It really depends on how big your area is and what you mean by changing the climate. You can make your backyard way more pleasant by increasing the plant cover, which will drop temperatures in the summer and provide homes for bugs and animals if you do it right. Fifty acres might be enough for you to notice just a general cooler climate if you replaced mowed grass or farm with a dense forest. It would also help slow evaporation from the soil. But you’re not gonna noticably change the amount of rain until you get into land areas comparable to a US state or maybe large city, unless you have very particular geography.