Ask a Master Gardener: Growing fennel | Home And Garden

Question: I have never grown fennel and would like to add it to my garden. I have been reading that there are many plants that should not be planted with fennel. I don’t know much about growing this plant and am curious. What information can you share?

Answer: It is actually best to grow fennel separately.

Fennel will actually inhibit the growth of nearby plants, especially bush beans, kohlrabi and tomatoes. Don’t plant fennel near dill because the two plants may cross pollinate and both will taste odd.

The ferny foliage and upright habit of fennel make this plant attractive when mixed with annuals or other herbaceous perennials. Plant it with butterfly weed (Asclepias tuberosa), coneflowers (Echinacea) and black-eyed Susans (Rudbeckia hirta).

There are two types of fennel. One, an annual bulb fennel, Foeniculum vulgare var. azoricum or Foeniculum vulgare var. dulce, is the crisp bulb vegetable with nutty anise flavor. The annual bulb fennel is a cool weather crop. It can be grown twice a year, in spring and fall, on a growing and planting schedule similar to that of broccoli.

Spring sown plants are more likely to bolt; however, there is a bolt-resistant variety called Zefa Fino which will produce large, firm bulbs in just 65 days.

Fennel is usually propagated directly from seed. Soak fennel seeds for a day or two for better germination.

If you are starting bulb fennel seeds indoors in early spring, plant seeds about eight weeks before your last frost, and set them out under cloches when they have one true leaf.

If you are sowing seed directly into the garden, a soil temperature of about 60 degrees is required to germinate. If you are planting a spring crop, it is best to use a soil thermometer so you aren’t guessing as to when the soil is warm enough.

Seeds should be sown at a depth of ¼ inch to 1 inch. Space plants at least 12 inches apart.

Start seeds for a fall planting of bulb fennel in midsummer, and set them out about eight weeks before your first fall frost date. Mix a standard application of a balanced organic fertilizer into the soil before setting out plants.

Fennel should be provided with regular irrigation to prevent stalks from splitting. Do not allow the plants to run dry once bulb formation has begun. Plants will benefit from the addition of nitrogen fertilizer but don’t overfeed the plants as it will result in a disproportionate amount of vegetative mass developing. Read the directions on the fertilizer package.

More is not better. This is true for all plants.

Fennel stalks should be cut just before flowering. Stalks are usually ready for harvest between five to seven months after planting. Seed heads should be collected promptly before they can scatter.

The seed heads are ready to harvest when they turn brown in color. Once the stalks have been harvested, the bulb can also be cleaned and stored.

Begin harvesting fennel bulbs after the bulbs are more than 2 inches across. Bulb fennel plants grown in the spring do not get extremely large and should be harvested before the weather turns hot. If you cut the bulb high, so that the root and the base of the bulb remain in the soil, the stub will regrow a couple of small crowns with miniature fennel fronds.

The second, a perennial herb fennel, Foeniculum vulgare, includes varieties blushed with bronze or purple, often called bronze fennel. Perennial fennel varieties with green foliage are used to produce fennel seeds grown for spice and medicine. The fine textured foliage resembles dill.

Flat topped clusters of yellow flowers appear in late summer. In western and central Oregon, fennel readily reseeds and can become invasive. Deadhead the plants to prevent unwanted reseeding.

Herb fennel will develop a deep tap root, so if you ever want to get rid of it, you will need to do some digging.

Deer will not bother your fennel plants, but rabbits might. The flowers on all varieties of fennel are very attractive to many beneficial insects including bees, small wasps, lacewings, as well as butterflies.

Fennel can be a challenging addition to your garden, and hopefully this information will help you make your decision.

Do you have a gardening question? Contact the Douglas County Master Gardeners via email at [email protected] by phone at 541-672-4461 or visit 1134 SE Douglas Ave., Roseburg.