Tansy phacelia or bee phacelia (Botanical name: Phacelia tanacetifolia) is an annual wildflower native to California. It was introduced as a bee plant to Europe in the early 1900’s. It is classified as a broad leaved cool-season annual forb (See Phacelia genus). It is sown as a rotation cover crop in vineyards in the North Coast of California. It grows rapidly in winter forming a dense, succulent stand. It flowers from March to May in the northern hemisphere.

Why used: 1) Erosion control: An annual plant, so it is unable to loosen really compacted soil says Uwe Hofmann, instead it grows around any compaction. 2) Weed suppression: Tansy phacelia grows quickly and suppresses weeds. It grows one to three feet tall (high biomass). When mature (April-June in the northern hemisphere) it is bushy, has fern-like foliage and blue-purple flowers. 3) When cut at flowering it apparently kills nematodes. 4) It rapidly decomposes after tillage due to its low C/N ratio. It provides 30 tonnes of organic matter per hectare. 5) Beneficial insects: Bart Arnst told me phacelia is “a good all-rounder for attracting beneficial insects, especially honeybees and hover flies. Uwe Hofmann tries to manage Phacelia so it naturally reseeds, by letting it grow every second row without cutting: sow early spring, for flowering between March-August and then it will re-seed itself for winter but dies in Europe over winter. 6) Nitrogen uptake It takes up large amounts of N during the winter.

Non-beneficials: In California phacelia harbours high densities of Lygus spp. and thus should be used with care.