slow-release. Water-soluble fertilizers are generally fast-acting and can correct nutrient deficiencies quickly when needed, but can also cause rapid growth resulting in a loss of flavor in the herbs. Slow-release fertilizers are generally granulated, require less maintenance and can last for months. Most retail fertilizers, both organic and synthetic, will have fertilizing interval times listed in the directions, indicating how long the product will provide nutrition.
Problems With Growing Herbs Indoors
Naturally, there are some potential problems that may arise with your indoor herb garden. The biggest of these is temperature and moisture. The inside air may be too dry during the winter months for some plants, and the plants will need some way to obtain additional moisture. One method that some people have tried is to place the herb container on a tray that is filled with pebbles and water. The water in the tray will evaporate and add humidity for the plant. Keep the tray filled with water as it evaporates.
Another way to help keep moisture in the soil is with a good mulch. The mulch will help hold the moisture in the soil, and it will help extend the watering times. Herbs should be watered early in the morning so the water can soak into the soil with less evaporation. Water the soil around the herb and not the leaves. Regular watering on the leaves can promote mildew as well as disease, so you want to avoid splashing the plant with water.
The containers that the herbs are planted in also need to have good drainage. Proper watering is one of the most essential aspects of growing herbs indoors. A general rule for proper watering is to water when the soil is dry when touched. Add enough water to the container for it to come out of the drainage holes, and then wait until the soil is dry before watering again.
Fungus, Mold and Mildew
Black fungus, leaf mold, and powdery or downy mildew can be a big problem with indoor plants and can even attract pests such as fungus gnats. You can eliminate a lot of fungus and mold problems by making sure you have appropriate air circulation.
If you do get mold or mildew, you might try copper sulfate spray on the area or, better yet, buy some organic oil spray which will not only treat mold, fungus, and mildew but also deter insects. These sprays made from oils like rosemary oil or sesame oil can be a bit expensive but they are totally organic and safe and a little bit goes a long way.
Since indoor herb plants can be prone to pests, they should be inspected regularly for insects, such as spider mites, white flies and other insects. The indoor plants are more apt to get these pests because there is no cold weather to kill the eggs of the insects, and the eggs will hatch and be seen crawling or flying near or on the leaves of the herbs in large numbers. Many herb gardeners use organic and homemade methods to get rid of these pests safely. Since the herbs are used in cooking, it is better to use chemical-free methods to control insects.
If the containers of herbs are easy to handle, to control these pests dip the plant part into a pail of soapy water that has been prepared especially for insects. Be sure to hold the soil with your hand to prevent it from falling out of the container. This can be done one or two times a week for several weeks to clear up these pests.
Another way to control the insects is to use the prepared soapy water in a spray bottle. Spray the leaves of the herbs with the soapy water. The eggs will hide on the underside of the leaves so be sure to spray under the leaves as well. Other natural ingredients can be added to the soapy water to help control insects. These homemade sprays should be used on the plants away from the direct sunlight since the sun can damage the leaves when they are wet with the spray. Herb gardens should be started with healthy plants for the best success since herb plants that are already infested with bugs will cause the other plants to become infected.
Herbs can grow well indoors if some consideration is used for the plants’ location. Each plant may require different amounts of light and moisture, and the location where the plant is placed will need to be matched with the plant that will grow best there. For instance, one type of fresh herb will grow good if placed on a windowsill indoors where it will receive adequate amounts of sunlight, but other plants will not do as well since they require less light. In addition, some herbs require humid areas to grow properly while others do not. For example, the rosemary herb requires dry soil, and it will not survive in moist and humid areas.
Signs to indicate that the herbs are not getting enough light is the length of the stems and the color of the leaves. Long stems and faded leaves or leaves that are falling off are good indications that the herbs need more light from the sun or some other source. Special lights can be used to provide the energy that the herbs need to grow sufficiently if there is not enough sunlight.