The below list is not exhaustive or rigorous.  I’m no expert.  The flowers I’ve thought of using will be added here as the blog progresses with a link to whether they may be edible or not.  Just because one internet source claims they’re edible, I can’t be certain so proceed at own risk. While I don’t intend to eat the flowers directly but propergate yeast and bacteria from them, there may be a chance that any toxins leach out.

Probably non-toxic:

Gorse all year https://www.eatweeds.co.uk/gorse-flower-cordial-recipe

Catkins http://arcadianabe.blogspot.co.uk/2012/02/catkins-can-we-eat-them.html http://forager101.blogspot.co.uk/2013/02/alder-and-catkinsedible.html

Primrose March http://www.countryfile.com/explore-countryside/food-and-farming/top-ten-food-forage-march-and-april

Wood Sorrel spring http://www.gallowaywildfoods.com/wood-sorrel-identification-distribution-and-edibility/

Blackthorn March/April http://www.naturessecretlarder.co.uk/wild-food-useful-plants/blackthorn-sloe-prunus-spinosa.htm

Cuckoo Flower (cardamine pratensis) March –  August http://www.wildfooduk.com/hedgerow-food-guide/ladies-smock-1-hedgerow/

Dandelion April – May https://www.eatweeds.co.uk/nasreddin-tale-dandelion

Hawthorn April – May https://www.permaculture.co.uk/articles/many-benefits-hawthorn

https://www.burningskybeer.com/product/saison-lhiver/

Woodruff April – May https://en.m.wikipedia.org/wiki/Galium_odoratum

Broom April – July Sacred and Herbal Healing Beers

Daisy summer http://www.edenproject.com/learn/for-everyone/edible-wild-food-ox-eye-daisies

Meadowsweet July https://www.woodlandtrust.org.uk/blogs/woodland-trust/2016/07/foraging-in-july/

Yarrow late April – September http://www.countryfile.com/explore-countryside/food-and-farming/top-ten-food-forage-march-and-april

Mallow July – September http://www.countryfile.com/explore-countryside/food-and-farming/top-ten-food-forage-march-and-april

Clover http://www.craftcommander.com/brewing/2016/7/14/brewing-beer-with-a-sense-of-place-foraging-yeast-for-beginners

Elderflower

Heather

Probably toxic:

Also some are rare or unsubstantial so I haven’t included them above.

Buttercup family including Lesser Celandine and Wood Anemone http://www.gallowaywildfoods.com/lesser-celandine-edibility-distribution-identification/

Red campion https://www.woodland-ways.co.uk/blog/flora/plant-fact-sheet/red-campion/

Dog Mercury http://www.thepoisongarden.co.uk/atoz/mercurialis_perennis.htm

Bluebells https://www.woodlandtrust.org.uk/blog/2017/04/are-bluebells-protected/

Birdfoot trefoil http://practicalplants.org/wiki/Lotus_corniculatus

Foxglove http://www.thepoisongarden.co.uk/atoz/digitalis.htm

Woody Nightshade http://www.thepoisongarden.co.uk/atoz/solanum_dulcamara.htm