Phacelia

Phacelia tanacetifolia

This fast green manure has feathery leaves and blue flowers that bees love. You grow it for the soil and dig it in later. It covers bare soil, holds on to leftover nutrients and adds organic matter when dug in. It isn't related to any of the usual vegetables, so it fits anywhere when you rotate crops.

Looking after it

Water: Phacelia needs little water and rain is usually enough. Only water to get a sowing going in dry soil. Feeding: It needs no feeding. It takes up the nutrients left in the soil and gives them back when you dig it in.

Cutting and digging in

Cut it down when it starts to flower. If you're leaving it for the bees, cut just after, but always before it sets seed. Chop it up and leave it to wilt for a few days. Then dig it into the top of the soil and wait two to three weeks before sowing. An autumn sowing can stay over winter and be dug in when spring comes.

What can go wrong

Seedlings everywhere. Seedlings come up all over the bed when plants are left to seed. Cut it down before the flowers fade. Pull or hoe the seedlings while they're small.
Itchy skin. The bristly stems and leaves can make some people's skin itch or go red. Wear gloves and long sleeves when you cut it and dig it in.

Growing facts: RHS, UC ANR and seed-company sowing guides. Phacelia as green manure: RHS. pH: USDA NRCS and British Columbia Ministry of Agriculture.