If you are growing basil indoors then you are going to be using a pot or other container, which can make maintaining proper moisture levels a challenge. Basil thrives in soil that drains well, so you will want to use soil that prevents standing water. So, rather than using soil from your garden in your pots, it may be better to buy a coarse-textured growing mix at the store. If you use soil that is too heavy or dense, you run the risk of having poor drainage. Contrary to popular belief, lining the bottom of your pot with gravel or rocks will not improve drainage but it will certainly inhibit plant growth.
The side-effect of having good drainage is that you will need to water container-bound herbs more frequently. So how often and how much should you water? Water when the soil is dry. If you can stick your finger a half inch into the soil and it feels dry, it is time to water. What is the best way to determine how much water to use? When planting, if you leave about a quarter-inch or half-inch of space between the top of the soil and the rim of the pot you can water to the top of the pot and that will be roughly the right amount. If you don’t want to worry about watering it consistently, you can use a special container such as the EarthBox which uses a reservoir to water your plants gradually over time.
Supplying your basil plant with proper nutrition is another challenge when growing in pots. Compost releases nutrients over months and years, more slowly than synthetic fertilizers, and may not provide all the nourishment desired for your container-bound plant. If you do use a fertilizer, we recommend using a relatively weaker mix or a diluted solution, and you can apply this every 3-4 weeks if needed. Please see the fertilizer section of care and maintenance where this topic is further discussed.
Pots and Containers
There are many types of pots and containers that you can use for growing basil indoors.Clay pots are porous and so you will likely be watering more often if you use these but the soil stays cooler in hot climates. Plastic containers are light and inexpensive and retain heat a little better for slightly cooler climates, but they tend to crack with age. Stone or concrete containers are durable but heavy, and likely something you won’t use indoors. Regardless of the container you choose, if you are reusing an old pot you may want to sterilize it first. Sometimes disease can persist from one plant to another if the same infected soil or pot is used. To disinfect, use a mild cleanser, soak the pot and then scrub and rinse it well. This will prevent any existing disease from spreading.
A common question people ask is regarding how many seeds they should plant. It depends on the container that is being used. With a long window box I recommend scattering a bit of seed along the length of the window box and thinning the weaker plants as needed. Once the plants are an inch or two tall you can use a spoon to dig under the roots and move them to better locations. With round containers, sowing a few seeds an inch or two apart should do the trick. Your basil seeds should be sown thinly and covered with approximately a quarter-inch (0.5 cm) of compost or fine soil. Keep the soil moist with a spray bottle and germination should occur within 5-7 days. New seedlings have two broad, “D”-shaped seed leaves. Once the seedlings have two pairs of true leaves you can thin out the weaker seedlings. Thin the plants to be 6-12 inches apart. Refer to care and maintenance for more information about tending your plants.
If you are using natural light you will want to place the herb as close to a window as possible. If you reside in the northern hemisphere, the plant will do best if placed near a south-facing window where it can receive at least 6 hours of sunlight a day. Basil can also be grown indoors using artificial light. You can use fluorescent grow lights or specially designed high-intensity lights. A basic high output fluorescent grow light can be had for less than $60 USD. One very good compact fluorescent grow light, which is quite inexpensive, is the Hydrofarm FLCDG125D 125-Watt Compact Fluorescent Grow Light System. Whatever your choice of lighting, normal fluorescent lamps should be kept a couple of inches from the tops of the plants. High output fluorescent and compact fluorescent lamps should be kept one foot above plants. High-intensity discharge lamps should be kept 2-4 feet above plants. To simulate a natural habitat it is recommended to have a fan rustling the seedlings at least two hours a day.
For more information on grow lights and best practices for growing basil, visit our page Artificial Lighting for Growing Basil.