Usually grown as a green manure, Phacelia tanacetifolia is also a popular pollinator plant, being extremely attractive to bees and other insects. It also makes a fantastic cut flower. Phacelia is native to parts of the United States and Central America and has become naturalised in New Zealand. Its common names include scorpion weed, purple tansy, fiddle neck and fernleaf fiddle neck.
Phacelia grows to a height of up to 1.2m (although this varies considerably), and has fern-like, pinnate green-grey leaves, and lavender-blue summer flowers.
Commonly used by farmers and vegetable growers, it works well as a green manure because it’s fast growing and tolerates lower temperatures – it may even survive a mild winter. Phacelia doesn’t fix nitrogen to the soil like leguminous plants but it does hold on to nitrogen, which is then dug back into the soil. Its root system improves soil structure and its growth habit and mass of fern-like foliage suppress weeds.
How to grow phacelia
Sow phacelia seed where you want it to flower, in well-prepared soil in full sun. Water in dry conditions only. Thin to 30cm apart if growing as a cut flower. If growing as a green manure, dig the plants back into the soil before flowering. If you can, allow some plants to flower to provide food for bees and other pollinators.
Where to grow phacelia
Grow phacelia in a well-prepared seed bed if growing as a cut flower, a vacant bed on your allotment or vegetable patch if growing as a green manure, or scattered into gaps in the border if growing as an ornamental bee plant. Phacelia can be grown in pots but bear in mind it can grow up to 1.2m tall.
How to grow phacelia
Sow seed from March to September where you want it to grow. If growing as a cut flower, thin seed to 10cm initially and then thin again to 30cm a few weeks later. If growing as a green manure then sow at a rate of 1g per sq m. Dig the plants back into the ground before flowering, when the leafy material is still soft and holds more material. If you can, leave some to flower for pollinators but bear in mind that phacelia self-seeds readily.
How to care for phacelia
Phacelia should flower around six to eight weeks after sowing. If growing as a green manure, make sure you dig the plants back into the soil before flowering, as this is when the plant material contains the most nutrients, and also you don’t run the risk of letting the flowers develop seeds that can spread everywhere. If growing as a cut flower, cut them as and when you need to. Bear in mind that phacelia will self seed readily if the flowers are not removed.
Growing phacelia: problem-solving
Phacelia is generally trouble free. The only issue with growing phacelia is that it self-seeds readily. if flowers aren’t removed it can become invasive. However, by simply removing flowers and/or controlling its spread by collecting seed yourself, you can prevent this problem.