Phacelia: a Green Manure and Bee Plant That Improves Your Soil

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Phacelia is a common sight in fields and gardens in spring and summer: low plants with lacy leaves and curling lilac-blue flower heads humming with bees. It is one of the most popular plants for improving soil. Here is why phacelia is so useful and how to grow it.

Flowers from your garden or from us: flower baskets and potted plants.

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What it is

Lacy phacelia (Phacelia tanacetifolia) comes from the south-western United States and Mexico. It is an annual 50–80 cm tall with finely divided leaves and coiled flower heads that open gradually. It is undemanding, grows fast and tolerates light frost, so it can be sown from early spring to late summer.

Why it is useful

Phacelia as a green manure

Green manures are plants grown to improve the soil. In 6–8 weeks phacelia produces plenty of leafy growth, and its dense fine roots loosen and structure the soil. Cut plants are left on the surface or lightly dug in, where they decompose into organic matter. Unlike lupins and other legumes, phacelia does not fix nitrogen, but it fits in before almost any crop because it is unrelated to most vegetables.

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A bee plant and garden helper

Phacelia is one of the best bee plants: its flowers are rich in nectar and bloom for several weeks. Its honey is pale and mild. As well as bees, it attracts hoverflies and other beneficial insects whose larvae eat aphids.

When to sow and cut

• Timing. From early spring to August; you can sow several times a season.
• Autumn (dormant) sowing. Late in autumn, once the soil is cold enough that seed will not sprout before frost — seedlings then appear in early spring.
• Seed rate. In a garden, 1.5–2 g per m²; on farmland roughly 10–15 kg/ha for green manure and less for a bee crop.
• Seedlings. Appear in about a week: first small hairy seed leaves, then feathery true leaves, and blue curled flower heads 6–8 weeks after sowing.
• Sowing. The seeds are small: scatter them over loosened soil, rake in lightly and water.
• Cutting. For soil improvement, cut at the start of flowering, before stems toughen and seeds form. For bees, let the plants finish flowering.
• Care. Hardly any: phacelia is drought-tolerant and smothers weeds itself.

Discover another soil-improving plant in lupins, natural feeding in natural fertilisers, and how to start a flower bed in a flower garden for beginners.

FAQ

Can I plant vegetables straight after phacelia?

Yes, usually 1–2 weeks after cutting and digging in the green growth.

Is phacelia harmful?

No, though the bristly hairs on the stems can irritate sensitive skin, so wear gloves. Like any honey, phacelia honey should not be given to babies under one year.

Phacelia benefits and drawbacks — are there any downsides?

Benefits are looser soil, fewer weeds and more bees and beneficial insects. Downsides are minor: in flower it draws lots of bees near paths and play areas, the bristly hairs can irritate skin, and if it sets seed it will pop up where you did not plant it.

When should I sow phacelia in spring, and can I sow it before winter?

In spring, as soon as the soil has thawed and dried a little, usually April; you can keep sowing until August. For a pre-winter sowing, wait until late autumn when the soil is cold so the seed only germinates in spring.

What is the phacelia seed rate?

For green manure, 1.5–2 g per m² in a garden; on farmland about 10–15 kg/ha. The seed is small, so mixing it with sand helps spread it evenly.

Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.

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