How to Grow Basil

Author’s note: This post is based on my personal experience growing basil in my home garden. I’ve added information from additional resources to clarify some information and provide more details. Those resources are linked to at the end of this article. All of the images were captured by me in my garden.

Basil (Ocimum) may be the easiest herb to grow and the most popular herb for home gardeners. This aromatic, leafy herb is a tender annual and is popular in many types of cuisine. It can be started from seed indoors or bought in pots for transplanting in your garden. Give basil enough light and not too much water, and it will provide harvests of delicious leaves all season long. The best part is that these compact plants will equally thrive in your garden, in a pot on your deck, or in a small pot on your windowsill (providing it’s a sunny windowsill).

There are many types of basil, each with its own epicurean delights. There is Sweet basil, Lettuce Leaf basil, Spicy Globe basil, Thai basil, Lemon, Lime or Cinnamon basil, and opal basil, among others. Leaves may be ruffled, smooth, large, or small and appear in shades of green, red, or purple. Depending on the variety, basil plants are 12-20″ tall.

Basil is native to southern Asia and islands in the South Pacific, so it needs warm weather to thrive – even a mild winter will kill any plants left standing or any seeds in the soil. That’s why in most of the U.S., Basil is grown as an annual from late spring through early fall. But indoors, give it a warm, sunny spot, and your plan can survive for a year or more.

Did you know? Basil is a member of the mint family.

How to start basil seeds indoors

Basil is really easy to start from seeds indoors. Follow our seed starting directions here and sow seeds in pots 6-8 weeks before your last frost date. Basil definitely benefits from using heat mats, especially if your seed starting setup is in a cool room. Expect basil seeds to germinate within 5 days if your seed is fresh and you’re using heat mats, but up to 2 weeks otherwise. Keep the seedlings under grow lights (or in a very sunny spot) until it’s time to harden them off.

“Hardening off” is the process by which you adapt your indoor-grown seedlings to outdoor temperature swings and sunlight. While in their pots, place them outdoors in a sheltered spot for an increasing number of hours each day until they graduate to 24 hours outdoors for a few days. This period should last 7-10 days. Hardening off thickens the stems and strengthens the leaf structure gradually so they can better tolerate wind and weather once in the garden bed.

Buy on Amazon: Basil seeds for your garden.

How and where to plant basil

Plant basil in your garden around the same time you plant tomatoes – when days are above 70 degrees Fahrenheit and nights don’t drop below 50 degrees Fahrenheit. Choose a very sunny spot to grow your basil – it loves moderate heat and sun and needs 8-10 hours of sunlight each day. Although basil is a pretty forgiving plant, wind can damage it quickly – it benefits from being planted in the shelter of taller plants like tomatoes. It’s a great companion plant for tomatoes and peppers, and I grow mine on the sunny side of the tomato bed or between pepper plants.

Make sure your garden soil drains well, as basil won’t survive with damp feet. It prefers life on the slightly dry side (but not dried out). After planting, add 2″ of compost around the root zone to provide rich organic matter. Raised beds are best for adequate drainage.

If you live in an area with a long growing season, basil seeds can be sown in your garden after the threat of frost has passed. Cover with 1/8″ of soil. Outdoors, basil seeds typically germinate in 5-7 days. In other hardiness zones, plant seedlings at least one week after your last frost date. Plant the seedlings a little deeper than you would other vegetables – basil has the ability to grow roots along the stem, just like tomatoes do. This will help to anchor the plants in case of windy weather. Basil can also be grown in a pot indoors if you have a very sunny window or in pots on your deck or patio.

Basil Growing Tips

• Go light on the fertilizer—if Nitrogen is too heavy, basil plants will be very thin. I only use fish emulsion twice a season, and my plants thrive.
• Soil pH of 6.0-7.5 is preferred.
• Two to three inches of soft mulch, such as compost or straw around the plants, helps insulate the roots from weather extremes and suppresses weeds.
• Irrigate with one inch of water once per week in the absence of rainfall. Concentrate the water on the root zone and keep the foliage dry to avoid fungal diseases. If growing in containers, watering more often, usually daily, will be necessary.
• When plants reach 7 inches, pinch off the center shoot with a pruner. This encourages lateral growth of more leaves and discourages flowering. Keep pinching during the season to keep the plant producing lateral leaves. Allowing the plants to flower and set seed will shorten the growing season, and the stems will become woody and thick. Pruning and pinching will also force a higher concentration of oils into the leaves. Note that only pinching off the flowers will not produce lateral growth – you also have to prune the plant. After pruning, new leaves will emerge on your basil plants in 1-2 weeks.
• For season-long fresh basil, use succession planting – plant seedlings two weeks apart.

When to harvest basil

You can harvest basil at any stage – just smell the leaves. Carefully snip leaves from the stem and use them as you see fit – fresh on salads or sandwiches or allow them to dry for storage.

But timing is important to take advantage of the leaves at full strength. The oils in the leaf that provide the flavor and aroma are at full strength when the plant starts to flower. You can harvest the entire plant at this time or pick off leaves as you need them. As the summer progresses, the leaves will become less pungent, even if you pinch the flowers, but it’s a slow decline. Personally, I keep my plants in flower for a good month before harvesting the entire plant and drying the leaves for use over winter. But if you’re making pesto, pungency is key – so harvest the plant shortly after flowering.

Alternative harvest: Cut the entire plant to within six inches of the ground. Leave one node with one or two shoots. This “new” plant will produce leaves that are ready to harvest in about 2 weeks.

Pests and disease

The most common and most dreaded diseases of basil are Basil downy mildew and powdery mildew. Powdery Mildew on basil looks as it does on other plants – a nasty white coating that quickly kills the plant. Basil Downy Mildew turns the leaves yellow in spots, followed by black spots and gray spores. Either of these diseases make the plant inedible, so destroy the entire plant as soon as you see signs of infection (do not compost!). If powdery mildew and downy mildew are persistent in your garden, consider varieties that are resistant to the diseases. As the spores are windborne, these fungi are very difficult to control and will be more prevalent in a damp and rainy season.

Japanese Beetles are a common insect pest – the tell-tale sign is holes eaten in the leaves. Other pests include earwigs, centipedes, and bacterial leaf spot. The best defense is to use companion planting and keep the leaves as dry as possible when irrigating. Any infected plant parts should be immediately pruned from the plant and placed in the trash. Learn more about deterring Japanese Beetles.

Resources: Royal Horticultural Society, How to Grow Basil; University of Minnesota Extension, Growing Basil in Home Gardens; University Of Florida Gardening Solutions, Basil; Utah State University Yard and Garden Extension, How to Grow Basil In Your Garden; UC Master Gardeners, Santa Clara County, CA, Basil.