You can grow fennel plants for both their seed and vegetables. It’s best to sow seeds outdoors in a prime location with well-draining soil and plenty of sun so you won’t need to transplant them later. Space seeds 12 inches apart, cover with a thin layer of soil, and water. Keep your beds weeded and watered, ensuring plants are kept dry to prevent mildew. Harvest for vegetable in late summer or early fall, or for seeds a few weeks into fall.
If you want to continue keeping your fennel plants indoors permanently, you can begin growing it indoors. However, fennel isn’t easy to transplant, so if you are looking to eventually plant it in your garden, it’s best to sow fennel seeds into your garden from the start.
You can plant your fennel seeds in late spring, after your region’s usual last frost. It’s best to find the perfect location for your plants so you won’t have to transfer them in coming years when they return. Fennel needs a garden area with well-draining soil and full sun exposure.
Raised garden beds are perfect for fennel, whose soil you’ll need to hill after you plant. Remember to keep fennel away from other garden plants, as it can easily cross-pollinate and produce odd-tasting mixtures. The best spot for fennel to grow is toward the back of the garden, in its own garden bed, or in pots in your garden.
Before you plant fennel, prepare its soil. Dig up the garden bed to loosen its soil, since fennel needs plenty of drainage. If you have a heavy or clay soil, you can add in sand to help it drain. Then, add in a compost or fertilizer for added nutrients.
Space your seeds about 12 inches apart, pushing them slightly into the ground. Fennel seeds only need a light layer of soil on top of them. To ensure maximum yield, you can plant more than one seed in one hole, and later, thin out the plants if needed.
Once you plant your seeds, ensure all of them are covered with soil. Water the soil thoroughly, taking care not to move the soil on top of the seeds.
If you end up getting an unexpected frost in your area after you have planted fennel, you can cover your seeds or seedlings with row covers to ensure protection.
Keep your fennel beds thoroughly weeded and watered. Once they are about 12 inches tall, you can add an organic fertilizer to your plants. Consider mulching in the early summer, once the ground begins to warm. This will keep your fennel plants in cool soil for optimal growth, and will help retain moisture in the soil.
Once your fennel begins to form a bulb at the base of its stalk, it’s time to begin hilling the soil. Fennel bulbs begin to grow above the ground rather than underneath, and you’ll want to keep soil on the bulb so it isn’t exposed to too much sunlight. As it grows, continue to check the bulb coverage and hill as needed.
If you live in a windy area, you may want to stake your fennel plants once they reach about 18 inches tall. Some fennel plants can reach heights of three feet or more, and can become damaged easily in winds.
Fennel is prone to certain pests and diseases if you aren’t careful about preventing them. Aphids, for example, can hide underneath fennel’s leaves and can be difficult to catch until there is a significant infestation. You may notice your fennel leaves yellowing or wilting, or molding on your plants from a sticky substance aphids create.
To cure fennel from aphids, you can spray your plants with a strong spray of water to remove aphids. Then, coat your plants with canola oil or insecticidal soaps to prevent them from infesting your fennel plants again.
Cutworms can also affect fennel by chewing through the plant stems, right by the soil level. They may be difficult to spot because they usually feed at night and hide through the day. You can prevent further infestation of cutworms by placing foil collars at the base of fennel plants.
Fennel is also prone to mildews if their leaves stay wet for too long, either from watering or from humidity in the air. This is why it’s important to keep fennel in a sunny location for ample drying time through the day.
Downy and powdery mildew can cause your fennel plants to turn yellow or wilt. You can help prevent these types of mildew by leaving plenty of space between fennel plants, planting in a sunny location, and avoiding excess watering and fertilization.
You can grow fennel for both its vegetable and its seeds. However, you can’t use a single fennel plant for both, so it’s best to plant several fennel plants so you can have some for each use, if desired.
If you’re harvesting fennel for its vegetable, you can harvest sooner than if you’re waiting for seeds. Fennel vegetables are usually ready for harvest in late summer or early fall, once the bulb of the plant is about the size of a tennis ball.
To harvest, you can cut the bulb at its base, right where it meets the soil. Keep the bottom of the bulb in the soil so its roots remain, and it will begin to produce more growth.
If you want fennel seeds from your plants, you’ll have to wait until later in the fall when the flowers begin to turn brown and the seeds are dry. Use a bowl to collect seeds from the plant. They usually fall off very easily, so be careful to catch them all so you don’t have random fennel plants growing in your garden next season.
Alternatively, snip the flowers and bring them indoors to collect, as shown in this video by Green Talk.