Though the Florida Keys, including Key Largo, can be enjoyed year-round, informed travelers can avoid the peak travel times that produce crowds of tourists and high prices for lodging and services. Florida's traditional "tourist season" occurs during the winter months, when flocks of northerners migrate south to escape the harsh cold. The increased demand for accommodations drives prices upward. In fact, the timing of peak season appears to be driven almost entirely by attempts to escape the weather north of the 39th parallel (above a line drawn from Kansas City east through Cincinnati to Delaware Bay). Hotel and rental rates during tourist season are often double (sometimes higher) those of the off-season; and national holidays create an additional surge in bookings that push prices even higher.

Visitors trying to keep costs down can head to Key Largo during the summer, especially in July, August and September, when hotel prices are generally at their lowest, though holidays (Independence Day and Labor Day) and the start of lobster season (the last consecutive Wednesday and Thursday in July) still cause prices to jump the week before and after. One trade-off will be Florida's famous humidity, which climbs with the temperatures, and mosquito populations surge, swarms of adult mosquitoes emerge about a week after marshes are flooded by unusually high tides or rainfall. Florida's reputation for fierce mosquitos, midges and biting flies is well earned. Though biting insects may occur anytime of the year, the largest hatches of mosquitoes most commonly follow the storm tides and heavier rain that are most common from May through October.

Though Key Largo and other coastal communities may be as humid at the rest of the state, they feel a bit cooler in the summer than inland Florida destinations. Coastal areas benefit most from onshore breezes, cooler air drawn in from the ocean to replace the warm air rising above the peninsula while, in the middle of the state, it sometimes seems the only breeze is straight up. By the time the sea breeze air makes it to... say, Orlando... it isn't very cool anymore, and does little but create intense afternoon thunderstorms. Generally, humidity falls steadily from October through April, and February through April normally bring the most pleasant temperatures.

Although "hurricane season" officially lasts from June 1 to November 30, Florida is most often affected by tropical weather systems during August, September and early October. These months also bring increased risk of rain and lightning, as well as potential for a real natural disaster. When hurricanes make national news, as several have in recent years, travelers become more cautious about booking travel to the Keys during the late summer and early autumn. This means that visitors willing to tolerate some risk of disrupted plans, or at least those who prudently purchase travel insurance, can find great deals on flights and hotels during hurricane season. 

Anyone who prefers to avoid the annual avalanche of college-age partiers (they may be staying in the hotel room next to yours), avoid travel to towns famous as party destinations (some examples include: Key West, Fort Lauderdale and Daytona Beach) during March, which is spring break for most universities. 

March and early April are also, on average, South Florida's windiest time of the year, a consideration if you are hoping to try watersports such as snorkeling, diving or fishing. Strong breezes (10 to 15 mph or more) can persist for days, sometimes weeks, and many snorkeling trips to the reef, or offshore fishing trips are cancelled or rescheduled (assuming you can wait for a calmer day). Good "windy day" alternatives in the Keys include any boat (or fish) with a sail, site-seeing, shopping or bar-hopping in Key West, kayaking and snorkeling in mangrove creeks (protected from the wind), fishing nearshore waters (where smaller boats can shelter in the lee of an island), or driving up to the Everglades where the late-dry season conditions will have the wildlife most concentrated (easily visible), colonies of wading birds and anhingas are nesting and raising chicks right alongside the trails and boardwalks, and mosquitoes and biting deer-flies are often non-existent.