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Bumblebee on phacelia flowers

How to grow phacelia

BBC Gardeners' World Magazine

Published: Friday, 8 October 2021 at 11:19 am

All you need to know about growing phacelia, both as a green manure and cut flower, in our Grow Guide.

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Plant Size:

Height: 120

Spread: 40

Spacing:

30 apart

30 between rows

Depth:

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

Phacelia flower

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:

Sow seeds 10cm apart initially
Thin again to 30cm a few weeks later

If growing as a green manure:

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

Digging phacelia into the ground, as a green manure

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

Collecting phacelia seeds

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.

Advice on growing phacelia

Always buy seed from a reputable supplier
Follow the instructions on the seed packet to ensure you sow seed at the correct time and depth

Where to buy phacelia

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