Quick answer: 82 native Delaware plants have a recorded bloom range that includes May.
82 species
- Allegheny chinquapin Castanea pumila · 9 states
- American basswood Tilia americana · 32 states
- American beech Fagus grandifolia · 24 states
- American bladdernut Staphylea trifolia · 15 states
- American holly Ilex opaca · 24 states
- American hornbeam Carpinus caroliniana · 29 states
- American mountain ash Sorbus americana · 18 states
- American plum Prunus americana · 25 states
- American wisteria Wisteria frutescens · 14 states
- Atlantic white cedar Chamaecyparis thyoides · 12 states
- Black cherry Prunus serotina · 32 states
- Black locust Robinia pseudoacacia · 12 states
- Black tupelo Nyssa sylvatica · 19 states
- Black walnut Juglans nigra · 33 states
- Bristly locust Robinia hispida · 9 states
- Butterflyweed Asclepias tuberosa · 37 states
- Canadian serviceberry Amelanchier canadensis · 17 states
- Cardinal flower Lobelia cardinalis · 37 states
- Chokecherry Prunus virginiana · 35 states
- Common elderberry Sambucus nigra ssp. canadensis · 16 states
- Common hoptree Ptelea trifoliata · 12 states
- Common ninebark Physocarpus opulifolius · 22 states
- Common persimmon Diospyros virginiana · 17 states
- Common yarrow Achillea millefolium · 31 states
- Coral honeysuckle Lonicera sempervirens · 16 states
- Coralberry Symphoricarpos orbiculatus · 20 states
- Cucumbertree Magnolia acuminata · 12 states
- Deerberry Vaccinium stamineum · 10 states
- Downy serviceberry Amelanchier arborea · 34 states
- Eastern purple coneflower Echinacea purpurea · 22 states
- Eastern red cedar Juniperus virginiana · 36 states
- Eastern red columbine Aquilegia canadensis · 36 states
- Eastern redbud Cercis canadensis · 30 states
- Eastern white pine Pinus strobus · 19 states
- Flowering dogwood Cornus florida · 22 states
- Foxglove beardtongue Penstemon digitalis · 31 states
- Fragrant sumac Rhus aromatica · 14 states
- Green ash Fraxinus pennsylvanica · 23 states
- Honey locust Gleditsia triacanthos · 9 states
- Indian blanket Gaillardia pulchella · 18 states
- Jacob's ladder Polemonium reptans · 17 states
- Lanceleaf coreopsis Coreopsis lanceolata · 28 states
- Lemon beebalm Monarda citriodora · 15 states
- Maypop passionflower Passiflora incarnata · 13 states
- Nannyberry Viburnum lentago · 23 states
- Narrowleaf evening-primrose Oenothera fruticosa · 10 states
- New Jersey tea Ceanothus americanus · 31 states
- Northern red oak Quercus rubra · 24 states
- Northern spicebush Lindera benzoin · 16 states
- Pagoda dogwood Cornus alternifolia · 25 states
- Pale purple coneflower Echinacea pallida · 9 states
- Pawpaw Asimina triloba · 17 states
- Pin oak Quercus palustris · 18 states
- Pitch pine Pinus rigida · 12 states
- Plains coreopsis Coreopsis tinctoria · 16 states
- Sassafras Sassafras albidum · 22 states
- Scarlet beebalm Monarda didyma · 18 states
- Scarlet oak Quercus coccinea · 17 states
- Shagbark hickory Carya ovata · 22 states
- Smooth hydrangea Hydrangea arborescens · 12 states
- Smooth sumac Rhus glabra · 34 states
- Sourwood Oxydendrum arboreum · 14 states
- Southern arrowwood Viburnum dentatum · 13 states
- Southern live oak Quercus virginiana · 13 states
- Southern red oak Quercus falcata · 6 states
- Spotted beebalm Monarda punctata · 14 states
- Striped maple Acer pensylvanicum · 11 states
- Sugar maple Acer saccharum · 28 states
- Sundial lupine Lupinus perennis · 25 states
- Swamp azalea Rhododendron viscosum · 7 states
- Sweet birch Betula lenta · 18 states
- Sweet-fern Comptonia peregrina · 10 states
- Sweetbay magnolia Magnolia virginiana · 12 states
- Sweetgum Liquidambar styraciflua · 22 states
- Tulip tree Liriodendron tulipifera · 17 states
- Umbrella tree magnolia Magnolia tripetala · 6 states
- Virginia bluebells Mertensia virginica · 14 states
- White ash Fraxinus americana · 31 states
- White fringetree Chionanthus virginicus · 14 states
- White oak Quercus alba · 33 states
- Wild blue Phlox divaricata · 32 states
- Willow oak Quercus phellos · 16 states