All About Basil: Answers to Frequently Asked Questions About Growing, Storing, and Cooking with Basil

Basil, Image Courtesy of James Barker,

Basil is an attractive herb available in shades of green and purple (though purple basil is not as sweet). In addition to the classic sweet basil, there are specialty varieties available, including cinnamon basil, clove basil, licorice basil, lemon basil, and spicy Thai basil.

When can I plant basil?

Plant basil outside in the spring when there is no more risk of frost, or start seeds indoors 6 to 8 weeks before the last anticipated frost (if you’re not sure about your last frost date, Google “last frost date” and your city or state/province; if the information isn’t available for your location, search for the nearest major city).

Basil seeds are most likely to sprout at 70 Fahrenheit (21 Celsius), though some seeds may sprout at a temperature as low as 60 Fahrenheit (16 Celsius).

Most sources recommend starting basil indoors April through June, or outdoors sometime in late May through July, depending on the local climate. If you start basil plants indoors, they’ll be ready to go out in 4-8 weeks. Don’t transplant until there are at least 2-4 pairs of true leaves.

If you start your plants indoors, make sure they’re in a well-ventilated area and the soil is kept moist but not soggy, because waterlogged plants in poorly ventilated areas are vulnerable to being killed by fungal infection (damping off).

You might be able to plant or transplant basil outdoors a little early if you provide some protection against cold nights, such as a cloche, cold frame, or greenhouse.

You can succession sow basil every 4 weeks or so in the late spring and summer for a more bountiful harvest.

Where should I plant basil seeds or transplants?

Basil requires a sheltered and, ideally, sunny spot. Many people grow basil near tomatoes because they believe it improves the flavour of the tomatoes and repels pests.

How deep should I plant basil seeds?

Plant basil seeds 1/4 inch deep.

Can I grow basil in a container?

You can grow basil in a container of any size, but to get full-sized plants, you’ll need one that’s at least 8 inches deep .

Basil can be grown in containers indoors year-round, provided you can give it a sunny spot or a grow light.

Can I grow basil in the shade?

Most sources recommend planting basil in a spot that gets at least 6 hours of sun per day, though I’ve found that it grows quite well in a sheltered, shady location, as long as temperatures are warm.

How long will basil seeds take to sprout?

If temperatures are warm enough, basil seeds should sprout in 5-10 days.

How big do basil plants get?

With sufficient space, basil grows 12-24 inches high and 6-12 inches wide, though you can grow smaller basil plants in little containers.

It’s important to give basil enough space between plants, because growing it too densely increases the risk of fungal and bacterial diseases. It will do better if the leaves have the space they need to dry quickly and thoroughly after rain.

Don’t grow more than 3-4 basil plants in a square foot of garden or container space, and allow at least 6 inches of space between plants (more for bigger plants).

What type of soil does basil need?

Basil grows best in nutrient-rich, moist, well-drained soil. Add some compost or well-aged manure to the top 6 inches of soil before planting. Vermicompost (worm compost) is an excellent addition that will increase the size and health of your plants.

What ongoing care does basil need?

Water regularly to keep soil most but not waterlogged. If you allow basil plants to dry out, they may bolt (put their energy into flower and seed production rather than leaves), but if you overwater, they’ll be more vulnerable to fungal infections.

Weed regularly so that the plants don’t have to compete with interlopers.

Mulch to retain moisture if your summer is hot and dry.

Regularly trim or pinch off the top leaves to encourage the plant to grow bushier and produce more leaves overall. This should be started when the plants are round 6-8 inches tall.

Remove flowers if they appear so that the plants will put their energy back into leaf production.

Should I fertilize basil?

There are many different recommendations regarding basil fertilizer timing, ranging from feeding once a week to once every 4-6 weeks, and an equally large number of recommendations regarding the type of fertilizer to use, so there is obviously no consensus on the subject. Some say you don’t need to fertilize at all if you’ve amended the soil with plenty of organic matter (compost) to begin with, and I’ve found this to be the case. My basil grows very well in a good quality potting soil (which typically contains some fertilizer) amended with worm compost, and I’ve never bothered adding additional fertilizer.

How long does basil take to grow?

Sweet basil, the most common kind, is usually big enough to start harvesting within about 30-60 days, though early harvests will probably be small.

When can I harvest basil?

You can start harvesting basil when the plants are around 6-8 inches tall and have multiple sets of true leaves.

Harvest all your plants completely if you’re expecting frost – basil plants are easily killed by cold. Alternatively, you can put them in pots and bring them into the house or a greenhouse to extend the harvest season.

How do I prevent slugs from eating my basil plants?

See How to Get Rid of Garden Slugs: Natural, Non-Toxic Solutions.

How do I stop aphids from eating my basil plants?

The easiest (and safest) way to get rid of aphids is to regularly blast them off with the hose. You can also divert them with a more appealing trap crop, such as nasturtiums.

Why does my basil have dark blotches?

This problem is usually caused by bacterial or fungal infection, nutrient deficiency, or cold temperatures killing off parts of the leaves.

Fungal infections often cause streaks on the stem or fuzz in addition to discoloured spots or blotches, whereas bacterial infection usually just causes dark spots. If you believe the problem is an infection, trim off the affected leaves if the infection is minor and localized, or remove the plant from the garden altogether if it is more extensive. If plants are too crowded, separate them or trim their leaves to allow for better air flow.

Potassium deficiency will usually affect the older, lower leaves. This problem may be caused by deficient soil or insufficient water (plants need water to absorb potassium from the soil).

If you believe the problem is cold temperatures at night, trim off the affected leaves and provide some protection against the cold, such as a cloche, cold frame, or greenhouse, or bring your basil plants indoors and keep them on a sunny windowsill.

Can I still harvest and use basil after it flowers?

Flowering Basil
Flowering Basil, Image Courtesy of Stoonn,

Yes. It won’t get really bitter like lettuce, though the leaves may not be quite as sweet. Just pinch or cut the flowering tips off and continue harvesting (if you don’t remove the flowers, basil plants will put more of their energy into making seeds rather than leaves).

Basil flowers are edible. If you plan to use them (some people like to add them to salads or sauces), pick them when they’re young and tender, before they produce seeds.  I haven’t tried eating them, but others say that they have a stronger flavour than basil leaves, and that they can become tough and chewy if left on the plant for too long.

How do I store basil, and how long will it keep?

You can store sprigs of basil in a vase or cup on the counter for a week or so with the stems submerged in a bit of water (change the water every couple of days). You can also store it for couple of days in the fridge in a plastic bag, though it will go off and turn black quite quickly in the cold (some sources recommend wrapping it in a damp paper towel to extend its storage life in the fridge a little).

For longer storage, basil can be frozen. There are a few techniques for this, the simplest of which is to chop basil leaves, add them to ice cube trays, cover them with water, and freeze. Once frozen, transfer the cubes to sealed freezer bags or containers. When you want to use them, just pop the herbal ice cubes into your soups or sauces. They should keep for around 4-6 months. Some people puree basil in a food processor, mix it with a bit of olive oil, and freeze the mixture in containers.

Basil can be dried, but it doesn’t retain its flavour as well as other herbs when stored this way. Drying needs to be done quickly, or the leaves will turn black. Oven drying is a fast and easy way to dry basil. Put the leaves on a baking sheet lined with parchment paper and bake for 2-4 hours on the lowest temperature setting. Then let the leaves cool, crumble them, add them to airtight containers, and store them in a cool, dark place. If you don’t want to oven dry your basil, you can spread the leaves out on paper towels to dry. If properly dried and stored, dried basil leaves should keep for at least a year.

How do I save basil seeds?

Basil is grown as an annual plant, and you can save seeds to grow it each year.  If you want to save basil seeds, just let the plants flower, but don’t collect seeds from the first plants to flower – it’s better to select seeds from plants that are slow to bolt, as these are the type you’ll want to grow.

Cut off the flowerheads when they’ve turned brown and let them dry for a few days in a warm, dry location. Then crush the flowerheads in a colander to separate the tiny seeds from the other plant material. Place the seeds in a sealed container and store in a dark, cool place.

Basil seeds keep for approximately 5-8 years when properly stored.

Bees will cross-pollinate different basil varieties, so don’t grow different types within 150 feet of one another if you want to save seeds.

You can also grow basil from cuttings, which is faster than starting it from seed.

What are the health benefits of basil?

Basil is rich in health-protecting antioxidants, and research indicates that is an anti-inflammatory food, and may be particularly effective for promoting cardiovascular health.

How do I use basil?

Making pesto is a popular way to use basil, and pesto can be frozen for longer storage.

Basil is also delicious in tomato sauces.

Caprese Salad
Caprese Salad, Image Courtesy of Tiramisustudio,

Raw basil leaves can be tossed into salads, either as mature leaves or microgreens. One of the most popular basil-based salads is the Caprese salad, which includes basil leaves, tomato, and mozzarella, usually topped with a balsamic reduction or a drizzle of olive oil, salt, and pepper.

Basil works well on bruschetta or pizza, especially with recipes that include tomato and mozzarella cheese.

Basil can be chopped and tossed with olive oil and garlic for a nice, light, healthy salad dressing.

For more vegetable and herb gardening articles, see the main Gardening page.


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