NH ticks activate at 40°F, not at "summer"
The single most important fact about tick season in New Hampshire: blacklegged ticks (deer ticks) become active any time the temperature climbs above 40°F. That's not a summer-only trigger — Seacoast NH routinely hits the 40°F threshold in late March, and even into December in mild years. Ticks don't wait for Memorial Day to start looking for hosts.
Add it up: between warming spring days, summer activity, and fall cooling, NH tick season spans roughly nine months every year. Treating tick protection as a "summer thing" is the most common mistake Seacoast homeowners make — and it's the reason so many people find their first tick of the year in April or October, when they assumed they were safe.
The month-by-month timeline
March–April: Adult activity ramps up
Adult blacklegged ticks emerge first, becoming fully active by mid-April. This is also when American dog ticks start appearing. By late April, the first deer tick nymphs of the season are emerging — and a mid-April yard treatment is your first line of defense. Waiting until May means you've already missed weeks of adult exposure.
May–June: The nymph peak — highest Lyme risk of the year
This is the danger window. Nymph blacklegged ticks peak in May and June — and nymphs, not adults, are responsible for most Lyme disease cases in NH. The reason is brutal: nymphs are poppy-seed sized (1–2mm), nearly invisible on the skin, and they carry Lyme at adult rates. Seacoast NH nymphs in particular show infection rates in the 20–36% range, among the highest in the state.
May and June also happen to be exactly when families are getting back outside — gardening, yard work, hikes, kids in the backyard. The tick calendar and the human calendar line up badly in the NH spring.
July–August: Summer cooldown for adults, but nymphs continue
Adult blacklegged tick activity dips in the summer heat (they desiccate in dry, hot conditions), but nymphs keep questing in shaded habitat — wooded edges, leaf litter, under brush piles. Lone star ticks, an emerging Seacoast NH species, peak between June and August and are more aggressive than deer ticks. They can transmit alpha-gal syndrome (red-meat allergy) and ehrlichiosis.
September–October: The fall re-peak everyone forgets about
Adult blacklegged ticks surge again in cooler fall temperatures, reaching a fall peak in October that's comparable in intensity to their April spring peak. NH DHHS Lyme surveillance regularly records cases attributed to October exposure across Rockingham and Strafford counties. Families drop their guard after Labor Day. Don't — October is the second-highest risk month of the year in Seacoast NH.
November: The slow ramp down
Activity drops sharply once temperatures stay below 40°F consistently. Active ticks can still be found on warm November days. The first hard freeze — not the calendar — is what really ends the season.
Bottom line for Seacoast NH: March to November, two peaks (May–June and October), one early-spring treatment window that makes the entire year work.
When should Seacoast NH homeowners treat their yard?
The optimal first yard treatment in Seacoast NH is mid-April — before nymph season and before the highest Lyme-transmission months arrive. Treating in April is prevention. Treating in June or July is reaction. A three-treatment year (April, July, September–October) covers nymph season, summer activity, and the fall adult re-peak. If budget allows only one treatment, the math is clear: April, every time.
What to do right now
If you're reading this in spring, your window is open — schedule a yard treatment before mid-May. If it's summer, you're still in time to catch the fall peak with a September application. And if it's October, you should be doing full tick checks right now; fall adult ticks are as dangerous as the spring ones. The full NH seasonal guide breaks down treatments by season if you want the deeper version.
For Seacoast NH homeowners who want season-long protection without thinking about tick calendars, our seasonal tick protection plans build the timing into the service: three barrier treatments timed to the NH tick calendar. If you'd rather see what's actually going on in your own yard first, the fastest move is a free yard inspection — we'll walk the property, identify the real risk zones (the lawn-woodland edge, stone walls, leaf litter), and give you a clear quote with no sales pressure.