I will never take the time to learn how stocks work. It's not like I could afford to invest anyways. But in Animal Crossing, I'm always playing the stocks, baby.
Or rather, the "Stalk Market," an ongoing stocks-like trade where turnips are shares; and the rates for how much you can sell them off for change from morning to evening. Most of the time, it's under profit or barely for a profit. Other times, you're like some folks I've seen on Twitter, with wildly high 500+ Bells rates for selling Turnips; basically, you can be on the road to being a Bellionaire. So, when you buy hundreds of Turnips every Sunday morning from sweet lil Daisy Mae, that's a good ass day. There's a twist too: You only have until the following Sunday to sell your turnips, or else, they rot.
There's always been one pesky catch with turnip trading: You can't just put them into your house's storage. If you try, the only options you have is to eat a turnip (why would you do such a stupid thing?) or drop them. If you're outside, you can bury them—but they don't plant a tree like fruits; they leave a mark on the ground, akin to where you're able to dig up fossils.
Basically, you have to get creative in storing your turnips. Luckily, my many years of Animal Crossing experience have your back. Here's just a few ways you can store your turnips in Animal Crossing: New Horizons. Without, y'know, actually storing them.
Just Drop Turnips In Your House
First things first: Just drop 'em in your house! Since you can't use your home's storage, you might as well use the space you got anyways. In Animal Crossing: City Folk and Animal Crossing: New Leaf, this was my tried and true method. I'd usually store them in the basement, with all my gyroids. (May gyroids R.I.P.—anyone else miss those things?) Here, you can see me store them in what I like to call my "toilet room." It is not a bathroom, it is just where I collect my many toilets. I moved them from my backyard into here.
Bury 'Em In Holes
Another handy method is just burying your turnips wherever. It can be in your backyard; it can be on a distant cliff. The important thing is you don't forget about where you buried them before next Sunday rolls around. Otherwise, you'll have some rotten, worthless turnips on your hand.
Fence Them Off!
A way that I've seen most people online adopt is fencing them in. Personally, this is my preferred method too. I use a barbed wire fence to signal that people should really stay away from my precious stalks. Of course, you can use a friendlier fence too—maybe a nice stone, or a country wooden fence? The choice is yours, of course. Next Sunday, I intend to invest far more in Turnips than I did this past week, so I'll definitely need to rethink my fencing area.
Build a Maze, and Put Turnips At the End of It
Another potential way to house your turnips is to use fencing to build a little maze, and keep your turnips at the end of it. Here, I made a little maze using stone fencing at the topmost section of my cliffside. It's not an elaborate maze, but I trust others can build some really elaborate mazes eventually. Think of it as a little reward for finding your way through it. Or lead a tarantula through it and catch them with perfect finesse with a swing of your net—the choice is yours.
Have Something (or Someone) Guard Them
Another handy solution is to have someone guard it. Maybe you can house it in an intimidating villager's yard. Or you can do what I did: and let your Godzilla-like monster guard the turnips from the shore. No one will want to mess with your turnips with a monster keeping watch. (Not that any of the "Best Friends" you denote on your friends list would dare to mess with your turnips when they visit anyway. Unless they are truly evil, like the folks who cheat.)
There are many a-ways to creatively keep your precious turnips safe until it comes time to sell them. Just remember to check stalk prices with Timmy and Tommy every morning and every night, lest you miss out on a potential killer profit. Then you won't have to chop down all the trees on a deserted Nook Miles island to spawn infinite tarantulas to farm anymore.