How to Grow Basil Herb from Seed

  • Days to Maturity: Annual, requires a sufficient summer
  • Planting Depth: 1/4-inch below the soil, just a light fluffy covering
  • Plant Spacing: 12-18 inches apart to allow room for branches to spread
  • Growth Habit: Will grow tall if unkempt; a well-trimmed basil plant should be fairly bushy
  • Soil Preference: A well-draining, rougher textured soil provide the aeration that basil needs
  • Temp Preference: A long period of warmth and heat
  • Light Preference: A long season of full sun is preferable
  • Color: Ranges from deep and pale green to cool purple and vibrant red tones
  • Flavor: Anise and licorice-like flavor with sweetness
  • Availability: See All Basil Herb Seed Varieties
Basil Herb Grow Guide Pic

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How to Understand Different Basil Varieties

Most popular basil varieties are cultivars of sweet basil (ocimum basilicum), with a few hybrid exceptions such as lemon basil (Ocimum basilicum X Ocimum americanum). Although native to tropical regions such Southwest Asia, sweet basil cultivars are annuals, even in warm tropical regions, basil will not produce indefinitely when prevented from bolting. It is the nature of these basil varieties to complete their lifecycle and go to seed. However, an exception is the hybrid, African Blue Basil (Ocimum basilicum X Ocimum kilimandscharicum) and Holy Basil (Ocimum teneflorum), AKA Tulsi, which is similar to basil but an altogether different species. Spice basil is sometimes marketed as "Holy Basil". These plants are grown as perennials in the regions they are native to.

In regards to hardiness zones, basil can be grown just about anywhere in the United States, as long as you have a good 60 to 90-day period of good sunlight.

Germinating Basil Herb Seeds

Most commonly, basil seeds are started indoors 3 to 4 weeks before the last frost with the intention of transplanting outdoors when temperatures are right. Start in plug trays or pellets and place in a warm spot. If you plan on keeping your basil outdoors but in a growing container, such as a pot, through the season, start your seeds in that pot. Make sure soil doesn’t go below 72 degrees during the germination phase, which takes 8 to 14 days. Once seeds sprout, move plug trays or growing container to a location where there is full sun. The seedlings must receive at least 6 hours of direct sunlight or 10 hours of artificial light each day to survive. The same rules apply if you opt to grow basil indoors for it's entire lifespan. Simply provide a container with at least 8 inches of soil depth and make sure that the container is in a suitable area with plenty of sun.

Sowing and Transplanting Basil

After about 3 to 4 weeks or when your local climate is well past the last frost date, it's time to get your basil outdoors. Whether you chose to plant in a container or a plug tray, your basil seedlings will need to be "hardened off", a process by which you acclimate the seedlings to outdoor temperatures and conditions by placing them outside for increasing periods of time. Over about two to three weeks, you basil seedlings should be able to be outside through the night. To place your tender seedlings outside for an entire day and night right away will most likely lead to transplant shock. If you opted to house your basil in a growing container, simply, place that container in a very sunny area. Otherwise, choose the place where you wish to transplant your basil seedlings permanently. Near tomatoes is recommended--see Companion Planting Section. Water upon transplant and allow the ground to become a little dry—a light-and-fluffy dry, not a dusty dry before watering again.

At this time you may also decide to direct sow your basil seeds outside in the soil which they will spend their lifespan. Simply, sow the seeds in the ground or container that you wish them to grow in where there is plenty of light. Basil benefits from a layer of mulch that will protect the soil in the prime heat of midsummer.

Growing and Maintaining the Basil Plant

Although basil loves the light and heat, it can burn or wilt under the extreme heat of midsummer. Mulch helps to keep the plant hydrated but shade cloths can offer reprieve from the extremities of the season. At the very least, you want to prevent the basil plant from bolting in the high heat. "Bolting" refers to the process by which the basil plant flowers and sets its seeds.

Basil plants showing signs of wiltingBasil plants wilting in the high heat

Water basil sufficiently but not too much. If the ground is still somewhat moist and the basil plant appears to be healthy, hold off on watering until soil dries out a bit. If your basil plant has wilted, either cover it and water immediately or plant the its growing container to a shaded area and water. Leave the plants that way for at least a day or until basil perks up. You may need to remove some leaves that are damaged beyond rejuvenation.

Harvesting Basil Leaves and Sprigs

Basil is a prolific herb, often classified as a "bumper crop", meaning it is a garden plant that has an unusually productive yield. To ensure this "over-productivity" of basil leaves, begin pruning the herb when it reaches 6 inches tall. Gently pinch the top set of leaves at the stem so the the two sets of leaves will branch out and develop further. This technique will lead to a bushier basil plant, and the bushier the basil plant, the more leaves to harvest. If your basil plant bolts, the resulting flavor of the leaves with be diminished and the texture leathery, even after you pinch off the flowers. Keep a close eye on basil during these hot days and pinch the tops where buds form. 

Pruning the plants before they set flowers will keep the plant producing fresh leaves throughout the season. This means a good pruning about once a month. A shot of liquid nitrogen fertilizer, at pruning time if your soil is not particularly fertile, will help the plants recover. Eat basil often and dry or freeze leaves throughout the summer. You can certainly get bountiful harvests from basil well into the waning summer and dawning fall. 

How to Treat Possible Basil Herb Diseases

  • Fusarium Wilt - common among sweet basil varieties, which happen to be most of the popular basil cultivars. Signs of fusarium wilt are stunted growth, wilted/yellow leaves, brown spots/streaks, twisted stems, and leaf drop. What causes this disease is a fungus in the soil. Unfortunately, the only way to combat fusarium wilt is to destroy the affected plants and turn soil over. Avoid planting in that spot for at least a year.
  • Leaf Spot or Shoot Blight - caused by the Psudomonas cichorii fungus when soil is splashed on the leaves of the plant as a result of sloppy watering. Treat by keeping leaves and stems of the plant dry. Don't over water and make sure that your soil has adequate drainage, which helps the roots to be able to breath. Good air circulation in general helps to remedy and solve these issues.
  • Downy Mildew - Signs of down mildew on basil are yellowing leaves and a fuzzy growth on the underside of the leaves. It usually is a result of the soil being too saturated with moisture. To treat, avoid watering the soil until it has sufficiently dried out a bit—the semi-dry, semi-wet kind of soil that basil loves. When you get that soil to that stage, keep it there. The idea is to keep oxygen circulating through the soil.

How to Treat Possible Basil Herb Pests

  • Japanese Beetles - a pest common in the summer just before temperatures get rise. Japanese beetles eat the leaf of the basil plant but not the veins, creating a holes much like the holes in swiss cheese. Remove them by hand.
  • Slugs - Too much water can be basil's worst enemy because slugs are a result of overwatering in addition to the aforementioned diseases. Likewise, attempt to dry out the soil by ceasing watering. Pluck off what slugs are present. The drier new drier condition of the soil will prevent them from returning.
  • Aphids and whiteflies - Probably the most common and infuriating pest that plague the vegetable garden, and although rare among basil plants (because of the natural repellant in the oil of basil), they can still end up on the leaves of your plant. Both aphids and whiteflies are small green or yellow pests, either with or without wings. The best and most common solution is to physically remove them by either spraying the leaves gently with water or sucking them up with a vacuum on its lowest setting. The key is to catch the infestation as early as possible, then introduce beneficial insects to the area, such as ladybugs, lacewings, and plastic wasps. Keep a close eye on your basil plants and continue to remove the tiny insects as they appear.

Can I Grow Basil Year-round Indoors?

If you provide the perfect conditions for basil to grow and you continue to pinch off developing branches as to keep it from bolting, you can keep it alive for a very long time--up to 6 to 9 months is the general consensus among gardeners. This is most likely due the fact that it IS and annual and it wants to bloom and go to seed--that is it's mission, so-to-speak. It is in basil's genetic coding to go to seed. If attempting to keep it year-round, the plant will eventually begin to yellow and weaken until it gives up producing altogether.

What do I do with Basil at the End of the Season?

Outdoors, basil should continue to produce up to 4 to 6 weeks before the first frost of the year. If growing in containers, you can opt to bring them indoors (in a place where they will continue to get enough light) where you can promote the longevity of the plant until its inevitable decline. Otherwise, about a month before the first frost, clip the plant at the main stem and harvest what leaves you can and make an end-of-year pesto. You can choose to pull up the entire plant to clear the space for next year's garden.

How to Store and Dry Basil

Basil leaves can be stored as you would leafy greens; place them a plastic baggie with a corner open and place in the refrigerator. Otherwise, you may dry your basil leaves and save them for later. Simply, place your leaves on a baking sheet and place in your oven at the lowest setting. After a few minutes they should be dry. Crumble and place in an airtight container and store with your other spices.

Is Basil a Good Companion Plant?

Short answer, yes. It just depends on what it is a companion plant for. In general, basil helps to attract beneficial pollinators while warding off harmful ones.

  • Asparagus - When planted near asparagus can repel the asparagus beetle—asparagus' worst nightmare.
  • Borage - borage actually is more of a companion to basil, enhancing the flavor of basil leaves. They also look very pretty together.
  • Chamomile, Oregano, and Chives - when planted near these herbs specifically, there is a mutually beneficial relationship where they enhance the essential oil content of each plant including basil. Avoid planting next to sage and rue, as they will inhibit each other's growth.
  • Marigolds - basil and marigold are a pest fighting team and are often planted together alongside crops to ward of common pests.
  • Tomatoes and Peppers - Basil is known to ward of the tomato hornworm, making them a best friend of tomato. Basil, while repelling pests, can also help to trap heat and humidity for peppers if planted in fairly close clusters around your pepper plants.
  • Root Vegetables - root vegetables have leafy tops that attract aphids and whiteflies, which basil can work to repel.

Read the Best Practices for Planning Your Herb Garden!

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