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Growing basil from seed should be on every gardeners to-do list. Why? Basil is easy to grow from seed and when you buy seeds instead of transplants you can choose from dozens of types and varieties available through seed catalogs. There are two ways to start basil seeds: indoors in a window or beneath a growlight, or by direct seeding outdoors. Keep reading to learn more about the simple steps of growing basil from seed.
Basil (Ocimum basilicum) is a tender annual herb grown for its aromatic leaves that are added to fresh and cooked dishes. Sweet basil, also called Genovese basil is the most widely grown due to its delicious anise clove flavor. There are many other types of basil available through seed catalogs including lemon basil, Greek basil, cinnamon basil, and Thai basil. Each one offers a variety of flavors, forms, leaf sizes, and even colors. Basil is often planted with tomatoes and peppers because they have similar growing conditions – well draining soil and 8 to 10 hours of sunlight. Basil is also used in companion planting as the mid to late summer flowers attract bees and beneficial insects to the garden.
Wondering if it’s worth your time to grow basil from seed? It absolutely is! Here are my four reasons for starting basil from seeds:
There are two ways to grow basil from seed. First, you can start the seeds indoors on a sunny windowsill or beneath grow lights. Eventually the young plants are transplanted into the garden. The second method is to direct sow basil seeds in garden beds or containers. Let’s look closer at each method so you can figure out which one is right for you.
Most gardeners start their basil seeds indoors to get a jump on the growing season. Success begins with sowing the seeds at the right time, 6 to 8 weeks before the last frost date. In my zone 5 garden that’s late May so I start my basil seeds indoors in late March. Sowing the seeds indoors even earlier doesn’t necessarily give you a head start on the basil harvest. It just means you’ll have bigger plants that need to be re-potted into larger containers. And they’ll take up a lot of space on a windowsill or beneath grow lights. Plus, transplanting mature basil plants into the garden often results in bolted plants that begin to flower instead of pushing out lots of fresh leaves. This reduces the overall harvest. Younger seedlings adapt better to transplanting and should be moved to the garden when they’re 6 to 8 weeks old.
Now that we know when to sow basil seeds indoors, we can consider containers. I typically use 10 by 20 trays with cell pack inserts to start most of my vegetable, flower, and herb seeds. They offer an efficient use of space under my grow lights and I re-use them from year to year. However, you can start basil seeds in pretty much any type of container as long as it’s clean and offers good drainage. If you’re up-cycling items like salad containers for seed starting be sure to pole holes in the bottom for excess water to drain away.
To cut down on plastic use I’ve recently bought a soil blocker for seed starting. A soil blocker forms lightly compressed cubes of soil – no container needed. I have several sizes and look forward to experimenting with starting basil seeds this way.
When starting seeds indoors a lightweight seed starting or potting mix is essential. These mixes are typically made up of materials like peat moss, coconut coir, compost, vermiculite, perlite, and fertilizers. The ideal growing medium for seed starting is one that retains water, but is also quick draining to promote healthy root growth. You can make your own (check out our DIY potting mix recipes here) or buy a bag online or from your local garden centre.
Once you’ve gathered your supplies, it’s time to get planting. Fill your containers with the pre-moistened potting mix. When sowing basil seeds in cell packs, plant 2 to 3 seeds per cell. If starting basil seeds in 4 inch pots, plant 6 to 8 seeds per pot. Whatever type of container you are using for the basil seeds, sow each seed about an inch apart. Plant the seeds a quarter of an inch deep. The exception to this is holy basil whose seeds need light to germinate. Instead of covering holy basil seeds, gently press them into the moist potting mix to ensure good soil-seed contact.
After the seeds have been planted place a clear dome or a piece of plastic wrap on top of the trays or pots. This keeps humidity high to promote good germination. Once the seeds sprout, remove any plastic coverings so air can circulate.
When the young plants have developed two sets of true leaves, thin them to one plant per cell, or three to four plants per 4 inch pot. You can carefully prick the surplus seedlings from their containers and transplant them into more pots. Let’s be honest, you can never have too much basil!
Providing sufficient light is perhaps the biggest challenge when starting seeds indoors. Most types of vegetables, flowers, and herbs need plenty of light to form strong, stocky seedlings. Relying on natural sunlight from a window can be a challenge, especially for those who live in Northern climates. Seedlings grown in insufficient light are tall, leggy, and tend to flop over. The solution is to use a grow light to start seeds like basil.
I have two types of grow lights: LED grow lights and fluorescent grow lights. I leave my grow lights on for 16 hours each day using an inexpensive timer to turn them on and off. You can DIY a grow light set up or buy one from a garden supply store. When I’m not starting seeds I use my grow lights to provide light to succulents, culinary herbs, and other indoor plants.
Basil is a heat-loving herb and the seeds germinate best in warm soil. The ideal temperature for basil seed germination is 70 to 75F (21 to 24C) with the seeds emerging in about 5 to 10 days. If you have a seedling heat mat you can use it provide bottom heat to both speed up germination and increase germination rates.
Basil seedlings can be prone to damping off, a soil-borne fungal disease that affects the stems and roots of young seedlings. I’ve found the two best ways to reduce damping off is to water the seedlings properly and provide good air circulation. First, let’s talk watering. Basil seedlings grow best in lightly moist, not wet soil. Water when the soil is dry to the touch, checking seedlings every day to gauge soil moisture. The other consideration for preventing damping off is air movement. I keep a small oscillating fan in the room near my grow lights. Good air circulation helps strengthen the seedlings, reduces mold growth on the soil surface (a sign of overwatering), and dries the leaves after watering.
When basil seedlings have developed their first set of true leaves I begin to fertilize. I use a liquid organic fertilizer diluted to half strength every 14 days. This promotes healthy growth and plenty of bright green leaves.
Hardening off seedlings is the final step when growing basil from seed. This is a step you don’t want to skip. The hardening off process acclimatizes seedlings to the sun, wind, and weather of the outdoor garden. Because basil is sensitive to heat don’t move the plants outside while there is still a risk of cold weather. I begin the hardening off process, which takes about five days, after the last expected date has passed.
Start by moving the seedlings outside on a mild day, placing the trays or containers in a shady spot. Cover them with row cover that night or bring them back indoors. On day two, give the plants some early morning or late afternoon sun, but shade during from mid-morning to mid-afternoon when the sun is most intense. Again, cover them up at night or bring them back inside the house. On days three to five continue to gradually introduce the plants to more light until by day five they are ready for full sun.
Hardened off basil seedlings can be moved into garden beds or containers once the risk of frost has passed and the weather has warmed. Don’t rush basil outside, however, as cold damage can occur when the day or night temperatures fall below 50F (10C). Once the conditions are right, transplant seedlings into a site with direct sunlight and well-draining fertile soil. I add all purpose compost to my beds or containers before transplanting. Space basil plants 8 to 10 inches apart. When the plants have five to six sets of true leaves you can start to harvest basil.
The other technique for growing basil from seed is to direct sow seeds outdoors. Because I live in a cold climate, I start my basil seeds indoors to give the plants a head start. Gardeners who live in zones 6 and above, however, can direct sow basil seeds outdoors in a garden bed or container. Choose a sunny site and amend the soil with a thin layer of compost. Plant the seeds in late spring or early summer, about a week or two after the last spring frost. The soil temperature should be at least 70F (21C). Sow the seeds a quarter of an inch deep and one inch apart.
Once the seeds are planted, water the seedbed often with a hose nozzle on a gentle setting. You don’t want a hard jet of water which could dislodge or wash away the seeds or young seedlings. Don’t let the soil dry out as the seeds are germinating. Once the basil seedlings have developed two to three sets of true leaves, thin them 8 to 10 inches apart.
For further reading on growing basil, be sure to check out these articles:
Are you growing basil from seed this spring?
