I studied for RHS level 2 and 3 qualifications in Horticulture and these are some websites I found very useful for background information:
The Seed Site – http://theseedsite.co.uk ….. Great for IDs
Jekkapedia – https://www.jekkas.com/collections/jekkapedia … Jekka McVicar’s online version of ‘Living Book of Herbs’ with 400+ detailed descriptions.
Roger Phillips Mushroom identification – http://www.rogersmushrooms.com/
Wild flowers of the British Isles – http://www.ukwildflowers.com/ … also covers butterflies
Wild flowers of the UK – https://wildflowerfinder.org.uk/ … searchable by colour, month, habitat, number of petals, flower symmetry etc
Seasonal Wild Flowers – http://www.seasonalwildflowers.com/ … A month by month look at flowers found in the countryside, UK
BBC Gardening – http://www.bbc.co.uk/gardening
BBC bitesize revision & tests – http://www.bbc.co.uk/schools/gcsebitesize/biology/
Gardeners World – magazine – http://www.gardenersworld.com
Forestry Commission – http://www.forestry.gov.uk
Trees and Shrubs online – https://www.treesandshrubsonline.org/
British Trees – http://www.british-trees.com
Grow Fruit & Veg Mag – http://growfruitandveg.co.uk//
Gardening Which – http://www.which.co.uk/gardeningwhich
Green Gardener products – http://www.greengardener.co.uk
National Plant Collections – http://www.nccpg.com
Plantlife http://www.plantlife.org.uk/
Bayer weed identification chart – http://www.bayercropscience.co.uk/your-crop/crop-diseases,-weeds-and-pests/
Edible Wild Food – https://www.ediblewildfood.com/ … US and Canadian resource
Oregon State – Botany – http://extension.oregonstate.edu/mg/botany
North Carolina – Horticulture – http://www.ces.ncsu.edu/depts/hort
Any place where I can get information about organic fertilizers ?
Some basic general information can be found here:-
https://www.planetnatural.com/big-stink/
https://saosis.com/blog/types-organic-fertilizers
https://theecologist.org/2011/may/20/five-bestnatural-and-organic-fertilisers
https://www.gardenorganic.org.uk/managing-your-soil a has a good section on Comfrey: https://www.gardenorganic.org.uk/comfrey
For getting products in the UK – https://www.organiccatalogue.com/feeding-soil-care/ is a good place to start.
Sarah Raven also does some organic fertilizers: https://www.sarahraven.com/gardening_kit/feeding_watering and so does Crocus: https://www.crocus.co.uk/search/_/search.organic-fertilizer/