Gameplay in Atomicrops is divided into levels of difficulty called Years. Before each run, the player can select which year they would like to play by interacting with a sundial at the Farmhouse. There are 10 years in Atomicrops currently. Each consecutive year is unlocked by beating the prior year and the difficulty increases with each year. Some years may unlock additional features the first time they are completed.
Year 2 will unlock a new playable character, Robusta.
Year 3 will unlock a new NPC, The Gamble Trader.
Year 4 will unlock a new playable character, Thyme.
Year 5 will unlock the achievement Demi-Decade Orchid
Every year that you advance increases enemy move speed and bullet speed, as well as enemy health, and the number of enemies that will attack your farm at night. Starting max health also decreases as years increase. Certain years will increase the number of shots certain enemies will fire per attack or add unique enemies, such as ancient weeds turning into monsters.
Year 7 will cause flaming skulls (those used by the final boss) to spawn randomly at the edges of your screen.