Spring Bloom in Maine: Peak Timing for 2027

National Park Service, Acadia National Park puts the window at June 1 to June 30, with the peak around June 14, though that peak is the midpoint of their window rather than a date they publish. Their words: "As you are driving the highways and byways in Maine in the spring you will almost always see a beautiful carpet of pink and purple picturesque flowers." That is a climatological typical. The panel at the top of this page then reads USA-NPN's Spring Index for Portland, Bar Harbor, Rangeley and tells you whether this particular spring is running ahead of or behind that.

No Spring Index anomaly is on file for Maine for 2026. That number comes from the USA National Phenology Network's Extended Spring Indices, a set of 4 km gridded models regenerated every day from PRISM temperature data. USA-NPN describes the calculation plainly: to determine how the current spring compares to normal, they difference the day of year the leaf out or bloom was reached this year from the long-term average day of year it was met. We read the grid at Portland, Bar Harbor, Rangeley and average.

No. Nothing USA-NPN publishes in this product suite is dated later than today. The Spring Index anomaly measures the spring that has already run so far this year. It is a leading indicator for the blooms still ahead of you, not a prediction of them. In the second half of the calendar year the live grid holds the spring that just finished, and this page stops shifting dates entirely rather than moving next spring by last spring's number.

USA-NPN publishes three, covering three different parts of spring. First Leaf is based on the leaf out of lilacs and honeysuckles, which are among the first plants to show their leaves in the spring. First Bloom is based on their flowering, and USA-NPN associates it with blooming of early-spring shrubs and leaf out of deciduous trees. The Late Bloom Index indicates when plants that bloom at the tail end of the season are flowering. Each species on this page is matched to whichever of the three normally fires closest to its own typical peak, and shifted by that one. At Portland the three normally land around day 115, day 145 and day 177 of the year.

Bigleaf lupine: Route 1 and the side roads Down East, Deer Isle, the Acadia roadsides, and the Rangeley Lakes around Oquossoc. Sundial lupine: Very rare. This is an identification story rather than a destination. Crabapple and apple blossom: Orchards statewide, with southern and coastal Maine earliest and the north last. Those locations are the ones the sources named; where a source named a species but no place, or a place but no month, the card carries what the source gives.

It is an assumption. The Spring Index models three cloned ornamental cultivars, a lilac and two honeysuckles, chosen because they are among the first woody plants to leaf out and bloom and are common across much of the country. It has never heard of the species on this page. What the shift assumes is that a plant blooming at roughly the same point in the season responds to the same accumulated warmth in roughly the same way, which is why each species is matched to the nearest of the three indices rather than to one generic number. Elevation, aspect, and local soil moisture will all move the real answer, and a hard late freeze can take a bloom out entirely.

The windows on this page do not; they are climatological typicals compiled from published guidance and they stay put. What changes is the spring. That is the entire reason the Spring Index panel is here: the researched window tells you where to start, and the anomaly tells you which way this particular year has moved it. Any single season commonly runs a week to a fortnight either side even before you account for the anomaly.

Yes, and you should. The Spring Index layers are published by the USA National Phenology Network at usanpn.org under a Creative Commons Attribution 4.0 licence, and their map service is open, so the same numbers this page shows are queryable by anyone. The bloom windows come from the institution named under each species card, with the sentence we relied on quoted directly so you can find it on their page.