Per the comments, Draco719 has indicated that he has unlocked the 1,000,000 achievement, but not this one.(this achievement, and all other similar, are for cumulative gold earned, you don't need it all at once)
Here are some tips to net 1,000,000 Gold
+ As you may, or may not know, some crops are worth much more than others due to base value, growing time, and number of harvests. These 3 are MUSTS for growing:
Spring - Strawberry Seeds
Summer - Blueberry Seeds
Fall - Cranberry Seeds
They can net you a lot of cash, even more so if you use fertilizer, you may even make them gold star crops.
Planting crops in a 3x3 pattern gives you a small chance of growing a GIANT version of that crop. Instead of 9 pumpkins, you might get 20+ after "breaking" the large one, and that's a lot of money.
+ If you can, turn your crops and produce in to their more lucrative counterparts. Milk - Cheese, Eggs, - Mayonnaise, etc, these sell for anywhere between 50g to 200g more, depending on the produce and quality.
+ Fishing and mining are pretty lucrative too, despite how much a pain in the ass fishing can be, if you level it up enough, you can make plenty of cash (or turn those fish into dishes). You might also hook something else other than fish.... ;)
Mining, you can unearth several precious gems, and depending on your skills level, obtain more than one per "harvest". Ores can sell for several hundred each, and stack fairly quickly, so don't turn your nose up at them!!
+ Seed Maker and Wine FTW. These two things can make you a TOOOOOON of cash. Wine sells for 400g plain, but up to 560g, if you dedicate a few casks to wine and you'll be set. Wine ages and is worth more as time passes, at 56 days, it will be "Purple" quality and sell for double the base price.
The Seed Maker can turn any crop into seeds, 1-3 to be exact. A full grown Ancient Plant, planted at the beginning of Spring, can earn you about 5,000g in its lifetime, and that's assuming it is of normal quality and you have no perks to increase the value, and that's just ONE plant.
Best of luck to ya!!