Quick answer: 60 native Nebraska plants have a recorded bloom range that includes May.
60 species
- American basswood Tilia americana · 32 states
- American bittersweet Celastrus scandens · 11 states
- American hazelnut Corylus americana · 16 states
- American plum Prunus americana · 25 states
- Black cherry Prunus serotina · 32 states
- Black walnut Juglans nigra · 33 states
- Broadleaf cattail Typha latifolia · 11 states
- Bur oak Quercus macrocarpa · 24 states
- Butterflyweed Asclepias tuberosa · 37 states
- Canada anemone Anemone canadensis · 22 states
- Canada wild rye Elymus canadensis · 18 states
- Candle anemone (thimbleweed) Anemone cylindrica · 5 states
- Cardinal flower Lobelia cardinalis · 37 states
- Chokecherry Prunus virginiana · 35 states
- Climbing prairie rose Rosa setigera · 8 states
- Common blue violet Viola sororia · 21 states
- Common hackberry Celtis occidentalis · 15 states
- Coralberry Symphoricarpos orbiculatus · 20 states
- Creeping juniper Juniperus horizontalis · 10 states
- Downy hawthorn Crataegus mollis · 7 states
- Downy serviceberry Amelanchier arborea · 34 states
- Eastern hop-hornbeam Ostrya virginiana · 18 states
- Eastern red cedar Juniperus virginiana · 36 states
- Eastern red columbine Aquilegia canadensis · 36 states
- Eastern redbud Cercis canadensis · 30 states
- Foxglove beardtongue Penstemon digitalis · 31 states
- Golden alexanders Zizia aurea · 12 states
- Grayhead coneflower Ratibida pinnata · 12 states
- Green ash Fraxinus pennsylvanica · 23 states
- Indigo bush Amorpha fruticosa · 16 states
- Jack-in-the-pulpit Arisaema triphyllum · 14 states
- Large penstemon (shell-leaf beardtongue) Penstemon grandiflorus · 8 states
- Longbract wild indigo (cream false indigo) Baptisia bracteata var. leucophaea · 5 states
- Mayapple Podophyllum peltatum · 18 states
- Mexican hat Ratibida columnifera · 17 states
- Nannyberry Viburnum lentago · 23 states
- Narrow-leaf coneflower Echinacea angustifolia · 9 states
- New Jersey tea Ceanothus americanus · 31 states
- Northern red oak Quercus rubra · 24 states
- Ohio buckeye Aesculus glabra · 12 states
- Prairie Junegrass Koeleria macrantha · 15 states
- Prairie blue-eyed grass Sisyrinchium campestre · 6 states
- Prairie crabapple Malus ioensis · 8 states
- Purple meadow-rue Thalictrum dasycarpum · 7 states
- Quaking aspen Populus tremuloides · 24 states
- Red-osier dogwood Cornus sericea · 22 states
- Richardson's alumroot Heuchera richardsonii · 8 states
- Rocky Mountain bee plant Peritoma serrulata · 22 states
- Shagbark hickory Carya ovata · 22 states
- Silver buffaloberry Shepherdia argentea · 11 states
- Smooth Solomon's seal Polygonatum biflorum · 13 states
- Smooth sumac Rhus glabra · 34 states
- Virginia creeper Parthenocissus quinquefolia · 27 states
- Virginia iris Iris virginica · 9 states
- Virginia strawberry Fragaria virginiana · 8 states
- White ash Fraxinus americana · 31 states
- White wild indigo Baptisia alba · 10 states
- Wild blue Phlox divaricata · 32 states
- Wild geranium Geranium maculatum · 11 states
- Winecup Callirhoe involucrata · 7 states