Learn About Basil
How to Sow
Basil may be grown from seed sown early indoors and transplanted outside after frost, or sown directly in the garden, or planted as a potted plant.
Sowing Seed Indoors:
- Sow basil seeds indoors 6-8 weeks before the last frost in spring using a seed starting kit
- Sow seeds ¼ inches deep in seed-starting formula
- Keep the soil moist at 70 degrees F
- Seedlings emerge in 7-14 days
- As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
- Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
- If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 3 pairs of leaves before transplanting to the garden so they have enough room to develop strong roots.
- Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.
Sowing Directly in the Garden:
- Direct sow in average soil in full sun after all danger of frost when the soil is at least 60 degrees F.
- Remove weeds and work organic matter into the top 6-8 inches of soil; then level and smooth.
- Sow seeds evenly and cover with ¼ inches of fine soil.
- Firm the soil lightly and keep evenly moist.
- Seedlings will emerge in 7-14 days, possibly longer in cooler soils.
Planting in the Garden:
- Select a location in full sun with good rich moist organic soil.
- Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Carefully remove the plant from its pot and gently loosen the root ball with your hands to encourage good root development.
- Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand.
- Use the plant tag as a location marker.
- Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water and reduce weeds.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
- Mulches also help retain soil moisture and maintain even soil temperatures. For herbs, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
- Keep plants well-watered during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It’s best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated. Basil should not be allowed to dry out.
- Pinch the stems to encourage bushiness. Pinch flowers off to prolong the harvest.
- Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
- Discard plants after they bloom.
- Pinch leaves from the tips of the stems as needed starting 60-90 days after the seedlings have two sets of leaves.
- If fresh, pick early in the morning for highest oil content.
- For drying or freezing, harvest leaves that have their maximum oil content, just before flowering.
- To harvest the leaves, pinch the stems just above a set of leaves as needed from the top. This will also help keep the plants bushy.
- Do not harvest too much of the plant at one time as this may weaken the plant.
- Flowers are also edible and may be used as a garnish.
- To dry, cut whole stems on a dry morning. Tie stems loosely together in small bunches and hang in a dry, airy location out of the sun. Basil may also be dried on a cheesecloth or a window screen in a dry, shady location. When thoroughly dry, store in a tightly sealed glass jar in a dry, dark location.
- Basil may be frozen dry on a cookie sheet and then sealed in zip lock bags, or it can be minced and frozen in an ice cube tray in water or olive oil.
- You can also preserve basil using sea salt. Place a layer of sea salt on the bottom of the container you will use. Place a leaf on top of the salt. Add a layer of salt to cover the leaf so the leaves do not touch each other. Make as many layers are you have room for and seal the container and place in the refrigerator.
Common Pests and Problems
Common Disease Problems
Bacterial Leaf Spot: Water-soaked brown or black spots appear on the leaves and streaking on stems. The spots are angular or irregular in shape. Burpee Recommends: Avoid planting in the same location in the future, planting in containers can help. This disease may not kill the plant.
Botrytis Blight: Also called gray mold, this causes a brown to gray fungus on plant leaves and stems. Diseased leaves die and fall off. If the infection is severe on the main stem the plant may die. The condition thrives in high humidity and cooler temperatures. Burpee Recommends: Remove infected plants and plant debris and clean tools before working with plants to avoid the spread of the disease and make sure plants have good air circulation.
Downy Mildew: Leaves turn yellow around the middle vein and the disease spreads, eventually turning grayish purple and fuzzy. Burpee Recommends: Make sure the plants have plenty of air circulation, avoid getting water of the foliage when watering, remove infected plant material. Do not plant susceptible plants in the same location next year. Planting in containers can help.
Fusarium Wilt: This soil borne disease causes stunted and wilted plants and yellowish leaves. Brown streaks may occur on the stems and later signs of the disease are twisted stems and leaf drop. The stem tissue is discolored. Burpee Recommends: Because the spores live many years in the soil, do not plant any members of the mint family in the same area. The disease is worse in poorly drained soil. Plant in containers.
Root-Knot Nematodes: Classified as either a disease or pest, nematodes are microscopic worms feeding on the roots and may cause what looks like a nutrient deficiency, wilting and poor growth. Burpee Recommends: Avoid planting in the same area as the nematodes are difficult to eradicate. Plant in containers.
Common Pest and Cultural Problems
Plants die after blooming: Basil is an annual that will stop producing after it blooms. Pinch off the flowers before they set seed to prolong the life of the plant.
Leaves turn black overnight: Basil is very sensitive to cold temperatures and will turn black with any frost.
Aphids: Greenish, red, black or peach colored sucking insects that can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Japanese Beetles: Burpee Recommends: Hand pick early in the morning into a bucket of soapy water.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Why does my basil taste bitter? Your plants have probably started to flower in the heat of summer and this will make the leaves taste bitter. At this stage the plants will no longer be productive.
How can I use basil in a vinegar? Take clean leaves of fresh picked basil. Use about ½ cup of fresh herbs to a pint of distilled white vinegar. Pour the vinegar over the basil into a clean glass bottle, cover tightly and place in a sunny location for two weeks to steep. After this time you can strain the liquid and rebottle if you prefer a clearer liquid. Taste the vinegar, and if you prefer it to be stronger add more leaves and steep for another two weeks.
How many plants do I need to make pesto? Six plants of a large leafed variety would be ideal for making pesto.
What is the best basil to use to make pesto? We recommend Genovese for pesto.
Can I grow basil hydroponically? Yes, basil works well as a hydroponic plant.