How to Plant, Grow, and Care for Phacelia
As one of the best multifunctional flowering plants, phacelia is remarkably underused in the garden. Former organic farmer Logan Hailey digs into how you can cultivate this easygoing wildflower for pollinator paradise, weed suppression, cover cropping, and more!
Any pollinator garden is incomplete without the marvelous fiddlehead swirls of phacelia flowers. This native California wildflower was initially cultivated as a honey plant because its blooms magnetize bees and butterflies. Today, phacelia is a cornerstone pollinator flower, a vegetable companion plant, and a weed-smothering cover crop.
The feathery foliage and stunning purple blooms are just as beautiful as they are functional. Better yet, phacelia is drought tolerant, deer resistant, and so easy to cultivate that it practically grows itself. This warm-weather flower eagerly produces nectar-rich blossoms all summer, drawing every bee in the neighborhood to your garden patch.
Let’s dig into everything you need to know about growing phacelia as a flowering ornamental, pollinator patch, cover crop, and companion plant.
Plant Type Annual herb
Plant Family Boraginaceae (Borage Family)
Plant Genus Phacelia
Plant Species tanacetifolia
Hardiness Zone Varies by species, 3-10
Planting Season Spring or fall
Bloom Time June to October
Plant Maintenance Low
Plant Height 2-4 feet
Fertility Needs Low
Temperature Winter kills at 20°F
Companion Plants Nasturtium, marigold, alyssum, calendula, vegetables
Soil Type Well-drained, loamy
Native California, Southwest, and Mexico
Plant Spacing 12-18 inches
Watering Needs Moderate
Sun Exposure Full
Days to Maturity 75-80
History and Cultivation
If you thought bee balm and salvia made the pollinators go wild, just wait until you see a patch of phacelia abuzz with activity. This lesser-known annual flower is an essential companion plant for any vegetable garden or wildflower planting. It attracts beneficial insects near and far, creating a thriving ecosystem of bees, hoverflies, and parasitic wasps. Moreover, it winter-kills after the first frost, leaving behind a luscious fluffy mulch of foliage perfect for weed suppression.
While the Phacelia genus contains over 200 species of annual and perennial herbaceous plants, this article will focus on the most popular cover crop and insectary plant, P. tanacetifolia, most widely available in garden stores and seed catalogs.
What is Phacelia?
Phacelia tanacetifolia, also known as lacy phacelia or scorpionweed, is a wildflower native to the Southwestern U.S. and northern Mexico. It grows to 1-3 feet tall and wide and blooms throughout the summer. It is used in gardens, vineyards, and agricultural fields as a cover crop and beneficial insectary plant. Its stunning coiling clusters of nectar-rich blooms, long flowering period, and striking lavender color have also garnered interest as a popular ornamental.
The word phacelia comes from the Greek phakelos, meaning “bundle,” referring to the flower spikes bundled in terminal fiddlehead-shaped clusters. The nectar-rich blooms open in sequence, creating an appearance of unfurling. The flowers are purplish-blue and bell-shaped, with five petals and five long stamens protruding beyond the bunch. The feathery leaves resemble tansy foliage and are covered in stiff, short hairs.
This striking member of the Boraginaceae (borage) family was recently reclassified as a member of the Hydrophyllaceae (waterleaf) family due to new molecular data, although some botanists consider the waterleaf plants as a subfamily of Boraginaceae. All complex taxonomy aside, phacelia has some relation to borage, forget-me-nots, and comfrey.
Why Grow Phacelia?
Phacelia is most popular for its insectary benefits. The nectar-rich flowers are tremendously beneficial for a range of helpful insects, from bees to predatory wasps to hoverflies. It also makes a great cover crop because the dense foliage quickly outcompetes weeds and dies back at the first frost, creating a thick layer of straw-like mulch.
Benefits to Your Garden
- Pollinator Attraction: The nectar-filled purple flowers of phacelia are irresistible to pollinators, especially bees. In peak summer, a patch of phacelia will be so full of buzzing activity that you can hear the party from several yards away. The honey from bees who forage on phacelia is also known to have superior mineral content.
- Weed Suppression: This fast-growing annual provides excellent weed suppression by shading out competitors with dense stands and smothering winter weed seeds with its mulch.
- Soil Improvement: The roots of P. tanacetifolia are very fibrous and reach up to 30 inches below the soil. The plant is known as a bioaccumulator because it “catches” excess nitrogen and other nutrients to prevent leaching or loss in groundwater. When you compost or mow down the patch, the nutrients are recycled into your soil, adding fertility and organic matter.
- Pest Control: Syrphid flies (hoverflies) and parasitic wasps are particularly fond of phacelia flowers. These natural enemies will feed on the blossoms and then fly to nearby vegetable crops to help control aphids and mites.
- Low Maintenance: Phacelia requires little to no maintenance besides a little water during extreme drought. No fertilization or weeding is necessary.
- Companion Planting: Growing phacelia near vegetables can improve yields by boosting pollination and reducing pest pressure. It is great for planting near tomatoes, peppers, squash, cucumbers, and other summer veggies in garden margins.
- Ornamental Value: The bright bell-shaped flowers in beautiful swirls are contrasted by feathery, lacy foliage that creates the perfect backdrop to low-growing flowers like white alyssum or marigolds. Phacelia is best for cottage gardens and less manicured wildflower patches, especially in open fields or borders where it can freely re-seed.
Is Phacelia Invasive?
Phacelia is a prolific self-seeder, but it is unlikely to become invasive in your garden. Only in some parts of the Northwest and Northeast can phacelia become an issue if frost does not kill it. If you are concerned with phacelia becoming a garden weed, mow it down or cut it back after the flowers bloom. Regular deadheading will prevent seed formation.
Sow phacelia from early spring onward in frost-free weather. The ultra-tiny seeds enjoy cool weather and need darkness to germinate. While you can start phacelia in cell trays indoors, direct sowing is most common.
You can seed phacelia in bare vegetable beds for cover cropping in late summer. The plant may not provide as much insectary benefit before fall frosts, but it will still accumulate enough biomass to produce effective weed suppression and fluffy mulch.
Prepare a seedbed around your last frost date by incorporating compost and raking smooth. The seeds need cool soil to germinate.
Direct seed thinly in rows of about six seeds per foot. Sow ⅛” to ¼” deep, but ensure the seed is lightly covered so the sunlight doesn’t dry it out. It needs darkness to germinate. For cover crops and wildflower mass plantings, broadcast about 3 ounces of seed every 1,000 square feet and then top with a thin layer of soil or compost.
Keep the surface moist until seedlings emerge in 7 to 14 days. For continuous blooms, sow 2 to 3 successions every two weeks through spring.
Phacelia does best when grown in mass plantings where large plant populations can shade out weeds and provide a safe haven for pollinators, but you can also toss a handful of seeds around garden borders and the edges of vegetable beds. The plants enjoy growing in clumps, but you can also thin to single plants with 10-12” of space from their neighbors. Remember that phacelia can reach 3-4 feet tall and shouldn’t be sown too close to any vegetables that dislike crowding.
Phacelia is commonly integrated into wildflower mixes like the Precious Pollinators Flower Mix, but you can also sow the seeds on their own for a dense patch of purple.
While direct sowing is the best option for bee forage and insectaries, you can transplant phacelia seedlings that you start indoors or purchase from a local nursery. Transplanting is a great option for ornamental landscapes and organized plantings in your vegetable garden.
How to Transplant
Starting phacelia indoors can give you a headstart on floriferous bee blooms earlier in the spring in regions with a short growing season. Sow the seeds in cell trays or pots in a cool indoor growing area about four weeks before the expected last frost. Remember, they need darkness to germinate, so be sure the seeds are well covered. Place the pots in a dark area until they sprout, then move them to a sunny location with plenty of bright light.
When transplants have filled out their pots and are ready to enter the garden (about 4-6 weeks after seeding indoors), amend the area with compost and loosen the soil as needed. Harden off the plants on a protected patio for a few nights before planting. Be sure they have at least two sets of true leaves and robust root systems.
Transplant phacelia seedlings as you would any vegetable start. Gently loosen the plant roots from the pots, holding it from its stem base. Use a hori hori or trowel to dig a hole a little bigger than the root ball and place the seedling in the hole. Backfill so the soil level remains the same. Avoid burying the leaves.
Thoroughly water in phacelia plants for the first week or two so they can get established. In cold northern areas, you may want to place a row cover over them to prevent transplant shock.
Space the seedlings 12-18” apart, giving them plenty of space to grow and flower in full glory. Phacelia transplants look great when lining walkway edges or interplanted amongst densely flowering insectaries like alyssum, calendula, and yarrow. If transplanting in a vegetable bed, be sure the phacelia has plenty of space to drape over the edge without crowding your crops.
How to Grow
Like most wildflower species, this beautiful lacy flower offers a lot of glorious beauty and benefits yet requires almost no care. If you can grow borage or forget-me-nots, you can easily grow this fuss-free relative!
Phacelia thrives in full sun to partial shade, making it suitable for almost anywhere in your garden. As long as it has a minimum of 6 hours of sunlight, it will flower prolifically. Afternoon shade is great for regions with intense heat, but too much shade can reduce the bloom production.
Consistently moist soil is essential during germination and initial growth, but the plant can withstand moderate drought once it’s established. If conditions get too dry, the foliage may turn brown, and flowers may wither. I recommend maintaining moderate moisture to keep phacelia looking its best all summer.
Drip irrigation is ideal because it delivers water straight to the base without soaking the leaves. If growing in clay soils, be sure the root zone is never soggy. Drainage is crucial for preventing root rot.
Your standard loamy garden soil is perfect for this feathery, frilly plant. It can adapt to many soil types, but compost-rich blends are ideal for optimal performance. A pH between 6.0 and 7.5 is just fine. The plant is not super finicky but puts on the prettiest display in rich loam.
Climate and Temperature
Moderate temperatures between 60-75°F are ideal for this plant, but it can tolerate temperatures as high as 90°F and as low as 20°F. Flowers may dry and struggle in extreme heat. At the end of the season, phacelia conveniently winter-kills with the first major frosts.
The cold sensitivity is great for cover cropping and mulching your fall beds because the plant debris acts like a weed-smothering straw. It breaks down fairly easily, contributing to soil organic matter levels throughout the winter and often decomposing before spring. I like to aid the process by chopping phacelia with loppers at the base or mowing it down to shred it into finer pieces.
P. tanacetifolia is a true warm-weather annual that will not survive winter. It is not hardy in any temperate climate with frosts. Many people mistake it as a perennial because it prolifically self-seeds. The seeds that fall at the end of the season will return when spring weather warms. However, relatives of lacy phacelia, such as P. sericea (silky phacelia), are long-lived perennials often grown in southwestern rock gardens.
There is no need to fertilize this wildflower. It is very successful at scavenging for spare nutrients in the soil.
Do not plant phacelia in beds with a lot of nitrates, or it may accumulate a bunch of greenery at the expense of flowering. While the lacy foliage is pretty, a phacelia patch without flowers would be a real bummer for the bees.
You don’t need to do much to maintain this plant. In a wild cottage-like garden, you can let it flow through its natural lifecycle. In a manicured garden, you may wish to deadhead spent flowers to maintain a tidier appearance and encourage continued blooming. Some florists enjoy phacelia stems in flower arrangements.
If you don’t want phacelia to self-sow and spread, you must cut back the flowers before they form seedheads. The end of summer is a great time to cut the plant back to the ground, walk over it, or mow over the top.
Phacelia is a diverse genus with over 200 species of flowering herbs. It was once classified in the Boraginaceae (borage) family, given its fuzzy hairs and coiled flowers.
However, botanists debate whether it belongs in the waterleaf family (Hydrophyllaceae) or a merging of the borage and waterleaf family. Either way, the physical characteristics of phacelia flowers are notably related, yet there are unique varieties for nearly any climate or usage.
Lacy Phacelia (P. tanacetifolia)
This is the most common species for gardens, wildflower plantings, and farm intercropping. You can find lacy phacelia in most seed catalogs or blended into wildflower seed packets.
It may also be labeled as scorpionweed, fiddleneck, or purple tansy. A true annual, this plant goes through its entire lifecycle in one season and dies at the first frost. The flowers produce the heaviest amounts of nectar and grow in attractive cyme shapes.
Desert Bluebells (P. campanularia)
This cool-season annual flower is native to the Mojave and Sonoran deserts and is often cultivated as an ornamental throughout California and Arizona. It has hairy erect stems and oval, toothed leaves that look very different from the frilly fern-like foliage of lacy phacelia. It has a mounding habit and produces familiar coiling clusters of bell-shaped flowers in vibrant blue.
The bloom season is in winter or spring in its native desert habitat. This plant loves sandy or gravelly soil and works great in desert plantings with creosote, ocotillo, and desert lavender.
Silky Phacelia (P. sericea)
This showy perennial phacelia is native to North America, growing at subalpine to alpine elevations even above the treeline. It has silky fine hairs covering its stems and leaves, the latter of which are finely toothed in a pinnate pattern.
The individual bell-shaped flowers look similar to those of lacy phacelia, but they are clustered in big panicles at the end of the stem like a bottlebrush. The deep purple to dark blue petals are a striking backdrop to the bright yellow and orange anthers. This is a great option for northern growers.
Rock Phacelia (P. californica)
Also known as California phacelia or scorpionweed, this wildflower grows on coastal bluffs and grasslands of northern California and Oregon. It has rough hairs and long, branching stems that grow close to the ground. The hairy flower cluster is very dense and shaped in the familiar coiling cyme arrangement.
The blooms range from white to pale blue to lavender purple. This native flower is an important food source for the Mission blue butterfly, an endangered species native to the San Francisco area. An essential native plant addition to northern California gardens and similar climates!
Beneficial Plant Pairings
Phacelia is an amazing plant that improves pollination in your vegetable garden and attracts beneficial predatory insects for natural biocontrol. Grow it alongside other insectary flowers, such as:
- White alyssum
If you want the most benefit for your veggies, I recommend seeding a mass planting of phacelia in a thin strip near your tomato or squash beds. However, keep phacelia contained in its own bed along the garden margins to ensure it doesn’t compete with your crops.
Pests and Diseases
Finally, a plant that is virtually pest-and-disease-free! Phacelia has very few pests and even fewer pathogen risks. It is highly resilient and more likely to help solve pest problems than create them.
As if there aren’t enough aphid species in the world, Aphis phaceliae is its own specialty species adapted to feeding on the stems of this plant. You’ll notice the little green bugs on the stems and undersides of leaves, potentially attracting ants with their honeydew. You can remove them with a heavy spray of water in the morning or apply a diluted neem solution in extreme outbreaks. However, limit the use of neem oil to times when pollinators are not likely to be at the plant, such as at dusk; allow it to dry in place overnight, and avoid spraying the flowers directly if you can.
Fortunately, phacelia attracts many voracious aphid eaters like parasitic wasps, minute pirate bugs, and syrphid flies, whose larvae feed on hundreds of aphids daily.
Phacelia is primarily grown as a pollinator, insectary, and beneficial partner plant. It is a phenomenal nectar source for honeybees, native bees, butterflies, and beneficial predatory insects. Thanks to its frost-killed fluffy foliage, it makes a great cover crop that can mulch your beds over winter. As an annual, phacelias striking purple fiddlehead-shaped flowers are beautiful in annual flower beds and floral arrangements.
Frequently Asked Questions
How Long Does Phacelia Bloom?
Lacy phacelia blooms from early summer through fall, often from June to October in temperate growing zones. If you deadhead the flowers, it prolongs the bloom production. The sugary nectar is favored amongst pollinators, and many growers sow multiple successions of phacelia every two weeks through the spring to ensure a continuous supply of bee forage.
Is Phacelia a Good Cover Crop?
Phacelia is an increasingly popular summer or fall-killed cover crop on farms and in gardens. It produces a large amount of biomass quickly and is known as a bioaccumulator if there are spare nutrients in the soil. The plant attracts beneficial insects when in bloom, then dies back at frost, creating a quickly biodegradable weed-suppressing mulch. Deadheading the flowers before seed set is the key to successful cover cropping with this plant. It will self-sow if you don’t cut it back in time.
Is Phacelia Toxic to Animals?
Phacelia is considered non-toxic to humans and pets. It is highly ornamental and poses no risk to pets. It is often used in forage blends for livestock. However, some phacelia species have irritating hairs that can cause a rash on sensitive individuals.
Is Phacelia Deer Resistant?
Much like borage, deer avoid the fuzzy, hairy leaves of phacelia. This plant is deer-resistant and great for landscape borders where forest visitors may munch attractive plants. The delightful sweet smell of phacelia is also a deterrent to many animals, yet an attractant to pollinators.
A pollinator planting or vegetable companion planting is incomplete without lacy phacelia! Direct seed this gorgeous wildflower in the spring after the risk of frost has passed, and sow a couple of successions to ensure a continuous dazzling bloom.
The plants don’t require much more than consistent moisture in the early stages and warm weather. When phacelia dies back, don’t fret! It will self-sow and return next year. If you don’t want it to self-seed, cut back the plants when the purple flowers begin to fade.