I shared most of this list with my permaculture buddies a few years ago. Originally, it was culled from photos taken here in my mid-New Hampshire garden and along surrounding trails during the previous few years (2010-2014), and since then I have added to it.

If you live in northern New England, these will probably be your early pollinator plants, critical for early insects, especially bumblebees; these should all bloom and attract pollinators between March and mid-May.

“Bees do have a smell, you know, and if they don’t they should, for their feet are dusted with spices from a million flowers.” ― Ray Bradbury, Dandelion Wine

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Wildflowers, Ephemerals, and Annuals

• Tussilago farfara aka Coltsfoot – March and April, first food for bees. Flowers bloom, then leaves sprout. Invasive.  
• Pansy 
• Dandelions (Taraxacum officinale) Dandelions as important spring pollinator plants
• Common Wintercress (Barbarea vulgaris), blooms from April to August
• Mouse-eared Chickweed (Cerastium fontanum), April through October, a small white-flowered plant often found in lawns
• Quaker Ladies aka Bluets (Houstonia caerulea and other Houstonia sp.), blooms April to June, often seen in woods, varying in shaded from white to deep blue 
• Violets 

• Trillium sp.
  

  

  
• Primula sp. (primrose) 
• flowers of peas (the vegetable) 
• rockcress
• ephemerals, including …  Erythronium americanum aka yellow adder’s tongue or yellow trout lily,  
  … Epigaea repens aka trailing arbutus,
  … Claytonia virginica aka Spring beauties, etc.,
  … Anemone acutiloba or Anemone americana aka hepatica (sharp- or round-lobed)

Bulbs and Corms

• Eranthus hyemalis aka winter aconite – Feb/March
• Galanthus nivalis  and G. elwesii aka Snowdrops – Feb to April 
• Crocus – March to April 
• Adonis amurensis ‘Fukujukai’ aka ‘Amur Adonis’ and Adonis vernalis (‘sweet vernal’) – usually bloom in March (this one at Arnold Arboretum in Boston was blooming in mid-February) 
  
• Chionodoxa aka Glory of the Snow – March/April 
• Iris reticulata aka dwarf Iris – March/April
• Scilla siberica aka Siberian Squill – tiny – March to May 
• some Fritillaria – April/May – available from tiny to giant plants and flowers
  

  

  
• Muscari aka grape hyacinth 

Perennials

• Hellebores aka Lenten Rose, usually blooms here in April or May: one of mine, Helleborus x. hybridus ‘Royal Heritage series’  … and another, Hellebore foetidus (shown with bumblebee, photo taken today)
• Sanguinaria canadensis aka bloodroot – April to May 
• Phlox stolonifera aka creeping Phlox 
• Saxifraga bryoides aka Mossy Saxifrage
• Pulsatilla vulgaris aka European Pasque Flower: Mine first blooms in late April to early May; great food source for early-emerging bumblebee queens, though possibly American Pasque Flower (Pulsatilla patens) would be a better choice in parts of the U.S. where it exists in the wild (not New England)
• Primula denticulata aka the Drumstick Primrose 
• Primula marginata – high alpine primrose
• Lathyrus vernus aka Spring Bush Pea or Spring Vetchling – one of the earliest perennials, attracts bees and butterflies 

Shrubs and Trees

• Hamamelis x intermedia and Hamamelis vernalis aka Witch Hazel – blooms February to April … I think the top photo, taken in February at Arnold Arboretum in Boston, is Hamamelis x intermedia and the second, taken at the end of March on the High Line in NYC, is the vernal witch hazel
• Forsythia (‘Northern Gold’ recommended) – blooms March to May 
• Viburnum x bodnantense ‘Dawn’ – zone 5 – March/April
• some winter-blooming heathers, Erica carnea – can bloom in snow, Feb-April and later … I’m not sure if this is a Calluna or an Erica but it’s blooming in my garden now and attracting pollinators 
• Lonicera Canadensis (native fly honeysuckle) – April or May 
• Amelanchier arborea aka flowering Shadbush, Serviceberry, Juneberry – April/May 
• some Azaleas and Rhododendrons: R. mucronulatum ‘Nana’ in early April is first to bloom in Northeast; R. ‘Northern Lights’ series azaleas in April; Rhododendron ‘April White’ in late April; R. ‘Olga Mezitt’ is a great one that usually blooms in May (I have it; pictured). 
• Pieris japonica (I love these things): varieties include Mountain Fire, Katsura, Valley Valentine 
• some Daphne odora — below is a photo of one blooming in the wild parts of my yard (I didn’t plant them). They flower between March and May.  
• some Magnolia: Magnolia stellata aka Star Magnolia (pictured) in April to May; also Magnolia x acuminata ‘Butterfly’- mid-April to May

• Lindera benzoin aka Spicebush – April (but it’s complicated: http://www.louistheplantgeek.com/a-gardening-journal/974-today-in-the-garden-of-a-lifetime-spice-bush-in-flower-but-with-smaller-flowers)… male pollinator needed for berries. It’s also a host bush for the spicebush swallowtail butterfly. I just picked up two more today that I had ordered from a local farm stand.
• Prunus x ‘Hally Jolivette’ – an ornamental cherry created at Arnold Arboretum in MA – late April/May
• Cornus mas (Cornelian cherry) flowers, which bloom before the tree leafs out (shown here with chionodoxa)
• Alnus serrulata aka Hazel or Smooth Alder – March/April catkin bloom
• Alnus rugosa aka Speckled Alder – March/April catkin bloom – this photo is from mid-March one year (not sure if it’s smooth or speckled alder)
• Corylopsis spicata aka Winter Hazel – April, hardy to zone 5, native to Japan
• Corylus americana aka American Hazelnut – April/May 
• some Salix aka willows with April and May catkin bloom
  

  

• some Acer aka maples 

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Here are some useful guides and lists of pollinators for New England and possibly beyond:

Pollinator Plant List from New England Wildflower Society — native plants that attract pollinators, spring-autumn
Pollinator Plants: Northeast Region, 3-pp PDF from the Xerxes Society; they offer lists for other regions, too. Arranged by bloom time.
Pollinator Plants for Northern New England Gardens from University of New Hampshire Extension, 4-pp PDF, listed by bloom time
Native Bees of New England, and some wild flowers they like, with bloom times
Attracting Pollinators to Your Garden Using Native Plants: Eastern U.S., 15 pp. PDF illustrated pamphlet from the U.S. Forest Service with details on types of bees and what kind of plants they like
Early Spring Pollinators and Their Flowers, blog post by Beatriz Moisset in Pennsylvania