A country as large as Argentina can be visited at any time of the year, but for areas like Patagonia it is best to travel outside of the winter months, when days are short, access difficult and many hotels close.
For Patagonia the season is October to April, which coincides with when most people look to visit Argentina. Peak months of January and February can be very busy in Patagonia and you need to plan well ahead if travelling at this time. It is also one of the windiest times to visit. Travelling in the shoulder months of October/November and March/April is a great time to head to the south of the country as trails and attractions are much quieter.
In the north-east of the country, Iguassu Falls and the Ibera wetlands tend to be warm and tropical throughout the year, although the winter months of July and August can be strangely cool in the jungle!
In Mendoza and the wine region the harvest begins at the end of February and continues until April.
For wildlife around the Valdes Peninsula, Southern Right Whales can be seen from June to December, but sightings are most common from August to October, when the adults come to mate. They can often be seen from shore or on boat trips from Puerto Piramides. Orcas can be seen at Caleta Valdes and Punta Delgada from September to November and in Punta Norte from February to April. It is here that you can see them launch themselves onto the sand, in a spectacular hunting technique. Penguins can be seen from November to March.