- Hairy Agrimony
- Hairy Beggarticks
- Hairy bittercress
- Hairy False Goldenaster
- Hairy Lungwort
- Hairy ruellia
- Hairy sedge
- Hairy Sedge
- Hairy Solomon's-seal
- Hairy tare
- Hairy vetch
- Hairy Violet
- Hairy Woodrush
- Hanging sedge
- Harbinger of spring
- Hard shield fern
- Hare's Tail Grass
- Hare's-foot Plantain
- Hart's-tongue fern
- Hawkweed Oxtongue
- Hay-scented fern
- Heart-podded Hoary Cress
- Heartleaf arnica
- Heartleaf keckiella
- Heath aster
- Heath speedwell
- Heath spotted orchid
- Heavenly bamboo
- Hedge Bedstraw
- Hedge bindweed
- Hedge mustard
- Hedge woundwort
- Hedgerow Crane's-bill
- Hemp agrimony
- Hemp dogbane
- Henbit deadnettle
- Henderson's shooting star
- Herb Paris
- Herb Robert
- Herb-of-Grace
- Hercules' club
- Himalayan balsam
- Hoary alyssum
- Hoary Plantain
- Hoary puccoon
- Hoary Rock-rose
- Hoary vervain
- Hobblebush
- Hogweed
- Hollowroot
- Hollyhock
- Hollyleaf cherry
- Hollyleaf redberry
- Holm oak
- Honewort
- Honey locust
- Honey mesquite
- Hooked buttercup
- Hookedspur violet
- Hooker's fairybells
- Hop goodenia
- Hop trefoil
- Horse Mint
- Horse-chestnut
- Horseradish
- Horseshoe vetch
- Horseweed
- Hound's-tongue