When I grow ‘Red Frills’ mustard in the winter garden I often let it flower and go to seed. Or rather, it just happens with benign neglect in spring.

benign neglect                                                                                    

noun

1. an attitude or policy of noninterference or neglect of a situation, which may have a more beneficial effect than assuming responsibility.  Dictionary.com

And my benign neglect in allowing the mustard to flower has had a more beneficial effect than if I had tidied up. The mustard flowers draw scads of hover flies to my garden.

The larvae of hover flies prey on aphids. One larva may consume 400 aphids before pupating. Aphids usually take out my kale and other cabbage family crops in late spring. The larvae also feed on cabbage worms, scale, mealy bugs and other insect pests that frequent my garden. 

Many of the 6000 species of hover flies are important pollinators. Some gardeners may know them as flower flies given their preference for annual flowers such as alyssum and bachelor buttons. One reference suggests they prefer white and yellow flowers. Another reason to grow flowers with your vegetables.

I welcome the hover flies to my garden and now I’m letting the parsley plant linger longer. To read more:
Attract Hoverflies for Organic Aphid Control, Barbara Pleasant in Mother Earth News
Hover fly, Wikipedia has a decent, well-referenced entry
All About Hover Flies, Microscopy UK, a more technical look from the UK
Syrphid, Flower or Hover flies, University of California IPM

UC-IPM

Hoverfly photo: Bonnie Plants